STATUS OF THESIS
Title of thesis
Geochemical, dolomitization and the impact on petrophysical properties of
carbonate rocks in Kinta Limestone
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Date : _____________________ Date : __________________
FATIN SHAHIRAH BINTI MANAN
DR. Maman Hermana Husen
No. 36, Lorong
Mahkota Impian, 2/21 Bandar Puncak
Alam, 42300 Kuala Selangor, Selangor
Darul Ehsan
28.6.2021 28.6.2021
UNIVERSITI TEKNOLOGI PETRONAS
GEOCHEMICAL, DOLOMITIZATION AND THE IMPACT ON
PETROPHYSICAL PROPERTIES OF CARBONATE ROCKS IN KINTA
LIMESTONE
by
FATIN SHAHIRAH BINTI MANAN
The undersigned certify that they have read and recommend to the Postgraduate Studies
Programme for acceptance this thesis for the fulfillment of the requirements for the degree
stated.
Signature: ______________________________________
Main Supervisor: ______________________________________
Signature: ______________________________________
Co-Supervisor: ______________________________________
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Head of Department: ______________________________________
Date: ______________________________________
DR. MAMAN HERMANA HUSEN
MUHAMMAD NOOR AMIN ZAKARIAH
DR. KHAIRUL ARIFIN MOHD NOH
28.6.2021
GEOCHEMICAL, DOLOMITIZATION AND THE IMPACT ON
PETROPHYSICAL PROPERTIES OF CARBONATE ROCKS IN KINTA
LIMESTONE
by
FATIN SHAHIRAH BINTI MANAN
A Thesis
Submitted to the Postgraduate Studies Programme
as a Requirement for the Degree of
MASTER OF SCIENCE
PETROLEUM GEOSCIENCE
UNIVERSITI TEKNOLOGI PETRONAS
BANDAR SERI ISKANDAR,
PERAK
JULY 2021
DECLARATION OF THESIS
Title of thesis Geochemical, dolomitization and the impact on petrophysical properties of
carbonate rocks in Kinta Limestone
I _________________________________________________________________________
hereby declare that the thesis is based on my original work except for quotations and citations
which have been duly acknowledged. I also declare that it has not been previously or
concurrently submitted for any other degree at UTP or other institutions.
Witnessed by
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Signature of Author Signature of Supervisor
Permanent address:________________ Name of Supervisor
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________________________________
________________________________
Date : _____________________ Date : __________________
FATIN SHAHIRAH BINTI MANAN
No. 36, Lorong
Mahkota Impian, 2/21 Bandar Puncak
Alam, 42300 Kuala Selangor, Selangor
Darul Ehsan
Dr. Maman Hermana Husen
28.6.2021 28.6.2021
v
DEDICATION
This thesis is dedicated to my beloved parents, Umi and Abah with grateful thanks
for all their patience and understanding.
vi
ACKNOWLEDGEMENTS
First and foremost, I would like to express my gratitude to the Almighty God for giving
me the patience and strength to face the challenges and obstacle to finally complete my
dissertation. I extend my gratitude to the Department of Geosciences at Universiti
Teknologi PETRONAS for the education opportunities I have received. My sincere
thanks to my supervisor, Dr. Maman Hermana Husen; ex-supervisors, Dr. Mirza
Arshad Beg and Mr. Askury Abd Kadir; and co-supervisor, Mr. Muhammad Noor
Amin Zakariah for their guidance and advice during this study.
Thank you to my research partner, Nurul Afiqah binti Mohammad Zahir for always
sharing the ideas on this project and helped me during fieldwork. I would like to thank
all SEACARL members for their inputs and suggestions on this research. Thank you to
my colleagues, Sean Lee, Fatimah Zahrah, Ekrahm Nawas Khan, Shamsimah Abd
Rahman, Azyan Syahira Azmi, Syifa Afiza Ayob, Marina Samsudin, and Ainuddin
Yasin for your understanding and moral support through this journey. I would also like
to thank my senior, Ali Imran for guiding me on how to do mapping. Thanks to Syed
Haroon Ali for his guidance on the understanding of diagenesis. Furthermore, I would
like to thank all lab technicians that involved in this research for helping me in
laboratory works. Thanks to the management of these quarries, Gunung Kanthan,
Gunung Rapat and Dolomite quarry for giving the opportunity to conduct this research
within the area.
Finally, I would like to thank my family for encouraging me to achieve my goals.
On behalf of thesis completion, I have a great person, Alif Akmal on my back that
always give me supports and motivation in the process of completing this research.
vii
ABSTRACT
This research aims to determine how dolomitization could give a better understanding
on the changes of reservoir properties by evaluating the porosity and permeability of
carbonates in Kinta Limestone and analyzing the changes of micro-porosity in dolomite
formation. The methods used in this study are geochemical (x-ray diffraction and x-ray
fluorescence), petrophysical (poroperm and micro-computed tomography scan),
petrographic and morphological (field emission-scanning electron microscope)
analyses. There are three lithotypes of carbonates in Kinta Valley, which are limestone,
dolomitic limestone and dolomite. The petrophysical results show limestone has wide
range of porosity and permeability with mostly good to moderate pore connectivity,
while dolomite and dolomitic limestone have low porosity and permeability with
mostly show moderate pore connectivity. Petrographic analysis indicates there are five
types of dolomite in Kinta Limestone which are Dolo-I, Dolo-II, Dolo-III, Dolo-IV,
Dolo-V. The replacive dolomites, Dolo-I, Dolo-II and Dolo-III are the product of early
to middle dolomitization retained the pre-existing porosity of rock matrix. While,
cement dolomites, Dolo-IV and Dolo-V are the product of late dolomitization that
reduced the porosity. The main diagenetic process that influence porosity value in
cement dolomite is dissolution process. The porosity created is up to 25% that
contributes from intercrystalline pores. Porosity in dolomite is not solely dependable
on dolomitization process, other diagenetic events had influenced on the changes of
porosity.
viii
ABSTRAK
Penyelidikan ini bertujuan untuk menentukan bagaimana pendolomitan dapat
memberikan pemahaman yang lebih baik mengenai perubahan sifat takungan dengan
menilai keliangan dan kebolehtelapan karbonat di Kinta Limestone dan menganalisis
perubahan mikro-keliangan dalam pembentukan dolomit. Kaedah yang digunakan
dalam kajian ini adalah analisis geokimia (difraksi sinar-x dan pendarfluor sinar-x),
petrofisik (poroperm dan imbasan tomografi mikro), petrografi dan morfologi
(mikroskop elektron pengimbas pelepasan medan). Terdapat tiga jenis batuan karbonat
di Lembah Kinta, iaitu batu kapur, batu kapur berdolomit dan dolomit. Hasil petrofisika
menunjukkan batu kapur mempunyai keliangan dan kebolehtelapan yang luas dengan
penyambungan liang yang baik hingga sederhana, sementara batu kapur berdolomit dan
dolomitik mempunyai keliangan dan kebolehtelapan yang rendah dengan
kebanyakannya menunjukkan kesambungan liang sederhana. Analisis petrografi
menunjukkan terdapat lima jenis dolomit di Kinta Limestone iaitu Dolo-I, Dolo-II,
Dolo-III, Dolo-IV, Dolo-V. Dolomit pengganti, Dolo-I, Dolo-II dan Dolo-III adalah
produk pendolomitan awal hingga pertengahan yang mengekalkan keliangan matriks
batuan yang ada sebelumnya. Sementara, dolomit simen, Dolo-IV dan Dolo-V adalah
produk pendolomitan akhir yang mengurangkan keliangan. Proses diagenetik utama
yang mempengaruhi nilai keliangan dalam dolomit simen adalah proses pembubaran.
Keliangan yang dihasilkan adalah sehingga 25% yang menyumbang dari keliangan
interkristal. Sebagai kesimpulan, keliangan dalam dolomit tidak hanya bergantung pada
proses pendolomitan, kejadian diagenetik lain telah mempengaruhi perubahan
keliangan.
ix
In compliance with the terms of the Copyright Act 1987 and the IP Policy of the
university, the copyright of this thesis has been reassigned by the author to the legal
entity of the university,
Institute of Technology PETRONAS Sdn Bhd.
Due acknowledgement shall always be made of the use of any material contained
in, or derived from, this thesis.
© Fatin Shahirah binti Manan, 2021
Institute of Technology PETRONAS Sdn Bhd
All rights reserved.
x
TABLE OF CONTENT
ABSTRACT ............................................................................................................................. vii
ABSTRAK .............................................................................................................................. viii
LIST OF FIGURES ................................................................................................................ xiv
LIST OF TABLES ................................................................................................................ xxiii
CHAPTER 1 INTRODUCTION ................................................................................... 1
1.1 Background of Study ......................................................................................... 1
1.2 Problem Statement ............................................................................................. 2
1.3 Objectives .......................................................................................................... 3
1.4 Study Area ......................................................................................................... 4
1.5 Scopes of Study ................................................................................................. 6
CHAPTER 2 LITERATURE REVIEW ........................................................................ 7
2.1 Regional Geological Settings ............................................................................ 7
2.1.1 Geological Settings of Kinta Valley .................................................... 10
2.1.2 Lithology of Kinta Valley ................................................................... 12
2.1.3 Stratigraphy of Kinta Limestone ......................................................... 14
2.1.4 Depositional Environment ................................................................... 16
2.1.5 Previous works on Dolomite in Kinta Valley ..................................... 18
2.2 Dolomite .......................................................................................................... 20
2.2.1 Dolomite Texture ................................................................................ 21
2.2.2 Relationship Between Dolomite Textures and Formation
Temperature ..................................................................................... 24
2.2.3 Hydrothermal Dolomitization ............................................................. 26
2.2.4 Hydrothermal Dolomite Groups based on Petrography ...................... 28
2.3 Dolomitization on Petrophysical Properties .................................................... 29
2.3.1 Porosity ................................................................................................ 30
2.3.1.1 Pore Types ............................................................................... 30
2.3.1.2 Common Pore Types in Dolomite Rock .................................. 32
2.3.2 Relationship of Dolomitization and Porosity Evolution ..................... 33
2.3.3 Permeability ........................................................................................ 36
CHAPTER 3 METHODOLOGY ................................................................................ 38
xi
3.1 Preliminary Study ............................................................................................ 39
3.2 Geological Fieldwork ...................................................................................... 39
3.3 Laboratory Analysis......................................................................................... 40
3.3.1 X-Ray Diffraction (XRD) ................................................................... 41
3.3.1.1 Sample Preparation .................................................................. 41
3.3.1.2 Procedure ................................................................................. 42
3.3.2 X-Ray Fluorescence (XRF) ................................................................. 43
3.3.2.1 Sample Preparation .................................................................. 43
3.3.2.2 Procedure ................................................................................. 44
3.3.3 Poroperm ............................................................................................. 45
3.3.3.1 Sample Preparation .................................................................. 46
3.3.3.2 Procedure ................................................................................. 46
3.3.4 Micro-Computed Tomography (CT) Scan .......................................... 47
3.3.4.1 Sample Preparation .................................................................. 47
3.3.4.2 Procedure ................................................................................. 48
3.3.5 Petrographic Analysis ......................................................................... 48
3.3.5.1 Sample Preparation .................................................................. 48
3.3.5.2 Procedure ................................................................................. 50
3.3.6 Field Emission-Scanning Electron Microscope-Energy Dispersive
X-Ray (FESEM-EDX) ..................................................................... 50
3.3.6.1 Sample Preparation .................................................................. 51
3.3.6.2 Procedure ................................................................................. 51
3.4 The Method of Data Analysis .......................................................................... 52
CHAPTER 4 RESULTS AND DISCUSSION ............................................................ 54
4.1 Field Observations ........................................................................................... 54
4.1.1 Field 1: Gunung Rapat ........................................................................ 56
4.1.2 Field 2: Sungai Siput Dolomite Hill .................................................... 63
4.1.3 Field 3: Hill B, Gunung Kanthan ........................................................ 69
4.1.4 Field 4: Hill E, Gunung Kanthan ........................................................ 75
4.1.5 Field Summary .................................................................................... 82
4.2 Geochemical Study .......................................................................................... 83
xii
4.2.1 Field 1: Gunung Rapat ........................................................................ 83
4.2.1.1 Mineralogy ............................................................................... 83
4.2.1.2 Elemental Analysis .................................................................. 86
4.2.2 Field 2: Sungai Siput Dolomite Hill .................................................... 89
4.2.2.1 Mineralogy ............................................................................... 89
4.2.2.2 Elemental Analysis .................................................................. 91
4.2.3 Field 3: Hill B, Gunung Kanthan ........................................................ 95
4.2.3.1 Mineralogy ............................................................................... 95
4.2.3.2 Elemental Analysis .................................................................. 97
4.2.4 Field 4: Hill E, Gunung Kanthan ...................................................... 101
4.2.4.1 Mineralogy ............................................................................. 101
4.2.4.2 Elemental Analysis ................................................................ 104
4.3 Petrophysical Properties ................................................................................ 107
4.3.1 Field 1: Gunung Rapat ...................................................................... 107
4.3.2 Field 2: Sungai Siput Dolomite Hill .................................................. 113
4.3.3 Field 3: Hill B, Gunung Kanthan ...................................................... 117
4.3.4 Field 4: Hill E, Gunung Kanthan ...................................................... 122
4.4 Petrographic Study......................................................................................... 130
4.4.1 Field 1: Gunung Rapat ...................................................................... 130
4.4.1.1 Petrography and Diagenetic Features .................................... 130
4.4.1.2 Pore Types and Percentage .................................................... 133
4.4.2 Field 2: Sungai Siput Dolomite Hill .................................................. 134
4.4.2.1 Petrography and Diagenetic Features .................................... 134
4.4.2.2 Pore Types and Percentage .................................................... 137
4.4.3 Field 3: Hill B, Gunung Kanthan ...................................................... 139
4.4.3.1 Petrography and Diagenetic Features .................................... 139
4.4.3.2 Pore types and percentage ...................................................... 143
4.4.4 Field 4: Hill E, Gunung Kanthan ...................................................... 146
4.4.4.1 Petrography and Diagenetic Features .................................... 146
4.4.4.2 Pore Types and Percentage .................................................... 151
4.5 Morphological Study ..................................................................................... 155
xiii
4.5.1 Field 1: Gunung Rapat ...................................................................... 155
4.5.2 Field 2: Sungai Siput Dolomite Hill .................................................. 158
4.5.3 Field 3: Hill B, Gunung Kanthan ...................................................... 160
4.5.4 Field 4: Hill E, Gunung Kanthan ...................................................... 163
4.6 Discussion ...................................................................................................... 170
4.6.1 Lithotypes of carbonate rocks in Kinta Valley .................................. 170
4.6.2 Porosity and permeability variations of carbonate rocks in Kinta
Limestone ....................................................................................... 173
4.6.3 Pore characterization of carbonate rocks in Kinta Limestone ........... 175
4.6.4 Carbonates microfacies and diagenetic processes in Kinta Valley ... 181
4.6.4.1 Types of calcite ...................................................................... 181
4.6.4.2 Types of dolomite .................................................................. 184
4.6.4.3 The origin of hydrothermal dolomites in Kinta Limestone ... 190
4.6.4.4 Diagenetic Processes of carbonates in Kinta Valley.............. 191
4.6.5 Implication of dolomitization in Kinta Limestone to micro-porosity
development ................................................................................... 197
4.6.5.1 Pore types and percentage variations of dolomite in Kinta
Valley ..................................................................................... 197
4.6.5.2 The porosity evolution of rock matrix before, during and
after dolomitization in Kinta Limestone ................................ 199
CHAPTER 5 CONCLUSIONS ................................................................................. 204
5.1 Conclusions ................................................................................................... 204
5.2 Research Contributions .................................................................................. 206
5.3 Recommendations.......................................................................................... 206
APPENDIX A XRD DATA ...................................................................................... 223
APPENDIX B XRF DATA ....................................................................................... 239
APPENDIX C CORE PLUG DESCRIPTIONS ........................................................ 242
xiv
LIST OF FIGURES
Figure 1.1: (Top) Map of Kinta Valley indicates the location of the study area;
(Bottom) Geological distribution of the Kinta Valley (Choong et al.,
2014) ........................................................................................................... 5
Figure 2.1: Peninsular Map combined with hillshade map shows geological
provinces of Peninsula Malaysia, divided into Western, Central and
Eastern belts (Ramkumar et al., 2019, Metcalfe, 2013) and distribution
of Palaeozoic limestone outcrops (unpublished). ....................................... 8
Figure 2.2: Diagrams of the major regional tectono-magmatic events, successive
stages and structural deformations in and around Kinta Valley in the
Western Belt, Western Malaysia (Ramkumar et al., 2019). ..................... 10
Figure 2.3: The Geological Map of Kinta Valley (modified from Choong et al.,
2014). ........................................................................................................ 12
Figure 2.4: Chrono-diagram shows different lithologies formed in the various
periods. ...................................................................................................... 14
Figure 2.5: (a) Stratigraphic scheme of Kinta Limestone (modified from Metcalfe,
2000); (b) The conodont biostratigraphy of Kinta Limestone indicate a
continuous succession of sediments from lower Devonian to upper
Carboniferous. ........................................................................................... 16
Figure 2.6: The slope structures (slumps) of Kinta Valley in Kek Look Tong
temple, Ipoh (Pierson et al., 2011). ........................................................... 17
Figure 2.7: Summary of dolomite rock texture, modified from (Gregg & Sibley,
1987). ........................................................................................................ 22
Figure 2.8: General configuration of (a) Idiotopic Dolomite Texture; (b)
Xenotopic Dolomite Texture (Gregg & Sibley, 1984). ............................ 23
Figure 2.9: Detailed classifications of Idiotopic dolomite texture and Xenotopic
dolomite texture (Gregg & Sibley, 1984). ............................................... 23
Figure 2.10: Classification of dolomite texture based on crystal-boundary shapes -
Planar-e/-s or Nonplanar (Gregg & Sibley, 1987). ................................. 24
xv
Figure 2.11: Common dolomite texture emphasizing the effect of temperature on
the behaviour of dolomite crystal (Sijing et al., 2014). .......................... 25
Figure 2.12: Hydrothermal dolomitization. Fluids from deep within a basin can
rapidly move up through fault planes to dolomitize carbonates at a
shallower area (Al-Awadi et al., 2009). .................................................. 27
Figure 2.13: Four components of porosity classification (Choquette & Pray, 1970). . 31
Figure 2.14: Pore Types of carbonate rocks-Fabric selective; Not fabric selective;
Fabric selective or not fabric selective (Choquette & Pray, 1970). ........ 32
Figure 2.15: Relationship of porosity to the percentage of dolomite in carbonate
rocks (Mazzullo, 2004). .......................................................................... 35
Figure 3.1: The flowchart of research methodology. ................................................... 38
Figure 3.2: Number of collected samples for each locality. ........................................ 40
Figure 3.3: Ten grams of powdered samples for XRD analysis. ................................. 42
Figure 3.4: XRD equipment (model: X’ Pert Powder PANalytical). .......................... 43
Figure 3.5: Powdered samples and sample cups. ......................................................... 44
Figure 3.6: XRF equipment (model: Bruker S8 Tiger). ............................................... 45
Figure 3.7: Poroperm Equipment (model: Coval 30). ................................................. 46
Figure 3.8: Micro Focus CT Scan Equipment (Model: InspeXio SMX-225CT). ....... 47
Figure 3.9: Stained thin sections for petrographic study. ............................................ 49
Figure 3.10: Two types of microscope used for petrographic study, (a) Standard
light polarized microscope; (b) Cathodoluminescence microscope. ...... 50
Figure 3.11: Supra55VP FESEM with Oxford EDX Equipment. ............................... 52
Figure 4.1: (a) Geological map of Kinta Valley with two study areas specifically
located in the north (b) and south (c) of Kinta Valley; (b) Three main
localities, Gunung Kanthan and Sungai Siput Dolomite Hill in the
north; and (c) Gunung Rapat in the south for this study. .......................... 55
Figure 4.2: An outcrop image of Gunung Rapat which consists of a highly
fractured massive-dolomite body. The occurrence of sepiolite is
observed near strike-slip faults. ................................................................ 57
Figure 4.3: (a) An irregular contact of limestone and dolomite bodies; (b) The
presence of calcite vein in dolomite body. ................................................ 58
xvi
Figure 4.4: A contact between (a) limestone and pale green sepiolite (b) between
dolomite and green-yellowish sepiolite. ................................................... 60
Figure 4.5: A left strike-slip fault observed near dolomite and sepiolite bodies. ........ 61
Figure 4.6: Sedimentary logging of outcrop in Gunung Rapat. ................................... 62
Figure 4.7: The photo of outcrop A in Sungai Siput Dolomite Hill. ........................... 64
Figure 4.8: The photo of outcrop B in Sungai Siput Dolomite Hill. ........................... 64
Figure 4.9: The photo of outcrop C in Sungai Siput Dolomite Hill. ........................... 65
Figure 4.10: A view of outcrop D shows a clear tilted bedding plane with intense
fracture. ................................................................................................... 65
Figure 4.11: The photo shows that the normal faults (red line) mostly striking in
N-S direction. .......................................................................................... 66
Figure 4.12: The presence of various size of calcite vein (a) from 0.5 cm to 1 cm
and (b) 2 cm to 15 cm in dolomite body. The calcite veins
cross-cutting the dolomite body in Sungai Siput Dolomite Hill. ........... 67
Figure 4.13: Sedimentary logging of the outcrop (section D) in Sungai Siput
Dolomite Hill. ......................................................................................... 68
Figure 4.14: A representative outcrop in Hill B, Gunung Kanthan. The outcrop
shows a tilted bed and variation colour for the lithology. ...................... 70
Figure 4.15: Two sections of dolomite bodies, (a) Pinkish dolomite in contact with
limestone; (b) Massive pinkish dolomite body is highly fractured and
intensely weathered. ............................................................................... 72
Figure 4.16: The reverse fault plane found in the limestone has a gentle dipping
and striking to the E-W direction (red arrow). ....................................... 73
Figure 4.17: The slickenside shows a right-lateral strike-slip fault plane. This fault
was striking almost to the N-S direction (red arrow). ............................ 73
Figure 4.18: Sedimentary logging of represented outcrop in Hill B, Gunung
Kanthan. .................................................................................................. 74
Figure 4.19: The photo of outcrop 1 in Hill E, Gunung Kanthan. ............................... 76
Figure 4.20: (a) Presence of paleo-cave deposits within limestone body; (b) The
bedrocks were tilted almost vertical striking north-south direction. ...... 77
xvii
Figure 4.21: The presence of slickenside probably indicates the strike-slip fault
plane that striking in the N-S direction. .................................................. 78
Figure 4.22: Sedimentary logging of outcrop 1 in Hill E, Gunung Kanthan. .............. 79
Figure 4.23: The brecciated limestone clasts in the dolomite body. ............................ 80
Figure 4.24: The photo of outcrop 2 in Hill E, Gunung Kanthan. ............................... 81
Figure 4.25: The calcite-dolomite-quartz ternary diagram showing the lithology of
carbonate rocks in Gunung Rapat based on Leighton and Pendexter
(1962) terminology. Dolomitic limestone and limestone are reported
in Gunung Rapat. .................................................................................... 84
Figure 4.26: XRD pattern obtained from limestone sample of AQ 10 containing
calcite and quartz. ................................................................................... 85
Figure 4.27: XRD pattern obtained from dolomitic limestone sample of AQ 76
containing calcite, dolomite and quartz. ................................................. 86
Figure 4.28: The trends of calcium (Ca) and magnesium (Mg) concentrations are
compared in rock samples of Gunung Rapat. ......................................... 87
Figure 4.29: The trend of calcium (Ca) concentration in limestone and dolomitic
limestone of Gunung Rapat. ................................................................... 87
Figure 4.30: The magnesium (Mg) concentration based on limestone and
dolomitic samples of Gunung Rapat. ..................................................... 88
Figure 4.31: The elemental variation graph of Si, Fe, Al, Sr, and Mn in percentage
based on samples from Gunung Rapat. .................................................. 89
Figure 4.32: The calcite-dolomite-quartz ternary diagram showing the Sungai
Siput Dolomite Hill is dominated by dolomite. ...................................... 90
Figure 4.33: XRD pattern obtained from dolomite sample of SB 6 containing
dolomite, calcite and quartz. ................................................................... 91
Figure 4.34: The trends of calcium (Ca) and magnesium (Mg) concentrations
based on dolomite samples of Sungai Siput Dolomite Hill. ................... 92
Figure 4.35: The calcium (Ca) concentration trend based on dolomite samples of
Sungai Siput Dolomite Hill. ................................................................... 93
Figure 4.36: The trend of magnesium (Mg) concentration based on dolomite
samples of Sungai Siput Dolomite Hill. ................................................. 93
xviii
Figure 4.37: The elemental variation of Si, Fe, Al, Sr, Mn and Cl based on
dolomite samples from Sungai Siput Dolomite Hill. ............................. 94
Figure 4.38: The calcite-dolomite-quartz ternary diagram showing the Hill B,
Gunung Kanthan consists of dolomite and limestone. ........................... 95
Figure 4.39: XRD pattern obtained from limestone sample of LB 62 containing
calcite, dolomite and quartz. ................................................................... 97
Figure 4.40: XRD pattern obtained from dolomite sample of LB 81 containing
dolomite and calcite. ............................................................................... 97
Figure 4.41: The trends of calcium (Ca) and magnesium (Mg) concentrations
based on outcrop samples of Hill B, Gunung Kanthan. ......................... 98
Figure 4.42: The trend of calcium (Ca) concentration in limestone and dolomite of
Hill B, Gunung Kanthan. ........................................................................ 99
Figure 4.43: The trend of magnesium (Mg) concentration in limestone and
dolomite samples of Hill B, Gunung Kanthan. .................................... 100
Figure 4.44: The elemental variation of Si, Fe, Al, Mn, Cl and Sr based on
outcrop samples from Hill B, Gunung Kanthan. .................................. 100
Figure 4.45: The calcite-dolomite-quartz ternary diagram showing the Hill E,
Gunung Kanthan is composed of limestone, dolomite and dolomitic
limestone. .............................................................................................. 101
Figure 4.46: XRD pattern obtained from limestone sample of LE 1-60 containing
calcite, sylvite and quartz. .................................................................... 103
Figure 4.47: XRD pattern obtained from dolomite sample of LE 2-3 containing
dolomite and calcite. ............................................................................. 104
Figure 4.48: The trends of calcium (Ca) and magnesium (Mg) concentrations
based on outcrop samples of Hill E, Gunung Kanthan. ........................ 104
Figure 4.49: The trend of calcium (Ca) concentration in limestone and dolomitic
limestone samples of Hill E, Gunung Kanthan. ................................... 105
Figure 4.50: The trend of magnesium (Mg) concentration in limestone and
dolomitic limestone samples of Hill E, Gunung Kanthan. ................... 106
Figure 4.51: The elemental variation of Si, Fe, Al, Sr, and Mn based on outcrop
samples from Hill E, Gunung Kanthan. ............................................... 106
xix
Figure 4.52: Porosity-permeability graph based on various lithologies of the mini-
cored plug from Gunung Rapat. ........................................................... 109
Figure 4.53: The red boxes show the presence of pores in core plugs of Gunung
Rapat, (a) Representative core plugs; (b) 3D µCT images of core
plugs. ..................................................................................................... 110
Figure 4.54: The µCT images of limestone and dolomitic limestone in Gunung
Rapat (a) 2D µCT image slice on top (b) 2D µCT image slice on the
front (c) 3D µCT image. ....................................................................... 112
Figure 4.55: Porosity versus permeability graph of dolomite rocks in Sungai Siput
Dolomite Hill. ....................................................................................... 114
Figure 4.56: The red boxes show pores in core plugs of Sungai Siput Dolomite
Hill, (a) Representative core plugs, (b) 3D µCT images of core
plugs. ..................................................................................................... 115
Figure 4.57: The µCT images of dolomite in Sungai Siput Dolomite Hill (a) 2D
µCT image slice on top (b) 2D µCT image slice on the front (c) 3D
µCT image. ........................................................................................... 116
Figure 4.58: The porosity-permeability cross plot of samples from Hill B,
Gunung Kanthan. .................................................................................. 118
Figure 4.59: The red boxes show pores in core plugs of Hill B, Gunung Kanthan,
(a) Representative core plugs; (b) 3D µCT images of core plugs. ....... 119
Figure 4.60: The µCT images of limestone and dolomite samples of Hill B,
Gunung Kanthan (a) 2D µCT image slice on top (b) 2D µCT image
slice on the front (c) 3D µCT image. .................................................... 122
Figure 4.61: The porosity-permeability trend of mini-cored plugs linked to
various lithology in Hill E, Gunung Kanthan. ...................................... 124
Figure 4.62: Limestone samples of section 1 in Hill B, Gunung Kanthan tested
for µCT scan (a) The image of representative core plugs (b) 3D µCT
images of core plugs the red dotted boxes show the microporous
zones. .................................................................................................... 125
xx
Figure 4.63: Limestone, dolomite and dolomitic limestone samples of section 2
in Hill B, Gunung Kanthan. The samples are associated with
brecciated limestone (a) ........................................................................ 126
Figure 4.64: The µCT images of limestone, dolomite and dolomitic samples of
Hill E, Gunung Kanthan (a) 2D µCT image slice on top (b) 2D µCT
image slice on front .............................................................................. 129
Figure 4.65: Photomicrographs of calcite and dolomite types in Gunung Rapat. ..... 133
Figure 4.66: The micropore types that present in Gunung Rapat. ............................. 134
Figure 4.67: Photomicrographs of dolomite rocks in Sungai Siput Dolomite Hill. .. 137
Figure 4.68: The micropore types present in dolomite of Sungai Siput Dolomite
Hill. ....................................................................................................... 139
Figure 4.69: Photomicrographs of calcite and dolomite types in Hill B, Gunung
Kanthan. ................................................................................................ 143
Figure 4.70: The micropore types present in dolomite of Hill B, Gunung Kanthan. 146
Figure 4.71: Photomicrographs of calcite and dolomite types in Hill E, Gunung
Kanthan. ................................................................................................ 151
Figure 4.72: The micropore types present in calcite and dolomite of Hill E,
Gunung Kanthan. .................................................................................. 154
Figure 4.73: FESEM images of limestone sample (AQ 10) from Gunung Rapat. .... 156
Figure 4.74: Energy Dispersive X-Ray (EDX) spectrum of sample AQ 10
showing the presence of Ca, C, and O elements. ................................. 157
Figure 4.75: FESEM images of dolomite sample (SB 6) from Sungai Siput
Dolomite Hill. ....................................................................................... 159
Figure 4.76: Energy Dispersive X-Ray (EDX) spectrum of sample SB 6 showing
the presence of Ca, Mg, Al, C, and O elements. .................................. 159
Figure 4.77: FESEM images of dolomite sample (LB 83) from Hill B, Gunung
Kanthan. ................................................................................................ 161
Figure 4.78: Energy Dispersive X-Ray (EDX) spectrum of sample LB 83
showing Ca, Mg, C, and O elements in cement dolomite, Dolo-V. ..... 161
Figure 4.79: Energy Dispersive X-Ray (EDX) spectrum of sample LB 83
showing Ca, Mg, C, and O elements in replacive dolomite, Dolo-II. .. 162
xxi
Figure 4.80: FESEM images of outcrop sample LE 1-60 from Hill E, Gunung
Kanthan. ................................................................................................ 164
Figure 4.81: Energy Dispersive X-Ray (EDX) spectrum of sample LE 1-60
showing Ca, C, and O elements in limestone sample. .......................... 164
Figure 4.82: FESEM images of outcrop sample LE 1-63 from Hill E, Gunung
Kanthan. Identification as calcite with siliciclastic mixture is based
on the distinctive. .................................................................................. 166
Figure 4.83: Energy Dispersive X-Ray (EDX) spectrum of sample LE 1-63
showing Ca, Mg, Si, Al, C, and O elements in the sample. ................. 166
Figure 4.84: FESEM images of outcrop sample LE 2-3 from Hill E, Gunung
Kanthan. ................................................................................................ 168
Figure 4.85: Energy Dispersive X-Ray (EDX) spectrum of sample LE 2-3
showing the presence of Ca, Mg, Fe, C, and O elements. .................... 169
Figure 4.86: Compositional ternary diagram of carbonates from Kinta Limestone
according to Leighton and Pendexter (1962) terminology. .................. 171
Figure 4.87: Mg concentration is increasing from south to north of Kinta Valley. ... 172
Figure 4.88: The porosity-permeability trend of mini-cored plugs that linked to
various lithologies in Kinta Limestone. ................................................ 175
Figure 4.89: Slices of µCT images from the top view of core plugs. Different
types of pore observed in different lithologies, (a) Interconnected
fractures (F) in ...................................................................................... 177
Figure 4.90: A schematic diagram of pore distribution types in carbonate rocks of
Kinta Valley. ......................................................................................... 178
Figure 4.91: Pore distribution types in different lithologies (a), (c), (e) and (g)
show a 2D cross-section of µCT image; (b), (d), (f) and (h) show a
3D µCT image ...................................................................................... 180
Figure 4.92: The photomicrographs of each type of calcite in Kinta Limestone
under PPL, (a) The presence of pyrite and Cal-II cuts through Cal-I;
(b) Cal-III and stylolite cuts through Cal-I with the presence of pyrite;
(c) Cal-IV cuts across Cal-II; (d) A very coarse calcite cement
develops within Dolo-V. ....................................................................... 184
xxii
Figure 4.93: The representative samples of replacive dolomites, Dolo-I, Dolo-II
and Dolo-III in CL and PPL, (a) Dolo-I shows fine dolomite matrix;
(b) Sucrosic dolomite (Dolo-II) has anhedral crystal boundary; (c)
The calcite veins cut across Dolo-III; (d) Dolo-III appears dull red
luminescence and calcite cement appears bright orange luminescence
under CL; (e) The fabric of Dolo-III in PPL; (f) CL image shows
floating dolomite rhombs. ..................................................................... 187
Figure 4.94: The representative samples of cement dolomites, Dolo-V and
Dolo-IV in CL and PPL, (a) Dolo-IV is associated with calcite vein;
(b) Dolo-IV appears red luminescence under CL and the crystal
boundary is planar-es to nonplanar-a; (c) ............................................. 189
Figure 4.95: The contact between micritized calcite matrix (Cal-I) and early
replacive dolomite (Dolo-I). ................................................................. 192
Figure 4.96: Mechanical and chemical compactions (a) Early fracturing cuts
through Cal-II; (b) Late stage of stylolite cuts across Cal-V and
Dolo-II. ................................................................................................. 193
Figure 4.97: (a) Framboidal pyrite; (b) Micropyrite .................................................. 195
Figure 4.98: (a) Breccia clasts of Dolo-II; (b) Breccia clasts of Dolo-V. .................. 196
Figure 4.99: Dedolomitization (Ded-I) is associated with late calcite cementation
(a) Ded-I view under PPL; (b) Ded-I view under CL. .......................... 197
Figure 4.100: The porosity modification through diagenetic events during pre-
dolomitization, syn-dolomitization and post-dolomitization in
Kinta Limestone ................................................................................. 203
xxiii
LIST OF TABLES
Table 1.1: The division scopes of study applied for this research. ................................ 6
Table 2.1: Types of lithology and descriptions in Kinta Valley (summarized from
Rajah, 1979). ............................................................................................. 13
Table 3.1: Number of tested samples for each analysis. .............................................. 41
Table 3.2: The results of etching and staining carbonate minerals (A. E. Adams &
MacKenzie, 1998). .................................................................................... 49
Table 3.3: Practical use for dolomite classification ..................................................... 53
Table 3.4: Grain size chart (Folk, 1962) ...................................................................... 53
Table 4.1: The list of mineral percentage and lithology types of rock samples in
Gunung Rapat. .......................................................................................... 84
Table 4.2: The list of mineral percentage and lithology type of rock samples in
Sungai Siput Dolomite Hill. ...................................................................... 90
Table 4.3: The list of mineral percentage and lithology type of rock samples in
Hill B, Gunung Kanthan ........................................................................... 96
Table 4.4: The list of mineral percentage and lithology type of rock samples in
Hill E, Gunung Kanthan.......................................................................... 102
Table 4.5: List of porosity and permeability values of different samples in
Gunung Rapat. ........................................................................................ 108
Table 4.6: List of porosity and permeability values of dolomites in Sungai Siput
Dolomite Hill. ......................................................................................... 113
Table 4.7: List of porosity and permeability values of different samples in Hill
B, Gunung Kanthan................................................................................. 117
Table 4.8: List of porosity and permeability values of different samples in Hill E,
Gunung Kanthan. .................................................................................... 123
Table 4.9: Summary of pore types and percentages based on calcite types in
Gunung Rapat. ........................................................................................ 133
Table 4.10: Summary of pore types and percentages based on dolomite types in
Sungai Siput Dolomite Hill. .................................................................... 138
xxiv
Table 4.11: Summary of pore types and percentages based on dolomite types in
Hill B, Gunung Kanthan. ........................................................................ 144
Table 4.12: Summary of pore types and percentages of calcite and dolomite types
in Hill E, Gunung Kanthan. .................................................................... 152
Table 4.13: The weight and atomic percentage of elements in sample AQ 10. ........ 157
Table 4.14: The weight and atomic percentage of elements in sample SB 6. ........... 159
Table 4.15: The weight and atomic percentage of elements in Dolo-V .................... 162
Table 4.16: The weight and atomic percentage of elements in Dolo-II..................... 162
Table 4.17: The weight and atomic percentage of elements in sample LE 1-60 ...... 164
Table 4.18: The weight and atomic percentage of elements in sample LE 1-63. ...... 167
Table 4.19: The weight and atomic percentage of elements in sample LE 2-3. ........ 169
Table 4.20: Summary of porosity and permeability data of each lithology in Kinta
Limestone ................................................................................................ 174
Table 4.21: Pore system characterization of carbonate rocks in Kinta Valley .......... 176
Table 4.22: Paragenetic sequence of carbonates in Kinta Limestone ....................... 191
Table 4.23: The summary of pore types and percentage of dolomite microfacies in
Kinta Valley ............................................................................................ 198
1
CHAPTER 1
INTRODUCTION
This chapter includes background study, problem statements, objectives, study area and
scopes of study.
