petrophysics analysis for reservoir characterization of

Journal of Applied Geology, vol. 1(1), 2016, pp. 43–52DOI: http://dx.doi.org/10.22146/jag.26959

Petrophysics Analysis for Reservoir Characterization of Upper PloverFormation in the Field “A”, Bonaparte Basin, Offshore Timor, Maluku,Indonesia

Sugeng Sapto Surjono∗and Indra Arifianto

Department of Geological Engineering, Gadjah Mada University, Yogyakarta, Indonesia

ABSTRACT. Hydrocarbon potential within Upper Plover Formation in the Field “A” hasnot been produced due to unclear in understanding of reservoir problem. This formationconsists of heterogeneous reservoir rock with their own physical characteristics. Reservoircharacterization has been done by applying rock typing (RT) method utilizing wirelinelogs data to obtain reservoir properties including clay volume, porosity, water saturation,and permeability. Rock types are classified on the basis of porosity and permeability distri-bution from routines core analysis (RCAL) data. Meanwhile, conventional core data is uti-lized to depositional environment interpretations. This study also applied neural networkmethods to rock types analyze for intervals reservoir without core data. The Upper PloverFormation in the study area indicates potential reservoir distributes into 7 parasequences.Their were deposited during transgressive systems in coastal environments (foreshore -offshore) with coarsening upward pattern during Middle to Late Jurassic. The porosity ofreservoir ranges from 1–19 % and permeability varies from 0.01 mD to 1300 mD. Based onthe facies association and its physical properties from rock typing analysis, the reservoirwithin Upper Plover Formation can be grouped into 4 reservoir class: Class A (Excellent),Class B (Good), Class C (Poor), and Class D (Very Poor). For further analysis, only classA-C are considered as potential reservoir, and the remain is neglected.

Keywords: Upper Plover Formation · Rock typing · Depositional environment · Bonapartebasin · Maluku · Indonesia.

1 INTRODUCTION

Plover Formation is the main target for hydro-carbon production in North West Offshore Aus-tralia as well as the Outer Banda arc of Indone-sia (Barber et al., 2003). However, in the Field“A” the upper part of this formation has notbeen produced and need to further study to re-veal the characteristics and hydrocarbon poten-tial within reservoir. Geographically, the studyarea took place in the offshore Maluku, about70 km to the south of the Selaru Island, MalukuProvinces (Figure 1) and geologically belong tothe Bonaparte Basin.

∗Corresponding author: S.S. SURJONO, Depart-ment of Geological Engineering, Gadjah Mada Univer-sity. Jl. Grafika 2 Yogyakarta, Indonesia. E-mail:[email protected]

The Upper Plover Formation was depositedduring transgression phase within transitionalto shallow marine environments, which pro-duce heterogeneous succession of sedimentaryrocks. Understanding of depositional environ-ment and petrophysics leads the grouping ofrocks types, which then useful to support mod-eling process and calculation of hydrocarbon inplace. The study was carried out to identify ver-tically facies succession of each sequence, to de-termine physical properties and fluid content ofreservoir, and to classify rock types of reservoirwithin interest zone.

This study utilized three wells data within re-search area, namely A-1; A-2 and A-3, includ-ing las data, geological drilling final report, rou-tine core analysis (RCAL) report, core descrip-tion, FMI log analysis reports, biostratigraphy

2502-2822/ c© 2016 Journal of Applied Geology

http://dx.doi.org/10.22146/jag.26959

SURJONO & ARIFIANTO

Figure 1: Research area located in the southern outer Banda Arc, of Offshore Maluku, where threeexploratory wells are available as primary data in this study.

reports and sedimentary facies logs. All dataare otillized to run reservoir characterizationusing IP (Interactive Petrophysics) software.

