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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


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Programme for acceptance this thesis for the fulfillment of the requirements for the degree

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Main Supervisor: ______________________________________

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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


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.

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Date : _____________________ Date : __________________


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


3.3.2.2 Procedure ................................................................................. 44

3.3.3 Poroperm ............................................................................................. 45


3.3.3.2 Procedure ................................................................................. 46

3.3.4 Micro-Computed Tomography (CT) Scan .......................................... 47


3.3.4.2 Procedure ................................................................................. 48

3.3.5 Petrographic Analysis ......................................................................... 48


3.3.5.2 Procedure ................................................................................. 50

3.3.6 Field Emission-Scanning Electron Microscope-Energy Dispersive

X-Ray (FESEM-EDX) ..................................................................... 50


3.3.6.2 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


4.2.3 Field 3: Hill B, Gunung Kanthan ........................................................ 95

4.2.3.1 Mineralogy ............................................................................... 95


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


4.4 Petrographic Study......................................................................................... 130


4.4.1.1 Petrography and Diagenetic Features .................................... 130

4.4.1.2 Pore Types and Percentage .................................................... 133






4.4.3.2 Pore types and percentage ...................................................... 143




4.5 Morphological Study ..................................................................................... 155

xiii





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


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


based on outcrop samples of Hill E, Gunung Kanthan. ........................ 104


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


Kanthan. Identification as calcite with siliciclastic mixture is based

on the distinctive. .................................................................................. 166


showing Ca, Mg, Si, Al, C, and O elements in the sample. ................. 166


Kanthan. ................................................................................................ 168


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


Hill B, Gunung Kanthan ........................................................................... 96


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


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


be achieved


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.


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).


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).


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).


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.


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.

62

Figure 4.6: Sedimentary logging of outcrop in Gunung Rapat.

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.

68

Figure 4.13: Sedimentary logging of the outcrop (section D) in Sungai Siput Dolomite

Hill.

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).

74

Figure 4.18: Sedimentary logging of represented outcrop in Hill B, Gunung Kanthan.

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).

76

Fig

ure

4.1

9:

The

photo

of

outc

rop 1

in H

ill

E, G

unung K

anth

an.

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.

79

Figure 4.22: Sedimentary logging of outcrop 1 in Hill E, Gunung Kanthan.

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.

81

Fig

ure

4.2

4:

The

photo

of

outc

rop 2

in H

ill

E, G

unung K

anth

an.

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.


4.2.1.1 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.


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.


4.2.2.1 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.



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.


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


4.2.3.1 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



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.


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


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


4.2.4.1 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



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.


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%.


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).


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.


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 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


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.


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


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.


LB 6 Limestone 1.25 0.07



LB 80 Dolomite 1.85 0.05



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.


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.


LE 1-7 Dolomitic Limestone 2.06 0.05

LE 1-24 Limestone 2.48 0.00


LE 1-54 Limestone 11.73 0.79

LE 1-60 Limestone 14.52 1.82




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.


4.4.1.1 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

131

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.

132


A micritic calcite matrix shows a presence of

an isolated opaque micropyrite with

euhedral shape. The surrounding matrix is

associated with stylolite and dissolution.


Photomicrograph shows two fractures (F-III

cuts F-II) in calcite cement and the presence

of irregular shape of pyrite.


The image shows late fracturing (F-IV) cuts

across blocky to drusy calcite cement (Cal-

IV) and brecciated clasts of sucrosic

dolomite (Dolo-II).


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.

133

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%.

134

Sample AQ 1 – PPL

The presence of intercrystalline pore with

1% porosity in pore-filling equant calcite

cement (Cal-II).


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.



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

135

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).

136

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.

137

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.


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.

138


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.

139

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.



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

140

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.

141

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.



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).


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.


The image shows the coarse crystalline

blocky to drusy calcite cement. There is

intercrystalline porosity of 10% in the

matrix.


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.


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

152

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


The image shows channel porosity in Cal-II

with 5% porosity. The intercrystalline

porosity of 1% also presents in the calcite

vein (Cal-III).


The intercrystalline porosity of 3% also

presents in Cal-III.


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.


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


The image shows morphology of

clear stacked equant

rhombohedra calcite cement, Cal-

II. The average grain size is 5µm.


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


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.


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.


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


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.


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


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.


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.


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


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


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.


C 15.57 22.31

O 59.45 63.96

Mg 10.75 7.61

Ca 14.24 6.11

163


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.


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.


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.


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.


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


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).


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.


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).


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.


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.


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.


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


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.


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


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.


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

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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)

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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

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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.

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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)

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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%.

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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)

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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

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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)

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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)

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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)

198

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

199

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

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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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223

APPENDIX A

XRD DATA

224

Appendix A1: XRD pattern of AQ 1


Cal (Calcite): 89.5%

Dolo (Dolomite): 10%

Qtz (Quartz): 0.5%

225




Dolo (Dolomite): 2%

Quartz: 0.1%


Qtz (Quartz): 0.1%

226




Qtz (Quartz): 0.1%


Qtz (Quartz): 0.2%

227


Appendix A8: XRD pattern of LB 6


Dolo (Dolomite): 33.3%

Qtz (Quartz): 0.2%

228



Ll



Qtz (Quartz): 0.4%

229



Dolo

230


Appendix A14: XRD pattern of LE 1-7

231



232



233



234



235



236

Appendix A25: XRD pattern of SA 1

Appendix A26: XRD pattern of SA 3


Cal (Calcite): 7%

Qtz (Quartz): 0.2%

237

Appendix A27: XRD pattern of SB 6

Appendix A28: XRD pattern of SC 15


Cal (Calcite): 5%

Qtz (Quartz): 0.1%

238

Appendix A29: XRD pattern of SD 5

Appendix A30: XRD pattern of SD 10

239

APPENDIX B

XRF DATA

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

242

APPENDIX C

CORE PLUG DESCRIPTIONS

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

(title of the thesis)* - utpedia - universiti teknologi petronas

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