1.1 Background of Study
Peninsular Malaysia is divided into three geological belts, which are Western, Eastern
and Central belts. The origin of Western Belt is from a continental block, Sibumasu
block, that drifted away from Gondwana in Early Palaeozoic time. While the eastern
and central belts are part of the single tectonic block, Indochina block (Metcalfe, 2013).
These two blocks collided during Permian resulting in the Sibumasu subducted under
Indochina block to form the Bentong-Raub Suture zone. These occurrences resulted in
the emplacement of granite intrusion underneath and east of Kinta Limestone from
Triassic to Jurassic (Ros & Yeap, 2000; Sautter et al., 2017; Searle et al., 2012). The
stratigraphy of Western Belt is different from eastern and central belts because they
have different tectonic origins. Based on Harbury et al. (1990), the Western Belt was
tectonically stable in the Upper Palaeozoic period. Most of the carbonates in Peninsular
Malaysia are widely distributed in Western Belt, which includes Kinta Valley.
Dolomite is distributed in few areas in the Western Belt of Peninsular Malaysia.
Dolomite is widely found in Perlis, northern part of Peninsular Malaysia. Few dolomite
quarries can be found in Chuping town, Perlis area. Dolomite can also be found in Setul
Formation, Langkawi and Kinta Limestone, Perak. Dolomite in Kinta Valley is more
complex because it is believed to be formed due to hydrothermal alterations
(Ramkumar et al., 2019). There are two main causes in the formation of dolomite: the
2
source of Mg2+ ions and the process that transfers the dolomitizing fluids through
carbonate sediment (Tucker & Wright, 1990).
In Precambrian, the presence of dolomite is not familiar as limestone. Dolomite
abundance is reduced from Palaeozoic through Mesozoic to Cenozoic. Recent dolomite
has different physical and chemical characteristics from ancient dolomite. Therefore,
modern dolomite is a questionable analogue for the origin of ancient dolomite
(Vahrenkamp & Swart, 1994). The lack of analogue for ancient dolomites led to the
view of dolomite problem (Tucker & Wright, 1990). This is because they overlook the
fundamental of ancient dolomite is subjected to greater diagenesis than modern
dolomite. Most the ancient dolomites have experienced multiple episodes of
dolomitization and intense diagenesis compared to modern dolomites (Purser et al.,
1994). Thus, the diagenetic overprint of ancient dolomite is undeniable.
Dolomitization is part of diagenesis that plays an essential role in dolomite
formation. Dolomitization takes part by changing the composition of limestone rocks
to dolostone. The existence of dolomite affects the physical and chemical of precursor
limestone and has important effects for hydrocarbon exploration and production. It will
eventually influence the reservoir properties such as porosity, permeability and
connectivity to source areas of petroleum (Carnell & Wilson, 2003). Dolomitized
carbonate reservoirs have high heterogeneity levels and show complex reservoir
characteristics. It is crucial to understand the changes of reservoir properties in
dolomitized area, as diagenesis influenced the development and destruction of porosity
and permeability.
1.2 Problem Statement
Carbonate reservoirs have become one of the key targets of hydrocarbon exploration.
Carbonate reservoirs contributed to 50% of oil production (Mazzullo, 2004). The
reservoir properties evaluation can be very complex to understand when it encounters
dolomitization. Based on Moore (2001), few studies show that no porosity is associated
with dolomitization. He stated that dolomite rock is less porous than precursor rock
3
when it develops as cement dolomite. Meanwhile, Carnell and Wilson (2004) stated
that dolomite can enhance porosity when it forms as replacive dolomite. Even though
many studies have been done on dolomite, still the porosity in dolomite is debated. The
porosity and permeability of dolomitized carbonate rock are mainly influenced by
diagenesis. The diagenesis of dolomitized carbonate rock is complex, and it needs an
understanding of the dolomitization process.
A decade ago, researches about Kinta Limestone were done, but there was no
specific study on the petrophysical properties of carbonate rocks. There are limited
publications on dolomite in Kinta Valley, possibly due to accessibility issues. The
changes in porosity and permeability of dolomitized carbonate rocks in Kinta Valley
remain unknown. The changes in porosity in dolomite are still debated among
researchers till now. It brings the subject to the questions of “what is the relationship
between porosity-permeability and dolomitization in Kinta Valley?” and “does
dolomitization in Kinta Valley enhances or destroys porosity of carbonate rocks?”
1.3 Objectives
This research aims to characterize the reservoir properties (sedimentology, porosity &
permeability) and the effect of dolomitization on Kinta Valley limestone. The following
are the objectives of the study:
1. To identify lithotypes of carbonate rocks in Kinta Valley.
2. To evaluate the porosity and permeability of Kinta Limestone by quantitative
and qualitative methods.
3. To analyze the porosity development in dolomite formation with a diagenetic
alteration.
4
1.4 Study Area
The study area is located in Kinta Valley, which is in the central part of Perak. The
valley is bounded by two granitic hills: the Kledang Range to the west and Main Range
to the east. There are five primary lithologies deposited in Kinta Valley from Devonian
to recent time. They are interbedded sandstone and mudstone, shale, limestone, granite
and alluvium (Choong et al., 2014). The focus of this study is mainly on dolomite. Kinta
Limestone is an extension of Baling Group. The age of Kinta Limestone is dated from
Silurian to Permian (Foo, 1983). Hutchison (2007) and Lee (2009) stated that limestone
at the Western Belt was possibly formed in a shallow shelf during the closure of Paleo-
Tethys. Few limestone hills can be observed along Tapah road area, with unique karstic
features. Quaternary continental deposits cover few limestone hills.
Three study sites were selected: a. Sungai Siput Dolomite Hill, b. Gunung Kanthan
is both located in the northern part of the valley, while c. Gunung Rapat is situated in
the southern part of the valley (Fig. 1.1). The area of Sungai Siput Dolomite Hill is 8.63
ha, Gunung Kanthan which is owned by Lafarge Quarry is 70.49 ha and Gunung Rapat
which Anting Quarry owns is 56.12 ha.
Gunung Kanthan is mainly composed of limestone and dolomite. The limestone has
massive and thin-bedded varieties, grayish-white colour with black carbonaceous spots,
and is associated with carbonaceous phyllite. The dolomite is massive, pinkish-white
colour and cuts across the central part of the quarry in the N-S direction (Zabidi et al.,
2016). Sungai Siput is mainly composed of fine-grained and light to dark grey of thinly
laminated limestone. The carbonate rock is interbedded with shale and siltstone (Haylay
et al., 2017).
5
Figure 1.1: (Top) Map of Kinta Valley indicates the location of the study area;
(Bottom) Geological distribution of the Kinta Valley (Choong et al., 2014)
6
1.5 Scopes of Study
The scopes of study cover the geochemical, petrophysical, petrographic, and
morphological properties of the limestone and dolomite as in Table 1.1. The data were
collected from geological outcrops in the northern and southern parts of Kinta Valley.
Table 1.1: The division scopes of study applied for this research.
Scopes of study Descriptions
Geochemical Study The geochemical study emphasizes the trend of significant
minerals and supports lithotype classification from field
observation.
Petrophysical Study This study involves both quantitative and qualitative data.
Quantitative information gives the porosity and
permeability values. The quantitative data is supported by
qualitative data that display pore network distribution of 3D
images from core plugs.
Petrographic Study The petrographic study covers mineralogy, carbonate
microfacies (calcite and dolomite crystals texture),
established a paragenetic sequence, porosity types and
estimated pore percentage.
Morphological Study The morphological study supports the petrographic analysis
by looking into micropores and microfacies in high-
resolution FESEM images.
7
CHAPTER 2
LITERATURE REVIEW
This chapter introduces the reader to previous works that have been done in Kinta
Valley on the dolomite, dolomitization process, diagenesis, hydrothermal
dolomitization and petrophysical properties.
2.1 Regional Geological Settings
The presence of limestone in Peninsular Malaysia is associated with the tectonic
activity of Peninsular Malaysia during the opening and closure of the Paleo-Tethys
ocean. Two continental blocks, the Sibumasu block that drifted away from Gondwana
in the Early Palaeozoic and Indochina block, made up the Peninsular Malaysia
(Metcalfe, 2013). These two blocks collided during the Late Triassic. The closure of
the Paleo-Tethys ocean marked the boundary between the Sibumasu and the Indochina
blocks. The subduction of Sibumasu block, beneath Indochina block, resulted in
forming the Bentong-Raub suture zone (Metcalfe, 2002 & 2001). Thus, Peninsular
Malaysia comprises two terranes, Sibumasu and Indochina blocks and later on divided
into three main tectonostratigraphic longitudinal belts, which are the Western Belt,
Central Belt and Eastern Belt (Fig. 2.1). The Western Belt is furthered divided into the
Northwest Domain (zone) that covers the northwest Peninsula. Tjia and Zaiton (1985)
have differentiated west Peninsular Malaysia and northwest Peninsular Malaysia based
on structural, even though there is no well-defined boundary between those two
geologic domains. There is no biostratigraphy correlation between Kinta Valley and
northwest Peninsular Malaysia and Peninsular Thailand. The stratigraphic successions
of the Western Belt of Peninsular Malaysia do not have a clear figure because of
complex structure, thermal events and lack of available stratigraphic units (Foo, 1983).
8
The carbonates in Peninsular Malaysia are primarily located in the Western Belt of
Peninsular Malaysia (Fig. 2.1). There are also carbonates distributed in Pahang.
Figure 2.1: Peninsular Map combined with hillshade map shows geological provinces
of Peninsula Malaysia, divided into Western, Central and Eastern belts (Ramkumar et
al., 2019, Metcalfe, 2013) and distribution of Palaeozoic limestone outcrops
(unpublished).
9
An unconformity observed in limestone (Metcalfe, 1983) during the Carboniferous
age indicates a massive rifting event with few fault blocks (Hassan et al., 2014). The
separation of Sibumasu continental terrane from Gondwana occurs during the
Palaeozoic probably refers to rifting events (Metcalfe, 1999). Then, the arrival of
Sibumasu in low latitude areas is during upper Early Permian with a record of warm
water fauna correlated to Cathaysian biotas (Shi & Waterhouse, 1991).
Foo (1983) stated that Kinta Limestone is mainly composed of limestone with
subordinate dolomite and interbedded with schist and phyllite. Folding and faulting of
Kinta Limestone took place during Late Permian to Middle Triassic. Later, the
limestone was subjected to contact metamorphism by the emplacement of Western Belt
Main Range granite during the Middle to Late Triassic to Early Jurassic (Ros & Yeap,
2000; Searle et al., 2012). Few parts of limestone were altered and marbleized at the
area closed to granite. Then, hydrothermal fluids (felsic) that are rich in ores such as
cassiterite released from the cooling of granitic magma and passed through the
lineaments such as pre-existing fractures and faults that are closed to contact of Main
Range granite and along pluton margin in Late Cretaceous (Sautter et al., 2017). These
lineaments were in abundance at the contact between granite and limestone. Even
though there is no record on these dykes, it conforms to recorded events’ flow. This
event indicates intense hydrothermal circulation at the end of the Mesozoic (Ramkumar
et al., 2019).
The event that took place in Kinta Limestone previously is known as the thermo-
tectonic event. Then, another phase of folding and faulting events occurred in the
Western Belt Main granite from Middle to Late Cretaceous (Harbury et al., 1990;
Kräahenbuhl, 1991; Ramkumar et al., 2019; Shuib, 2009). A thermo-tectonic event in
Kinta Valley is visualized as in Fig. 2.2. This Late Cretaceous thermal event resulted in
recrystallization and dolomitization at certain area of Kinta Limestone (Foo, 1983;
Suntharalingam, 1967). The fluids that were passing through along the faults in Late
Cretaceous resulted in the alteration of Palaeozoic and Triassic rocks (Metcalfe, 1983;
Richter et al., 1999).
10
Figure 2.2: Diagrams of the major regional tectono-magmatic events, successive
stages and structural deformations in and around Kinta Valley in the Western Belt,
Western Malaysia (Ramkumar et al., 2019).
2.1.1 Geological Settings of Kinta Valley
There is scenic views of Kinta limestone hills that can be seen along the north-south
highway (Island & Ridzuan, 2001). The unique landscape of karst and caves features
can be observed in Kinta Valley. Kinta Valley is situated at the centre of Perak state.
The shape of Kinta Valley is elongated for almost 50 km in the North-South direction.
The valley has an inverted V-shaped widen to the south with the width 30km at the
south and 10km at the north of the valley (Choong et al., 2016).
Two granitic hills bound Kinta Valley, Main Range to the east and Kledang Range
to the west (Kassa et al., 2012). The Main Range is also known as the backbone of
Peninsular Malaysia with more than 400 km long that oriented from the North to South
direction (Choong et al., 2014). The western side of the valley is bounded by Kledang
Range, which is 40 km long and oriented from the Northeast to Southwest. The two
granite bodies are highly fractured and eroded. The large granite bodies intruded into
the surrounding rocks during Late Triassic (Bignell & Snelling, 1977; Darbyshire,
1988; S. Kassa, 2013; Krahenbuhl, 1991). The adjacent lithologies had altered and
metamorphosed due to the heat produced from granite bodies. The texture of limestone
11
was changed due to contact metamorphism at the time of granite intrusion (Cobbing et
al., 1992). The degree of metamorphism is different from one limestone hill to another
hill. Less metamorphosed limestone is in the north area of Kinta Valley, while high
metamorphosed limestone is in the south of Kinta Valley.
The carbonate facies in Kinta Valley is known as Kinta Limestone Formation (Foo,
1983). Kinta Limestone age from Silurian to Permian based on fossils evidence. The
Palaeozoic Kinta Limestone is exposed for a very long time and subjected to
dissolution. The remaining visible parts on the surface are remnants of limestone hills
that come out from the valley’s bedrock. Thirty percent (30%) of Kinta Limestone is
exposed to the surface and formed as limestone hills, while the remaining formed as
subsurface karst (Muhammad, 2003). The thickness of Kinta Limestone is estimated to
be 3000 m (Aiman Fitri, 2014).
The occurrence of dolomite in the Kinta Valley is believed due to hydrothermal
alteration. The presence of lode tin deposits in Kinta Valley indicates hydrothermal
origin, which has been discovered in granitoids and sedimentary rocks, mainly in
limestone and schist (Zabidi et al., 2016). The granite is pushed up and created a deep-
seated fault. The fluids rich in hydrothermal minerals, with some magnesium ions are
carried through the deep-seated fault to the surface and alter the rock wall of limestone
to dolomite. The limestone has massive and thin-bedded varieties, grayish-white colour
with black carbonaceous spots, and is associated with carbonaceous phyllite. While, the
dolomite is massive, pinkish-white colour and has cut across the central part of the
quarry in the N-S direction (Mazzullo, 2004). The limestone is also interbedded with
schists and phyllite. Ingham and Bradford (1960) stated that Kinta Limestone is part of
the ‘Calcareous Series’.
The limestone, which is believed to be the basement of valley, is currently covered
by Quaternary deposits of alluvium (Choong et al., 2016). Based on Raj, Tan, and Wan
Hasiah Abdullah (2009), Kinta Valley is covered by Old Alluvium (Simpang
Formation) overlain by Young Alluvium (Beruas Formation). Tin ores were discovered
and mined from the alluvium.
12
Figure 2.3: The Geological Map of Kinta Valley (modified from Choong et al., 2014).
2.1.2 Lithology of Kinta Valley
Rajah (1979) has grouped the lithology of Kinta Valley into six types of rocks, which
are (1) calcareous rock, (2) argillaceous rock, (3) arenaceous rock, (4) tourmaline-
corundum rock, (5) granitoid and (6) alluvium. Table 2.1 are descriptions for each rock
type describe by Rajah (1979).
13
Table 2.1: Types of lithology and descriptions in Kinta Valley (summarized from
Rajah, 1979).
Lithology Descriptions
(1) Calcareous
rocks
Kinta Valley mainly underlies by the sedimentary of calcareous
rocks. Calcareous rocks are composed of pure limestone,
dolomitic limestone, dolomite and ferroan dolomite. At some part
of the valley, the limestone has recrystallized and altered to
marble. The limestone was formed during Devonian to Permian
age.
(2) Argillaceous
rocks
The argillaceous rocks are composed of shale, phyllite and schist
with minor siltstone and sandstone. These rocks are highly
weathered to clay, forming Western Boulder Clays, Tekka Clays
and Gopeng Bed. The argillaceous rock is dated as Silurian,
Devonian and Carboniferous in age based on fossil evidence.
(3) Arenaceous
rocks
The arenaceous rocks dominantly consist of sandstone
interbedded with subordinate conglomerate, siltstone, and shale.
Ingham and Bradford (1960) believed the arenaceous series
formed during the Triassic age.
(4) Tormaline-
corundum
rocks
They are limited to the western part of the Kinta River, whereas
pure corundum rocks can be found only in the eastern region.
(5) Granitoids
Granitoids are formed as the basement of the valley. Two masses
of granitoids are known: Main Range granite flanks to the east of
valley and Kledang Range granite flanks to the west. The age of
granite intrusion is dated at the very end of the Triassic.
(6) Alluvium
Most of the Kinta Valley region is covered by alluvium. Walker
(1956) identified four types of alluvium: boulder beds, old
alluvium, young alluvium, organic mud and peat. The alluvium is
dated on the Quaternary age.
Meanwhile, Choong et al. (2014) have grouped Kinta Valley into five main
lithologies, which are (I) granite, (II) interbedded sandstone and mudstone, (III) shale,
(IV) limestone, and (V) recent alluvium (Fig. 2.4). The deposition initially starts with
interbedded sandstone and mudstone during Devonian. Then, it is followed by fine-
grained shale during Carboniferous. After that, limestone is deposited from Silurian to
Permian. Next, granite intruded the pre-existing rocks after limestone deposition during
14
Late Triassic to Early Jurassic. Lastly, the recent Quaternary sediments are deposited
and covered the floor of the valley. The metamorphism due to granite intrusion had
altered the composition of surrounding rocks. For instance, the limestone is altered to
marble, shale is altered to phyllite or schists, and interbedded sandstone and mudstone
are altered to quartzite and slate.
Figure 2.4: Chrono-diagram shows different lithologies formed in the various periods.
2.1.3 Stratigraphy of Kinta Limestone
Ingham and Bradford (1960) suggested Kinta Limestone is a Carboniferous age.
Meanwhile, Suntharalingam (1968) found mollusks and tabulate corals fossils in West
Kampar and proposed the age of Kinta Limestone to be from Middle Devonian to
Middle Permian. Lee (1971), on the other hand, believed Kinta Limestone age is from
Silurian to Middle Permian. Based on biostratigraphy, Kinta Valley has been dated
from Upper Ordovician to the Permian, where most of the fossils found are from
Permian (Fontaine, Tien, Vachard, & Vozenin-Serra, 1986). Metcalfe (2002) stated the
15
metamorphosed limestone at the north has Devonian to Carboniferous age based on
conodont dating.
Despite all the arguments, most researchers agreed with Metcalfe (2000) when he
proposed a stratigraphic scheme ranging from Silurian to Permian (Fig. 2.5 (a)) based
on the missing conodonts assemblage in Kinta Valley, and there is a hiatus from Upper
Devonian to Lower Carboniferous. However, the recent study of higher resolution on
conodonts assemblage in unaltered sediments by Haylay et al. (2017) shows that the
limestone has continuous succession from lower Devonian to upper Carboniferous as
in Fig. 2.5 (b). The recent study indicates there is no age gap in sedimentation of Kinta
Limestone from Silurian to Permian.
16
Figure 2.5: (a) Stratigraphic scheme of Kinta Limestone (modified from Metcalfe,
2000); (b) The conodont biostratigraphy of Kinta Limestone indicate a continuous
succession of sediments from lower Devonian to upper Carboniferous.
2.1.4 Depositional Environment
Pierson et al. (2008 & 2009) stated the paleo-depositional environment of Kinta
Limestone had been interpreted as shallowing marine and slope in deep water that
above Calcite Compensation Depth (CCD). The Kinta Limestone was deposited
progressively in a shallowing marine condition after clastic sedimentation during
Silurian. It was supported by the evidence of shallow marine benthic organisms from
17
Devonian to Permian age (Pierson et al., 2008 & 2009). The interpretation is also based
on the evidence of thinly bedded micritic limestone that indicates low energy setting
and slump structure at the base of the slope close to the deep sea.
Slope structures such as slumps can be observed in Kek Look Tong Temple near
Ipoh (Abd Kadir et al., 2009) (Fig. 2.6). This event could explain the mixture of shallow
marine and deep marine. Significant slumps with direction towards the west, and the
slump axis is from the North-South direction. Based on paleogeographic reconstruction,
the eastern part of Kinta Valley is identified as a shallow marine platform.
Figure 2.6: The slope structures (slumps) of Kinta Valley in Kek Look Tong temple,
Ipoh (Pierson et al., 2011).
Tsegab and Chow (2019) also stated the paleo-depositional environment of Kinta
Limestone is from shallow to deep marine settings. They stated that the Kinta
Limestone environment is deep marine settings that are slightly deeper slopes in the
northern part of Kinta Valley and progressively shallowing towards the southern part
of the valley. In the Sungai Siput section at the north part of the valley, Kinta Limestone
18
is mainly composed of fine-grained carbonate mudstone. Besides, the north part of the
valley also has chert, black shale, siltstone and mudstone. These lithofacies suggested
low energy depositional environment. The lithofacies colour variations in Kinta Valley
are somehow influenced by total organic content in the rock. In the northern part, the
lithofacies of Kinta Limestone has light to dark grey and black colour. This indicates
limestone is deposited in a prohibited oxidation of organic content environment, either
in lagoon or deep marine settings. Shell fragments found in Sungai Siput limestone
indicate that Kinta Limestone was formed at a depth shallower than Calcite
Compensation Depth (CCD).
Granite intrusion during the Late Triassic to Early Jurassic formed the Main Range
and Kledang Range (Foo, 1983). Older rocks have been metamorphosed and
transformed to marble and schist due to direct contact with granite bodies. After the
collision between Sibumasu and East Malaya, the blocks were uplifted and formed a
terrestrial environment. Ramkumar et al. (2019) also stated the limestone is uplifted to
the surface by tectonic activity and exposed to humid tropical during the Mesozoic age.
2.1.5 Previous works on Dolomite in Kinta Valley
Recently, dolomite in Kinta Valley become an interesting topic to be discussed as the
researchers believed the dolomite is from hydrothermal origin. The precious studies
agreed that dolomites occurred within the fractures and voids of the host rocks (Nurul
Afiqah et al., 2020; Ramkumar et al., 2019). Therefore, the dolomites in Kinta Valley
were identified as localized hydrothermal dolomite bound within the strata and
fractures. Localized hydrothermal dolomitization only requires a small amount of
magnesium supply compared to pervasive (large-scale) hydrothermal dolomitization.
The possible magnesium source of replacement dolomite in Kinta Valley comes from
the host rocks. The magnesium is circulated in hot basinal water and becomes
hydrothermal when they are transferred into cooler areas during tectonic activities and
capable of precipitating or replacing dolomite (Hardie, 1991). Geochemical data shows
limestone is marine origin, while dolomite shows different geochemical results from
19
limestone (Ramkumar et al., 2019). Thus, they assumed the origin of dolomite is
probably non-marine.
Based on the previous study, the dolomite in Kinta Valley is believed from
hydrothermal origin, where isotopic data shows depleted stable isotope oxygen 18
(δ18O) values from -18.4% to -16.37% (Shukri, 2010). Shah and Poppelreiter (2016)
also mentioned that the fine to medium dolomite matrix and coarse crystalline dolomite
cement in Kinta Limestone is originated from hydrothermal fluids based on isotopic
data that show high depletion of stable isotope oxygen-18 (δ18O) from -13.75% to -
11.10% VPD and -18.75% to -15.04% VPBD respectively (M.M. Shah, Poppelreiter,
Kadir, & Choong, 2018). The hydrothermal dolomitization is predicted to occur by the
end of the Mesozoic (Ramkumar et al., 2019).
The dolomite in Kinta Valley is recently studied by a few researchers. Ramkumar
et al. (2019) have identified five types of dolomites facies at a specific area in Lafarge
Quarry, which are (1) early replacement dolomite, (2) sucrosic dolomite, (3)
metamorphosed dolomite, (4) late replacement dolomite, and (5) brecciated limestone
and dolostone. The dolomite facies occurred along the bedding plane (strata-bound) and
major faults and fractures (structure-controlled). There are three sets of fractures that
cut across the facies. The oldest set of fractures is parallel and perpendicular to a
bedding plane. The second oldest fracture is thinner than the oldest set of fractures, and
it has an irregular orientation. The youngest group of fractures is millimetre-thick and
has many veins orientation that cut through whole facies.
Besides, Nurul Afiqah et al. (2020) also identified the five types of dolomite facies
in Kinta Valley based on two groups of dolomites: matrix dolomite and cement
dolomite. There are three types of matrix dolomite, which are: (1) very fine to fine
crystalline nonplanar-a dolomite, (2) fine to coarse crystalline nonplanar-a to planar-s
dolomite, (3) fine to medium crystalline planar dolomite. Two types of cement
dolomite, which are (1) coarse crystalline planar saddle dolomite and (2) coarse to very
coarse crystalline nonplanar to planar dolomite. Few dolomites show intercrystalline
pores with low porosity. Coarser dolomite shows late precipitation. The appearance of
20
dolomite breccia in Kinta Limestone indicates hydrofracturing that release from
overpressure upwards flows from hydrothermal fluids.
The matrix dolomites are believed to occur at the early diagenesis and replace the
host limestone. The dolomite in early diagenesis is not hydrothermal dolomite but
localized dolomite that occurs probably during post-dating Permian-Triassic Sibumasu-
East Malaya collision or during middle Late Cretaceous folding and faulting of the
Malay Peninsula (Ramkumar et al., 2019). Nurul Afiqah et al. (2020) stated the
brecciation and cementation take place after early dolomitization. After that, the next
generation of dolomitization occurs in the fractures due to overpressured hydrothermal
fluids (Nurul Afiqah et al., 2020; Ramkumar et al., 2019). A late stage of dissolution
resulted in de-dolomitization by meteoric water. Nurul Afiqah et al. (2020) stated the
de-dolomitization occurred between two generations of types of dolomite cement,
where it highly destroyed first dolomite cement generation. There is late mineralization
where sepiolite was found and calcitization postdated the dolomites.
Nurul Afiqah et al. (2020) had mentioned the intercrystalline pores could be found
in dolomite and de-dolomitized rocks. However, the previous research did not state
which types of dolomite the pores are present and the percentage of porosity in
dolomite. The research gaps here can be resolved and discovered to understand how the
diagenetic process influenced the porosity changes.
2.2 Dolomite
Dolomite rock is a sedimentary carbonate rock composed of mainly mineral dolomite
and has a chemical formula of CaMg (CO3)2. Rocks that have 10-50% of mineral
dolomite are recognized as dolomitic and known as dolostone (Highley et al., 2006).
The term dolostone was introduced in 1948 to differentiate between rock and mineral,
where dolostone referred to a rock formed from dolomite mineral (Al-Awadi et al.,
2009). The rock is considered pure dolomite when it has minimal 40% MgO content
(Highley et al., 2006). Dolomite precipitated directly from fluids composed of
magnesium, calcium and carbonate ions to form cement or lithified sediment (Al-
21
Awadi et al., 2009). Most dolomites form from chemical alteration and replace the pre-
existing limestone, and the replacement process is known as the dolomitization process
(Highley et al., 2006). Most dolomites replace CaCO3, and it can be expressed by the
chemical equation,
Tucker and Wright (1990) stated two main factors of dolomite formation, which are
the source of Mg2+ ions and the transport system that carried dolomitizing fluids
through carbonate sediments. The possible fluid sources are seawater, meteoric water,
subsurface marine fluids, Mg2+ could be expelled from high-Mg calcite and smectite
clays.
2.2.1 Dolomite Texture
Rock texture is referred to the relationship of basic rock properties such as crystal shape,
size, orientation and packing. The study of dolomite texture is vital to understand the
dolomitization process. Dolomite rock textures can be categorized according to crystal
size distributions and crystal boundary shapes. Crystal size distributions are categorized
as unimodal or polymodal, while crystal boundary shapes are categorized as planar or
nonplanar. Unimodal size distribution specifies a single nucleation occurrence on the
unimodal substrate, while polymodal size distribution indicates multiple nucleation
occurrences on a unimodal or polymodal substrate. The crystal that undergoes faceted
growth is identified as planar boundaries, otherwise, crystal that undergoes non-faceted
growth is called nonplanar boundaries. Nonplanar boundaries develop at a high
temperatures of more than 50°C and at great supersaturation (Gregg & Sibley, 1987).
2CaCO3 + Mg2+ CaMg (CO3)2 +Ca2+
22
Figure 2.7: Summary of dolomite rock texture, modified from (Gregg & Sibley,
1987).
In terms of crystal boundary shape, Gregg and Sibley (1984) initially divided it
into two main categories, which are xenotopic dolomite and idiotopic dolomite (Fig.