2 REVIEW OF PLOVER FORMATION

Research area is considered as northern partof the passive Australian plate boundariesand lies on Calder Graben, Bonaparte Basin.Calder Graben has southeast rifting patternthat formed northeast - southwest trendingstructures. This Graben has thick succession ofJurrasic – Cretaceous sediments that accordingto Barber et al. (2003), the early Jurassic massiveerosion truncate the Abadi High Pre-Cambrianto the Triassic interval. Continental to shelfalmarine sedimentation continued throughoutEarly to Middle Jurassic, leading to depositionof the Malita Formation red beds and overlyingPlover Formation fluvio-deltaic sediments upto 1500–2000 m thick, and terminated by rifting(break-up) on the Australian continental crustduring the Oxfordian.

According to Helby et al. (1987), the charac-teristics of lithology in conjunction with bios-tratigraphic control indicate that sedimentationpatterns during Plover Formation times weredominated by a series of widespread braidedtrunk river systems feeding a relatively narrowwave-dominated coastline and beyond a wide

marine shelf. The river system has relativelynorthwest – southeast directions along a line ofweakness provided by the axis of the GoulburnGraben. Study area is most probably situatedin the shoreface area where rivermouths dis-tributed sediments northward to the shelf (Fig-ure 2).

Nagura et al. (2003) divided Plover Forma-tion into four intervals (Figure 3). The follow-ing are description for each zone from the bot-tom to the top part. The Zone 4 is consider-ered as Lower Plover Formation of deltaic sed-iments with limited reservoir potential. Suc-cession delta is terminated by thin shale asso-ciated with verrucosa MFS flooding event. TheZone 3 overlying the Zone 4 marked by veru-cossa MFS. This zone begins from a lower in-terval of offshore shales with thin storm sands,into lower shoreface silts and fine sands andeventually into fine to medium grained, pla-nar and cross-bedded, extensively bioturbatedupper shoreface sands. The Zone 2 overly-ing above base indotata MFS were tested in theAbadi-1 and Abadi-3 wells as main reservoir. Inlower part, this zone consist of shales, silt andsands of offshore to upper shoreface environ-ments. To the upper part, this zone is capped bythe massive, extensively bioturbated, predomi-nantly medium grained sands. In the well logs,

44 Journal of Applied Geology

PETROPHYSICS ANALYSIS FOR RESERVOIR CHARACTERIZATION OF UPPER PLOVER FORMATION

Figure 2: Paleogeography of Upper Plover Formation indicate fluvial to shelfal depositional envi-ronments during Middle Jurassic (Barber et al., 2003).

it is characterized by a blocky log profile andexcellent reservoir properties. The Zone 1 is thetop of Plover Formation, which then overlainby Echuca Shoals and marked by regional un-conformity. It comprises a thin succession ofnon-reservoir quality sands possibly represent-ing deposits of an offshore. This interval onlydevelop in Abadi-1 well and mostly are absentin other area due to erosion.

Based on the crossplot porosity versus per-meability core plug data (Nagura et al., 2003),Plover sandstone indicates three different litho-fasies. Lithofacies 1 shows high porosity andpermeability values, consist of medium tocoarse-grained quartzarenite with excellentvisible porosity resulted by tidal delta sedimen-tation. Lithofacies 2 is characterized by fineto medium grained, moderately to well sortedquartzarenite to subarkose/ sublitharenite. Al-though the magnitude of lithofacies 2 is lowerthan Facies 1, but it still retains good reser-voir properties. Lithofacies 3 is predominantlymedium-grained, moderately to well sorted,clean quartzarenite. It is below the gas watercontact and characterized by diagenetic calcitecement dominant.

3 RESEARCH METHODS

To run the reservoir characterization using IPsoftware, well data including wireline log andcore are used as input data. Qualitative analy-sis to interpret lithofacies and depositional en-vironment as well as quantitative analysis topetropysics calculation have been done in thisstudy. Before all analyses were carried out, thefirst step is to do well quality control data. Ashorizons marker for interval are given in eachwell, stratigraphic correlations among wells aresequentially carried out to determine reservoirzone intervals and to ensure that they are ap-propriate for further analysis. The next step isdetermining the facies and depositional envi-ronment of each stratigraphic sequence in eachwell with lithology data (core) and wireline logsdata using electrofacies method then followedby quantitative analysis.