2.8). Xenotopic dolomite texture results from the replacement of limestone by dolomite
or neomorphic recrystallization of pre-existing dolomite at elevated temperature. In
comparison, Idiotopic dolomite texture shows straight and compromises crystals
boundaries and usually has rhombic shape (Gregg & Sibley, 1984). Xenotopic texture
is common in dolomites of pre-Cenozoic age, and Idiotopic texture is common in
dolomites of all ages (Tucker & Wright, 1990). The detailed classifications of dolomite
texture have been explained by Gregg and Sibley (1984) (Fig. 2.9). Later, Gregg and
Sibley (1987) classified crystal-boundary shapes as planar or nonplanar (Fig. 2.10),
which are described before as idiotopic and xenotopic, respectively.
23
Figure 2.8: General configuration of (a) Idiotopic Dolomite Texture; (b) Xenotopic
Dolomite Texture (Gregg & Sibley, 1984).
Figure 2.9: Detailed classifications of Idiotopic dolomite texture and Xenotopic
dolomite texture (Gregg & Sibley, 1984).
24
Figure 2.10: Classification of dolomite texture based on crystal-boundary shapes -
Planar-e/-s or Nonplanar (Gregg & Sibley, 1987).
2.2.2 Relationship Between Dolomite Textures and Formation Temperature
Few factors are controlling the texture of dolomite, such as nucleation effects and
mechanism of crystal growth (Gregg & Sibley, 1984). However, Braithwaite and Heath
(1996); Gregg and Sibley (1984) suggested that the major factor controlling the crystal
growth that eventually affects dolomite texture is the temperature. Temperature effects
on dolomite texture are very important as dolomite in Kinta Valley is hydrothermal
origin.
The mode of crystal growth and texture are controlled by the temperature
(Braithwaite & Heath, 1996). Gregg and Sibley (1984 &1987) mentioned the crystal
boundary shape is affected by growth kinetics that is partially controlled by
temperature. The boundary between the formation temperature of planar dolomites and
nonplanar dolomites is 50°C to 60°C, which is known as critical roughening
temperature (CRT) (Fig. 2.11) (Sijing et al., 2014). Tucker and Wright (1990) stated
the CRT for dolomite was from 50 ºC to 100 ºC, while calcite is around 25 ºC.
At the low temperature of dolomitization, the dolomite tends to preserve the fabric
(Sijing et al., 2014). From crystal growth theory, the crystal surface is smooth at low
temperature, and the crystal mosaics comprise euhedral to subhedral crystals (Tucker
& Wright, 1990). At high temperature, whereas above a ‘critical roughening
25
temperature’ (CRT), the dolomite would crystallize and produce coarse, rough surface
and undulatory texture. The common texture deals with high temperature
dolomitization is xenotopic dolomite that has an anhedral crystal face. While dolomite
does not go through deep burial and high temperature, it will not have xenotopic texture;
instead, it has idiotopic texture of dolomite, resulting in euhedral crystal.
Growth in temperature or length of time leads more systematic stoichiometric
dolomite (Gregg & Sibley, 1984). Xenotopic textures are formed from burial
dolomitization of limestone or burial recrystallization of near-surface dolomite at early
formation. However, some idiotopic textures of dolomite crystals can also be formed at
higher temperatures where it develops into cavities is affected by clay and organic
matter (Tucker & Wright, 1990). It is believed that cement dolomite genesis has a
higher formation temperature than replacive dolomite (Sijing et al., 2014). Idiotopic
textures are not typical since calcite has low CRT, which is almost 25 ºC. Most of
limestone that undergoes neomorphism have xenotopic texture (Tucker & Wright,
1990).
Figure 2.11: Common dolomite texture emphasizing the effect of temperature on the
behaviour of dolomite crystal (Sijing et al., 2014).
26
2.2.3 Hydrothermal Dolomitization
There are few mechanisms of dolomitization that researchers have recognized. The
mechanisms include evaporative and reflux dolomitization, mixing zone and Coorong
dolomitization, burial dolomitization, and hydrothermal dolomitization (MacDonald et
al., 2015). Commonly, that low temperature of dolomitization always increases the
reservoir properties, while the elevated temperature of dolomitization reduces the
reservoir properties (MacDonald et al., 2015).
The word “hydrothermal” is defined as warm and hot fluids to some temperature
above ambient surface temperature. By extension, dolomites developed at lower
temperatures than ambient temperature are not considered hydrothermal
dolomitization, although they formed at quite high temperatures (Machel & Lonnee,
2002). The hydrothermal may occur with the condition that the fluids at least must
experience the temperature of 5°C greater than ambient formation temperature as they
are moved upward into cooler and shallower parts of the basin. Convection heat flows
have explained that the fluids migrate from warmer to cooler before their heat dissipates
into the formation. Hydrothermal fluids pressure also can be greater than ambient
formation pressures (Al-Awadi et al., 2009). Hydrothermal dolomite commonly forms
pervasive dolomites that are confined around faults (Fig. 2.12).
27
Figure 2.12: Hydrothermal dolomitization. Fluids from deep within a basin can
rapidly move up through fault planes to dolomitize carbonates at a shallower area (Al-
Awadi et al., 2009).
Hydrothermal dolomites (HTD) are formed within zones of elevated temperature.
Hydrothermal dolomite forms from deep basinal fluids as they transmitted upward
through permeable path flow, such as faults and thrust planes. The hydrothermal
concept is the fluids at first circulate downward and become warm due to local
geothermal gradient. With continuous heating, the fluids become more buoyant, and
then they migrate upwards through faults and bedding planes. Later, the carried fluids
alter the composition of surrounding rocks (Al-Awadi et al., 2009).
One of the examples of hydrothermal dolomite is at Tarim Basin. Usually, saddle
dolomite texture is found in the deep burial or hydrothermal origin at shallower depths
(Trotter, 2014). Saddle dolomite signifies the last stage of dolomitization caused by
hydrothermal dolomitization (Jiang et al., 2016). The type of dolomite that is a common
indicator for hydrothermal dolomite association is saddle dolomite (Lavoie & Chi,
2006). The presence of saddle dolomite indicates high-temperature formation (Machel
& Lonnee, 2002). Saddle dolomite is the unique crystal shape that usually develops at
high temperature and is both void fillings and matrix replacing. Other features typically
associated with a hydrothermal origin are breccia, zebra fabrics, leached limestone,
28
leached dolomite, barite, celestite, sulphide minerals, quartz, bitumen, and microporous
limestone (Copp, 2008).
Another example of hydrothermal dolomite is Ratburi Limestone in Thailand.
Mansyur (2017) stated these dolomites developed as replacive dolomite (RD) at earlier
stage and cement dolomite (CD) at a later stage. During the earlier phase, dolomite is
derived from marine meteoric water and formed a replacive dolomite. While, during
the late stage, cemented dolomite is produced from high-temperature fluids circulation
due to granite emplacement during Cretaceous (Carnell & Wilson, 2003). The
dolomites result from hydrothermal solutions that moved upwards through fault
systems and causing in extensive dolomite. The migration probably has been forced by
overpressure and fluids flow from deep-seated fault shears or granite emplacement.
This kind of case has completely blocked matrix porosity (Mansyur, 2017).
2.2.4 Hydrothermal Dolomite Groups based on Petrography
The characteristics of dolomite were well studied previously through petrography.
There are three groups of dolomites commonly found in hydrothermal region: replacive
dolomite (RD), cemented dolomite (CD) and baroque dolomite. The replacive dolomite
is a dolomite that partly or completely replaces the matrix and consists of micritic or
calcitic inclusions. Dolomite occurred as a replacement product of the host limestone,
which occurs when calcite exists (Lucia, 2002, Shah et al., 2012). A typical
characteristic of replacive dolomites is they have euhedral rhombs with cloudy
occurrence due to solid micritic or calcitic inclusions. Other characteristics of these
dolomites are they appear as non to dull cathodoluminescence character with
uncommon bright patches and have a single-phase liquid aqueous inclusion. Usually,
the best reservoir quality happens when dolomites are developed as a replacive phase
because they tend to enhance the porosity and permeability as they are related to
dissolution (Wilson et al., 2007). The term sucrosic is often applied to a porous mosaic
of euhedral rhombs. Dolomite crystals in these mosaics usually have cloudy centers and
clear rims. The cloudiness comes from the empty microcavities.
29
Meanwhile, cemented dolomites, also known as void-filling, usually form after all
calcites have been replaced (Lucia, 2002). When forming as a cement, dolomite
negatively impacts reservoir quality, in which these cements decrease both porosity and
permeability (Carnell & Wilson, 2003). They have a texture of euhedral to subhedral
shape and are usually made up of closely interlocking hypidiotopic mosaics. The
characteristics of cemented dolomite have a nonluminescent to dull properties and
comprise rare single-phase and two-phase liquid vapour primary aqueous inclusions.
The range of crystal size is between 200 to 800μm. Usually, cemented dolomites tend
to occlude the pore space as they are associated with precipitation of dolomite cement,
resulting in low porosity and permeability. They are also formed at greater depths and
higher temperatures (Wilson et al., 2007).
There is one more group of dolomites that can be cement dolomite or replacement
dolomite. It is known as baroque dolomite and can be called ‘saddle’ dolomite. It has
curved crystal faces and cleavage planes. Most the baroque dolomite is Ca-rich, and it
consists of iron content. When it occurs as cement or cavity-fill dolomite, the dolomite
mostly has a xenotopic texture of uneven crystal boundaries within the mosaic curve.
While, when it forms as replacement dolomite, the dolomite usually appears coarse
xenotopic mosaics. The baroque dolomite rhombs may be distributed through
limestone. The occurrence is also common in veins, fractures and associated with
sulphide mineralization (Tucker & Wright, 1990).
2.3 Dolomitization on Petrophysical Properties
The dolomitization in carbonate may affect the petrophysical rock properties, porosity
and permeability. Tucker and Wright (1990) stated the porosity of a rock is defined as
the ratio of total pore space to the total volume of the rock. The permeability is also
crucial in determining the flow of fluids. The carbonate reservoir rocks have a very
complex pore space structure which will eventually affect the reservoir properties. The
differences in the permeability and porosity of carbonate reservoir rocks are mainly due
to differences in the geometry and connectivity of pores (Kuzmin & Skibitskaya, 2017).
30
It has been acknowledged that porosity and permeability change with dolomitization
(Sun, 1995).
2.3.1 Porosity
The porosity is divided into two stages, which are primary porosity and secondary
porosity. Primary or initial porosity occurs during a pre-diagenesis, and usually, it is
affected by microstructural factors. It consisted of two primary stages, which are pre-
depositional and depositional stages. Pre-depositional stage is when the individual
particles start to form and commonly develop the intragranular pores; the depositional
stage is when the final deposition happens (Moore, 2001). Besides, the secondary
porosity forms due to post-depositional dissolution at any moment after final
deposition. Most porosities in limestone and dolomite reservoirs originated from
secondary derivation, and primary porosity is rarely preserved (Mazzullo, 2004). Moore
(2001) mentioned the porosity in carbonate mainly generated by dissolution and
modified due to dolomitization, brecciation and fracturing.
2.3.1.1 Pore Types
Pore types in carbonate rock are various compared to clastic rock (Choquette & Pray,
1970). This complexity is due to the biological overprint of carbonate sediments that
resulted in porosity between grains and fossils; and chemical reactivity usually forms a
secondary porosity due to persistent diagenetic processes such as dolomitization
(Moore, 2001). The most often used classification of carbonate porosity is from
Choquette and Pray (1970) that emphasize fabric selectivity based on basic porosity
types, time, the porosity origin, abundancies, pore size and shape (Tucker & Wright,
1990).
Moore (2001) stated the Choquette-Pray porosity classification comprises four
components: genetic modifier, size modifier, basic porosity type and abundance
modifier (Fig. 2.13). The genetic modifier is the information regarding the processes
responsible for the porosity modification, such as solution or cementation, time of
31
formation, and the porosity changes during the burial cycle. Size modifier is used to
distinguish the numerous size classes of pore systems, such as mega-pores and micro-
pores. Finally, an abundance modifier is utilized to identify the percentage of pore types
in carbonate rock.
Figure 2.13: Four components of porosity classification (Choquette & Pray, 1970).
Choquette and Pray (1970) have classified carbonate pore types into three
categories: fabric-selective, non-fabric-selective and fabric-selective or non-fabric-
selective as shown in (Fig. 2.14). The fabric-selective porosity types mean the pores are
associated with fabric elements of the rock, like grains or crystals. The non-fabric-
selective porosity types are defined as the pores not influenced by the fabric elements,
instead of cross-cutting the actual fabric of the rock, such as fracture porosity (Tucker
& Wright, 1990). Therefore, it is vital to assess the fabric selectivity in order to
understand and classify carbonate porosity.
32
Figure 2.14: Pore Types of carbonate rocks-Fabric selective; Not fabric selective;
Fabric selective or not fabric selective (Choquette & Pray, 1970).
2.3.1.2 Common Pore Types in Dolomite Rock
The most common pore type that develops in dolomitized rock is intercrystalline pore.
Vugs and intercrystalline pores tend to develop in greater dolomite phases in the rocks
(Choquette & Pray, 1970). Most types of porosity in dolomites is originated from a
precursor sedimentary fabric. Fracture pore types are important in reservoir
development and common in dolomites. The common pore types in hydrocarbon
reservoirs are intercrystalline and dissolutional pores (Purser et al., 1994). Tucker and
Wright (1990) stated there are five distinct pore types in dolomites, which are: (1)
fabric-replacive porosity, (2) dissolution, vugs and mould, (3) Intercrystalline porosity,
(4) Intracrystalline dolomouldic porosity, (5) Fracture and breccia porosity.
33
Fabric replacive porosity is the porosity preserved from any modification by
dolomite cement, and the porosity is closed to the precursor carbonate rock. Usually,
porosity is preserved in microcrystalline dolomites. The vuggy porosity may predate
and postdate dolomite formation. The dissolution that occurs before dolomitization is
considered as predolomite vugs. Syndolomite vugs occurred within dolomitized rocks
that are associated with dissolution and dolomite precipitation. Postdolomite vugs result
from local dissolution of unstable dolomite, although they are porous, the postdolomite
vugs tend to have low permeability due to fine crystal dolomites. Intercrystalline
porosity is typical in dolomite reservoirs and is a result of dolomitization.
Intercrystalline porosity is usually well developed in between coarse crystalline
dolomite. However, most the Palaeozoic dolomites have low porosity due to diagenetic
modification, crystal growth and recrystallization. Intracrystalline dolomouldic
porosity results from near-surface telogenetic diagenesis. The fracture is typical
porosity in dolomite. Few pores in dolomite are related to pre-existing porosity in
precursor limestone (Tucker & Wright, 1990).
2.3.2 Relationship of Dolomitization and Porosity Evolution
Reservoirs in carbonate rocks usually composed of multi-porosity systems that impart
petrophysical heterogeneity to the reservoirs (Mazzullo, 2004). In many cases,
dolomitized rock generally has better reservoir properties than limestone. This is
because chemically, during the dolomitization process, two moles of calcite are
transformed to one mole of dolomite, causing a net rise in porosity. However, other
factors need to be considered as they may affect porosity changes during
dolomitization, such as the characteristics of precursor sediments, subsequent leaching
and cementation (Al-Awadi et al., 2009).
Dolomitization can enhance, preserve or destroy porosity relative to the parent
carbonate rocks (Al-Awadi et al., 2009; Sun, 1995). However, the porosity in dolomite
does not necessarily depend on dolomitization. The porosity may inherit from precursor
limestone rocks, such as interparticle pores and voids. Porosity that results from
dolomitization happens due to dissolution at one site and incomplete cementation.
34
Other pores that postdate dolomitization, such as fractures, dissolution, breccias and
others. Most of the dolomites texture and interconnected porosity are apparently from
diagenetic origin. Thus, dolomitization fundamentally enhances the porosity. However,
the fundamental overlooks that porosity has a lower value in most ancient dolomites
and limestones than modern carbonate (Purser et al., 1994).
Mazzullo (2004) stated the porosity reduces as the percentage of dolomite increases
to 50% in the rock. After that, porosity starts to increase when dolomite increase
continuously above 50%. Then, the porosity and permeability decline when dolomite
reaches 80% and above. As dolomite comes 95%, the rock becomes solely
impermeable, and porosity is occluded. The relationship of porosity and percentage of
dolomite is shown as in (Fig. 2.15) below. Overall, it is proven that porosity increases
as the percentage of dolomite increases (Mazzullo, 2004). At an early stage of
dolomitization, dolomite growth is associated with porosity reduction. As dolomite
increases, the dolomite crystal develops a supporting texture that prevents the original
porosity from compaction and porosity loss. Then, porosity will reduce again after all
carbonate sediment is replaced by dolomite due to the higher volume of dolomitizing
fluids that pass through the rocks. It causes an increase in crystal size and interlocking
of dolomite crystal. The dolomite porosity is well preserved if the growth of dolomite
crystals stopped after the replacement of precursor limestone by dolomite. Dolomite
has greater physical and chemical strength compared to limestone. Thus, it is more
susceptible to porosity preservation (Sun, 1995).
35
Figure 2.15: Relationship of porosity to the percentage of dolomite in carbonate rocks
(Mazzullo, 2004).
The porosity evolution in dolomites is very complicated. Few may dissolve to
enhance porosity, others may recrystallize and reduce porosity, and still, others may
withstand alteration and maintain porosity. Purser et al. (1994) have come out with three
possible porosity evolutions with dolomitization. Firstly, the porosity could be
destructive due to dolomitization. It reduces precursor limestone porosity due to crystal
growth within an open system with CaCO3 and Mg2+ supply. The porosity decreases as
the rate of dolomite precipitation is more significant than the rate of dissolution. This
case commonly occurs during burial and mechanical compaction. The presence of
many low-porosity dolomites later will be occluded by coarse crystalline dolomite
cement.
36
Secondly, the pre-existing pore space may rearrange during dolomitization, and
there is no reduction or enhancement of porosity. Logically, the dolomitization
encompasses the dissolution of precursor carbonate and later the precipitation of
dolomite. Conversely, this comparison is slightly misleading because calcite and
dolomite do not have similar diagenesis processes. The diagenesis of limestone does
not need any external source even related to water movement. Furthermore, the
limestone diagenesis acquired a closed system associated with calcium and carbonate
ions, while dolomitization is an open system that involves at least the magnesium ion.
Therefore, the redistribution of pre-existing pore space that involves a volume
equilibrium between the input of MgCO3 and the output of CaCO3 is an ambiguous
situation (Purser et al., 1994).
Thirdly, porosity may increase due to dolomitization. The porosity may enhance if
carbonate ions are preserved during dolomitization. The rock does not experience
compactions if the rate of precursor carbonate dissolution is higher than the rate of
dolomite precipitation. The porosity will grow due to alteration in molar volume.
Nevertheless, dolomitization is an open diagenetic system. Thus, it possibly has two
occurrences: excessive dissolution of precursor carbonate or excessive precipitation of
dolomite cement (Purser et al., 1994). Porosity enhances as dissolution rate is higher
than precipitation rate. Dissolution commonly occurs in intense zones like hot, basinal
derived fluids that migrate upwards through faults are mixed with shallower formation
fluids. The characteristic of deep hot fluids is commonly associated with hydrothermal
margin. The common features in hydrothermal region are dissolution vugs and breccias
with saddle dolomite texture and sulfide minerals, associated with the dissolution
process (Sun, 1995). The evidence of porosity enhancement during dolomitization is
intercrystalline voids and mouldic pore type within carbonate grains and matrix (Purser
et al., 1994).
2.3.3 Permeability
Permeability is an expression of fluids’ movement through a rock (Reep, 2009).
Permeability of “tight” rocks is a challenging matter to accurately characterize,
37
although the condition of permeability is less complex than porosity (Kuzmin &
Skibitskaya, 2017; Purser et al., 1994). Reservoir permeability may differ from one
reservoir to a different reservoir, even they have a similar open porosity and equivalent
pore-size distribution (Kuzmin & Skibitskaya, 2017).
The permeability of carbonate rocks does not depend on porosity value (Hayley &
Schmoker, 1997). Lucia (2002) also agreed that there is no relationship between
porosity and permeability in dolomites. However, few researchers claim there is a
relationship between porosity and permeability due to the diagenetic process of
dolomite (Machel, 2004). The diagenetic process can be studied by looking at the
dolomite textures, by which usually, the euhedral dolomites showed higher
permeability increment than subhedral texture. Also, pore types play a role in giving a
different value of permeability in dolomite. For example, dolomites that are consisted
of intercrystalline or interparticle pores always have a larger permeability than micrite
and microsparite crystals (Hatampour et al., 2015).
Other than looking into the dolomite texture, the fault zone and tectonic fracture
also influence pore types, the creation and destruction of permeability. The fault zone
and tectonic fracture can be studied by looking at the distributed strain. The distributed
strain increases if the heterogeneity level of rock increases and will eventually result in
increased permeability. Thefore, high permeability is a good indication of excellent
reservoir quality. Sometimes, very high permeability can result in losing fluids which
reduces the level of production. But, in most cases, high permeability increases
production. Thus, the interpretation of highly deformed areas can also help to
understand the permeability and nature of fluids flow (Reep, 2009).
38
CHAPTER 3
METHODOLOGY
This chapter contains detailed descriptions of research methodology, and the workflow
(Fig. 3.1). The methods begin with preliminary study, then followed by geological
fieldwork, laboratory analysis and data analysis.
Figure 3.1: The flowchart of research methodology.
Preliminary Study:
1. Geological Settings of
Kinta Valley
2. Dolomite Study
3. Petrophysical Study
Geological Fieldwork:
1. Field Observation
2. Sedimentary Logging
3. Sampling
Sample Preparation (Core plugs,
rock slabs, powdered sample)
Laboratory Analysis and
Interpretation
Objective No. 1 will
be achieved
Objective No. 2 will
be achieved
Objective No. 3 will
be achieved
Mineralogical and
Geochemical Study
Petrophysical Study
Petrographic Study
Morphological Study
XRD & XRF
Poroperm &
Micro-ct scan
Photomicrograph
FESEM
39
3.1 Preliminary Study
A preliminary study was carried out with a literature review. The literature review
covered the geological settings of Kinta Valley, the dolomite and dolomitization
process, and how it influences petrophysical properties. This study is very significant
to get the early ideas on the research project. Then, the geological map was modified
from Choong (2014) and constructed by using ArcGIS software.
3.2 Geological Fieldwork
The outcrops from three localities in Kinta Valley were chosen for this study: Sungai
Siput Dolomite Hill, Gunung Kanthan and Gunung Rapat. The localities were chosen
based on outcrop accessibility and the presence of dolomites. Geological fieldwork was
conducted to observe the lithology, construct sedimentary logging and sample
collection.
The followings are detailed works during field excursion:
1. Define the lithologic units and structural. Hydrochloric acid with 10% of 37mol
concentration was used to distinguish between limestone and dolomite rocks in
the field. Structures such as faults and fractures were recorded in the outcrop.
The lineaments were measured using the Suunto compass.
2. Sedimentary logging was constructed based on outcrop descriptions such as the
grain size, sorting, angularity, colour, lithology, structure, and additional
features. Then, the selected data were transferred into Sedlog software.
3. The block samples were collected horizontally along the outcrops based on
systematic sampling of one (1) metre interval for detailed analysis and based on
the accessibility of the outcrop hill’s surface. A total number of 241 rock
samples were collected for further laboratory analysis (Fig. 3.2).
40
Figure 3.2: Number of collected samples for each locality.
3.3 Laboratory Analysis
The laboratory analysis is divided into four categories: mineralogical analysis,
petrophysical analysis, petrographic analysis and morphological analysis. The
mineralogical analysis includes X-Ray Diffraction (XRD), X-Ray Fluorescence (XRF);
petrophysical analysis includes Poroperm and Computed Tomography (CT);
petrographic analysis includes thin section study, and morphological study includes
Field Emission-Scanning Electron Microscope-Energy Dispersive X-Ray (FESEM-
EDX). Table 3.1 shows the number of selected samples for each analysis. The limitation
in sample collection is most of the outcrops are highly fractured, and the samples
cracked while coring. Thus, the sample selection is based on non-defective core plugs
and dolomite rocks in the area. This is because most of the quarries in Kinta Valley is
calcitic than dolomitic.
41
Table 3.1: Number of tested samples for each analysis.
No. Laboratory Analysis Number of Samples
Sungai Siput
Lafarge- Hill B
Lafarge- Hill E
Anting Total
1. X-Ray Diffraction (XRD) 6 6 11 7 30
2. X-Ray Fluorescence (XRF) 6 6 7 7 26
3. Poroperm 6 6 11 7 30
4. Computed Tomography (CT) Scan
6 6 11 7 30
5. Petrographic Analysis 6 6 11 7 30
6. Field Emission-Scanning Electron Microscope-Energy Dispersive X-Ray (FESEM-EDX)
1 1 3 1 6
3.3.1 X-Ray Diffraction (XRD)
X-Ray Diffraction Analysis identifies the unknown crystalline materials (Penuel et al.,
2017). XRD analysis will provide information on the existence of crystalline
components and atomic spacing of a material based on its diffraction patterns. For
qualitative analysis, XRD measurements need about 1 gram of a sample consisting of
extremely fine-grained powder to achieve good result. The minerals were identified
using Cu-K radiation (Tunik et al., 2009).
3.3.1.1 Sample Preparation
The samples were crushed and ground into powder approximately 10 grams for each
sample (Fig. 3.3). Then, the powdered samples were sieved using a sieving pan of
63µm. The grains that passed through the sieving pan were used for XRD analysis. The
recommended grain size is less than 75µm, but the best is 10µm to 50µm (Pecharsky
& Zavalij, 2009).
42
Figure 3.3: Ten grams of powdered samples for XRD analysis.
3.3.1.2 Procedure
The parameters needed for XRD analysis are scan range, exposure time and step size.
The scan range used for this analysis is from 10º to 80º with 100s/step of exposure time.
The step size for the sample is 0.02º/step. The samples were sent to Centralized
Analytical Laboratory (CAL), Universiti Teknologi PETRONAS for analysis. The
XRD spectrometer model used is X’ Pert Powder PANalytical (Fig. 3.4). The X-ray
source for this model is Cu-K radiation. At first, the system started with the initialization
process. Then, the tube power was set to 30 kV and 10 mA. Next, the tube and detector
were transferred to the samples point. Then, the diffractometer was switched on, and
the results were displayed in the computer system. The results were interpreted by using
Jade 9 XRD software. The peaks were searched in the software by matching them with
standard peaks from International Centre for Diffraction Data (ICDD) database. Lastly,
the percentage for each mineral in the samples was generated by the software.
43
Figure 3.4: XRD equipment (model: X’ Pert Powder PANalytical).
3.3.2 X-Ray Fluorescence (XRF)
X-Ray Fluorescence (XRF) is an analytical method to identify the elemental
composition of constituents. XRF analyses the chemistry of a sample by calculating the
fluorescent X-ray produced from a sample when it is excited by a primary X-ray source.
It is an excellent technique for determining the elemental composition of the material
and each element in the materials will produce its own set of fluorescent characteristics.
The XRF analysis was conducted at X-Ray Fluorescence Laboratory, Block 17 under
Centralized Analysis Laboratory (CAL), Universiti Teknologi PETRONAS.
3.3.2.1 Sample Preparation
Similar samples powdered were used as in XRD analysis. The samples were crushed
and ground into powder approximately 10 grams for each sample. Then, the powdered
samples were sieved by using a sieving pan of 63µm. The grains that passed through
44
the sieving pan were used for XRF analysis. The recommended grain size is less than
75µm, but the best is 10µm to 50µm (Pecharsky & Zavalij, 2009).
3.3.2.2 Procedure
Firstly, the powdered samples were transferred and pressed into the sample cups (Fig.
3.5) to produce a flat and smooth surface. Then, the sample cups were arranged in the
XRF machine according to sample names in rotating rays. Only 6 sample cups can be
run at one time. The power button located at the operation panel was turned on. Then,
the X-ray was generated by a spectrometer to analyze the chemical compositions of the
material. The equipment model used was Bruker S8 Tiger (Fig. 3.6). The steps above
were repeated for other samples.
Figure 3.5: Powdered samples and sample cups.
45
Figure 3.6: XRF equipment (model: Bruker S8 Tiger).
3.3.3 Poroperm
The purpose of using poroperm equipment is to determine both porosity and
permeability of core plugs. The equipment is run by a specific automatic software that
modifies the contact pressure and controls the gas flow rate. The equipment accurately
computes under confining pressure up to 200 psi and the porosity and permeability to
helium gas. The equipment is composed of a Hassler core holder, pressure transducers,
control valve and computer station that acquire data (Fig. 3.7). In particular, the
expansion of helium and the implementation of Boyle’s law and Charles’ law were used
to determine pore volume and porosity. The permeability is determined by gas
measurements of the unsteady-state pressure fall-off method, where the pressure is
reducing over time. The analysis was performed at Core Analysis Laboratory, Block
15, Universiti Teknologi PETRONAS. The software used in poroperm study is
Applilab software that attached to the equipment.
46
Figure 3.7: Poroperm Equipment (model: Coval 30).
3.3.3.1 Sample Preparation
The core plugs of one (1) inch diameter and two (2) inches length were prepared.
Similar samples as helium porosimeter were used in this testing.
3.3.3.2 Procedure
The weight, length and diameter of clean core plugs were measured. Then, the core
plugs were placed in the core holder vertically. The confining pressure of helium gas
was applied up to 200 psi. Then, the calibration button in Applilab software was clicked.
Lastly, the computer system will automatically generate the result of porosity and
permeability for each sample. Then, the steps above were repeated for all samples.
47
3.3.4 Micro-Computed Tomography (CT) Scan
Micro-Computed Tomography (CT) scanner is a high resolution X-ray scanner to view
the structure of internal rocks. This method provides an approach to visualize three-
dimensional (3-D) image of internal core structure a CT scanner can capture. It is a non-
destructive imaging method that preserves the core plugs from damage. It is highly used
in imaging and computing complex fracture systems of the reservoir (Kennedy et al.,
2014). The CT scanner model used in this study was InspeXio SMX-225CT (Fig. 3.8).
The CT scan analysis was held at Research and Development (R&D) Building,
Universiti Teknologi PETRONAS.
Figure 3.8: Micro Focus CT Scan Equipment (Model: InspeXio SMX-225CT).
3.3.4.1 Sample Preparation
Thirty (30) core plugs of one (1) inch diameter and two (2) inches length as in Helium
Porosimeter and Poroperm tests were used in this analysis.
48
3.3.4.2 Procedure
The computer and InspeXio software were turned on. The jig was placed into the hole
at the centre of the CT stage. The core plug was attached to the provided oil clay to
prevent the sample from moving. Next, the X-ray button was clicked to display a live
image. The images were scanned with 4 microns voxels resolution, 200kV voltage and
80µA current. After that, the X-ray source was turned off, and the sample and jig were
taken out from the CT scanner. Then, the calibration button was clicked to perform air
calibration. Later, a calibration jig was put on to perform the centre calibration. The
sample was put again with jigs, and a folder was created to save the CT image. The test
was performed by clicking the start button. Finally, the CT image was displayed in the
window after scanning was done. The steps above were repeated for all samples. The
VGStudio Max software used to analyse the results of the micro-CT scan.
3.3.5 Petrographic Analysis
For this research, the petrographic study is proposed to differentiate the texture of
dolomite and calcite, understand the diagenesis and study on micropores. Type of pores
was classified based on Choquette and Pray (1970). The petrographic analysis will be
performed by using petrologic tools of transmitted-light binocular microscope and
Cathodoluminescence (CL). CL helps in the fundamental understanding of the texture,
sediment source, and diagenetic history. The colour and intensity of
cathodoluminescence regions of carbonates can reflect the origin and environment, dull
luminescence reflecting relative anoxia associated with deeper burial, while bright
luminescence reflecting oxidation that is associated with shallow diagenetic
environments (Braithwaite & Heath, 1996).
3.3.5.1 Sample Preparation
The bulk samples were slabbed into small pieces of rocks for thin sections. Then, the
pieces of rocks were cleaned from any grit. A total of 30 rock slabs were prepared
before sending them to Core Laboratory Analysis Sdn. Bhd. for thin sections making.
49
Initially, the samples were vacuum-impregnated with blue-dyed epoxy resin to
differentiate the porosity from thin sections. Then, the thin sections were etched with
Alizarin Red Solution and Potassium Ferricyanide to differentiate calcite from dolomite
cements and identify carbonate facies (ferroan and non-ferroan) variations. The stained
thin sections used to determine carbonate rock minerals based on the colour appears
under the conventional microscope (Table 3.2). The thin sections were polished and
uncovered from the glass slide (Fig. 3.9).
Table 3.2: The results of etching and staining carbonate minerals (A. E. Adams &
MacKenzie, 1998).
Mineral Stain colour
with Alizarin
Red S
Stain colour with
Potassium Ferricyanide
Combined results
Calcite (non-
ferroan)
Pink to red-
brown None
Pink to red-
brown
Calcite
(ferroan)
Pink to red-
brown
Pale to deep blue
depending on iron content Mauve to blue
Dolomite
(non-ferroan) None None Unstained
Dolomite
(ferroan) None Very pale blue Very pale blue
Figure 3.9: Stained thin sections for petrographic study.
50
3.3.5.2 Procedure
There are two types of microscopes used in the study, which are standard light polarized
microscope and cathodoluminescence (CL) microscope, respectively (Fig. 3.10 (a-b)).
The analysis was conducted in the petrographic room, SEACaRL laboratory, using
Olympus BX43 model with analySIS® Five software. For CL Analysis, it must be
conducted in a dark room. Firstly, the uncovered thin sections were put in the vacuum
chamber. Then, the vacuum pump and transformer were turned on until it reaches 60µ
torr, 250Å, and 12-15kV. After that, the photomicrographs were displayed on the
computer. The photomicrographs were taken by Canon camera under 4x
magnifications. The other sections of the thin section can be analyzed by adjusting the
rotating knobs.
Figure 3.10: Two types of microscope used for petrographic study, (a) Standard light
polarized microscope; (b) Cathodoluminescence microscope.
3.3.6 Field Emission-Scanning Electron Microscope-Energy Dispersive X-Ray
(FESEM-EDX)
Field Emission-Scanning Electron Microscopy (FESEM) is one technique used to study
minerals and rocks. FESEM is a high-resolution technique for microscale studies of the
pore space in rocks, and the images always have more excellent resolution than those
found by optical microscopy (Hall & Lloyd, 1981; Kuzmin & Skibitskaya, 2017).
51
FESEM gives high-resolution images of the sample by sending a focus electron beam
through the surface and sensing secondary or backscattered electron signal. FESEM has
a high magnification range between 10X to 20,000X.
3.3.6.1 Sample Preparation
The FESEM samples were prepared by cutting the rock to an ideal size ranging from
0.5 to 1 cm.
3.3.6.2 Procedure
The samples are covered with a thin layer of conductive material, like gold. The purpose
of coating the samples with conductive material is to obtain a better image of the rock
sample. Then, the samples were put in the FESEM chamber, and the analysis was run.
The images of FESEM were displayed on the computer. The images were snapped and
EDX produced a graph for the percentage of elements that existed in the selected region.
Fig. 3.11 below shows the equipment of Supra55VP FESEM with Oxford EDX. The
analysis was conducted in Centralized Analytical Laboratory (CAL), Universiti
Teknologi PETRONAS.
52
Figure 3.11: Supra55VP FESEM with Oxford EDX Equipment.
3.4 The Method of Data Analysis
The data were analyzed by using a different approach of data analysis for each
subdivision scope of the study. For the geochemical study, the graph of XRD is
analysed based on peaks displayed in the graph. The percentage of minerals were
identified by using Jade 9 XRD software. The rocks from XRF data were analysed by
looking into the trend of certain elements and elemental ratio graphs.
For the petrophysical study, the data approached is in quantitative and qualitative
methods. The graph of porosity versus permeability is produced based on the type of
lithology for each locality. The micro-CT scan analysis will show the interconnected
pores in a 3D image.
The authors referred to practical use for dolomite classification for petrographic
study (Table 3.3) in determining types of dolomite and crystallized calcite (Flügel,
2004). The classification helps in understanding the diagenesis of dolomite in the Kinta
Valley. The identification of crystal size is based on Folk’s (1962) crystal size scale as
53
Table 3.4. The terminology of dolomite texture proposed by Gregg and Sibley’s (1987),
and type of pores was classified based on (Choquette & Pray, 1970).
Table 3.3: Practical use for dolomite classification
Criteria Descriptions
Crystal size Fine, medium or coarse crystalline
Crystal size texture Equigranular (unimodal), inequigranular (multi/polymodal)
or extremely fine (aphanotopic)
Fabric Peloidal, mosaic, porphyrotopic, or poikilotopic
Crystal distribution Tightly packed, loosely packed, isolated patches, crystal
isolated or floating
Crystal shape Anhedral, euhedral, subhedral
Table 3.4: Grain size chart (Folk, 1962)
Crystal Size Classification
<30µm Fine Crystalline
30-150µm Medium Crystalline
>150µm Coarse Crystalline
54
CHAPTER 4
RESULTS AND DISCUSSION
In this chapter, the results are presented and discussed, including all the findings on
field observations, lab analysis and interpretations. The results were divided and
delivered based on four sub-divisions, which are (1) field observations, (2)
petrophysical properties, (3) petrographic, and (4) morphological and mineralogical
studies.
4.1 Field Observations
There are two main parts of the study area, which are in the north and south of Kinta
Valley, as in Fig. 4.1 (b-c). Three localities, (1) Gunung Rapat in the south as in Fig.
4.1 (c), (2) Sungai Siput Dolomite Hill and (3) Gunung Kanthan in the north as in Fig.
4.1 (b) of Kinta Valley. All the quarries are actively operating for mining activity.
Tsegab and Chow (2019) stated the lithofacies in the northern part of Kinta Valley
is mainly associated with dark to black carbonate mudstone, black shale beds and
siltstone intervals. Sungai Siput rock has fine-grained, light-to-dark grey to black and
thin lamination carbonate mudstone. It shows a sharp boundary between light to dark-
coloured carbonate mudstone, chert and black shale lithologies. Most of the rocks in
the Sungai Siput area are highly compacted, stylolized, and less affected by dissolution.
Besides, the Kanthan area is dominated by fine-grained, light grey, and thick to thin
intercalations of carbonate mudstone beds. There is little white to white pinkish
coloured lithofacies that closed to granite contact.
While, in the southern part of the valley, the Kinta Limestone consisted of limestone
with minor clastic intervals. The Kinta Limestone in the southern part of the valley has
55
a coarser grain texture than the northern part. Therefore, it indicates the Kinta
Limestone section is older in the north rather than south of the valley (Haylay et al.,
2017).
Figure 4.1: (a) Geological map of Kinta Valley with two study areas specifically
located in the north (b) and south (c) of Kinta Valley; (b) Three main localities,
Gunung Kanthan and Sungai Siput Dolomite Hill in the north; and (c) Gunung Rapat
in the south for this study.
56
4.1.1 Field 1: Gunung Rapat
Fig. 4.2 shows a representative outcrop for Gunung Rapat. The outcrop is highly
weathered, but some part has exposed fresh rocks and falling blocks due to blasting
activity. The quarry consisted of limestone as a host rock. The limestone body is
massive and highly fractured. There are few structures observed in the quarry, such as
faults, fractures, dolomite veins and calcite veins.
Other lithologies observed in Gunung Rapat are dolomite and sepiolite. It is hard to
differentiate between limestone and dolomite bodies from the outcrop because they
exhibit almost similar white to light pink colour. However, a few sections of the outcrop
show an irregular boundary between dolomite and limestone bodies (Fig. 4.3 (a)). A
drop of hydrochloric (HCL) acid helps distinguish between limestone and dolomite by
looking into the reaction of rocks with the acid. Most of the rocks tested along Gunung
Rapat’s outcrop produced a vigorous fizz, especially limestone. This is because the
outcrop is more calcitic than dolomitic. The dolomites would react with weak fizz and
release only a few bubbles of carbon dioxide gas on the rock surface. There are many
calcite veins (approximately 1 cm thick) in the dolomite body as shown in Fig. 4.3 (b).
The calcite precipitated into open fracture when there is enough source of calcium ion.
Both dolomite and limestone are solid and hard to break. There are lots of iron stains
observed on limestone and dolomite bodies, probably due to weathering process.
57
Fig
ure
4.2
: A
n o
utc
rop i
mag
e of
Gunung R
apat
whic
h c
onsi
sts
of
a hig
hly
fra
cture
d m
assi
ve-
dolo
mit
e body. T
he
occ
urr
ence
of
sepio
lite
is
ob
serv
ed n
ear
stri
ke-
slip
fau
lts.
58
Fig
ure
4.3
: (a
) A
n i
rreg
ula
r co
nta
ct o
f li
mes
tone
and d
olo
mit
e bodie
s; (
b)
The
pre
sen
ce o
f ca
lcit
e v
ein i
n d
olo
mit
e body.
59
Sepiolite has different colour, characteristic and texture. Sepiolite is a clay mineral
under the palygorskite group where it has soft, waxy and fibrous physical
characteristics. The colour of sepiolite is green-yellowish (Fig. 4.4). There are two
points of sepiolite occurrences in Gunung Rapat, one is close to the limestone body,
and the other one is close to the dolomite body. The sepiolite in Pulai Kramat, Kinta
Valley is believed to be the first recorded occurrence in Malaysia by Chin (1990). It
can be found primarily on veins and fractures of abandoned limestone quarry. Weaver
and Pollard (1973) stated that sepiolite can be formed under two conditions, either
through hydrothermal activity or sedimentation. Chin (1990) believed sepiolite in Kinta
Valley is probably associated with a hydrothermal activity formed at the end of granite
intrusion.
60
Fig
ure
4.4
: A
conta
ct b
etw
een (
a) l
imes
tone
and p
ale
gre
en s
epio
lite
(b)
bet
wee
n d
olo
mit
e an
d g
reen
-yel
low
ish s
epio
lite
.
61
From the observation, the presence of sepiolite and dolomite bodies are close to
fault systems. There are slickensides observed at the outcrop’s surface that is associated
with faults. The strike-slip fault is present in dolomitic limestone and the left strike- slip
fault (LSSF) near to the dolomite and sepiolite bodies as recorded in sedimentary
logging in Fig. 4.5. A summary of Anting’s outcrop observation is represented in
sedimentary logging as in Fig. 4.6.
Figure 4.5: A left strike-slip fault observed near dolomite and sepiolite bodies.
63
4.1.2 Field 2: Sungai Siput Dolomite Hill
Sungai Siput Dolomite Hill is located in the northern part of Kinta Valley, near Gunung
Kanthan and operated by Dolomite Sdn Bhd. The dolomite hill consisted of four
outcrops as shown in Fig. 4.7 to Fig. 4.10. Few samples are taken from each section.
The represented outcrops are highly weathered, fractured and surrounded by few
vegetations. The Sungai Siput Limestone is Carboniferous to Permian age
(Gebretsadik, Hunter, & Sum, 2014). The outcrops exhibit light to dark grey colour,
which may indicate the replacive dolomite. Based on Shah and Poppelreiter (2016),
dolomite cement usually has pink, white and purple, while replacive dolomite has dark
grey colour. The dolomite body in outcrops A, B and C is massively bedded, whereas
the dolomite bed in outcrop D is varied from massive to thinly bedded. The bedding
plane can only be observed in the outcrop at section D, where the bed is tilted as shown
in Fig. 4.10.
64
Figure 4.7: The photo of outcrop A in Sungai Siput Dolomite Hill.
Figure 4.8: The photo of outcrop B in Sungai Siput Dolomite Hill.
65
Figure 4.9: The photo of outcrop C in Sungai Siput Dolomite Hill.
Figure 4.10: A view of outcrop D shows a clear tilted bedding plane with intense
fracture.
66
. For structural observation, there are many fractures observed, especially in outcrop
section D. A major normal fault is found within the dolomite body (Fig. 4.11). A normal
fault is associated with extensional forces, thus provides an opening path for fluids to
come in rather than other fault types. Four outcrops are composed of replacive dolomite
with abundance of calcite veins as in Fig. 4.12 (a-b). The calcite veins cut through the
dolomite body. There is no other lithology found within the hill except dolomite. The
dolomite rock is tested earlier with hydrochloric (HCL) acid and most of it did not react
with the acid. Only dolomite that associated with calcite vein produced bubbles and
fizz. Fig. 4.13 shows sedimentary logging of Sungai Siput’s outcrop in section D.
Sedimentary logging is carried out only for this section because the outcrop provides
clearer bed and structures than other sections.
Figure 4.11: The photo shows that the normal faults (red line) mostly striking in N-S
direction.
67
Fig
ure
4.1
2:
The
pre
sen
ce o
f var
ious
size
of
calc
ite
vei
n (
a) f
rom
0.5
cm
to 1
cm
and (
b)
2 c
m t
o 1
5 c
m i
n d
olo
mit
e body. T
he
calc
ite
vei
ns
cross
-cutt
ing t
he
dolo
mit
e body i
n S
ungai
Sip
ut
Dolo
mit
e H
ill.
69
4.1.3 Field 3: Hill B, Gunung Kanthan
Gunung Kanthan is located in the north of Kinta Valley. There are two hills studied in
Gunung Kanthan which are Hill B and Hill E. Both outcrops are highly fractured and
weathered. Both of Hill E and Hill B in Gunung Kanthan show almost same distribution
types of lithology and geological features.
In Hill B, the outcrop’s bedding is tilted and has various colours (Fig. 4.14). Few
structures observed such as en-echelon fault, reverse fault, and right strike-slip fault.
The outcrop is composed of two main lithologies, which are crystalline limestone and
dolomite. Some parts of limestone have been crystallized and associated with pyrite.
The pyrite has a gold colour and is known as “fools’ gold” since it shows similar the
colour as real gold. Pyrite is the most common iron sulfide (FeS2) in carbonate rocks
(De Arruda Cabral et al., 2019). Pyrite formed by weathering or hydrothermal activity
(Murakami & Nakano, 1999). Each lithology exhibits different colors. Dolomite has
light pink colour, while limestone has a white to light grey colour. The limestone and
dolomite crystals show very fine to fine crystal size.
70
Fig
ure
4.1
4:
A r
epre
senta
tive
outc
rop i
n H
ill
B, G
unung K
anth
an. T
he
outc
rop s
how
s a
tilt
ed b
ed a
nd v
aria
tion c
olo
ur
for
the
lith
olo
gy.
71
The occurrence of dolomite bodies in Hill B is easily differentiated from other
lithologies. There are two sections of dolomite bodies found in the outcrop. One is
dolomite associated with dyke-like bounded by limestone and the other is massive
dolomite body as in Fig. 4.15. There is sharp contact between dolomite and limestone
body. The thickness of dolomite dyke-like dolomite is around 3m thick and 10m in
height. While massive dolomite is 30m wide and 15m in height. The dolomite dyke-
like is close to the en-echelon fault, where it has a sigmoidal shape. There are visible
vugs observed in the massive dolomite body formation. The dolomite in Hill B with
pink colour could be a cement dolomite mentioned by Shah and Poppelreiter (2016).
The outcrop in Hill B is associated with the reverse fault and right-strike slip faults (Fig.
4.16 – 4.17)
The sedimentary logging (Fig. 4.18) shows the summary of geological observation
in Hill B. The limestone is associated with thin black bio-lamination, presence of
stylolite and calcite veins from the outcrop observation. Most of the fractures are
infilled by calcite. While dolomite is associated with some euhedral pyrite, calcite veins
and visible macro-pores.
72
Fig
ure
4.1
5:
Tw
o s
ecti
ons
of
dolo
mit
e bodie
s, (
a) P
inkis
h d
olo
mit
e in
conta
ct w
ith l
imes
tone;
(b)
Mas
sive
pin
kis
h d
olo
mit
e body i
s
hig
hly
fra
cture
d a
nd i
nte
nse
ly w
eath
ered
.
73
Figure 4.16: The reverse fault plane found in the limestone has a gentle dipping and
striking to the E-W direction (red arrow).
Figure 4.17: The slickenside shows a right-lateral strike-slip fault plane. This fault
was striking almost to the N-S direction (red arrow).
75
4.1.4 Field 4: Hill E, Gunung Kanthan
There are two represented outcrops in Hill E, which are outcrop 1 and outcrop 2.
Outcrop 1 in Gunung Kanthan at Hill E is highly weathered and intensely fractured
(Fig. 4.19). Outcrop 1 is composed of limestone and dolomite. It is hard to identify the
dolomite from the limestone body because each lithology’s colour appearance is almost
similar. They exhibit shades of grey. From the observation, the colour changes from
dark grey to whitish-grey towards the younger bedrock which give some hints on the
sea level cycles during that time. Most of the darker colour indicates the rock has high
content of mafic minerals like magnesite and iron, indicating the drowning phase of
carbonate rock. The lighter colour indicates that the rock has a low content of mafic
minerals and gives a clue that the carbonate rock was exposed to the surface during that
time. A phase of exposure occurs when carbonate rock is exposed to the shallow surface
because of sea-level drop, while drowning occurs when carbonate rock is submerged in
a deep area due to high sea level.
The grain size also changed from medium grain to very fine grain towards the
younger bed. The texture cannot be identified directly from the outcrop because the
limestone texture has changed due to contact metamorphism. However, it can be
determined in the further study under thin section by looking at the crystal growth. It
has very fine to medium grain and well to moderately sorted grain from older to younger
beds.
Furthermore, calcite crystal growth was also found within the outcrop and it shows
the presence of karst or paleo-cave as in Fig. 4.20 (a). Besides, there is stylolite found
within limestone and dolomite bodies. The stylolite results from a pressure solution,
where it reduces the porosity and acts as permeability barriers. The limestone bed was
tilted almost vertical and striking north-south direction as in Fig. 4.20 (b).
77
Fig
ure
4.2
0:
(a)
Pre
sence
of
pal
eo-c
ave
dep
osi
ts w
ithin
lim
esto
ne
body;
(b)
The
bed
rock
s w
ere
tilt
ed a
lmost
ver
tica
l st
rikin
g
nort
h-s
outh
dir
ecti
on.
78
Field observations discovered that dolomite bodies are closed to N-S oriented faults
in the recrystallized limestone. They are mainly associated with strike-slip fault (Fig.
4.21). Fig. 4.15 shows the sedimentary logging of outcrop 1 in Hill E, Gunung Kanthan
(Fig. 22). From recorded sedimentary logging, the dolomite sections are unevenly
distributed. The dolomites are not properly distributed because the presence of local
structural influenced it. The dolomites have a light to pink-greyish color, which is
almost the same as the limestone body. There are several calcite veins found in
limestone body and few in dolomite body.
Figure 4.21: The presence of slickenside probably indicates the strike-slip fault plane
that striking in the N-S direction.
80
The brecciated clasts of host limestone were found within dolomite bodies as in
Fig. 4.23. It is an indicator of fault-related hydrothermal dolomitization. As has been
mentioned by Gregg J.M. & Sibley (1984), the presence of box work or brecciated
textures within the crystalline dolomite and sutured crystal contacts suggest that the
dolomitization process is a post-depositional process and greatly controlled by
structural-induced conduit. This brecciation is commonly found in the hydrothermal
region. Limestone breccias in dolomite show the intensity of migrating fluids upwards.
Another section of Hill E, outcrop 2 (Fig. 4.24) shows the lithology of limestone
and brecciated limestone in dolomite. The limestone has a white to dark grey colour,
while dolomite has a pink to pale grey colour. The boundary between all lithology is
difficult to identify and the bed’s orientation could not be determined.
Figure 4.23: The brecciated limestone clasts in the dolomite body.
82
4.1.5 Field Summary
There are two types of carbonate rocks observed in the field which are limestone and
dolomite. The limestone is highly fractured and coloured from white to light-dark grey
colour. The limestone is massively bedded in Gunung Rapat and the thin to thickly
bedded in Gunung Kanthan. It has crystallized texture, rough surface, hard to break and
few chalky textures. The limestone bed found is tilted almost vertical and striking north-
south direction. From field observations, the bedrocks are mainly associated with faults,
fractures, stylolites, calcite veins, dolomite veins, limestone clasts, paleo-cave and the
presence of other minerals such as pyrite and sepiolite.
The presence of dolomite is closed to faults in recrystallized limestone. Dolomite
in Sungai Siput is hard to break and associated with lots of calcite veins. Besides,
dolomite in Hill B, Gunung Kanthan formed as massive dolomite body and dyke-like
dolomite. There are also limestone clasts observed in the dolomite of Hill E, Gunung
Kanthan. The presence of dolomite in the north of Kinta Valley is easy to recognize
compared to the south because they exhibited distinct colour from limestone such as
pink and dark grey. While in the south, the dolomite has light pink colour, the same as
limestone. The dolomite in the north also acts no to less vigorous after tested with HCL
acid. While limestone is highly vigorous and produced bubbles when it reacts with HCL
acid. Thus, it is easier to recognize and differentiate dolomite from limestone compared
to the southern part. In the south region, there is no clear boundary between limestone
and dolomite body. The limestone and dolomite reactions toward HCL acid is almost
the same. Both dolomite and limestone react less to moderate reaction.
83
4.2 Geochemical Study
For the mineralogical study, XRD data were interpreted from XRD peak pattern
(APPENDIX A) and XRF data (APPENDIX B) from elemental graphs. The percentage
of minerals obtained in XRD were plotted in the calcite-dolomite-quartz ternary
diagram.
4.2.1 Field 1: Gunung Rapat
4.2.1.1 Mineralogy
There are two types of lithology reported based on calcite-dolomite-quartz ternary
diagram: limestone and dolomitic limestone as in Fig. 4.25. Two samples fall under
dolomitic limestone which is AQ 1 and AQ 76 (Table 4.2). While the other samples of
AQ 10, AQ 23, AQ 28, AQ 45, AQ 60 are categorized as limestone. The plotted data
in the ternary diagram is taken from X-ray diffraction (XRD) data. The percentage of
calcite obtained from XRD analysis ranges from 66.5% to 99.9%, dolomite from 2% to
33.3%. and quartz from 0.1% to 0.5% (Table 4.2).
84
Figure 4.25: The calcite-dolomite-quartz ternary diagram showing the lithology of
carbonate rocks in Gunung Rapat based on Leighton and Pendexter (1962)
terminology. Dolomitic limestone and limestone are reported in Gunung Rapat.
Table 4.1: The list of mineral percentage and lithology types of rock samples in
Gunung Rapat.
Samples Mineral percentage
Lithology Calcite Dolomite Quartz
AQ 1 89.5 10 0.5 Dolomitic Limestone
AQ 10 99.9 0.0 0.1 Limestone
AQ 23 97.9 2.0 0.1 Limestone
AQ 28 99.9 0.0 0.1 Limestone
AQ 45 99.9 0.0 0.1 Limestone
AQ 60 99.8 0.0 0.2 Limestone
AQ 76 66.5 33.3 0.2 Dolomitic Limestone
Two samples of Gunung Rapat from different lithology are represented: a limestone
sample of AQ 10 and dolomitic limestone sample of AQ 76 (Fig. 4.26 and Fig. 4.27).
The highest diffraction peak for both samples is calcite with 99.9% for AQ 10 and
85
66.5% for AQ 76. Both samples are associated with a minor amount of quartz. The
quartz shows a very low-intensity peak with the percentage of 0.1% to 0.2%. In sample
AQ 76, few peaks are identified as dolomite mineral with a total of 33.3%.
Figure 4.26: XRD pattern obtained from limestone sample of AQ 10 containing
calcite and quartz.
86
Figure 4.27: XRD pattern obtained from dolomitic limestone sample of AQ 76
containing calcite, dolomite and quartz.
4.2.1.2 Elemental Analysis
The elemental variations are studied through XRF data-plotted graph. The data shows
calcium (Ca) concentration is high in all samples of Gunung Rapat, with ranges from
94% to 97.6%. In comparison, magnesium (Mg) concentration is very low overall with
ranges from 0.36% to 3.23%. Ca concentration trend is against Mg concentration in all
samples as shown in Fig. 4.28.
The calcium content of limestone is slightly higher than dolomitic limestone (Fig.
4.29). The limestone has 98.2% to 99% Ca percentage, while dolomitic limestone has
94% to 97.6%. The Ca content suddenly drops to 94% for the dolomitic limestone
sample of AQ 76. Overall, the trend of calcium concentration of outcrop samples in
Gunung Rapat shows more minor variation.
87
Figure 4.28: The trends of calcium (Ca) and magnesium (Mg) concentrations are
compared in rock samples of Gunung Rapat.
Figure 4.29: The trend of calcium (Ca) concentration in limestone and dolomitic
limestone of Gunung Rapat.
88
Based on the trend of elements, Ca concentration is higher in limestone compared
to dolomitic limestone, while Mg concentration is higher in dolomitic limestone than
limestone samples. The trend of Mg concentration is against Ca concentration. The
percentages of Mg content in limestone are very low, from 0.36% to 0.82% (Fig. 4.30).
However, Mg content is found slightly higher in dolomitic limestone samples (AQ 1
and AQ 76) with 1.26% and 3.23%.
Figure 4.30: The magnesium (Mg) concentration based on limestone and dolomitic
samples of Gunung Rapat.
Other elemental concentrations studied in the outcrop samples of Gunung Rapat are
silica (Si), iron (Fe), aluminium (Al), strontium (Sr) and manganese (Mn). The trends
of elements concentration are shown in Fig. 4.31. Silica shows the same trend as the
Mg trend, where it has low values for limestone samples (AQ 10, AQ 23, AQ 28, AQ
45 and AQ 60) and slightly higher in dolomitic limestone samples of (AQ 1 and AQ
76). The same goes for the Al percentage trend, with ranges from 0.09% to 0.21%.
While there is almost no difference in Sr percentage for all samples. For manganese
(Mn), the dolomitic limestone sample of AQ 76 shows a minimal percentage increment
with a maximum value of 0.29% compared to limestone.
89
Figure 4.31: The elemental variation graph of Si, Fe, Al, Sr, and Mn in percentage
based on samples from Gunung Rapat.
4.2.2 Field 2: Sungai Siput Dolomite Hill
4.2.2.1 Mineralogy
From the calcite-dolomite-quartz ternary diagram, all samples are categorized as
dolomite (Fig. 4.32). The plotted data in the ternary diagram is taken from X-ray
diffraction (XRD) data. The percentage of dolomite mineral in Sungai Siput Dolomite
Hill is very high compared to Gunung Rapat, which make the samples fall under
dolomite lithotype in the ternary diagram. The dolomite percentage ranges from 90.5%
to 95.5%, while calcite composition is ranging from 4.5% to 9.5% and quartz 0% to
0.2%. The percentage of calcite and quartz minerals are very low in dolomite.
90
Figure 4.32: The calcite-dolomite-quartz ternary diagram showing the Sungai Siput
Dolomite Hill is dominated by dolomite.
Table 4.2: The list of mineral percentage and lithology type of rock samples in Sungai
Siput Dolomite Hill.
Samples Mineral percentage
Lithology Calcite Dolomite Quartz
SA 1 4.5 95.5 0.0 Dolomite
SA 3 7.0 92.8 0.2 Dolomite
SB 6 5.0 94.4 0.1 Dolomite
SC 15 6.0 93.9 0.1 Dolomite
SD 5 9.5 90.5 0.0 Dolomite
SD 10 5.5 94.5 0.0 Dolomite
91
Fig. 4.33 shows the XRD pattern of represented dolomite sample in Sungai Siput
Dolomite Hill. From the XRD pattern, the highest intensity peak belongs to the
dolomite mineral. The dolomite formed as a major mineral in the SB 6 sample with
94.4%, followed by minor calcite with 5% and quartz 0.1%. Thus, the mineral
compositions of the SB 6 sample are mainly dolomite associated with calcite probably
contributed from calcite veins which can be observed in the outcrop itself.
Figure 4.33: XRD pattern obtained from dolomite sample of SB 6 containing
dolomite, calcite and quartz.
4.2.2.2 Elemental Analysis
The elemental variation of calcium (Ca) in dolomite samples is high with ranges from
82.4% to 85.4% as in Fig. 4.34. However, the Ca concentration in Sungai Siput is not
as high as limestone in other quarries. The magnesium (Mg) shows low concentration
but is considered high compared to other lithologies from different quarries. The Mg
concentration across all dolomite samples in Sungai Siput is ranging from 10.7% to
12.9%.
92
Based on Fig. 4.35 and 4.36, both Ca concentration and Mg concentration between
all dolomite samples in Sungai Siput Dolomite Hill show less variation. Ca
concentration has an average of 83.9% and Mg concentration has an average of 11.7%.
Figure 4.34: The trends of calcium (Ca) and magnesium (Mg) concentrations based
on dolomite samples of Sungai Siput Dolomite Hill.
93
Figure 4.35: The calcium (Ca) concentration trend based on dolomite samples of
Sungai Siput Dolomite Hill.
Figure 4.36: The trend of magnesium (Mg) concentration based on dolomite samples
of Sungai Siput Dolomite Hill.
94
Besides, other element concentrations in the dolomite sample of Sungai Siput
Dolomite Hill are presented in Fig. 4.37. The elemental variations of Si, Fe and Al
appeared as the same pattern, where the element concentration is suddenly increased in
sample SA 3 and drops in sample SB 6. Si and Fe elements have higher concentration
compared to Al. The average Si content is around 1.3%. The concentration range for Si
in dolomite samples of Sungai Siput Dolomite Hill is from 0.95% to 2.4%. While Fe
concentration ranges from 1.03% to 2.35%. The Al content ranges from 0.39% to
0.96%. Other elements such as Sr, Mn and Cl have a relatively low concentration of
less than 0.5% in dolomite.
Figure 4.37: The elemental variation of Si, Fe, Al, Sr, Mn and Cl based on dolomite
samples from Sungai Siput Dolomite Hill.
95
4.2.3 Field 3: Hill B, Gunung Kanthan
4.2.3.1 Mineralogy
The calcite-dolomite-quartz ternary diagram shows lithotype in Hill B, Gunung
Kanthan is associated with dolomite and limestone (Fig. 4.38). The ternary diagram is
constructed based on a percentage of mineral presents in the samples as in Table 4.3.
The percentage of calcite in limestone ranges from 99.4% to 99.8%, with a low
percentage of dolomite and quartz which is less than 0.5%. While the percentage of
dolomite mineral in dolostone ranges from 97% to 97.5%, with a low amount of calcite
and quartz minerals. The calcite percentage in dolomite rocks ranges from 2.5% to 3%,
while quartz is extremely low in percentage with less than 0.2%.
Figure 4.38: The calcite-dolomite-quartz ternary diagram showing the Hill B, Gunung
Kanthan consists of dolomite and limestone.
96
Table 4.3: The list of mineral percentage and lithology type of rock samples in Hill B,
Gunung Kanthan
Samples Mineral percentage
Lithology Calcite Dolomite Quartz
LB 6 99.7 0.0 0.3 Limestone
LB 24 99.8 0.0 0.2 Limestone
LB 62 99.4 0.2 0.4 Limestone
LB 80 2.5 97.5 0.0 Dolomite
LB 81 3.0 97.0 0.0 Dolomite
LB 83 2.5 97.4 0.1 Dolomite
The representative outcrop samples of Hill B for XRD analysis are LB 62 and LB
81 (Fig. 4.39 and 4.40). The intensity peak indicates calcite as the dominant mineral for
sample LB 62. Besides, sample LB 62 is associated with a minor amount of quartz and
dolomite. The minerals show very low-intensity peaks. While, the intensity peaks for
sample LB 81 are highly dominated by dolomite with 97% and constituent calcite
mineral with 3%. The sample of LB 62 is classified as limestone, while LB 81 is
dolomite.
97
Figure 4.39: XRD pattern obtained from limestone sample of LB 62 containing
calcite, dolomite and quartz.
Figure 4.40: XRD pattern obtained from dolomite sample of LB 81 containing
dolomite and calcite.
4.2.3.2 Elemental Analysis
The elemental concentrations of Ca and Mg are plotted as a graph in Fig. 4.41. The
trends of Ca and Mg show inverse patterns. The data shows calcium (Ca) concentration
is high in all samples of Hill B, Gunung Kanthan. The Ca percentage ranges from 81.3%
to 99.7%, while magnesium (Mg) concentration is very low in overall with ranges from
0% to 13.2%.
98
Figure 4.41: The trends of calcium (Ca) and magnesium (Mg) concentrations based
on outcrop samples of Hill B, Gunung Kanthan.
The calcium content in limestone samples is higher than the dolomite sample as
shown in Fig. 4.42. The limestone samples (LB 6, LB 24 and LB 62) consisted of
99.7%, 97.3% and 99.5% of Ca percentage. The Ca content drops to 81.5% for dolomite
samples of LB 80 and LB 81. The lowest Ca percentage is 81.3% which belongs to
sample LB 83. Overall, the calcium concentration trend in Hill B shows a variation
across different lithologies from limestone to dolomite samples.
99
Figure 4.42: The trend of calcium (Ca) concentration in limestone and dolomite of
Hill B, Gunung Kanthan.
Ca concentration is higher in limestone compared to dolomite, while Mg
concentration is vice versa. It is higher in dolomite compared to the limestone sample.
From Fig. 4.43, the Mg concentration shows a sudden increase at dolomite samples of
LB 80, LB 81 and LB 83 with Mg percentage of 12.8%, 13% and 13.2%, respectively.
While the Mg element only presents in one limestone sample (LB 62) with a very low
percentage of 0.85%.
Other elemental concentrations studied in the outcrop samples of Hill B, Gunung
Kanthan is silica (Si), iron (Fe), aluminium (Al), manganese (Mn), Chlorite (Cl) and
strontium (Sr) as in Fig. 4.44. The elements of Fe, Si, Mn, Al, and Cl show the same
trend as the Mg trend, where they show low values for limestone samples (LB 6, LB
24, and LB 62) and slightly higher in dolomite samples of (LB 80, LB 81, and LB 83).
Besides, there is almost no difference in Sr percentage for all samples. The Sr element
has a very low value, ranges from 0.03% to 0.06%.
100
Figure 4.43: The trend of magnesium (Mg) concentration in limestone and dolomite
samples of Hill B, Gunung Kanthan.
Figure 4.44: The elemental variation of Si, Fe, Al, Mn, Cl and Sr based on outcrop
samples from Hill B, Gunung Kanthan.
101
4.2.4 Field 4: Hill E, Gunung Kanthan
4.2.4.1 Mineralogy
Based on the plotted mineral percentage of XRD data in the calcite-dolomite-quartz
ternary diagram (Fig. 4.45), the samples from Hill E are composed of dolomite,
limestone and dolomitic limestone. Two samples are characterized as dolomitic
limestone, LE 1-7 and LE 2-5; and two dolomite samples, LE 2-2 and LE 2-3 (Table
4.4). While, the other samples of LE 1-24, LE 1-45, LE 1-54, LE 1-60, LE 1-62, LE 1-
63 and LE 2-2 are categorized as limestone.
Figure 4.45: The calcite-dolomite-quartz ternary diagram showing the Hill E, Gunung
Kanthan is composed of limestone, dolomite and dolomitic limestone.
The plotted data in the ternary diagram is based on calcite, dolomite and quartz
minerals from X-ray diffraction (XRD) data. The percentage of calcite obtained from
XRD analysis for limestone is ranging from 66.5% to 99.9%. There are no dolomite
102
mineral presents in the limestone sample and there is minor amount of quartz with 0.1%
in limestone (Table 4.4). While, the mineral composition in dolomitic limestone
consisted of dolomite mineral with 34% and 34.5%, and calcite mineral with 66% and
65.5%. The dolomite rocks mainly composed of dolomite mineral with 94% and 95%
and subsequent calcite mineral of 5% and 6%.
Table 4.4: The list of mineral percentage and lithology type of rock samples in Hill E,
Gunung Kanthan
Samples Mineral percentage
Lithology Calcite Dolomite Quartz
LE 1-7 65.5 34.5 0.0 Dolomitic Limestone
LE 1-24 100 0.0 0.0 Limestone
LE 1-45 100 0.0 0.0 Limestone
LE 1-54 99.9 0.0 0.1 Limestone
LE 1-60 100 0.0 0.0 Limestone
LE 1-62 100 0.0 0.0 Limestone
LE 1-63 99.9 0.0 0.1 Limestone
LE 2-2 99.9 0.0 0.1 Limestone
LE 2-3 5.0 95.0 0.0 Dolomite
LE 2-4 6.0 94.0 0.0 Dolomite
LE 2-5 66.0 34.0 0.0 Dolomitic Limestone
There are two representative samples from Hill E, Gunung Kanthan, which are
limestone sample of LE 1-60 and dolomite sample of LE 2-3 for XRD analysis. The
diffraction peak for LE 1-60 is referred to as 100% calcite mineral with no other mineral
association (Fig. 4.46).
103
Figure 4.46: XRD pattern obtained from limestone sample of LE 1-60 containing
calcite, sylvite and quartz.
In sample LE 2-3, the dominant intensity peaks are referred to as dolomite mineral
with a total of 95% contribution in the sample (Fig. 4.47). Next, the minor constituent
mineral from other intensity peaks is interpreted as calcite with a 5% contribution in
the sample.
104
Figure 4.47: XRD pattern obtained from dolomite sample of LE 2-3 containing
dolomite and calcite.
4.2.4.2 Elemental Analysis
The calcium (Ca) element in all samples from Hill E shows high percentage values
ranging from 98.4% to 99.9% as in Fig. 4.48. On the contrary, the magnesium (Mg)
shows a very low concentration in all samples. The Mg concentration across all selected
samples in Hill E is ranging from 0% to 0.52%.
Figure 4.48: The trends of calcium (Ca) and magnesium (Mg) concentrations based
on outcrop samples of Hill E, Gunung Kanthan.
The Ca concentration shows almost a flat trend as in Fig. 4.49 with an average of
99.3%. There is not much difference in Ca concentration between all samples. Based
on figure 4.43, the Mg concentration also shows minimal variations as Ca concentration
between all outcrop samples in Hill E, Gunung Kanthan. Only three limestone samples
of LE 1-45, LE 1-54 and LE 1-63 have Mg elements with a concentration of 0.35%,
105
0.3% and 0.52%. Other than that, there is no Mg element presents in dolomitic
limestone and few limestone samples (Fig. 4.50).
Figure 4.49: The trend of calcium (Ca) concentration in limestone and dolomitic
limestone samples of Hill E, Gunung Kanthan.
106
Figure 4.50: The trend of magnesium (Mg) concentration in limestone and dolomitic
limestone samples of Hill E, Gunung Kanthan.
Besides, other element concentrations in the outcrop sample of Hill E, Gunung
Kanthan are presented as in Fig. 4.51. The elemental variations of Fe and Mn appeared
as the same trend, where the element concentrations show higher value in sample LE
1-7 and LE 1-24. Then, the values drop in limestone sample LE 1-60. Generally, Fe and
Mn elements have higher values in dolomitic limestone (LE 1-7) compared to
limestone. While, Si element shows an inconsistent trend across all samples in Hill E.
It shows a similar trend as Mg concentration, where only three samples have Si
percentage value. The samples are LE 1-45, LE 1-54 and LE 1-63 with 0.13%, 0.19%
and 0.31% respectively. Other elements such as Sr and Al have a relatively low
concentration of less than 0.1% in representative samples of Hill E.
Figure 4.51: The elemental variation of Si, Fe, Al, Sr, and Mn based on outcrop
samples from Hill E, Gunung Kanthan.
107
4.3 Petrophysical Properties
The petrophysical properties are important to assess the reservoir quality. There are two
main petrophysical properties discussed in the subtopic: effective porosity () and
permeability (Kair) for each field. The measured porosity and permeability values are
determined from the changes in helium pressure. Berrezueta, Kovacs, & Luquot (2017)
stated that the porosity changes affected the pore morphology which can be seen in
microscopic observations.
There are thirty samples from Kinta Valley scheduled for porosity and permeability
testing. Six (6) samples from Hill B, Gunung Kanthan; eleven (11) samples from Hill
E, Gunung Kanthan; seven (7) samples from Gunung Rapat and six (6) samples from
Sungai Siput Dolomite Hill. Core sample descriptions (APPENDIX C) are made before
proceeding with porosity and permeability testing.
The qualitative study of micro-CT (µCT) scan is displayed in a 3D image of grey
shades, where white to grey color signifies the matrix, dark grey voxels resemble
microporous zones comprising pore space and matrix at one time, and black signifies
the pores. The micro-porosity is identified in the core plugs (macroscale). The pore-
throat size and connectivity can be observed in 2D/3D µCT images. The macropores of
µCT image are validated with experimental data and mostly show good agreement.
4.3.1 Field 1: Gunung Rapat
The porosity and permeability values measured for core plugs from Gunung Rapat are
presented in Table 4.5 below. The results indicate very tight porosity and low
permeability values, with porosity ranging from 1.10% to 3.24% and permeability is
less than 1mD. The highlighted green font in Table 4.5 shows the highest porosity and
permeability data, while red font shows the lowest values.
The highest porosity value belongs to the dolomitic limestone sample (AQ 76). The
sample is close to the fault area (right-strike slip fault) as in Fig. 4.6 (sedimentary
logging). The lowest porosity belongs to the limestone sample (AQ 60) with 1.10%
108
porosity with low permeability of 0.13mD, however, AQ 60 has the highest
permeability values among the samples from Gunung Rapat. The sample observed is
near to sepiolite section and associated with left-strike slip fault as recorded in Fig. 4.6.
The rock may have the lowest porosity probably because it is close to the sepiolite area.
This suggests that sepiolite may be partially responsible for porosity reduction because
it has a high tendency to block the pathways of fluid. However, there is a small amount
of permeability that is probably associated with small fractures.
The permeability values of Gunung Rapat’s samples are very low. All the samples
have permeability less than 1mD with most of the samples show no permeability (less
than 0.01mD). Only three samples have the permeability values, which are AQ 28
(0.01mD), AQ 60 (0.13mD) and AQ 76 (0.03mD). The highest documented value for
permeability is 0.13mD, where it belongs to limestone.
Table 4.5: List of porosity and permeability values of different samples in Gunung
Rapat.
Sample Name Lithology Porosity (%) Permeability, air (mD)
AQ 1 Dolomitic Limestone 1.58 0.00
AQ 10 Limestone 1.37 0.00
AQ 23 Limestone 1.44 0.00
AQ 28 Limestone 2.23 0.01
AQ 45 Limestone 1.35 0.00
AQ 60 Limestone 1.10 0.13
AQ 76 Dolomitic Limestone 3.24 0.03
Porosity-permeability cross plot of Anting’s samples is constructed as in Fig. 4.52.
From the cross plot, a dolomitic limestone sample (AQ 76) shows higher porosity than
limestone samples (AQ 28 and AQ 60). The porosity increases when it is associated
with dolomite in Gunung Rapat. It shows that the porosity values are not necessarily
corresponding to permeability values. However, the lithology and secondary structures
such as fractures, fault and sepiolite presence play a minor impact in the development
and destruction of porosity and permeability in localized area. AQ 60 has low
permeability than AQ 28, but AQ 60 has higher permeability than AQ 28. Overall, the
109
carbonate samples in Gunung Rapat have tight porosity and low permeability.
Limestone has lower porosity than dolomitic limestone except AQ 28, but higher
permeability than dolomitic limestone. Dolomitic limestone has the highest porosity
but lower permeability than limestone.
Figure 4.52: Porosity-permeability graph based on various lithologies of the mini-
cored plug from Gunung Rapat.
The qualitative analysis is conducted by 2D and 3D imaging of carbonate core plugs
at a macroscopic scale. There are three core plugs of Gunung Rapat that show
significant properties to support the porosity and permeability data. The selected
samples are as in Fig. 4.53.
0.01
0.10
1.00
10.00
0 0.5 1 1.5 2 2.5 3 3.5
Pe
rme
abili
ty (
mD
)
Porosity (%)
Limestone
Dolomitic Limestone
AQ 76
AQ 60
AQ 28
110
Figure 4.53: The red boxes show the presence of pores in core plugs of Gunung
Rapat, (a) Representative core plugs; (b) 3D µCT images of core plugs.
All the samples show a tight matrix. Two types of pores are recognized from µCT
scan images of Gunung Rapat’s samples (Fig. 4.54), fractures and isolated pores. The
fractures (F) present in limestone and dolomitic limestone samples, AQ 10 and AQ 76
respectively (Fig. 4.54). Whereas isolated pores (IsoP) only present in limestone
a b
)
Limestone
Sample:
AQ 10
a b
)
a b
)
Limestone
Sample:
AQ 60
Dolomitic
Limestone
Sample:
AQ 76
Pink
calcite
vein
5.0
8cm
5
.08
cm
5.0
8cm
2.54cm
2.54cm
2.54cm
111
sample, AQ 60. The majority of the pores remained disconnected in limestone samples
compared to dolomitic limestone.
Few micropore spaces remain open and isolated without any infills such as in
sample AQ 60. From porosity and permeability data, AQ 60 has the lowest porosity of
1.1% and permeability of 013mD. The average pore-throat size is 250µm. In contrast,
sample AQ 76 has the highest porosity of 3.24% and low permeability of 0.03mD. We
can observe few fracturing episodes in dolomitic limestone sample AQ 76 compared to
limestone sample AQ 10, which only have one episode of fracturing. The early fracture
(F1) is being cut across by late fracture (F2). The pore-throat is connected and called
cross-linked fractures. The pore-throat size is ranging from 200-425µm. The fractures
in dolomitic limestone are partially filled by dolomite (Dol), which reduces
permeability value. The dolomite appears light grey to white colour in µCT image.
While, limestone sample of AQ 10 has a moderate porosity value compared to AQ
60 and AQ 76 with 1.37%. The permeability value is less than 0.001mD, which
automatically counted as no permeability. The pore type presence in AQ 10 is a single
fracture (F). The macro pore-throat size ranges from 180-200µm. Fig. 4.54 (a) for a
sample of AQ 10, it shows the fracture is partly infilled either by dolomite or calcite
that exhibit pink colour. However, the µCT scan images proved that the fracture in
sample AQ 10 is partly infilled by calcite veins. They exhibit similar shades of grey
that indicate the same density between calcite vein and limestone matrix. The boundary
between the calcite vein within a limestone matrix cannot be recognized in µCT scan
because of the same shade of grey, but it can be observed in core plugs as in Fig. 4.54
(a).
112
Sample AQ 10: Micro-fracture (F) development in limestone.
Sample AQ 60: Isolated Pores (IsoP) with pore size of 250µm in limestone.
Sample AQ 76: The presence of cross-linked fractures, F1 cuts by F2
Figure 4.54: The µCT images of limestone and dolomitic limestone in Gunung Rapat
(a) 2D µCT image slice on top (b) 2D µCT image slice on the front (c) 3D µCT
image.
a) b)
F F
F1
Dol
a)
F1
Dol
F1
IsoP IsoP
IsoP
F
b) c)
a) b) c)
F2
F2
5.0
8 c
m
5.0
8 c
m
5.0
8 c
m
2.54cm
2.54cm
2.54cm
c)
113
4.3.2 Field 2: Sungai Siput Dolomite Hill
There is no limestone sample in Sungai Siput Dolomite Hill, since all the outcrops only
represent a dolomite rock. The main lithology is dolomite rock with some calcitic veins.
The dolomite in Sungai Siput has coarser grain compared to other rocks in other
quarries. In general, rocks with coarser grain tends to have high permeability. However,
in Sungai Siput Dolomite Hill, the permeability values are very low and tight porosity.
The porosity and permeability values measured for mini-core plugs of Sungai Siput are
presented in Table 4.6. The porosity values range from very little with 1.29% to 2.02%.
The permeability values range from almost 0.0mD to 0.07mD.
Table 4.6: List of porosity and permeability values of dolomites in Sungai Siput
Dolomite Hill.
Sample Name Lithology Porosity (%) Permeability, air (mD)
SA 1 Dolomite 1.90 0.06
SA 3 Dolomite 1.86 0.05
SB 6 Dolomite 2.02 0.07
SC 15 Dolomite 1.63 0.05
SD 5 Dolomite 1.76 0.05
SD 10 Dolomite 1.29 0.00
A dolomite sample of SB 6 shows the highest porosity and permeability values.
Meanwhile, the dolomite sample of SD 10 shows the lowest porosity and permeability
values. There is no significant difference in porosity and permeability between the
dolomite samples in Sungai Siput Dolomite Hill. They may be grouped into one type
of dolomite mentioned earlier in field observation as replacive dolomite.
The porosity and permeability trend of dolomite in Sungai Siput Dolomite Hill
corresponds to each other as shown in Fig. 4.55. The permeability value of dolomite
rocks in Sungai Siput Dolomite Hill increases when porosity increases. From the
analysis of petrophysical properties, the dolomites in Sungai Siput Dolomite Hill have
lower porosity than dolomites in Gunung Kanthan. Although they have similar
lithology and close locality, the porosity values varied significantly. These variations
114
may be influenced by other factors such as secondary structural, dolomite microfacies,
the presence of breccia and other diagenetic processes.
Figure 4.55: Porosity versus permeability graph of dolomite rocks in Sungai Siput
Dolomite Hill.
Fig. 4.56 shows the images of core plugs and 3D visualization of dolomite in Sungai
Siput Dolomite Hill. Three dolomite samples of SA 3, SB 6 and SD 5 will be discussed
and compared with the experimental value of porosity and permeability. The dolomites
in Sungai Siput Dolomite Hill have low porosity and permeability. One reason is the
abundance of calcite veins in the dolomite body (Fig. 4.12) filling up the pore spaces
such as fractures and vugs. The presence of micro-stylolite is observed in sample SD 5.
The consistency of grey shade is almost similar for all three samples, except at the pore
sections.
There are three types of pores identified from µCT images of Sungai Siput samples
(Fig. 4.57), which are isolated vug (V), fracture (F) and stylolite-pore (S). Isolated vug
of 1mm size is found in the dolomite sample of SA 3. It is surrounded by a tight
dolomite matrix. At the same time, fracture is observed in the dolomite sample of SB
6. Some parts of the fractures are filled by calcite cement, while others are preserved
from cementation. From porosity and permeability data, SB 6 shows the highest
porosity and permeability values. Conversely, sample SD 5 has the lowest porosity and
0.01
0.10
1.00
10.00
0 0.5 1 1.5 2 2.5
Pe
rme
abili
ty (
mD
)
Porosity (%)
Dolomite
SC 15
SD 5
SA 3
SA 1
SB 6
115
permeability compared to two samples of SA 3 and SB 6. The presence of stylolite is
observed in sample SD 5. The stylolite could act as a conduit for fluid flow (Heap et
al., 2014). The calcite veins are also present in the dolomite sample of SD 5.
Figure 4.56: The red boxes show pores in core plugs of Sungai Siput Dolomite Hill,
(a) Representative core plugs, (b) 3D µCT images of core plugs.
a b
)
Dolomite
Sample:
SA 3
a b
)
a b
)
Dolomite
Sample:
SB 6
Dolomite
Sample:
SD 5
Calcite
vein
Micro-
stylolite
Calcite
infills
Calcite
vein
4.5
0 c
m
5.0
8 c
m
4.5
0 c
m
2.54cm
2.54cm
2.54cm
116
Sample SA 3: Isolated vug (V) in dolomite. The pore size is around 1mm.
Sample SB 6: Fracture (F) partially infills with calcite vein in dolomite body. The
pore size is around 110µm.
Sample SD 5: The presence of stylolite-pore (S) and calcite vein (Cal) in the dolomite
body. The pore-throat size is around 260µm.
Figure 4.57: The µCT images of dolomite in Sungai Siput Dolomite Hill (a) 2D µCT
image slice on top (b) 2D µCT image slice on the front (c) 3D µCT image.
a) b) c)
V V
Cal
S
a)
S
Cal
S
F F
F
V
b) c)
a) b) c)
Cal
4.5
0 c
m
4.5
0 c
m
5.0
8 c
m
2.54cm
2.54cm
2.54cm
117
4.3.3 Field 3: Hill B, Gunung Kanthan
The section of Hill B, Gunung Kanthan, has two main lithologies which are limestone
and dolomite. The porosity and permeability data of Hill B are shown in Table 4.7
below. The porosity values of samples in Hill B, Gunung Kanthan ranged from 3.08%
to 1.14%. The dolomite sample (LB 81) has the highest porosity among all samples,
while the limestone sample (LB 62) has the lowest porosity. From the data obtained,
most the dolomite samples in Hill B show higher porosity than limestone. The porosity
range of dolomite samples is from 3.08% to 1.8%. Meanwhile, the porosity of limestone
samples ranges from 1.14% and 1.25% porosity.
The permeability of mini-cored plug samples in Hill B show low permeability,
ranging from 0.0mD to 0.07mD. The highest permeability value is owned by the
limestone sample of LB 6. The second highest permeability is referred to dolomite
samples, LB 81 and LB 80, with 0.06mD and 0.05mD, respectively. Then, it is followed
by a limestone sample, LB 24 with 0.04mD and LB 62 with 0.02mD.
Table 4.7: List of porosity and permeability values of different samples in Hill B,
Gunung Kanthan.
Sample Name Lithology Porosity (%) Permeability, air (mD)
LB 6 Limestone 1.25 0.07
LB 24 Limestone 1.47 0.04
LB 62 Limestone 1.14 0.02
LB 80 Dolomite 1.85 0.05
LB 81 Dolomite 3.08 0.06
LB 83 Dolomite 1.80 0.00
The porosity-permeability cross plot of Hill B is shown as in Fig. 4.58. The graph
shows the permeability of the dolomite sample increases as porosity increases. On the
contrary, the permeability of limestone samples increases when porosity decreases. By
referring to the limestone of Hill B, the porosity and permeability are not ascending
evenly. The porosity increases when corresponding with dolomite. Limestone has lower
porosity-permeability than dolomite. In summary, the carbonate samples of Hill B,
Gunung Kanthan have low porosity and permeability.
118
Figure 4.58: The porosity-permeability cross plot of samples from Hill B, Gunung
Kanthan.
The qualitative analysis of µCT scan is conducted for all samples in Hill B. The
selected limestone and dolomite samples (LB 24, LB 80, LB 81, LB 83) are displayed
in Fig. 4.59. The dolomite crystals are well-developed. Few characteristics are observed
in core plugs, such as the presence of stylolite, fracture and isolated vug.
0.01
0.10
1.00
10.00
0 0.5 1 1.5 2 2.5 3 3.5
Pe
rme
abili
ty (
mD
)
Porosity (%)
Limestone Dolomite
LB 6LB 80
LB 62
LB 24
LB 81
119
Figure 4.59: The red boxes show pores in core plugs of Hill B, Gunung Kanthan, (a)
Representative core plugs; (b) 3D µCT images of core plugs.
a b
)
Limestone
Sample:
LB 24
a b
)
a b
)
Dolomite
Sample:
LB 80
Dolomite
Sample:
LB 81
Stylolite
Vug
Vug
b
)
a
Dolomite
Sample:
LB 83
Crystallized
dolomite
Crystallized
dolomite
Crystallized
dolomite
2.54cm
2.54cm
2.54cm
2.54cm
5.0
8 c
m
5.0
8 c
m
4.3
0 c
m
5.0
8 c
m
120
The presence of stylolite in the limestone sample of LB 24 is observed as shown in
Fig. 4.60, where it has a low to high amplitude of peak stylolite. The fracture porosity
in sample LB 24 is connected to stylolite porosity. The average pore-throat size is
200µm. It shows good connectivity of pores between stylolite and fracture. Based on
porosity and permeability data, LB 24 has 1.47% and 0.04mD. Fracture also developed
in the dolomite sample of LB 80. The fracture is remained open without any cement
and connected to the vug. The pore size is ranging from 170µm to 850µm with 1.85%
porosity and 0.05mD permeability.
LB 81 show the highest porosity, 3.08% and second-highest permeability among
all samples, 0.06mD. There are lots of vugs and fractures created in these dolomite
body. Few vugs in the sample are isolated from one another, while few are connected
to fracture. The estimated range of pore size is from 100µm to 1100µm. Qualitatively,
the pore connectivity is identified as medium to good. LB 83 has 1.8% porosity and
associated with vugs and fracture pore type. The fracture is connected to a vug. The
fracture is initially developed and later enhanced the pore space to vuggy porosity
through dissolution. However, the sample of LB 83 has low permeability because the
fracture is not continuous and was terminated at the top section of the core plug. The
estimated pore size from a 2D slice of µCT image is ranging from 80µm to 3000µm.
121
Sample LB 24: Fracture (F) cuts across stylolite (S) in limestone sample as in 3D
µCT image (c). The average pore size is 200µm.
Sample LB 80: Micro-fracture (F) development in dolomite rock creates vug
porosity. The pore size is around 170µm to 850µm.
Sample LB 81: The presence of vugs (V) and fractures (F) in dolomite core plug. The
range of pore size is estimated from 100µm to 1100µm.
F F
V
V
V
F
b) c)
S
S
S
F
a)
b)
c)
F
F
V
5.0
8 c
m
5.0
8 c
m
4.3
0 c
m
2.54cm
2.54cm
2.54cm
122
Sample LB 83: The presence of vug (V) connected to fracture (F) in dolomite. The
pore size is ranging from 80µm to 3000µm.
Figure 4.60: The µCT images of limestone and dolomite samples of Hill B, Gunung
Kanthan (a) 2D µCT image slice on top (b) 2D µCT image slice on the front (c) 3D
µCT image.
4.3.4 Field 4: Hill E, Gunung Kanthan
The porosity values of carbonate samples in Hill E are ranging from 2.06% to 14.52%
(Table 4.8). The dolomitic limestone sample of LE 1-7 shows the lowest porosity value,
conversely, limestone samples of LE 1-60 show the highest porosity value. While, the
dolomite samples of LE 2-3 and LE 2-4 have low porosity with 2.32% and 5.75%,
respectively. Among all lithologies, the only limestone displayed a wide range of
porosity, starting from 4.06% to the highest, 14.52%. Overall, carbonate samples of
Hill E indicate poor to good porosity.
Most of the samples in Hill E has a permeability value less than 1mD. However,
two limestone samples have quite significant permeability values compared to others,
which are LE 1-54 (0.79mD) and LE 1-60 (1.82mD). The limestone samples show
various permeability values, ranging from 0.0mD to 1.82mD. The highest and lowest
permeability refers to limestone samples of LE 1-60 and LE 1-24, respectively. The
second lowest refers to dolomitic limestone with 0.05mD to 0.08mD. Whereas,
dolomite samples have better range permeability than dolomitic limestone with 0.07mD
to 0.46mD.
F
V
F F
a) b) c)
V V
5.0
8 c
m
2.54cm
123
Table 4.8: List of porosity and permeability values of different samples in Hill E,
Gunung Kanthan.
Sample Name Lithology Porosity (%) Permeability, air (mD)
LE 1-7 Dolomitic Limestone 2.06 0.05
LE 1-24 Limestone 2.48 0.00
LE 1-45 Limestone 6.77 0.07
LE 1-54 Limestone 11.73 0.79
LE 1-60 Limestone 14.52 1.82
LE 1-62 Limestone 4.06 0.05
LE 1-63 Limestone 9.06 0.07
LE 2-2 Limestone 5.72 0.04
LE 2-3 Dolomite 5.75 0.46
LE 2-4 Dolomite 2.32 0.07
LE 2-5 Dolomitic Limestone 4.22 0.08
The porosity versus permeability graph shows a clear distribution of lithology
regarding to porosity and permeability data (Fig. 4.61). The cross plot shows porosity
and permeability increase proportionally. As the porosity increases, the permeability
also increases. Although the variation in permeability of limestone numerically does
not appear to be large, the trend still exhibits a high peak of 1.82mD. Generally,
porosity-permeability cross plot indicates that limestone has higher porosity and
permeability than other lithologies. The second highest is the dolomite samples and
followed by dolomitic limestone.
124
Figure 4.61: The porosity-permeability trend of mini-cored plugs linked to various
lithology in Hill E, Gunung Kanthan.
For qualitative analysis, four samples (LE 1-45, LE 1-54, LE 1-60, LE 1-63)
from section 1 as in Fig. 4.62 and three samples (LE 2-2, LE 2-3, LE 2-5) from section
2 as in Fig. 4.63 were observed. Most of the limestone samples in section 1 of Hill E
consisted of open fracture. While, most of the samples in section 2 of Hill E are
associated with limestone breccias. The boundary between limestone and dolomite is
observed in sample LE 2-5. Overall, the carbonate in Hill E indicates a good pore
system.
a b
) Limestone
Sample:
LE 1-45
2.54cm
5.0
8 c
m
125
Figure 4.62: Limestone samples of section 1 in Hill B, Gunung Kanthan tested for
µCT scan (a) The image of representative core plugs (b) 3D µCT images of core plugs
the red dotted boxes show the microporous zones.
a b
)
a b
)
Limestone
Sample:
LE 1-54
Limestone
Sample:
LE 1-60
b
)
a
Limestone
Sample:
LE 1-63
Fracture
Fracture
Fracture
2.54cm
2.54cm
2.54cm
5.0
8 c
m
5.0
8 c
m
5.0
8 c
m
126
Figure 4.63: Limestone, dolomite and dolomitic limestone samples of section 2 in
Hill B, Gunung Kanthan. The samples are associated with brecciated limestone (a)
The image of representative core plugs (b) 3D µCT images of core plugs and
the red boxes show the microporous zones.
The carbonate samples of Hill E, Gunung Kanthan are highly heterogeneous. From
the observation of µCT scan images (Fig. 4.64), the samples in Hill E show various
porous zones with different pore types. Two types of pores are recognized in the
samples which are fractures and vugs. Vugs can be observed in limestone, dolomite and
dolomitic limestone. The pore radius of the vug in the limestone sample (LE 1-45)
a b
)
Limestone
Sample:
LE 2-2
a b
)
a b
)
Dolomite
Sample:
LE 2-3
Dolomitic
Limestone
Sample:
LE 2-5
LE 2-5
Dolomite
Dolomite
Brecciated
Limestone
Limestone
Brecciated
Limestone Limestone
2.54cm
2.54cm
2.54cm
5.0
8 c
m
5.0
8 c
m
5.0
8 c
m
127
ranges from 100µm to 1000µm. The pores are isolated and clustered in the porous zone.
While, dolomite and dolomitic limestone samples show the vugs formed in clusters
within limestone breccias, with pore size ranging from 220µm to 1350µm. Fractures
are also present in limestone, dolomite and dolomitic limestone samples. Fracture in
limestone sample (LE 1-63) is partly infilled by calcite cement. While, the rest of the
fractures remained as open space without any types of cement. Few fractures in the
dolomite sample (LE 2-3) are connected to the vugs pore type.
Sample LE 1-45: The presence of vugs (V) in limestone sample. The pores are
continuous from the top to the bottom section of the core plug. The pore size is
ranging from 100µm to 1000µm.
Sample LE 1-54: Two parallel fractures (F) develop in limestone. The average pore
radius is around 312µm.
F
F F
V
V V
c)
Dol vein
b)
b) c) a)
a)
5.0
8 c
m
5.0
8 c
m
2.54cm
2.54cm
128
Sample LE 1-60: The presence of fractures (F) and channel (Ch) pore types in
limestone sample. The diameter of pore size is from 416µm to 1875µm.
Sample LE 1-63: The presence of vug (V) and fracture (F) in limestone sample. Few
parts of the fracture are filled by calcite cement as in (a). The pore size is ranging
from 80µm to 3000µm. Two sections of calcite, a dark grey area are associated with
pores and a light grey area is not associated with any pores. They might be a different
generation of calcite that will be discussed in petrographic sections.
Sample LE 2-2: Brecciated limestone has vuggy porosity and the pore size ranges
from 125µm to 1300µm.
a)
Pore-filling
calcite cement
F
F
F F
b) c)
b) c)
V
F F
V
BL
V
V
F
Cal Cal
Cal
Cal
BL
b) c)
a)
a)
5.0
8 c
m
5.0
8 c
m
5.0
8 c
m
2.54cm
2.54cm
2.54cm
129
Sample LE 2-3: The dolomite sample is associated with limestone breccia. The
brecciated limestone shows a cluster of pores, which is vug (V) pore type. The range
of pore size is from 625µm to 2500µm. Fractures (F) is observed in dolomite rock.
Sample LE 2-5: This sample shows the boundary between limestone (Cal) and
dolomite (Dol) bodies. The dolomite (Dol) is associated with a porous zone. The pore
types present are fracture (F) and vug (V). The pore size ranges from 220µm to
1350µm.
Figure 4.64: The µCT images of limestone, dolomite and dolomitic samples of Hill
E, Gunung Kanthan (a) 2D µCT image slice on top (b) 2D µCT image slice on front
(c) 3D µCT image.
a)
F
V
F
b) c)
V
V
F
V
F
F
b) c)
Cal
V
Cal
Cal
BL
Dol
a)
5.0
8 c
m
5.0
8 c
m
2.54cm
2.54cm
130
4.4 Petrographic Study
Petrographic details such as crystal size, shape, contact, texture, distribution and
morphology of Kinta Limestone were analyzed using the terminology of crystal texture
description from Gregg and Sibley (1987 & 1984) and nomenclature for dolomite
classification from Flügel (2004). In addition, the grain size chart established by Folk’s
(1962) is used to quantify the crystals size distribution.
4.4.1 Field 1: Gunung Rapat
4.4.1.1 Petrography and Diagenetic Features
Based on petrographic observations in Fig. 4.65, there are four calcite types found in
Gunung Rapat, which are: micritic calcite matrix (Cal-I), equant calcite cement (Cal-
II), micritic to equant calcite cement (Cal-III) and blocky to drusy calcite cement (Cal-
IV). The calcite matrix has no fossil and is tightly packed. Micritic calcite matrix has
fine to medium crystal size with most of the size of the crystals below than 50µm. The
equant calcite cement shows an interlocking boundary between calcite crystals, with
subhedral to anhedral shape. Micritic to equant calcite cement has a very fine crystal
size, and the crystal shape is hard to recognize under photomicrographs. While, blocky
to drusy calcite cement has a coarse crystal size ranging from 100µm to 800µm.
Calcite cement exhibits dull orange to brown luminescence under
cathodoluminescence (CL), while dolomite crystals show dull red luminescence.
Dolomite in Gunung Rapat is identified as replacive dolomite or matrix dolomite. It has
a fine crystal size ranging from 10µm to 50µm and classified as microdolomite (Dolo-
I). It shows morphology of nonplanar-a to planar subhedral (planar-s), from xenotopic-
A to hypidiotopic. Sucrosic dolomite (Dolo-II) comprised the same characteristics as
microdolomite under CL. However, it is found brecciated in the calcite matrix and has
fine to medium crystal size. Besides, few samples show the presence of stylolites and
fractures. There is also the presence of pyrite in the samples. Pyrite in Gunung Rapat is
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divided into two types, which are irregular pyrite and anhedral pyrite. These types of
pyrite appear opaque in plane-polarized light (PPL) and CL.
Sample AQ 1 - Under PPL
A fine crystalline micritic calcite matrix
(Cal-I). In average, most of the size of the
crystals are below 50µm, with fracture cuts
across the matrix.
Sample AQ 1 - CL
Cal-I shows dull to non-luminescent and
brown colour with irregular crystal shapes.
While, Dolo-I appears dull luminescent red
with very fine crystal size. The fractures are
infilled by calcite cement.
Sample AQ 10 – PPL
The presence of two types of calcite
cements, which are equant calcite (Cal-II)
and blocky to drusy calcite (Cal-IV) in
calcite matrix.
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Sample AQ 45 – PPL
A micritic calcite matrix shows a presence of
an isolated opaque micropyrite with
euhedral shape. The surrounding matrix is
associated with stylolite and dissolution.
Sample AQ 60 – PPL
Photomicrograph shows two fractures (F-III
cuts F-II) in calcite cement and the presence
of irregular shape of pyrite.
Sample AQ 76 – PPL
The image shows late fracturing (F-IV) cuts
across blocky to drusy calcite cement (Cal-
IV) and brecciated clasts of sucrosic
dolomite (Dolo-II).
Sample AQ 76 – PPL
The image shows the contact between two
different calcite types (Cal-I and Cal-IV) and
dolomite (Dolo-II) with late fracturing (F-
IV). Dolo-II has an equigranular anhedral
crystal with less than 100µm in size.
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Sample AQ 76 – CL
The dolomite (Dolo-II) appears dull red
luminescent with no clear rim, nonplanar-a
and brecciated. In contrast, the calcite
matrix shows bright orange colour in CL.
Figure 4.65: Photomicrographs of calcite and dolomite types in Gunung Rapat.
4.4.1.2 Pore Types and Percentage
Three types of micropores are recognized from photomicrographs in Gunung Rapat:
intercrystalline pore, stylo-pore and fracture. The intercrystalline porosity is observed
in equant calcite cement (Cal-II) as in Fig. 4.66 (a). While, the presence of stylo-pore
and fracture are observed in micritic calcite matrix (Cal-I) as in Fig. 4.66 (b) and Fig.
4.66 (c), respectively. Calcite cements partly fill the fractures. Overall, stylo-porosity
has a slightly higher porosity value than intercrystalline and fracture porosity. However,
they are still considered as tight porosity. There is no porosity observed in the dolomite
matrix. Table 4.9 is a summary of pore types and percentage based on calcite types in
Gunung Rapat.
Table 4.9: Summary of pore types and percentages based on calcite types in Gunung
Rapat.
Cal-I Micritic calcite matrix has stylo-porosity with 1-3% and fracture
porosity with 1%.
Cal-II Equant calcite cement is partly filled the pore spaces and associated
with intercrystalline porosity of 1%.
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Sample AQ 1 – PPL
The presence of intercrystalline pore with
1% porosity in pore-filling equant calcite
cement (Cal-II).
Sample AQ 45 – PPL
Stylo-porosity is originated from dissolution
along stylolite in Cal-I. The porosity
observed is 3%.
Sample AQ 76 - PPL
The fracture cuts across Cal-I with 1%
porosity.
Figure 4.66: The micropore types that present in Gunung Rapat.
4.4.2 Field 2: Sungai Siput Dolomite Hill
4.4.2.1 Petrography and Diagenetic Features
Based on Fig. 4.67, two calcite cement types observed in PPL and CL, which are blocky
to drusy calcite cement (Cal-IV) and blocky to poikilotopic calcite cement (Cal-V).
Both are identified as pore-filling calcite vein, where they entirely or partially infill the
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pore spaces. They also appear orange with bright luminescence under CL. Cal-IV has
a crystal size ranging from 250µm to 300µm with no core nucleui present. While, Cal-
V has coarser crystal size ranging from 400µm to 500µm. The CL patterns show Cal-
V has complex zonation, where the core nuclei are euhedral rhombic, with luminescent
and non-luminescent centres and irregular bright orange luminescent rims. The crystals
have inequigranular grain size and most of them exhibit a planar-s shape.
Dolomite in Sungai Siput Dolomite Hill is initially identified as replacive dolomite
in the field outcrop observations. However, after a detailed petrographic study, the
dolomite in Sungai Siput Dolomite Hill composed of replacive and cement dolomite
with majority samples showed replacive dolomite. Dolo-II and Dolo-III are categorized
under replacive dolomite, while Dolo-IV is cement dolomite. Sucrosic dolomite (Dolo-
II) has fine to medium crystalline, with crystal size ranging from less than 50µm to
150µm. Dolo-II has equigranular (unimodal crystal size) and inequigranular
(polymodal crystal size) texture, with mosaic fabric. The crystal boundary shows a
nonplanar anhedral, with mostly curved and lobate shape. Dolo-II is considered poorly
fabric preserving. Besides, there is late fracturing (F-IV) cuts through the Dolo-II and
partly infilled by Cal-V.
While, fabric destructive fine crystalline dolomite (Dolo-III) has crystal size
ranging from 10µm to less than 50µm. The crystal is inequigranular and has a
porphyrotopic texture, where there is a floating dolomite rhomb in the dolomite fabric.
The floating dolomite rhomb has a crystal size of 100µm, with planar euhedral to
subhedral. It is an isolated crystal in a fine-grained matrix. CL photomicrograph shows
the dolomite mosaic has dull red luminescent with no clear rhomb, while floating
dolomite crystals show dull red luminescent with dark cortices and bright rim.
Dolo-IV has coarse to very coarse crystal with size ranging from 300µm to 900µm.
The fabric is an equigranular mosaic and it is tightly packed. The crystal boundary is
not easy to determine because the dolomite fabric is destructive. Besides, Dolo-IV is
associated with the late calcite vein (Cal-IV).
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Sample SD 5 – PPL
Pore-filling calcite cements (Cal-IV and
Cal-V) cuts through a fine crystalline
dolomite texture (Dolo-III), with the
presence of intercrystalline pore.
Sample SD 5 – CL
Calcite exhibits a bright luminescence
orange colour under CL. Cal-V has complex
zonation, where the core nuclei have
euhedral rhomb with luminescent and non-
luminescent centres. While, dolomite
appears dull luminescence red colour with
no clear rhombs.
Sample SD 10 - PPL
The dolomite matrix shows a fine crystalline
fabric destructive texture.
Sample SD 10 - CL
In CL, the isolated planar euhedral to
subhedral dolomite crystals are floating in
the dolomite matrix. The crystal fabric is
known as porphyritic. The dolomite crystals
have dull luminescence red colour with dark
cortices and a bright rim.
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Sample SC 15 - PPL
The image shows a coarse crystalline
dolomite matrix is associated with fractures
and fracture-filling calcite veins.
Sample SB 6 - PPL
A calcite cement cuts through sucrosic
dolomite matrix. There are fracture porosity
and stylolites present in the dolomite matrix.
Figure 4.67: Photomicrographs of dolomite rocks in Sungai Siput Dolomite Hill.
4.4.2.2 Pore Types and Percentage
Three pore types are observed in photomicrographs (Fig. 4.68) of Sungai Siput
Dolomite Hill, which are stylo-pore, fracture and intercrystalline. All pore types are
present in dolomite types. No micropores are observed in calcite cements. The stylo-
pore is found in sucrosic dolomite with a range from 1% to 2% porosity. While, the
fracture is identified in sucrosic dolomite (Dolo-II) and fabric destructive fine
crystalline dolomite (Dolo-IV) with 1% to 3% porosity, respectively. The highest
porosity recorded is 5% from fabric destructive fine crystalline dolomite (Dolo-III),
mainly contributed by intercrystalline pores. Intercrystalline pores also present in Dolo-
II with 3% of porosity. Table 4.10 below shows the summary of pore types and porosity
of microfacies in Sungai Siput Dolomite Hill.
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Table 4.10: Summary of pore types and percentages based on dolomite types in
Sungai Siput Dolomite Hill.
Dolo-II This nonplanar dolomite has intercrystalline pores, with an estimation
of 3% porosity. Meanwhile, stylo-porosity consisted of 2% porosity.
Dolo-III Even though Dolo-III mosaic is tightly packed, massive fracturing
enhanced the dissolution porosity. The percentage porosity observed is
5%.
Dolo-IV There are fracture and intercrystalline pores with an estimation of 2%
porosity.
Sample SD 5 – PPL
The image shows sucrosic dolomite matrix
(Dolo-II) is associated with stylo-porosity
(2%) with pore-filling calcite cement.
Sample SD 5 - CL
The pore type present in Dolo-III is
intercrystalline with 5% porosity.
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Sample SA 3 - PPL
The presence of intercrystalline pore with
3% porosity in anhedral sucrosic dolomite
matrix (Dolo-II).
Sample SC 15 - PPL
Photomicrograph shows the fractures cut
across the dolomite matrix and calcite
cement. The pore type present is a fracture
with 2% porosity. The fractures are partly
infilled by calcite.
Sample SC 15 - PPL
Coarse crystalline dolomite matrix (Dolo-
IV) is associated with fracture porosity of
3% and intercrystalline porosity of 1%.
Figure 4.68: The micropore types present in dolomite of Sungai Siput Dolomite Hill.
4.4.3 Field 3: Hill B, Gunung Kanthan
4.4.3.1 Petrography and Diagenetic Features
Limestone in Hill B consisted of four types of calcite which are micritic calcite matrix
(Cal-I), equant calcite cement (Cal-II), micritic to equant calcite cement (Cal-III) and
blocky to poikilotopic calcite cement (Cal-V). Cal-I has very fine a crystal matrix with
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crystal size less than 30µm. The matrix is tightly packed with no porosity observed.
Cementation intensely occurs in Cal-I, which is associated with many calcite veins
(Cal-II and Cal-III). The pyrite is also present in Hill B, where it shows an irregular
shape, contradictory with the pyrite in Gunung Rapat which exhibits an anhedral shape.
There are a lot of micro-stylolites observed in Cal-I. Besides, Cal-II has a medium
crystal size of 150µm. Cal-II is vein-filling calcite cement that are present in the calcite
matrix. It destroys the porosity generated by early fracturing. Cal-III also has fine
crystal size, approximately 50µm. Cal-III is also the same as Cal-II, they represent pore-
filling calcite cements in micritic calcite matrix. While, blocky to poikilotopic calcite
cement (Cal-V) has very coarse crystal size, more than 500µm. It appears dull
luminescent orange colour under CL. Cal-V is a late-stage calcite cement that fills in
pore spaces after late fracturing and dissolution.
There are three types of dolomites observed in Hill B, which are sucrosic dolomite
(Dolo-II), (Dolo-IV) and saddle dolomite (Dolo-V). Dolo-II has fine to medium
crystalline, with crystal size ranging from 50µm to 150µm. Dolo-II has an
inequigranular (polymodal crystal size) texture, with mosaic fabric. The crystal shape
is nonplanar anhedral mostly curved and lobate intercrystalline boundaries. This
nonplanar dolomite infills the intercrystalline pores. There is a late fracture (F-VII) cuts
through the Dolo-II.
Dolo-IV shows fabric destructive under plane-polarized light. Dolo-IV has coarse
to very coarse dolomite crystalline from CL images, ranging from 300µm to more than
500µm. The crystal shape is planar-s to nonplanar-a. Most photomicrograph showing
Dolo-IV has an equigranular sieve and sutured mosaic with a clear rim, no zoning and
core. It appears bright red luminescent under CL. While, there is one photomicrograph
shows Dolo-IV has an inequigranular texture with floating dolomite rhomb as in Figure
4.62 (d). The isolated dolomite crystals float in the dolomite vein. The crystal size
ranging from 100µm to 500µm, with planar-s to nonplanar-a. It shows bright red
luminescent with no clear rim, no zoning and core under CL. Dolo-IV is highly
fractured and associated with calcite and dolomite vein.
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Dolo-V is identified as saddle dolomite, which cement dolomite forms at the late
stage of dolomitization. The dolomite can be classified as nonplanar-a to planar-s
dolomite, where most of Dolo-V forms a planar-s with crystals of 50µm to 2000µm in
diameter. Dolo-V is grouped under xenotopic-C pore-lining saddle shape. Such
dolomite is often developed as vein- or fracture filling. It has a half moon-like
termination pointing towards the centre of pore spaces (Fig. 4.69 (f)). Dolo-V is in
contact with late calcite cementation (Cal-V). CL photomicrograph of Fig. 4.69 (g)
showing bright red luminescent with no zoning and a bright core. It displays clear thick
dolomite rims. A dark brown rim can accentuate the rhombs edges. Late fracturing (F-
VII) cuts through Dolo-V and there is the presence of pyrite before the late stage of
calcite cementation as in Fig. 4.69 (e).
Sample LB 62 - PPL
The infilling of calcite vein (Cal-II) in
calcite matrix (Cal-I) with the presence of
pyrite.
Sample LB 62 - PPL
Cal-I shows very fine crystalline
(size<10um). Micritic to equant calcite
cement (Cal-III) cuts through calcite matrix
(Cal-I). Besides, there is stylolite and
irregular shape of pyrite in Cal-I.
142
Sample LB 80 - PPL
The image shows a fabric destructive
dolomite matrix (Dolo-IV).
Sample LB 80 - CL
This photomicrograph is the same image as
Fig. 4.8 (c). The floating rhomb crystals are
observed under CL (isolated dolomite
crystal floating in dolomite vein) with
planar-s to nonplanar-a. It exhibits bright
luminescent red colour with no clear rim, no
zoning and core.
Sample LB 83 - PPL
Saddle dolomite (Dolo-V) has very coarse
crystalline (size>500um) and associated
with blocky to poikilotopic calcite cement
(Cal-V). The presence of euhedral pyrite in
the dolomite matrix. It shows that the calcite
cement (Cal-V) fills in the pores at a later
stage than pyrite.
143
Sample LB 83 - PPL
Figure shows a lobate crystal face junction
between saddle dolomite (Dolo-V) and
blocky to poikilotopic calcite cement (Cal-
V).
Sample LB 83 - CL
With the same section as Fig. 4.69 (f), Dolo-
V appears bright luminescent red with
planar-es, clear thick rim, no zoning and
core. While, Cal-V appears dull luminescent
orange.
Figure 4.69: Photomicrographs of calcite and dolomite types in Hill B, Gunung
Kanthan.
4.4.3.2 Pore types and percentage
In Hill B (Gunung Kanthan), the porosity is found only in dolomite types as in Fig.
4.70. There is no porosity in calcite cements. The pore types present are stylo-pore,
intercrystalline, vug and fracture. Stylo-pore presents in Dolo-V with 1% porosity.
Vugs are also present in Dolo-V with 5% porosity. While, intercrystalline pores have a
wide range of porosity from 4% to 25% observed in cement dolomites, Dolo-IV and
Dolo-V. Besides, channel pore type is identified in Dolo-IV with 7% porosity. Whereas
fracture porosity is recognized in all dolomite types of Hill B. Fracture pores have very
low porosity ranging from 1% to 2%. In general, the replacive dolomites (Dolo-IV and
Dolo-V) in Hill B have higher porosity than cement dolomite (Dolo-II) as summarized
in Table 4.11 below. The dissolution enhanced the porosity of late-stage dolomite
cements, Dolo-IV and Dolo-V.
144
Table 4.11: Summary of pore types and percentages based on dolomite types in Hill
B, Gunung Kanthan.
Dolo-II The sucrosic dolomite has a fracture with 2% porosity.
Dolo-IV There are intercrystalline (6%), channel (7%) and fracture (1%)
porosity in fabric destructive coarse crystalline dolomite (Dolo-IV).
Dolo-V Saddle dolomite (Dolo-V) has loosely packed crystals. The highest
porosity observed in Dolo-V is 25%. The pore types include vug,
fracture, stylo-pore and intercrystalline pores with 5%, 1-2%, 1% and
4-25% porosity.
Sample LB 80 – PPL
The image shows vug presence in the
dolomite matrix (Dolo-V) with some infills
of broken fragments. The vug has a diameter
of 500µm and 5% porosity.
Sample LB 80 – PPL
Saddle dolomite (Dolo-V) is also associated
with brecciation and has 1% of stylo-
porosity.
145
Sample LB 80 - PPL
The photomicrograph shows fabric
destructive coarse crystalline dolomite
(Dolo-IV) is associated with fracture
porosity (1%) and channel porosity (7%).
Sample LB 83 - PPL
The intercrystalline porosity (9%) is
observed in sucrosic dolomite (Dolo-V). The
fracture porosity (1%) is observed in
sucrosic dolomite (Dolo-II). Dolo-V has
coarse crystalline because the crystal has
enough space to develop when dissolution
occurs before dolomitization of Dolo-V.
Sample LB 83 - PPL
The image shows intercrystalline porosity in
the dolomite matrix (Dolo-V) with good
porosity of 25%. The intercrystalline pore is
believed to associate with enhanced-pore
dissolution. The dolomite matrix is loosely
packed.
146
Sample LB 81 - PPL
There is a fracture with 2% porosity cuts
across brecciated dolomite matrix of planar-
s to nonplanar-a fabric destructive coarse
crystalline (Dolo-V) and sucrosic dolomite
(Dolo-II).
Sample LB 83 - PPL
The image shows intercrystalline porosity
(25%) in the dolomite matrix (Dolo-V).
Sample LB 83 - CL
Under CL, the intercrystalline porosity
exhibits dark colour. The dolomite crystals
of planar- es display the clear rims with no
zoning and bright core. They have a bright
luminescent red colour. A dark brown rim
accentuates the rhombs edges.
Figure 4.70: The micropore types present in dolomite of Hill B, Gunung Kanthan.
4.4.4 Field 4: Hill E, Gunung Kanthan
4.4.4.1 Petrography and Diagenetic Features
From photomicrographs observation, five types of calcite were observed in Hill E,
which are micritic calcite matrix (Cal-I), equant calcite cement (Cal-II), micritic to
147
equant calcite cement (Cal-III), blocky to drusy calcite cement (Cal-IV) and blocky to
poikilotopic calcite cement (Cal-V). Micritic calcite matrix (Cal-I) has fine crystalline
size, which is 30µm. There are isolated corroded dolomite crystals floating in the calcite
matrix. The calcite matrix is associated with the irregular shape of pyrite mineral, and
micro-stylolite. Besides, Cal-II has fine to medium crystal size of 50µm to 150µm with
nonplanar-a crystal boundary. Besides, micritic to equant calcite cement (Cal-III) has
fine to medium crystal size, approximately from 50µm to 100µm. Cal-III is a pore-
filling calcite cement in the limestone matrix, and it cuts across Cal-II. Whereas, blocky
to drusy calcite cement (Cal-IV) has coarse crystals size ranging from 100µm to more
than 700µm, with mostly coarser grain. It is identified as void-filling calcite vein, where
it completely or partially infills the pore space. There is a floating euhedral dolomite
crystal observed in Cal-IV. Another type of calcite cement is blocky to poikilotopic
calcite cement (Cal-V) with very coarse crystals. The crystal size is ranging from
500µm to 800µm. It is also identified as pore-filling calcite. This type of calcite cement
fills in the pore spaces within saddle dolomite (Dolo-V) as in Fig. 4.71 (g). There are a
few microstylolites cut through Cal-V.
Hill B also consisted of five types of dolomite texture, which are microdolomite
(Dolo-I), sucrosic dolomite (Dolo-II), fabric destructive fine crystalline dolomite
(Dolo-III), fabric destructive coarse crystalline dolomite (Dolo-IV) and Saddle
dolomite (Dolo-V). Firstly, microdolomite (Dolo-I) has fine crystalline dolomite
cement. It has the smallest crystal size compared to other types of dolomite, which is
less than 30µm. The crystal texture is inequigranular with nonplanar-a. While, sucrosic
dolomite (Dolo-II) has a medium crystalline, with crystal size ranging from 100µm to
150µm. Dolo-II has an equigranular (unimodal crystal size) texture, with mosaic fabric.
The crystal shape is nonplanar anhedral, with mostly curved and lobate intercrystalline
boundaries.
The other type of dolomite is (Dolo-III). It has a floating dolomite crystal in the
calcite matrix. The dolomite crystal shows a corroded surface. It shows a porphyrotopic
(isolated rhombs) with planar-es to nonplanar-a under photomicrograph. The isolated
crystal is equigranular and tightly packed. CL images show Dolo-III has fine isolated
148
crystals that exhibit dull red luminescent with dark cortices as in Fig. 4.71 (l). In
contrast, Dolo-IV has very coarse crystalline, ranging from 500µm to more than
2000µm. The crystal shape is planar -es to nonplanar-a. It shows the bright red
luminescent, clear dark outer rim and no zoning or core detected under CL. There is an
isolated Dolo-IV crystal floating within the calcite vein. The isolated crystal has 700µm
in size with crystal boundary of planar euhedral to subhedral. A trace of dolomite crystal
shape can be seen and replaced by calcite as in Fig. 4.71 (e). The diagenesis is known
as de-dolomitization. It is replaced by calcite types cement (Cal-II/Cal-III) and known
as calcitized dolomite. The compaction had occurred and can be observed in Fig. 4.71
(g) that lead to fracturing.
Next, saddle dolomite (Dolo-V) has medium to very coarse crystal sizes ranging
from 100µm to more than 2000µm. The formation of large crystal size is because of
the availability of adequate pore spaces created by dissolution at late diagenesis. Large
pore space is needed to develop and fill in the pore spaces for a large crystal size. Dolo-
V crystals are inequigranular with planar-es to nonplanar-a. The cements are loosely
packed and the pore spaces are partly infilled by late calcite cement (Cal-V). In CL,
Dolo-V appears bright luminescent red with a clear outer rim, dark core and no zoning
as in Fig. 4.71 (i). Few sections of Dolo-V cement have been undergone intense
dissolution, but still retained the dolomite crystal shape.
Sample LE 1-7 – PPL
The infilling of late calcite cement (Cal-V)
in calcite matrix (Cal-I) with the presence of
framboidal pyrite.
149
Sample LE 1-60 - PPL
The figure shows fine crystalline equant
calcite cement (Cal-II) and blocky to drusy
calcite cement (Cal-IV).
Sample LE 1-62 - PPL
There is blocky to drusy calcite cement (Cal-
IV) in the micritic calcite matrix (Cal-I) and
floating euhedral dolomite crystal (Dolo-IV)
in the calcite cement.
Sample LE 1-63 - PPL
The image shows the coarse crystalline
blocky to drusy calcite cement. There is
intercrystalline porosity of 10% in the
matrix.
Sample LE 1-63 - PPL
A trace of dolomite crystal shape can be seen
under CL and it has been replaced by calcite.
The process is known as de-dolomitization
(Ded-I) or calcitized dolomite. Then, it has
undergone compaction that leads to
fracturing.
150
Sample LE 2-2 - PPL
The red-dotted line shows a boundary
between the micritic calcite matrix (Cal-I)
and the nonplanar anhedral microdolomite
(Dolo-I).
Sample LE2-4 - PPL
The occurrence of a coarse crystalline (size>
2000µm) saddle dolomite is characterized
by scimitar-like terminations of curved
crystal faces toward the pore spaces. The
pore spaces within the dolomite crystals are
infilled by the late stage of calcite cement.
Sample LE2-3 - PPL
Microscopic texture of saddle dolomite
showing the presence of intercrystalline pore
with 5% porosity.
Sample LE2-3 - CL
Microscopic view of saddle dolomite (Dolo-
V) showing 100-500µm sized planar-es
crystal with a cloudy dark core and clear rim.
It exhibits a bright luminescent red colour.
151
Sample LE2-5 - PPL
The figure shows an isolated rhomb of
euhedral to subhedral dolomite (Dolo-III)
floating in a micritic calcite matrix (Cal-I).
Sample LE2-5 - PPL
The microscopic texture of micritic calcite
has very fine crystalline size that is less than
30µm.
Sample LE2-5 - CL
Under CL, the matrix is associated with
corroded dolomite crystals (Dolo-III). The
corroded dolomite crystals have crystal size
ranges from 100-150µm. It showed a planar-
es to nonplanar-a with porphyrotopic fabric.
Dolo-III appears dull luminescence red
colour under CL.
Figure 4.71: Photomicrographs of calcite and dolomite types in Hill E, Gunung
Kanthan.
4.4.4.2 Pore Types and Percentage
The dominant pore type in Hill E is intercrystalline pores, where it can be found in
calcite and dolomite cements as summarized in Table 4.12. Fig. 4.72 shows the
photomicrographs of dolomite and calcite types that are associated with pores. The
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lowest intercrystalline porosity is 1% which has been observed in Cal-III. While, the
highest intercrystalline porosity value is 17-15% observed in late dolomite cement
(Dolo-V) and calcitized dolomite (Ded-I). Besides, vuggy pore type is only recognized
in fabric destructive fine crystalline dolomite (Dolo-III) with 3% porosity. The other
pore types observed is channel type with 5-6% porosity in equant calcite cement (Cal-
II). Whereas, fracture porosity is present in Dolo-II and Dolo-IV with 1-2% porosity.
Table 4.12: Summary of pore types and percentages of calcite and dolomite types in
Hill E, Gunung Kanthan.
Cal-II A channel porosity of 5% is recognized in equant calcite cement.
Cal-III Micritic to equant calcite cement partly fills the pore spaces and
is associated with an intercrystalline porosity of 1-3%.
Dolo-II The sucrosic dolomite has a fracture porosity of 1%.
Dolo-III Dolo-III consisted of vuggy porosity of 3%.
Dolo-IV This type of dolomite is associated with intercrystalline porosity
of 5% and fracture porosity of 1-2%.
Dolo-V Saddle dolomite has the highest porosity of 17%, which is
observed from the intercrystalline pore type. Intercrystalline
porosity in this dolomite is ranging from 5-17%.
Ded-I The de-dolomitization is associated with dissolution by Ca-rich
fluids and precipitation of calcite cement. The calcite cement has
a wide range of porosity from 3% to 15%, which is contributed
by intercrystalline pores.
153
Sample LE 1-54 – PPL
The image shows channel porosity in Cal-II
with 5% porosity. The intercrystalline
porosity of 1% also presents in the calcite
vein (Cal-III).
Sample LE 1-54 – PPL
The intercrystalline porosity of 3% also
presents in Cal-III.
Sample LE 1-63 - PPL
Intercrystalline porosity (15%) is observed
in blocky to drusy calcite cement (Cal-IV).
It is associated with de-dolomitization and
dissolution.
Sample LE 2-2 - PPL
The image shows a dissolution in saddle
dolomite (Dolo-V) and developed the pore
spaces. The intercrystalline pores are
identified in the dolomite with 17% porosity.
154
Sample LE 2-3 - PPL
A planar euhedral to subhedral saddle
dolomite (Dolo-V) has intercrystalline
porosity of 10%.
Sample LE 2-4 - PPL
The image shows an open fracture that cuts
across a nonplanar anhedral sucrosic
dolomite (Dolo-II) with a porosity of 1%.
Sample LE2-3 - PPL
The photomicrograph shows fabric
destructive coarse crystalline dolomite
(Dolo-IV) is associated with fracture
porosity of 1-2%.
Sample LE2-5 - PPL
The vuggy porosity of 3% presents in the
micritic calcite matrix (Cal-I). Cal-I
comprises of isolated corroded dolomite
crystal floating in the matrix which can be
seen clearly in CL as in Fig. 4.72 (l).
Figure 4.72: The micropore types present in calcite and dolomite of Hill E, Gunung
Kanthan.
155
4.5 Morphological Study
The FESEM images will show calcite, dolomite and pore morphology from different
magnification ranges of FESEM. The elemental analysis of FESEM shows quantitative
data, but somehow not much significance to the study compared to qualitative data of
FESEM images.
4.5.1 Field 1: Gunung Rapat
Identification as calcite is based on the distinctive EDX spectrum yielding Ca, C and
O. The calcite has a very fine grain size, ranging from 1-5µm. Clear calcite rhombs are
observed. The calcite cements are identified as pore-filling minerals, yet the micropore
is almost invisible in the FESEM images since it has been impeded. The intercrystalline
pore is shown as in Fig. 4.73 (a). There are two types of calcite in this sample, which
are micritic calcite, Cal-I (Fig. 4.73 (a)) and equant calcite, Cal-II (Fig. 4.73 (b)). The
morphology of Cal-I and Cal-II are shown in Fig. 4.73. Some parts of the calcite are
weathered probably due to dissolution from meteoric water. The calcite morphology
observed for this sample is euhedral to subhedral with angular edges. The sample show
a tightly packed calcite matrix.
Magnification: 5000x.
This figure shows the pore-filling
of blocky equant rhombohedra
calcite cement, Cal-II and sugary
texture of weathered calcite, Cal-
I. The average grain size is 2µm.
Note the pores in a black area.
156
Magnification: 5000x.
The image shows morphology of
clear stacked equant
rhombohedra calcite cement, Cal-
II. The average grain size is 5µm.
Magnification: 3000x.
Various grain of rhombohedra
calcite. The grain size ranges
from 1µm to 4µm in diameter.
Figure 4.73: FESEM images of limestone sample (AQ 10) from Gunung Rapat.
From previous field observation, most of Gunung Rapat samples dominantly
indicate calcitic rock than dolomitic rock. The elements of Ca, C and O as shown in
Fig. 4.74 indicate a calcite mineral. The intensity peaks are associated with the
element’s concentration, not atomic or weight percentages.
157
Figure 4.74: Energy Dispersive X-Ray (EDX) spectrum of sample AQ 10 showing the
presence of Ca, C, and O elements.
The EDX result displays the weight and atomic percentages of elements that present
in the sample. The atomic percentage is determined by the number of atoms in a specific
compound while the weight percentage is determined by the atomic weight of the
element of that compound. The weight and atomic percentages of elements in sample
AQ 10 is as followed in Table 4.13.
Table 4.13: The weight and atomic percentage of elements in sample AQ 10.
Element Weight (%) Atomic (%)
C 9.35 16.03
O 48.34 62.23
Ca 42.31 21.74
158
4.5.2 Field 2: Sungai Siput Dolomite Hill
The dolomite of Sungai Siput Dolomite Hill shows a rhombohedral crystal morphology
(Fig. 4.75). The FESEM images indicate the sucrosic dolomite (Dolo-II) develops layer
by layer in the matrix with subhedral to anhedral boundary. Dolo-II is identified in SB
6 as well under petrographic with the same characteristic of crystal boundary. Few areas
of dolomite in SB 6 has a perfect rhombohedral shape. The average crystal size
observed in FESEM is 4µm. There is no clay material and fractures observed in the SB
6 sample. Besides, there is no significant porosity observed within the dolomite crystals.
Based on Fig. 4.76, the EDX spectrum indicates Ca, Mg, Al, C, and O elements.
Meanwhile, Table 4.14 shows the weight and atomic percentage of elements. A very
small percentage of iron (Fe) content in the sample did not contribute as part of the
major elements in SB 6.
Magnification: 1000x.
Dolo-II presents in dolomite
sample of SB 6. It shows various
crystal shape, with crystal
boundary of subhedral to
anhedral. No pores are observed in
the sample.
Magnification: 3000x.
The image marks by a red arrow
are showing a dolomite crystal
that appears as almost perfect
rhombohedral shape. The crystal
size has a 4µm diameter.
159
Magnification: 5000x.
The image shows Dolo-II at a
different angle. Dolo-II shows
the edge-face flake orientation in
microfabric. It appears as a stack
of layered dolomite crystals.
Figure 4.75: FESEM images of dolomite sample (SB 6) from Sungai Siput Dolomite
Hill.
Figure 4.76: Energy Dispersive X-Ray (EDX) spectrum of sample SB 6 showing the
presence of Ca, Mg, Al, C, and O elements.
Table 4.14: The weight and atomic percentage of elements in sample SB 6.
Element Weight (%) Atomic (%)
C 15.63 22.65
O 57.88 62.98
Mg 10.74 7.69
Ca 14.49 6.29
Fe 1.26 0.39
160
4.5.3 Field 3: Hill B, Gunung Kanthan
Fig. 4.77 shows the dolomites of Dolo-V and Dolo-II are separated by the fracture.
Saddle dolomite (Dolo-V) has approximately 3µm to 4µm in diameter and 0.1µm thick,
while sucrosic dolomite (Dolo-II) has approximately 2µm to 4µm in diameter and
thickness. Dolo-V is more porous than Dolo-II, where the intercrystalline pores are
present in Dolo-V. Meanwhile, Dolo-II is compacted, non-porous, and appeared as an
euhedral to subhedral shape. Dolo-V is identified as pore-filling minerals. Initially, the
dissolution takes place first, then infills by dolomite cement, Dolo-V. Dolo-V is formed
at a later stage than Dolo-II. The diagenetic processes of dissolution, precipitation and
recrystallization have modified the original precursor rock texture.
Magnification: 5000x.
Two types of dolomite, which are
Dolo-II and Dolo-V are found in this
sample. The figure also shows the
presence of fracture porosity. The
fracture forms at the boundary of
Dolo-V and Dolo-IV. The fracture
diameter is around µm.
Magnification: 5000x.
A zoom in image of Dolo-V. Dolo-
V has the morphology of pore-filling
subhedral dolomite with flaky
stacked crystal. The crystal size of
Dolo-V is ranging from 3-4µm
diameter, and 0.1µm thick. The
micropores can be observed between
dolomite crystals with a pore
diameter of 0.1-0.5µm.
161
Magnification: 5000x.
A zoom in the image of Dolo-II
shows Dolo-II has cubical rhomb
dolomite with subhedral to
anhedral boundary. The crystal
size is ranging from 2-4µm
diameter, and 2-4µm thick. There
is no pore observed in Dolo-II.
Figure 4.77: FESEM images of dolomite sample (LB 83) from Hill B, Gunung
Kanthan.
Fig. 4.78 and 4.79 show the EDX analysis consisted of Ca, Mg, C and O elements.
The presence of Mg elements in the sample indicates the dolomite minerals. It also has
been validated by petrographic that the sample of LB 83 is dolomite. Even though both
EDX graphs show dolomite mineral, they have different characteristics in term of
morphology discussed in Fig. 4.77.
Figure 4.78: Energy Dispersive X-Ray (EDX) spectrum of sample LB 83 showing Ca,
Mg, C, and O elements in cement dolomite, Dolo-V.
162
Figure 4.79: Energy Dispersive X-Ray (EDX) spectrum of sample LB 83 showing Ca,
Mg, C, and O elements in replacive dolomite, Dolo-II.
The weight and atomic percentages of elements in Dolo-V and Dolo-II show almost
the same percentages in each element. This is because both exhibit the same type of
mineral, which is dolomite.
Table 4.15: The weight and atomic percentage of elements in Dolo-V
Element Weight (%) Atomic (%)
C 14.74 21.48
O 57.81 63.23
Mg 11.67 8.40
Ca 15.78 6.89
Table 4.16: The weight and atomic percentage of elements in Dolo-II.
Element Weight (%) Atomic (%)
C 15.57 22.31
O 59.45 63.96
Mg 10.75 7.61
Ca 14.24 6.11
163
4.5.4 Field 4: Hill E, Gunung Kanthan
There are three selected samples in Hill E tested for FESEM analysis. The samples are
LE 1-60, LE 1-63 and LE 2-3. The sample of LE 1-60 shows the rhombic morphology
of the calcite crystal (Fig. 4.80). The calcite has very fine to fine grain size, ranging
from 1-10µm. The calcite cements are identified as pore-filling minerals. The calcite
fills in the pore spaces after dissolution. Then, micritization occurs that resulted from
recrystallization of carbonate mud or direct precipitation from calcite. Few areas of
calcite are corroded probably due to weathering and dissolution. The type of pore
presents in sample LE 1-60 is intercrystalline pore. The EDX spectrum of Fig. 4.81
contains the elements typical in calcite, which are Ca, C and O. Table 4.17 shows the
actual weight and atomic of each element in sample LE 1-60.
Magnification: 1000x.
Pore-filling calcite cements with
the presence of micrite. Some
parts of the calcite are weathered.
The calcite crystal size is ranging
from 1-10µm diameter. The
micropores are visible in the
sample.
Magnification: 5000x.
A zoom in image of Fig. 4.80 (a)
shows a well-developed pore-
filling rhombohedra calcite
crystal. The crystal size is
ranging from 1-2µm diameter
and 2-3µm thick. The presence of
164
intercrystalline pores with a
diameter of 1-5µm.
Magnification: 5000x.
The FESEM image shows a clear
rhombic calcite crystal, Cal-II
with a large crystal size of 6µm
diameter and 4µm thick. The
intercrystalline pore is observed
in the sample.
Figure 4.80: FESEM images of outcrop sample LE 1-60 from Hill E, Gunung
Kanthan.
Figure 4.81: Energy Dispersive X-Ray (EDX) spectrum of sample LE 1-60 showing
Ca, C, and O elements in limestone sample.
Table 4.17: The weight and atomic percentage of elements in sample LE 1-60
Element Weight (%) Atomic (%)
C 10.64 17.64
O 50.76 63.18
Ca 38.60 19.18
165
For sample LE 1-63, FESEM images revealed the morphology of calcite, chlorite
and palygorskite. The micritic calcite matrix (Cal-I) has very fine grain size, ranging
from 0.1-2.5µm. The calcite is slightly dissolved, and some parts are corroded. The
intercrystalline pores are observed between calcite crystal and partly infilled by clay
mineral of chlorite and palygorskite as in Fig. 4.82 (b-c).
The clusters of disc-like authigenic chlorite crystals (Chl) partly filling a depression
within micritic calcite (Cal-I). Sample LE 1-63 shows a mixture of silicates content in
carbonate rocks. The individual crystal of chlorite is part of clay minerals. The
authigenic chlorite in this sample is found to be pore-filling minerals.
The other mineral is clay mineral exhibits a fibrous form called palygorskite (Pal).
It formed like clusters of ribbons or needles. The palygorskite partly fills in the pores
within calcite (Cal-I).
Magnification: 5000x.
The image shows corroded
calcite (Cal-I) with the presence
of micropores. The calcite crystal
size is ranging from 0.1µm to 2.5
µm diameter.
Magnification: 5000x.
Clusters of platy and disc-like,
authigenic chlorite (Chl) partly
filling a depression within a
detrital calcite crystal (Cal-I).
The presence of micrite and clay
mineral of palygorskite (Pal).
166
The pores are observed in the
sample.
Magnification: 10,000x.
The zoom in image shows the
clusters of fibrous (needle-like),
Palygorskite (Pal) partly filling
the pores within calcite crystals
(Cal-I).
Figure 4.82: FESEM images of outcrop sample LE 1-63 from Hill E, Gunung
Kanthan. Identification as calcite with siliciclastic mixture is based on the distinctive.
EDX spectrum yielding Ca, Mg, Al, Si, C and O (Fig. 4.83). The siliciclastic
mixture involved clay minerals, which are chlorite and palygorskite as mentioned in
Fig. 4.83. The weight and atomic percentage of elements in sample LE 1-63 are stated
as in Table 4.18.
Figure 4.83: Energy Dispersive X-Ray (EDX) spectrum of sample LE 1-63 showing
Ca, Mg, Si, Al, C, and O elements in the sample.
167
Table 4.18: The weight and atomic percentage of elements in sample LE 1-63.
Element Weight (%) Atomic (%)
C 14.32 21.37
O 59.06 66.17
Mg 1.00 0.74
Al 0.55 0.36
Si 0.78 0.50
Ca 24.29 10.86
The other representative sample of Hill E is LE 2-3. Based on Fig. 4.84, FESEM
images show sample LE 2-3 consisted of a dolomite mineral. The dolomite is identified
as saddle dolomite, Dolo-V which was also determined in photomicrographs. Some
parts of dolomite are well-preserved with euhedral to subhedral crystal shape. However,
few areas of dolomite crystals are corroded. The corrosion of dolomite happens due to
weathering from surrounding fluids. Besides, there is no porosity observed in the
dolomite sample of LE 2-3.
Magnification: 1000x.
Dolo-V presents in dolomite
sample of LE 2-3. The dolomite
crystals show the sharp edges
between each other. There are no
pores visible in the sample. Most
of the Dolo-V have crystal size
more than 10µm in diameter.
168
Magnification: 10,000x.
The zoom in image shows perfect
rhombohedral dolomite. Dolo-V
exhibits a characteristic of well-
preserved euhedral dolomite
crystal. The crystal size is around
3µm.
Magnification: 10,000x.
In few parts, Dolo-V shows
corroded or weathered dolomite.
It appears as a stacked euhedral to
subhedral dolomite crystal. The
grain size is 2µm diameter.
Figure 4.84: FESEM images of outcrop sample LE 2-3 from Hill E, Gunung Kanthan.
The EDX spectrum shows sample LE 2-3 consisted of Ca, Mg, Fe, C and O
elements (Fig. 4.85). The presence of Mg elements in the sample indicates dolomite
minerals. The presence of iron (Fe) content in the sample contributes to the major
elements in sample LE 2-3. The dolomite is probably associated with iron-dolomite.
Table 4.19 shows various weight and atomic percentage for all elements in LE 2-3.
169
Figure 4.85: Energy Dispersive X-Ray (EDX) spectrum of sample LE 2-3 showing
the presence of Ca, Mg, Fe, C, and O elements.
Table 4.19: The weight and atomic percentage of elements in sample LE 2-3.
Element Weight (%) Atomic (%)
C 15.63 22.65
O 57.88 62.98
Mg 10.74 7.69
Ca 14.49 6.29
Fe 1.26 0.39
170
4.6 Discussion
4.6.1 Lithotypes of carbonate rocks in Kinta Valley
Classification of carbonate lithology from the outcrop observation is verified and
evaluated by mineralogical composition in the rocks. The ternary diagram is commonly
used in geochemistry to allocate the mineral assemblage in geological samples. The
ternary diagram of dolomite, calcite and non-carbonate minerals are designated as in
Fig. 4.86. The terminology of ternary diagram is followed according to chemical
classification of calcareous rocks by Leighton and Pendexter (1962), which are pure
limestone, pure dolomite, pure dolomitic limestone, pure calcitic dolomite, impure
limestone, impure dolomite, impure dolomitic limestone, impure calcitic dolomite and
non-carbonates.
There are three types of lithology observed in all quarries, which are limestone,
dolomite and dolomitic limestone. Based on Al-Awadi et al. (2009), Leighton and
Pendexter (1962), the rocks are identified as limestone when the dominant mineral is
calcite with more than 90%, followed by dolomite and other non-carbonate minerals
with less than 10%. While, dolomite rocks are associated with dolomite mineral
percentage above 90%, followed by calcite and non-carbonate minerals with less than
10%. For dolomitic limestone, the range of calcite is between 50% to 90%, dolomite is
10% to 50% and non-carbonate mineral is less than 10%.
The X-Ray diffraction data confirmed the limestones, consisting mainly of calcite
with contents of 99.4% to 100%, with low content of dolomite mineral ranges from
0.2% to 2% and quartz ranges from 0.1% to 0.4%. While, dolostones have dolomite
mineral ranges from 90.5% to 97.5%, with a minor calcite from 2.5% to 9.5%, and
quartz from 0.1% to 0.2%. Dolomitic limestone samples in the study area are associated
with 66% to 89.5% calcite, 10% to 34.5% dolomite, and very little content of quartz
which is less than 1%. From the interpretation, limestone is mainly associated with
calcite mineral, while dolostone is dominated by dolomite mineral, while dolomitic
limestone has a high amount of calcite than dolomite with more than 50%, however the
calcite content is lesser than in limestone. Thus, the percentage of mineral plays a role
171
in supporting the identification of lithology from the outcrop based on a geochemical
basis.
Figure 4.86: Compositional ternary diagram of carbonates from Kinta Limestone according to
Leighton and Pendexter (1962) terminology.
The Gunung Rapat is composed of limestone and dolomitic limestone. It is very
difficult to differentiate limestone and dolomitic limestone by just looking at the
outcrop itself. Thus, geochemical analysis is conducted to help in recognizing more
specific lithofacies of carbonates. Gunung Rapat located at the south of Kinta Valley
has more calcitic rocks than other quarries. This is proven by elemental analysis, where
Anting’s rock samples indicate a high percentage of Ca. Haylay (2016) also mentioned
that the carbonates in Kinta Valley’s south area are mainly more calcitic. While, the
carbonate rock samples from the northern area of Kinta Valley is associated with
various lithotypes such as limestone, dolomitic limestone and dolomite.
The lithology of Sungai Siput Dolomite Hill at the northern area of Kinta Valley is
solely composed of dolomite rock that has light to dark grey colour. Besides, Gunung
172
Kanthan also located in the northern area has variable lithotypes such as dolomite,
limestone and dolomitic limestone. The Mg concentrations observed in rock samples
of Sungai Siput and Lafarge quarries are higher than in Gunung Rapat. The Kinta
Limestone showed an increase of Mg concentration from south to north (Fig. 4.87).
However, Haylay (2016) stated the Mg is increasing from north to south, with very low
Mg content generally. These differences might be due to different samples locations
and carbonate heterogeneity. It is believed that Mg concentration varies on local. The
results from three quarries indicated dolomitization took place at the northern area more
than the southern area of Kinta Valley.
Figure 4.87: Mg concentration is increasing from south to north of Kinta Valley.
The carbonate rocks in Kinta Valley are dominated by Ca element and a limited
low amount of Mg element. According to Flungel (2009), calcite and dolomite are the
most common carbonate minerals found in ancient carbonate rocks. Other elements
such as Sr, Mn, Fe and Si are found in tiny amounts, which do not give too much
variation to the mineral contents in carbonates. Other studies have stated that carbonates
in Kinta Valley have a low silicate-derived elements (Haylay, 2016; Haylay & Sum,
2019). The presence of these elements shows there is an association of pyrite in the
173
outcrop. The pyrite can be found in Gunung Kanthan and Gunung Rapat. The other
mineral like sepiolite is found in the outcrop of Gunung Rapat.
On a general basis, the studied samples have shown that the variation of the major
minerals is directly related to carbonates’ lithotypes in Kinta Limestone. The
geochemical content of carbonate rocks justify carbonate lithotypes by looking at the
minerals and elements concentration in the samples (Anua & Zabidi, 2018). It helps to
justify the petrographic analysis and reduce the uncertainty of carbonate mineral
classification in petrographic analysis.
4.6.2 Porosity and permeability variations of carbonate rocks in Kinta Limestone
There are two factors in determining reservoir quality which is porosity and
permeability. In carbonate reservoirs, the porosity and permeability are affected by the
porosity amount, type of pores and pores interconnectivity. These are in turn controlled
by diagenetic alterations such as cementation, precipitation, re-crystallization,
compaction, and dissolution (Rashid et al., 2015).
The summary of porosity and permeability data from all quarries are presented in
Table 4.20 below. The limestone shows the highest and lowest porosities between all
lithologies, with 14.52% and 1.1% respectively. While dolomitic limestone and
dolomite samples show a lower porosity than most limestone samples in Kinta Valley.
The highest amount of porosity recorded for dolomitic limestone is 4.22%. On the other
hand, the dolomite rock shows the second highest porosity after limestone with 5.75%.
The permeability values range from 0.0 to 1.82 mD. The highest permeability
among all lithologies belongs to limestone, then followed by dolomite and dolomitic
limestone. The limestone samples show various permeability values, ranging from 0
mD to 1.82mD. While the dolomitic limestone has a low amount of permeability ranges
from 0 mD to 0.08 mD. Whereas dolomite samples have better permeability ranges than
dolomitic limestone, from 0 mD to 0.46 mD.
174
Most of the carbonates in Kinta Limestone have low porosity and permeability,
which is considered moderate to a poor reservoir. Haylay (2016) stated the carbonates
in Kinta have insignificant porosity and permeability, which reduces the rock formation
tendency to be a good reservoir. The permeability of carbonates in Kinta Limestone is
very low with the insignificant capability to allow fluids movement through its pore
systems (Haylay, 2016). However, there are few samples tested show good porosity
and permeability. For example, the limestone sample, LE 1-60 has 14.52% of porosity
and 1.82mD of permeability. Although most limestone samples have high porosity
values, the permeability values are inconsistent and have moderate to poor correlation
with porosity. The relationship of permeability in the formation does not necessarily
depend on porosity. However, high permeability is commonly linked to high porosity
(Sadeq et al., 2015). Overall, the correlation between porosity-permeability of
carbonates in Kinta Valley exhibits a trend of good to low porous and low permeable
rocks.
Table 4.20: Summary of porosity and permeability data of each lithology in Kinta
Limestone
Lithology Highest
(%)
Lowest
(%)
Highest
Kair (mD)
Lowest
Kair (mD)
Petrophysical
properties
Limestone 14.52 1.1 1.82 0.0
Good to poor
porosity, Limited
permeability
Dolomitic
Limestone 4.22 1.58 0.08 0.0
Poor porosity, Poor
permeability
Dolomite 5.75 1.29 0.46 0.0 Poor porosity, Poor
permeability
The porosity and permeability heterogeneity mainly reflect various lithology of
carbonate rocks in Kinta Valley as in Fig. 4.88. Most of the limestone samples show a
better correlation between porosity and permeability. However, few limestone samples
have a poor correlation between porosity and permeability. The porosity might reduce
because of few factors such as the structure, changes in mineral composition and mainly
influenced by diagenesis. While, the dolomite samples show a poor correlation of
porosity-permeability than limestone. Carnell and Wilson (2003) stated dolomite has
175
an inconsistent influence on reservoir properties, but most of it is associated with good
porosity and permeability. Whereas, dolomitic limestones indicate poor porosity-
permeability correlation.
Figure 4.88: The porosity-permeability trend of mini-cored plugs that linked to
various lithologies in Kinta Limestone.
4.6.3 Pore characterization of carbonate rocks in Kinta Limestone
The characterization of pore system in carbonate reservoirs is of utmost importance to
the oil and gas industry to provide the optimum enhanced oil recovery, geological
carbon storage and many more (Lin et al., 2016). The pore system helps understand of
variations in petrophysical properties influenced by different pore type, pore
distribution and connectivity (Kułynycz & Maruta, 2017). The pore system
characterization of carbonates in Kinta Limestone is presented in Table 4.21.
0.01
0.10
1.00
10.00
0 2 4 6 8 10 12 14 16
Pe
rme
abili
ty (
mD
)
Porosity (%)
Limestone
Dolomitic Limestone
Dolomite
176
Table 4.21: Pore system characterization of carbonate rocks in Kinta Valley
Lithology Pore Types Pore Radius
(µm) Pore distribution
Pore
Connectivity
Limestone
1. Fracture
2. Vug
3. Stylo-pores
100-3000
(Small to large
pore radius)
1. Throat pore
2. Isolated pore
3. Dead-end pore
Good to
moderate
connectivity
Dolomitic
Limestone
1. Fracture
2. Vug
200-1350
(Small pore
radius)
1. Isolated pores
interconnected
with throat pore
2. Cross-linked
pore
Moderate
connectivity
Dolomite 1. Fracture
2. Vug
80-3000
(Small to large
pore radius)
1. Isolated pores
interconnected
with throat pore
2. Isolated pore
3. Dead-end pore
Moderate
connectivity
Based on Table 4.21, limestone has various pore types, which is dominated by
fractures and stylo-pores. The impact of stylolite has been discussed in many studies,
which helps in enhancing the porosity and permeability. Based on Paganoni et al.
(2015), stylolite acts as a conduit for hydrocarbon flow in the reservoir. However, the
stylolite pores in Kinta carbonates are mostly filled with calcite cement. Cementation
can reduce permeability by blocking the pores and pore throats (Kashif et al., 2019).
Thus, calcite-infilled pores reduced the effect of preserving the porosity and providing
conduits for the fluid movement. While, dolomitic limestone and dolomite composed
of two types of pore, which are fracture and vug. It is very common in dolomite
reservoirs to have isolated pore as vuggy porosity and fracture increasing permeability
significantly (He et al., 2014). But, most of the isolated vugs in carbonate samples of
study area contribute to non-effective porosity and no fluid flow, unless it is
interconnected to other pores.
The fracture is more intense in limestone than dolomite and dolomitic limestone.
The main factor that enhances the permeability of the carbonate reservoir is the
presence of fracture porosity (Tucker & Wright, 1990; Watts, 1983). A limestone
sample of LE 1-60 that contains open fractures has a permeability of 1.82mD, which is
177
more significant than unfractured rocks. The carbonate samples in this study associated
with open fracture have better permeability than partially cemented fracture. The open
fractures have significant effects on enhancing permeability and hydraulic connectivity
(Glover et al., 1997). Although open fractures are found in the samples, partially
cemented fractures are more common in carbonate samples of Kinta Valley. The
fracture pore type can be observed in all carbonates type in Kinta Valley as in Fig. 4.89.
Few fractures are connected to other fracture and vugs, which positively impact
porosity and permeability values.
Figure 4.89: Slices of µCT images from the top view of core plugs. Different types of
pore observed in different lithologies, (a) Interconnected fractures (F) in
limestone; (b) Fracture and vug (V) in dolomitic limestone; (c)
Interconnected fracture and vug in dolomite.
b) Dolomitic Limestone (LE 2-5)
c) Dolomite (LB 83)
a) Limestone (LE 1-60)
178
Another aspect that is important in the pore system is pore distribution. Pore
distribution tells how each type of pores distributed in rocks. Five type of pore
distributions have been identified in collected samples: isolated pore, dead-end pore,
throat pore, cross linked pores, and isolated pore interconnected with throat pore. The
schematic diagram of the pore distribution of carbonates in Kinta Valley is presented
in Fig. 4.90.
Figure 4.90: A schematic diagram of pore distribution types in carbonate rocks of
Kinta Valley.
Fig. 4.91 shows the representative samples of carbonates that consisted of all pore
distribution types. Isolated pore is an individual pore that is not connected to any pore
network, and dead-end pore is an isolated pore but occurs at the rock wall. The throat
pore is a large pore with a narrow throat, which the diameter of the pore is smaller than
the length of the pore throat. While, cross-linked pore is an interconnection or joining
of two or more throat pores in the rock. Based on pore distribution, throat pore and
cross-linked pore have better flow and connectivity than others. The isolated pore can
be significant when connected with throat pore, which gives better flow and
connectivity. This type of pore distribution is found in dolomite and dolomitic
limestone samples. He et al. (2016) mentioned that pore distributions’ connectivity has
greatly influenced the fluid flow of porous zone.
By looking at lithology, the limestone is mainly associated with throat pores
distribution (Fig. 4.91 (a-b)) which contributed to a good pore connectivity and higher
179
permeability than other lithology. Although, the pore radius of limestone is mostly
smaller than dolomite and dolomitic limestone, few limestone samples exhibit good
porosity and permeability. This is because limestone hasa small pore radius with a
higher number of interconnected pores, which makes it better than less connected pore
with a large pore radius. Usually, the less interconnected pores resulted in low porosity
and permeability, while highly interconnected pores resulted in good porosity and
permeability. Only two limestone samples, AQ 10 and LE 2-2 show a dead-end pore.
The dead-end pores have no pore connectivity (Fig. 4.91 (d)). Although there were few
pores in the rocks, the fluid could not flow through these pores because they were not
connected (Kułynycz & Maruta, 2017).
Meanwhile, both dolomitic limestone and dolomite have isolated and clustered
pores. Although both have isolated pores, they are still interpreted as moderate
connectivity. This is because the isolated pores are interconnected with a small throats
such as fractures (Fig. 4.91 (g-h)), resulting in moderate connectivity. The dolomite and
dolomitic limestone show poor ranges of porosity and permeability compared to
limestone. Adams (2005) stated the dolomitization complicates pore geometry and
connectivity. The dolomite also has a better range of pore radius than dolomitic
limestone, but it is less different than limestone samples (Table 4.21). The dolomite has
lower porosity and permeability than limestone even though they have an almost similar
pore radius range. This is because dolomite has moderate pore connectivity, while
limestone has good connectivity. Large pore radius becomes insignificant to pore
connectivity when they are not connected.
In summary, the pore radius, pore distributions and connectivity play roles in
petrophysical evaluation. Pore connectivity is important because it affects the porosity
and permeability influenced by pore distributions and pore types. Throat pores and
cross-linked pores have contributed to good connectivity. In contrast, isolated pores
interconnected with throat pore contributed to moderate connectivity and dead-end
pores show no connectivity in the rock matrix.
180
Sample LE 1-60
(Limestone)
The figures (a-b) show an
example of throat pore
distribution in the
limestone sample.
Sample AQ 60
(Limestone)
Figure (d) shows the
dead-end pore in a 3D
view of µCT.
Sample AQ 76 (Dolomitic
Limestone)
Figure (f) indicates the
cross-linked pores when
two fractures (F1 & F2)
cross each other.
Sample LE 2-3
(Dolomite)
The figures (g-h) show
the isolated pore
interconnected with the
throat pore.
Figure 4.91: Pore distribution types in different lithologies (a), (c), (e) and (g) show a
2D cross-section of µCT image; (b), (d), (f) and (h) show a 3D µCT image
a)
F
5.0
8 c
m
F
b)
2.54cm
c) 5
.08 c
m
Dead-end
pore
d)
2.54cm
e)
F1
f)
F2
5.0
8 c
m
2.54cm
g)
h)
5.0
8 c
m
2.54cm
F1
Cross linked
pore
Throat pore
Isolated
pore connected
to throat
pore
Isolated
pore
connected
to throat
pore
181
4.6.4 Carbonates microfacies and diagenetic processes in Kinta Valley
Diagenesis plays the main role in the changes of carbonate texture. The calcite and
dolomite crystals were distinguished based on crystal size, texture, boundary by using
classification from Gregg and Sibley (1987).
4.6.4.1 Types of calcite
There are five types of calcite (Cal-I, Cal-II, Cal-III, Cal-IV and Cal-V) observed in all
carbonate samples of Kinta Valley. The classification of calcite depends on the crystal
size and texture. These differences of texture occurred at different stages of timing. The
early stage of calcite has finer grain compared to the late stage. A detailed explanation
of each type of calcite is presented below.
1. Cal I: Miciritic Calcite Matrix
Micritic calcite matrix (Cal-I) has fine to medium crystal, ranging from 10µm to
<100µm. On average, most of the size of the crystals are less than 50µm in Gunung
Rapat. Meanwhile, Cal-I in Gunung Kanthan has a mostly smaller grain size than
Gunung Rapat with less than 30µm. Under cathodoluminescence (CL) images, Cal-I
shows dull to non-luminescent and orange to brown colour with irregular crystal shapes.
Few photomicrographs showing stylolization has taken places and undergone a
dissolution that led to a formation of stylo-porosity. Few microstylolites can be
observed in Hill B and Hill E of Gunung Kanthan. The matrix is tightly packed with a
little porosity observed in Gunung Rapat.
There is also an early fracture (F-I) that cuts across Cal-I. Besides, the intense
cementation occurred in Cal-I. This type of calcite is associated with numerous calcite
veins (Cal-II and Cal-III) in Hill B and Cal-V in Hill E. There is also a presence of
pyrite in Cal-I as shown in Fig. 4.23 (a-b). The pyrite formed as a single isolated
euhedral crystal floating on Cal-I and showed a non-luminescent dark colour
characteristics under CL. However, pyrite in Gunung Kanthan shows an irregular shape
182
that is not similar to rhombic pyrite in Gunung Rapat. In addition, isolated corroded
dolomite crystals are floating in the calcite matrix in Gunung Kanthan.
2. Cal-II: Equant Calcite Cement
Equant calcite cement (Cal-II) has medium to coarse crystal, ranging from 50µm to
250µm in Gunung Rapat. Meanwhile, it has a medium crystalline size from 50µm to
150µm in Hill E and Hill B, Gunung Kanthan. The grain size of Cal-II is smaller in
Gunung Kanthan compared to Gunung Rapat. The cement crystals have planar
subhedral to non-planar anhedral shape. Cal-II represents a vein-filling calcite cements
that present mainly within interparticle pore spaces in micritic calcite matrix. It fills the
first generation of fractures and partially or completely fills the interparticle porosity.
Cal-II has cut across Cal-I as shown in Fig. 4.92 (a).
3. Cal-III: Micritic to Equant Calcite Cement
Micritic equant calcite cement (Cal-III) has a very fine crystal, which is less than
10µm in Gunung Rapat, but it has fine to medium crystal from 50µm to 100µm in
Gunung Kanthan. The crystal shape is unrecognizable because it has a very fine crystal
size. Cal-III also the same as Cal-II, they represent pore-filling calcite cements in
micritic calcite matrix as in Fig. 4.92 (b). It cuts through Cal-I, Cal-II and Dolo-I. It
appears dull brown luminescence under CL.
4. Cal-IV: Blocky to Drusy Calcite Cement
This type of cement has a coarse crystal size, approximately ranging from 100µm
to 800µm with mostly more than 500µm. From the CL image, Cal-IV appears bright
orange luminescent and no core nuclei present. It is identified as a void-filling calcite
vein, where it entirely or partially infills the pore space. The cement size is large and
forms at a later stage than Cal-III and Cal-II. Fig. 4.92 (c) shows Cal-IV cuts through
Cal-II. Besides, there is also floating euhedral dolomite crystal (Dolo-IV) found in Cal-
IV.
183
5. Cal-V: Blocky to Poikilotopic Calcite Cement
Blocky to Poikilotopic calcite cement (Cal-V) has coarse to very coarse crystal. The
crystals have inequigranular grain size with tightly packed cement. The crystal size
ranging from 400µm to 500µm in Gunung Rapat and 500µm to 800µm in Gunung
Kanthan. The crystal appears pink under PPL. The CL patterns show Cal-V has
complex zonation, where the core nuclei are euhedral rhombic, with orange dull
luminescent and non-luminescent centre. It also has an irregular bright orange
luminescent rim. Furthermore, the crystal appears in as a planar subhedral shape. This
type of cement is identified as a late-stage calcite cement which fills in the pore spaces
within saddle dolomite (Dolo-V) as in Fig. 4.92 (d). The late cementation occurred after
late fracturing and dissolution. It partially occludes the remaining voids within the
previous fracture sets and partly or fills some vugs, hence occluding the porosity and
reservoir quality. Besides, there are microstylolite cuts through Cal-V in Gunung
Kanthan.
Sample: LB 62 (PPL)
184
Figure 4.92: The photomicrographs of each type of calcite in Kinta Limestone under
PPL, (a) The presence of pyrite and Cal-II cuts through Cal-I; (b) Cal-III and stylolite
cuts through Cal-I with the presence of pyrite; (c) Cal-IV cuts across Cal-II; (d) A
very coarse calcite cement develops within Dolo-V.
4.6.4.2 Types of dolomite
There are five types of dolomite observed under photomicrograph. Three types of
dolomite, Dolo-I, Dolo-II, Dolo-III are categorized under replacive dolomite. While,
Dolo-IV and Dolo-V is grouped under cement dolomite. Replacive dolomite usually
occurs at the early and middle stages of diagenesis, where dolomite replaces limestone
with enough amount of Mg2+ source. While, cement dolomite occurred at the late
diagenesis and known as pore-filling dolomite. Commonly, that cement dolomite has a
Sample: LB 62 (PPL)
Sample: LE 1-60 (PPL) Sample: LB 83 (PPL)
185
larger crystal size than replacive dolomite because more pore spaces tend to develop at
a late stage of diagenesis. Replacive dolomite usually retains the original texture of
precursor limestone which it has finer grain compared to cement dolomite. A detailed
explanation of each type of dolomite is presented below.
1. Dolo I- Microdolomite
Dolo-I is fine crystalline dolomite as in Fig. 4.93 (a). The crystal size is ranging
from 10µm to 30µm. It shows a morphology of nonplanar-a (anhedral) to planar-s
(subhedral). Most of the fine dolomite crystals consisted of anhedral texture. Dolo-I
shows a well-preserved fabric. The crystal texture is inequigranular with prophyrotopic
(contact rhomb) fabrics and isolated patches. It appears dull red luminescence with no
clear rim. Dolo-I is identified as replacive or matrix dolomite. This kind of dolomite
existed in Gunung Rapat and Hill E, Gunung Kanthan.
2. Dolo-II: Sucrosic Dolomite
Sucrosic dolomite (Dolo-II) has fine to medium crystal, ranging from 10µm to
150µm. Dolo-II has equigranular (unimodal crystal size) and inequigranular
(polymodal crystal size) texture, with mosaic fabric. The crystal shape is non-planar
anhedral, with mostly curved and lobate intercrystalline boundaries as in Fig.4.93 (b).
CL photomicrograph showing red colour, dull luminescent dolomite cement, with no
clear rim and poorly preserved matrix. Subordinately, the brecciated clasts of Dolo-II
are also present in the photomicrograph of Sungai Siput Dolomite Hill. This nonplanar
dolomite infills the intercrystalline pores. Late fracturing (F-IV and F-VII) cut through
the Dolo-II and partly infilled by Cal-V. The matrix is tightly packed and has very low
porosity with less than 5%.
3. Dolo-III: Fabric Destructive Fine Crystalline Dolomite
Fabric destructive fine crystalline dolomite (Dolo-III) has a crystal size ranging
from 10µm to less than 50µm. The crystal is inequigranular and has porphyrotopic
texture, where there is floating dolomite rhomb in the dolomite fabric as in Fig. 4.93
(f). The floating dolomite rhomb has a crystal size of 100µm to 150µm, with planar-es
186
to nonplanar-a under photomicrograph. The dolomite crystal is already corroded and
isolated in a fine-grained matrix. CL photomicrograph showing the dolomite mosaic
has dull red luminescent with no clear rhomb while floating dolomite crystals show dull
red luminescent with dark cortices and bright rim. The isolated crystals are equigranular
and it is tightly packed. Even though Dolo-III mosaic is tightly packed, massive
fracturing enhanced the dissolution porosity. Calcite cement has partly filled the
porosity as in Fig. 4.93 (c-d). The percentage porosity observed is 5%, which develops
from fracture porosity. Dolo-III is identified as replacive dolomite that forms at a later
stage than Dolo-II.
187
Figure 4.93: The representative samples of replacive dolomites, Dolo-I, Dolo-II and
Dolo-III in CL and PPL, (a) Dolo-I shows fine dolomite matrix; (b) Sucrosic dolomite
(Dolo-II) has anhedral crystal boundary; (c) The calcite veins cut across Dolo-III; (d)
Dolo-III appears dull red luminescence and calcite cement appears bright orange
luminescence under CL; (e) The fabric of Dolo-III in PPL; (f) CL image shows
floating dolomite rhombs.
Sample: LE 2-2 (PPL) Sample: SB 6 (PPL)
Sample: SD 10 (PPL) Sample: SD 10 (CL)
Sample: SD 5 (PPL) Sample: SD 5 (CL)
188
4. Dolo-IV: Fabric Destructive Coarse Crystalline Dolomite
Fabric Destructive Coarse Crystalline Dolomite (Dolo-IV) has a very coarse
crystalline, size ranging from 300µm to more than 2000µm, with mostly more than
500µm. In Gunung Rapat, the crystal boundary is not easy to determine because the
dolomite fabric is destructive and not showing the crystal shape. However, Dolo-IV in
Gunung Kanthan shows the crystal shape is planar euhedral-subhedral to nonplanar
anhedral as in Fig. 4.94 (b). It shows the bright red luminescent, clear dark outer rim
and no zoning or core detected under CL. Besides, Dolo-IV is highly fractured and
associated with calcite vein (Fig. 4.94 (a-c)). It has undergone compaction that leads to
fracturing.
5. Dolo-V: Saddle Dolomite
Saddle dolomite (Dolo-V) has medium to very coarse crystal size ranging from
50µm to more than 2000µm, with mostly more than 500µm. The crystal size is large
because there are large pore spaces which probably created due to dissolution. Dolo-V
only can be observed in Gunung Kanthan. Dolo-V crystals are inequigranular with
planar-es to nonplanar-a. Dolo-V is grouped under xenotopic-C pore-lining saddle
shape. Such dolomite is often developed as vein- or fracture filling. It has a lobate
crystal face junction (Fig. 4.94 (e)). Dolo-V is in contact with late calcite cementation
(Cal-V), where Cal-V is partly infilled the pore spaces between Dolo-V crystals as in
Fig. 4.94 (d). CL photomicrograph showing bright red luminescent with clear outer rim,
bright and dark core, and no zoning as in Fig. 4.94 (f). It displays clear thick dolomite
rims. A dark brown rim can accentuate the rhombs edges. Few sections of Dolo-V
cement have undergone intense dissolution but still retained the dolomite crystal shape.
Late fracturing (F-VII) cuts through Dolo-V and there is the presence of pyrite. The
porosity mainly develops due to dissolution and creates voids. The porosity observed
in this type of dolomite is up to 2%.
189
Figure 4.94: The representative samples of cement dolomites, Dolo-V and Dolo-IV in
CL and PPL, (a) Dolo-IV is associated with calcite vein; (b) Dolo-IV appears red
luminescence under CL and the crystal boundary is planar-es to nonplanar-a; (c)
Pore-filling calcite cements cut across Dolo-IV; (d) Dolo-V grows towards the
pore spaces and infilled by Cal-V; (e) A lobate crystal face junction; (f)
Dolo-V has thick rims and appears red luminescence under CL.
Sample: LE 2-4 (PPL) Sample: SC 15 (PPL)
Sample: LB 83 (PPL) Sample: LB 83 (CL)
Sample: LB 80 (PPL) Sample: LB 80 (CL)
190
4.6.4.3 The origin of hydrothermal dolomites in Kinta Limestone
Hydrothermal dolomite tends to become good reservoirs to many oil and gas due for
porous dolomite characteristics. Thus, understanding this dolomitization is part of the
primary economic consideration (Shah et al., 2010). Hydrothermal dolomites formed at
high temperature with permeable pathways for hydrothermal fluids such as faults
(Warren, 2000) and are constrained on particular pathways that are not laterally
extended through the strata. The dolomitization fluids migrated upwards and altered the
limestone host rock to hydrothermal dolomite (Davies et al., 2000) and it formed at a
higher temperature than host rock formation (Machel & Lonnee, 2002).
Based on this study, the dolomites in Kinta Limestone are formed close to faults
and not extend laterally. This indicates dolomitization in Kinta Valley is controlled by
structure. Petrographic data support the evidence of hydrothermal origin in this study.
Nonplanar-anhedral textures are typical in dolomites, Dolo-I, Dolo-II, and Dolo-III.
This type of texture is usually formed at high temperatures exceeding critical
roughening temperature above 50°C (Gregg & Sibley, 1984; Warren, 2000). Besides,
the occurrence of saddle dolomites, Dolo-V in Kinta Limestone is the proof of high-
temperature hydrothermal fluids (Machel & Lonnee, 2002).
The carbonates in Kinta Valley have undergone subaerial exposure, including
dolomite. Dolomite in Kinta is being the product of early and late diagenetic processes.
In the early phase of dolomitization, the replacement of Mg2+ iron has taken place in
precursor limestone rock and the dolomite is called replacive dolomite. While, the late
diagenetic process of dolomitization produced cement dolomite, where dolomite
cements fill up the pore space.
191
4.6.4.4 Diagenetic Processes of carbonates in Kinta Valley
The changes in reservoir properties in tight carbonates are mainly depended on the
diagenetic processes that modified the rock texture (Rashid et al., 2015). The
paragenetic sequence of Kinta Limestone is established as in Table 4.22. The
paragenetic sequence is represented through the timing of calcite and dolomite
development according to diagenetic processes. The diagenetic processes involved in
Kinta Limestone include micritization, stylolization, fracturing, dissolution, calcite
cementation, pyritization, dolomitization, brecciation, and dedolomitization.
Table 4.22: Paragenetic sequence of carbonates in Kinta Limestone
Diagenetic Events Relative Timing
Early Middle Late
Micritization (Cal-I)
Stylolization (Initial Compaction)
Fracturing (F-I)
Dissolution
Early calcite cementation (Cal-II)
Pyritization
Fracturing (F-II, F-III)
Pore-filling calcite cementation (Cal-III)
Early Dolomitization (Dolo-I, -II)
Brecciation
Fracturing (F-IV)
Dissolution
Replacive Dolomitization (Dolo-III)
Massive fracturing (F-V)
Cementation (Cal-IV)
Dissolution
Late Cement Dolomitization (Dolo-IV, -V)
Brecciation
Fracturing (F-VI & F-VII)
Dissolution
Pore-filling calcite cementation (Cal-V)
Stylolization & fracturing (F-IV)
Dissolution
Dedolomitization (Ded-I)
Dolo-IV Dolo-V
F-VI F-VII
192
1. Micritization
Micritization is identified as the early diagenetic process of carbonates in Kinta
Limestone. Cal-I is a product of the calcite matrix that has been micritized (Fig. 4.95).
Micritization commonly occurs in calm environments, so microbial activities can fill
the pore spaces between the grains. Micritization may occur throughout the diagenesis
that will lead to the destruction of the original grain (Adenan et al., 2017).
Figure 4.95: The contact between micritized calcite matrix (Cal-I) and early replacive
dolomite (Dolo-I).
2. Compaction
Compactions are dominant in Kinta Limestone and divided into two groups, which
are mechanical and chemical compactions. Mechanical compaction is shown by
fractures, deformed grain and broken rock fragments (Adenan et al., 2017). There are
early and middle fracturing occurs in Gunung Rapat. Early fracturing (F-I, F-II and F-
III) cuts through calcite matrix and cement (Fig. 4.96 (a)). It occurs before the phase of
early dolomitization. While, late fracturing (F-IV) occurs after replacive dolomitization
and late stage of cementation. As in a previous study, Ramkumar et al. (2019) also
stated multi phases of fracturing in Kinta Limestone.
Stylolization that occurs at the initial and late stages of diagenesis is known as
chemical compaction. The presence of microstylolite indicates pressure dissolution,
Sample: LE 2-2 (PPL)
193
where dewatering of limestone occurs intensely. An early stage of stylolite has a low
amplitude which reflects highly cemented rocks. Usually low amplitude stylolite forms
in clay associated carbonate microfacies, do not have impact porosity generation
(Carozzi & Bergen, 1987). While, the late stage of stylolite has high amplitude and
associated with fractures. The late stylolization may enhance porosity and permeability
generally (Carozzi & Bergen, 1987).
Figure 4.96: Mechanical and chemical compactions (a) Early fracturing cuts through
Cal-II; (b) Late stage of stylolite cuts across Cal-V and Dolo-II.
3. Dissolution
Dissolution affects the porosity and permeability of Kinta carbonate. It has a
positive impact on porosity development and reservoir quality. The dissolution occurs
when there is fluids movement along with the pore spaces like fractures and grain to
grain contact. It happens at the early, middle and late stage of diagenesis.
4. Calcite cementation
Cementation is a process of mineral precipitation that fills in the pore spaces
between crystals. Four types of calcite cement in Kinta Limestone have been
differentiated by their texture: Cal-II, Cal-III, Cal-IV and Cal-V. The calcite
cementation has different generations. Cal-II and Cal-III are identified as the early
calcite cements, while Cal-IV occurs after early phase of calcite cementation and Cal-
V is late calcite cement. Cal-II and Cal-III have micritic to equant calcite cement which
Sample: AQ 45 (PPL) Sample: SD 5 (PPL)
194
usually formed within interparticle pore spaces in the matrix. Cal-IV is blocky to drusy
calcite cement, showing larger size towards the centre of interparticle pores. Usually,
drusy calcite cement forms in meteoric water conditions at late cementation during
burial diagenesis (Flügel, 2004). Thus, it is suggested the calcite experienced
dissolution by meteoric water and cementation during burial diagenesis.
The Cal-V is blocky to poikilotopic calcite cement forms at the late stage where it
tends to occlude the pore spaces. Calcite cementation formed as void-filling cement. It
occurs after the matrix has undergone fracturing and dissolution. Then, calcite cement
fills in the voids. Host limestone shows multiple episodes of calcite-filled fractures. The
cementation altered and lessen the pore network connectivity by either filling or
blocking passage for fluid flow (Rashid et al., 2015).
5. Pyritization
Pyrite in Kinta Limestone is formed at the early and late stages of diagenesis and it
occurred under reducing conditions. The pyritization is associated with iron sulphide
(FeS2) in carbonate rocks, replacing the organic matters (Cabral et al., 2019). There are
two types of pyrite present in Kinta Limestone, which are framboidal pyrite (Fig. 4.97
(a)) and micropyrite (Fig. 4.97 (b)). The framboidal pyrite has a spheroidal shape that
is anhedral, equant to the curve crystal shape (Brand & Morrison, 1987). This type of
pyrite can be found abundantly in Cal-I matrix of Gunung Kanthan and minor in the
Cal-I matrix of Gunung Rapat. Meanwhile, micropyrite has a euhedral crystal shape
and can be found in the Cal-I of Gunung Rapat and Dolo-V of Hill B, Gunung Kanthan.
195
Figure 4.97: (a) Framboidal pyrite; (b) Micropyrite
6. Dolomitization
There are two groups of dolomites in Kinta Limestone, which are replacive
dolomite and cement dolomite. As mentioned before, Dolo-I, Dolo-II and Dolo-III are
identified as replacive dolomite, while Dolo-IV and Dolo-V are classified as cement
dolomite. Based on Shah et al. (2010), replacive dolomite forms when there is
substitution of the Mg2+ into host rock and replaces the original precursor limestone
rock matrix. It is also known as the dolomite matrix. The timing for the development
of replacive dolomite is always earlier than cement dolomite. It is interpreted as the
initial stage of dolomitization as shown by the occurrence of Dolo-I replacing calcite
cements. Then, Dolo-II’s coarser grain size is post-dated fine grain Dolo-I, which
indicates the recrystallization had occurred. After that, dissolution and fracturing had
occurred, making a new phase of dolomitization by the presence of Dolo-III.
Then, other phases of dissolution and fracturing create pore spaces for cement
dolomite. The cement dolomite develops when there is enough pore space within the
dolomite or calcite matrix. It fills the cavities and fractures which also known as pore-
filling dolomite. This type of dolomite occurs at the late stage of diagenesis. Late-stage
dolomite usually occurs pervasively, whereas most of the limestone has been replaced
by dolomite and dolomite may fill in the cavities as cement. Shah et al. (2016) stated
dolomitization could create and destroy porosity.
Sample: AQ 45 (PPL) Sample: LE 1-7 (PPL)
196
7. Brecciation
Most of the breccia deposits are influenced by late diagenesis which can be found
in Dolo-II (Fig. 4.98 (a)) and Dolo-V (Fig. 4.98 (b)). The dolomite breccias are
identified as tectogenic-diagenetic breccia, influenced by tectonics and close to main
faults, and subsequently altered by diagenesis. The term tectogenic-diagenetic breccia
is used for brecciated rocks that result from local diagenetic alteration and tectonics
influence (Vlahović et al., 2002).
Figure 4.98: (a) Breccia clasts of Dolo-II; (b) Breccia clasts of Dolo-V.
8. Dedolomitization
The trace of dolomite crystal can be seen in Hill E and partially replaced by calcite.
The diagenetic process of this event is known as de-dolomitization. Dedolomitization
is believed to occur after burial, during the meteoric stage after uplifting. The dolomite
is replaced by late calcite cementation. The process is also known as calcitization of
dolomite (Vandeginste & John, 2012). The dolomite in Kinta Valley is replaced by fine-
grained calcite. Dedolomitization usually associated with meteoric diagenesis that
enhances the intercrystalline and mouldic porosity as in Fig. 4.99 (a-b).
Dedolomitization is common in near-surface of vadose zones that may suggest
subaerial exposure (Flügel, 2004).
Sample: AQ 76 (PPL) Sample: LB 81 (CL)
197
Figure 4.99: Dedolomitization (Ded-I) is associated with late calcite cementation (a)
Ded-I view under PPL; (b) Ded-I view under CL.
4.6.5 Implication of dolomitization in Kinta Limestone to micro-porosity
development
4.6.5.1 Pore types and percentage variations of dolomite in Kinta Valley
The porosity developed more in the dolomite than the calcite matrix of Kinta
Limestone. Most of the calcite cements occluded the porosity. Several pore types
present within a sample and this condition indicates high pore heterogeneity. The pore
types and percentages are not consistent in all dolomite types. Table 4.23 shows the
pore types and percentages for all dolomite types in Kinta Valley.
The petrographic interpretation shows Dolo-I has a tight matrix and no porosity
observed under photomicrographs. The low porosity of Dolo-I and Dolo-III is because
this type of replacive dolomite preserved the original porosity from calcite cements.
The porosity in calcite cements are less than 5% which is not much different from
replacive dolomites. Dolo-II commonly has intercrystalline porosity with 3-5%,
fracture porosity with 1-3% and stylo-porosity with 1-2%. While, Dolo-III shows the
presence of vug porosity with 3% and fracture porosity with 5%.
The results show that intercrystalline porosity is the dominant type in almost all
dolomite samples and it offers good porosity value. Lucia (2007) stated dolomitization
Sample: LE 1-63 (PPL) Sample: LE 1-63 (CL)
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might enhance the intercrystalline porosity resulting in good reservoir properties. This
type of porosity is most abundant in cement dolomites, Dolo-IV and Dolo-V. Dolo-IV
and Dolo-V’s intercrystalline porosity ranges from 5-10% and 4-25% respectively.
Other porosity types are fracture porosity with less than 2%, stylo-porosity with only
1%, vuggy porosity with 5% and channel porosity with 7%. The fracture and stylo-
porosities show a very low amount of percentage, which not have a significant impact
on reservoir properties.
Table 4.23: The summary of pore types and percentage of dolomite microfacies in
Kinta Valley
Dolomite groups Dolomite
microfacies
Types of pores and percentages
Replacive
Dolomite
Dolo-I Tight matrix (No pores visible under
photomicrographs)
Dolo-II Intercrystalline pore (3-5%), Fracture (1-3%),
Stylo-pore (1-2%)
Dolo-III Fracture (5%), Vug (3%)
Cement
Dolomite
Dolo-IV Fracture (1-2%), Intercrystalline pore (5-10%),
Channel (7%)
Dolo-V Intercrystalline pore (4-25%), Vug (5%),
Fracture (1-2%), Stylo-pore (1%)
The replacive dolomite tends to have a similar host rocks porosity since they
preserved the original fabric of precursor rocks from compaction (Carnell & Wilson,
2003). In Kinta Limestone, the porosity in replacive dolomite is low as it retained the
original porosity of the precursor limestone rocks. When forming as a cement, dolomite
negatively impacts on reservoir quality, in which these cements decrease both porosity
and permeability. The reduction of reservoir quality is depends on the volume of
cementation (Carnell & Wilson, 2003). They have a texture of euhedral to subhedral
shape and usually made up of closely interlocking hypidiotopic mosaics (Shah et al.,
2016). However, in the Kinta Limestone case, the porosity in cement dolomite is higher
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than replacive dolomite. It may be due to late dissolution before the last stage of
dolomitization, where it enhanced the intercrystalline porosity of cement dolomite.
4.6.5.2 The porosity evolution of rock matrix before, during and after dolomitization
in Kinta Limestone
a) Pre-Dolomitization
Before phases of dolomitization in Kinta Limestone, the host rocks have undergone
micritization, early stylolization, dissolution, early calcite cementation, pyritization,
and fracturing. The micritization, early stylolization, early calcite cementation and
pyritize reduced porosity, while fracturing and dissolution enhanced porosity. The
micritized calcite, Cal-I, initially has a very low porosity value. The morphological
analysis shows the presence of clay mineral such as palygorskite (Fig. 4.81) in
micritized calcite, Cal-I which also contributed towards porosity destruction in the rock
matrix. Then, the porosity remains low after early stylolization until dissolution takes
place. The dissolution has a good impact on porosity development. However, in the
Kinta Limestone case, the initial stage of dissolution only contributed to a very low
increment of porosity. This might indicate a low rate of dissolution due to limited access
to fluids. After that, another phase of cementation, Cal-II has occurred and followed by
pyritization. Pyrite had a significant role in destroying the porosity of the reservoir
(Zamanzadeh et al., 2011). The pyrite in Kinta Limestone had filled in the pore spaces
between calcite cement, however, it is not found very frequently. Then, the fractures
(F-II and F-III) in the calcite matrix have cut across Cal-III. These fracturing thus post-
dated Cal-III. Cal-III partly fills the fractures.
b) Syn-Dolomitization
During the dolomitization process in Kinta Limestone, few other diagenetic
processes are also involved, such as brecciation, fracturing, dissolution and
cementation. The brecciation and cementation are reducing the porosity, while
200
fracturing and dissolution are enhancing porosity. Dolomitization plays a role in
preserving and reducing the porosity.
The process usually produces a fabric-preserving dolomite formed by phreatic
meteoric water during subaerial exposure (Carozzi and Bergen, 1987). The
photomicrographs (Fig. 4.92 (a-b)) show the early dolomitization of Dolo-I and Dolo-
II are fabric-preserving, where they retain the calcite matrix characteristics of fine-
grained. However, Dolo-III shows a poorly preserved matrix. This occurrence of
poorly fabric-preserving is due to multi phases of fracturing and tectonic impacts that
altered the dolomite texture. The multi phases of tectonic events in Kinta Valley are
also recorded by Ramkumar et al. (2019). Dolostone in Kinta Valley has numerous
phases of calcite and dolomite that show a sequence of fluid pulse ejected from the
fractures. The hydrothermal fluids that carry magnesium ions due to hydrothermal
activity moved upwards through existing fractures, penetrated and altered host
limestone or pre-existing dolomites into replacive dolomite (Ramkumar et al., 2019).
The extend of the dolomitization is influenced by dolomitization period and fluid
composition.
The early replacement of limestone matrix to dolomite might not alter the original
porosity, but it retained the porosity of the precursor rock matrix. This is proven in
petrographic analysis The early replacive dolomites, Dolo-I and Dolo-II, exhibit the
similar amount of porosity and pore types as observed in early calcite cements and
matrix. However, Dolo-III’s second phase of dolomitization, has better porosity than
Dolo-I and Dolo-II due to massive fracturing. The fractures are created as due to the
tectonic event (Ramkumar et al., 2019). They are very common in carbonates due to
their brittle nature and often associated with faulting that acted as pathways for hot
fluids (Moore, 1989).
The third phase of dolomitization is the late stage of cement dolomites, Dolo-IV
and Dolo-V. The presence of saddle dolomite, Dolo-V indicates the interaction of high-
temperature hydrothermal fluids. Late-stage dolomitization allows the dolomites to
rearrange to more stable forms, changing into better stoichiometry (Warren, 2000). The
fracturing and dissolution have created the pore spaces for the development of cement
201
dolomite. This is proven by photomicrographs (Fig. 4.93), Dolo-IV and Dolo-V grow
into coarse crystalline because the crystals have enough space to develop within the
matrix. These types of dolomite also known as pore-filling dolomite due to its
characteristic fill in the pore spaces. The most dominant pore types in cement dolomite
of Kinta Valley is intercrystalline pores. Based on previous studies, late stage cement
dolomite tends to occlude porosity (Hiatt & Pufahl, 2014). However, the porosity
observed in the cement dolomite of Kinta Valley is higher than the replacive dolomite.
This is because of previous dissolution process had influenced massively on the
porosity enhancement in the rock matrix. The late dolomitization itself is believed to
reduce the porosity and formed as cement dolomite. Purser et al. (1994) stated the
cement dolomite would occlude the porosity only if there is an extensive supply of
dolomite substance within the system. The cement dolomite in Kinta Valley might not
have prolonged the supply of Mg2+. This is because the cement dolomite in Kinta Valley
has not fully occluded the porosity. The porosity is partly reduced from pre-existing
porosity created by dissolution, but it is still considered good and better than replacive
dolomite.
c) Post-dolomitization
After the late stage of dolomitization, brecciation and fracturing had occurred. The
dolomite crystals are sheared and tectonized. Brecciation might indicate the shear
occurred along fractures resulting in reduced permeability (Wilson et al., 2007).
Fracture at the late stage remains open, thereby increasing porosity by 1-2%. Then,
another phase of dissolution enhanced the porosity, and calcite starts to re-precipitate
in the pore matrix of Dolo-V. Pore-filling late calcite cement of Cal-V has destroyed
the porosity. Then, porosity starts to increase again during the late stylolization and
fracturing phase. The late stylolization may have a good impact on reservoir properties
(Carozzi & Bergen, 1987). Then, dissolution and replacement of limestone took place.
The dolomite in Kinta Valley is replaced by fine-grained calcite. The changes from
dolomite to calcite might result from a temperature drop (Carpenter, 1980) and
depletion of Mg2+ ions in the locally sourced fluid (Ramkumar et al., 2019). The process
is known as dedolomitization. Dedolomitization in Kinta Limestone may take places at
202
subaerial exposure, which had enlarged the intercrystalline porosity. Dedolomitization
had enlarged the moldic pores and intercrystalline pores (Braithwaite et al., 2004),
making the intercrystalline pores more dominant among other pore types.
d) Summary
Porosity formed through dolomitization remains speculative. The dolomite fabric
itself is not significant in controlling the porosity. Based on this study, the porosity
evolution is relative to dolomitizing systems, which in theory, does not facilitate its
expectation that cement dolomite should destroy porosity. Nonetheless, extensive
crystal growth led to reduce porosity due to enough supply of Mg2+ in sourced fluids
(Purser et al., 1994). The effect of pre-existing porosity is documented to understand
the changes of porosity seen in dolomite. The porosity observed in dolomite is not
necessarily created due to dolomitization. Other diagenetic processes also contributed
to porosity development in dolomite (Fig. 4.100). The understanding of porosity
development is vital to the interpretation of reservoir properties. Thus, in summary the
process affecting porosity development in Kinta Limestone is classified into three
categories: enhancing, retaining, and reducing processes. The enhancing processes
include dissolution, compaction (fracturing), and dedolomitization, while the reducing
processes are dolomitization, cementation, micritization and brecciation and the
retaining process is only at the early stages of dolomitization.
203
Fig
ure
4.1
00:
The
poro
sity
modif
icat
ion t
hro
ugh d
iagen
etic
ev
ents
du
ring p
re-d
olo
mit
izat
ion, sy
n-d
olo
mit
izat
ion a
nd p
ost
-
dolo
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izat
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n K
inta
Lim
esto
ne
204
CHAPTER 5
CONCLUSIONS
5.1 Conclusions
The carbonates in Kinta Limestone composed of three main lithology, which are
limestone, dolomite and dolomitic limestone. The carbonate lithotypes are determined
by geochemical content and field observation. The porosity and permeability
heterogeneity mainly reflect the various lithology and diagenetic response. Limestone
shows varied porosity and permeability among all samples, while dolomite and
dolomitic limestone have low porosity and permeability. The internal structure of the
rocks is observed by 2D and 3D images of micro-CT scan. The evaluation of the pore
system includes pore radius, pore distributions and connectivity. The results show tight
pore radius did not affect the pore connectivity in the rock matrix. Pore connectivity is
affected by pore distributions and pore types. The pore distributions have a big
influence in pore connectivity. Throat pores distribution leads to good connectivity,
while isolated pores that are interconnected with throat pores show moderate to good
porosity and dead-end pores display no connectivity in the rock matrix. Limestone is
dominated by throat pores with good to moderate pore connectivity. While, dolomite
and dolomitic limestone are mainly associated with an isolated pore interconnected to
fractures, with mostly moderate pore connectivity.
The carbonates in Kinta Limestone are associated with hydrothermal
dolomitization. The dolomite bodies were found close to faults. The thermo-tectonic
event in Kinta Limestone has led to multi phases of fracturing and several stages of
dolomitization. Petrographic analysis indicates five types of dolomite (Dolo-I, Dolo-II,
Dolo-III, Dolo-IV, Dolo-V) in Kinta Limestone. The paragenetic sequence has been
205
established to observed how dolomitization, which is part of diagenetic processes
controlled the porosity in dolomite. Early dolomitization resulted in replacive
dolomites, Dolo-I, Dolo-II and Dolo-III that preserved the porosity of rock matrix.
While, late dolomitization resulted in cement dolomites, Dolo-IV and Dolo-V that
reduced the porosity. The main control on porosity value in cement dolomite is the
dissolution process, which created the intercrystalline pores up to 25% porosity. The
cement dolomite also has been exposed to porosity-enhancing meteoric dissolution
processes and transform into calcite at a later stage, which creates more porosity. Not
only dolomitization played a role in controlling the porosity of the rock matrix, other
complex diagenetic histories had impacted to the changes of porosity. The diagenetic
processes that enhanced the porosity in Kinta Limestone are dissolution, fracturing, and
dedolomitization. The other diagenetic processes such as dolomitization, cementation,
micritization and brecciation had reduced the porosity in rock matrix.
Thus, the dolomitization and petrophysical properties study of carbonate rocks in
Kinta Limestone reveals the following conclusions:
1) There are three types of lithology identified in selected Kinta Valley’s quarries:
limestone, dolomite and dolomitic limestone.
2) Porosity and permeability of carbonate rocks varied based on lithology. The
rocks associated with dolomite minerals such as dolomitic limestone and
dolostone have lower porosity and permeability values than limestone.
3) The dolomitization in Kinta Valley maintained and destroyed the porosity.
Replacive dolomite (early stage of dolomitization) retained the porosity from
precursor limestone while, cement dolomite (late stage of dolomitization)
reduced the porosity.
4) Dolomitization is not the only process that plays a role in the changes of
porosity. Other diagenetic processes also contributed to porosity development
such as dissolution, compaction (fracturing), and dedolomitization.
206
5.2 Research Contributions
1. Provide an insight into the potential of fluid flow and storage in the carbonate
rocks of Kinta Valley.
2. The understanding of how diagenesis in Kinta Limestone modified the porosity
in dolomites.
5.3 Recommendations
1. A detailed measurement of porosity and permeability using high pressure
mercury injection capillary pressure will help obtain the percentage of pore
throat distributions.
2. The limitations on access of the samples and heterogeneity might lead to these
differences in the weightage of Mg concentration of north and south of Kinta
Valley, which contradicts with Haylay (2016). More pervasive areas can be
conducted to increase the accuracy of data and interpretations.
3. Implemented other methods to identify and support the lithology such as elastic
properties (Vp, Vs).
207
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Appendix A1: XRD pattern of AQ 1
Appendix A2: XRD pattern of AQ 10
Cal (Calcite): 89.5%
Dolo (Dolomite): 10%
Qtz (Quartz): 0.5%
225
Appendix A3: XRD pattern of AQ 23
Appendix A4: XRD pattern of AQ 28
Cal (Calcite): 97.9%
Dolo (Dolomite): 2%
Quartz: 0.1%
Cal (Calcite): 99.9%
Qtz (Quartz): 0.1%
226
Appendix A5: XRD pattern of AQ 45
Appendix A6: XRD pattern of AQ 60
Cal (Calcite): 99.9%
Qtz (Quartz): 0.1%
Cal (Calcite): 99.8%
Qtz (Quartz): 0.2%
227
Appendix A7: XRD pattern of AQ 76
Appendix A8: XRD pattern of LB 6
Cal (Calcite): 66.5%
Dolo (Dolomite): 33.3%
Qtz (Quartz): 0.2%
228
Appendix A9: XRD pattern of LB 24
Appendix A10: XRD pattern of LB 62
Ll
Cal (Calcite): 99.4%
Dolo (Dolomite): 0.2%
Qtz (Quartz): 0.4%
236
Appendix A25: XRD pattern of SA 1
Appendix A26: XRD pattern of SA 3
Dolo (Dolomite): 92.8%
Cal (Calcite): 7%
Qtz (Quartz): 0.2%
237
Appendix A27: XRD pattern of SB 6
Appendix A28: XRD pattern of SC 15
Dolo (Dolomite): 94.4%
Cal (Calcite): 5%
Qtz (Quartz): 0.1%
241
Ca
Mg
Si
Fe
PA
l Sr
Mn
KS
Cl
TiC
uZn
ZrM
oN
i
AQ
197
.61.
30.
30.
30.
20.
20.
00.
00.
00.
00.
00.
00.
00.
000
3.51
30.
000
0.00
0
AQ
10
98.7
0.5
0.3
0.2
0.2
0.1
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.00
00.
000
0.00
00.
000
AQ
23
98.2
0.8
0.2
0.3
0.2
0.1
0.1
0.0
0.0
0.0
0.0
0.0
0.0
0.00
00.
116
52.4
970.
000
AQ
28
99.0
0.4
0.1
0.1
0.2
0.1
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.00
00.
000
0.00
00.
000
AQ
45
98.6
0.4
0.2
0.3
0.2
0.1
0.0
0.0
0.0
0.0
0.0
0.1
0.0
0.00
00.
000
0.00
00.
000
AQ
60
98.7
0.4
0.1
0.4
0.2
0.1
0.1
0.0
0.0
0.0
0.0
0.0
0.0
0.00
00.
148
51.9
240.
000
AQ
76
94.0
3.2
0.7
1.2
0.2
0.2
0.1
0.3
0.0
0.0
0.0
0.0
0.0
0.00
00.
000
0.00
00.
000
LB 6
99.7
0.0
0.0
0.2
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
43.7
9715
.540
0.00
00.
000
LB 2
497
.30.
90.
60.
60.
30.
30.
10.
10.
00.
00.
00.
00.
00.
000
0.00
00.
000
0.00
0
LB 6
299
.50.
00.
00.
40.
00.
00.
10.
10.
00.
00.
00.
00.
00.
000
0.00
00.
000
0.00
0
LB 8
081
.512
.80.
92.
00.
40.
40.
01.
60.
00.
00.
20.
10.
00.
138
0.00
00.
000
0.00
0
LB 8
181
.513
.01.
11.
50.
40.
50.
01.
60.
00.
00.
20.
10.
00.
000
0.00
00.
000
0.00
0
LB 8
3 81
.313
.21.
11.
30.
40.
50.
01.
80.
10.
00.
20.
10.
00.
000
0.00
00.
000
0.00
0
LE 1
-799
.40.
00.
00.
40.
00.
00.
00.
20.
00.
00.
00.
00.
016
.046
0.00
00.
000
0.00
0
LE 1
-24
99.7
0.0
0.0
0.2
0.0
0.0
0.0
0.1
0.0
0.0
0.0
0.0
0.0
0.00
013
.273
0.00
055
.038
LE 1
-45
98.9
0.4
0.1
0.2
0.2
0.0
0.1
0.1
0.0
0.0
0.0
0.0
0.0
0.00
068
.000
0.00
00.
000
LE 1
-54
99.0
0.3
0.2
0.2
0.2
0.0
0.0
0.1
0.0
0.0
0.0
0.0
0.0
0.00
08.
086
0.00
00.
000
LE 1
-60
99.9
0.0
0.0
0.1
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.00
00.
852
0.00
00.
000
LE 1
-62
99.8
0.0
0.0
0.1
0.0
0.0
0.0
0.1
0.0
0.0
0.0
0.0
0.0
0.00
013
.884
0.00
064
.051
LE 1
-63
98.4
0.5
0.3
0.2
0.3
0.1
0.1
0.1
0.0
0.0
0.0
0.0
0.0
0.00
00.
000
0.00
00.
000
SA 1
84.0
11.6
1.3
1.5
0.4
0.5
0.1
0.2
0.1
0.0
0.2
0.2
0.0
0.00
00.
000
0.00
00.
000
SA 3
82.4
10.7
2.4
2.4
0.4
1.0
0.1
0.1
0.2
0.0
0.1
0.3
0.0
0.00
00.
000
71.4
170.
000
SB 6
84.6
12.1
1.0
1.0
0.3
0.4
0.1
0.2
0.1
0.0
0.2
0.1
0.0
0.00
00.
000
0.00
00.
000
SC 1
582
.612
.91.
31.
40.
40.
60.
00.
40.
10.
00.
20.
20.
00.
000
0.19
10.
000
0.00
0
SD 5
85.4
10.9
1.0
1.3
0.4
0.5
0.1
0.2
0.1
0.0
0.2
0.1
0.0
0.00
00.
000
0.00
00.
000
SD 1
084
.311
.91.
11.
30.
40.
40.
10.
20.
10.
00.
20.
10.
00.
000
0.00
00.
000
0.00
0
Sam
ple
Nam
e
Elem
ents
' Co
ncen
trat
ion
(%)
Wt.
%PP
M
Ant
ing
Qua
rry
Hill
B,
Lafa
rge
Qua
rry
Hill
E,
Lafa
rge
Qua
rry
Sg. S
iput
Qua
rry
Qua
rry
Appen
dix
B1:
XR
F d
ata
from
rep
rese
nte
d s
ample
s in
all
quar
ries
243
Appendix C1: The core plug descriptions from all quarries
AQ 1Dolomitic
LimestoneLight pink colour, tight pores
AQ 10 Limestone Light pink colour, presence of calcite vein, iron stains, tight
AQ 23 Limestone Pink whitish colour, crystalline, tight pores
AQ 28 Limestone Light grey colour, crystalline, iron stains, tight pores
AQ 45 Limestone Light pink colour, tight pores
AQ 60 Limestone Light grey colour, tight pores
AQ 76Dolomitic
Limestone
Light pink colour, presence of clay mixture of sepiolite (green-
yellowish), tight pores
SA 1 Dolomite Light grey colour, crystalline, presence of calcite vein, tight
SA 3 Dolomite Dark grey colour, crystalline, calcite infills, tight pores
SB 6 Dolomite Dark to light grey colour, crystalline, calcite infills, tight pores
SC 15 Dolomite Light grey colour, crystalline, calcite infills, tight pores
SD 5 Dolomite Light grey colour, crystalline, presence of calcite vein, tight
SD 10 Dolomite Light grey colour, crystalline, presence of calcite vein, tight
LB 6 Limestone Light grey colour, presence of calcite vein, tight pores
LB 24 Limestone Dark grey colour, microstylolite, tight pores
LB 62 Limestone Light grey colour, tight pores
LB 80 Dolomite Pink whitish colour, crystalline, tight pores
LB 81 Dolomite Pink whitish colour, crystalline, visible isolated microvugs
LB 83 Dolomite Pink colour, visible isolated microvugs (0.5cm) but tight pores
LE 1-7Dolomitic
LimestoneDark grey colour, presence of calcite vein, tight pores
LE 1-24 Limestone Light grey colour, presence of calcite vein, microstylolite, tight
LE 1-45 Limestone White colour, microvugs, fractured, tight pores
LE 1-54 LimestoneLight grey colour, chalky, fractured, microvugs, brown-dotted
stains, moderately porous
LE 1-60 Limestone White colour, chalky, fractured, light weight and porous
LE 1-62 Limestone Light grey colour, powdery, brown-dotted stain, fractured,
LE 1-63 Limestone Grey-brown colour, fractured, contact with dolomite, porous
LE 2-2 Limestone Light grey colour, limestone breccia with micropores, porous
LE 2-3 Dolomite Pink colour, brecciated limestone clasts in dolomite,
LE 2-4 Dolomite Pink, brecciated limestone clasts in dolomite, crystalline, tight
LE 2-5Dolomitic
Limestone
Pink, crystalline, boundary between dolomite and limestone,
crystalline, tight pores
Hill E-Outcrop
2, Lafarge
Quarry
LocalitySamples
NameLithology Core Plug Description
Anting Quarry
Sg. Siput Quarry
Hill B, Lafarge
Quarry
Hill E-Outcrop
1, Lafarge
Quarry