The quantitative analysis is done by petro-physical analysis of well log data and vali-dating by routine core analysis data (RCAL).Petrophysical analysis is conducted to obtainrock properties such as clay volume, poros-ity and water saturation (Tiab and Donaldson,1996). Rock typing (RT) carried out to clas-

Journal of Applied Geology 45

SURJONO & ARIFIANTO

Figure 3: Reservoir correlation between Abadi-1, 2ST and 3. (Modified after Nagura et al., 2003).



sify the rock type of routine core analysis data(RCAL), followed by distributing rock type us-ing neural network for rock intervals that donot supported by core data. Result of those an-alyzes will be used to identify the character ofthe reservoir. Rock type form whole well logis predicted by neural network method. Thismethod has been proven to successfully appliedas a predictive tool lithofasies by Bohling andDubois (2003).

In this study, reservoir rock typing in the “A”Field is carried out by “Windland R35” meth-ods by Windland (1972) Equation 1 and usingHydraulic Flow Unit (HFU) by Amaefule et al.(1993) Equations 2-4. The concept of these twomethods is to identify and characterize rocktypes based on geological conditions and phys-ical parameters of the pore size (Radiansyah,2014).

log R35 = 0.732 + 0.588 log k−0.864 log φ

(1)

RQI = 0.0314 ×√

kφe

(2)

φz =

(φe

1 − φe

)(3)

FZI =RQIφz

(4)

4 RESULTS AND DISCUSSION

Facies and depositional environmentCore description (Figure 4) provides typicalsedimentary succession of Upper Plover For-mation for Zone-2. It consists of sandstoneand claystone lithofacies with coarsening up-ward succession. In the lower part, biotur-bated sandstone-claystone (SC-b), laminatedsandstone-claystone (SC-l) and laminated clay-stone (C-l) vertically develop with total thick-ness around 4.5 m. to the upper part, lithofacieschanges to sandstone dominant including bio-turbated sandstone (Sb), and interbedding oflaminated sandstone (S-l1) and massive sand-stone (S-m) to form thickly bedded successionup to around 10 m. In the Well A-2 lithofacies S-l1 and S-b identified in more cemented becomelithofaceis cemented laminated sandstone (Sl-c)and cemented bioturbated sandstone (Sb-c).

Table 1: Facies association of progradationshoreline depositional environment

Lithofacies assemblage with associated insedimentary attributes lead to depositional en-vironment interpretation (Miall, 1990) is termedas facies association. In the study area, six fa-cies association interpreted based on the coredescription and interpretation, which then cor-relate to well logs analysis. Facies associationrepresents depositional environment and com-posing lithofacies served in Tabel 1, which are:(1) foreshore (FS), (2) upper shoreface (USF),(3) lower shoreface (LSF), (4) offshore transi-tion (OT), (5) marine embayment (ME) and (6)offshore (OS). General succession for UpperPlover is coarsening upward, where depo-sitional environment relatively change frommarine to transitional zone of shoreface or evenestuarine (Figure 2–4.

StratigraphyStratigraphic correlation in this study is basedon the concept of sequence stratigraphy. Somemarkers were obtained from biostratigraphicanalysis in the well report, where 5 markers aredefined from fossil analysis of core and side-wall cores. The name of the marker is takenfrom the dinoflagellates fossil (Helby and Par-tridge, 2001). Marker interpretation for strati-graphic correlation for Plover Formation in thestudy area and their age are described as fol-low: (1) Dissiliodinium caddaense marker asflooding surface 1 (fs-1) at Middle Jurassic; (2)Wanaea verrucosa marker as flooding surfaces(fs-3 and fs-4) at Middle Jurassic; (3) WanaeaIndotata marker as flooding surface 5 (fs-5) atLate Jurassic; (4) Rigaudella Aemula marker asflooding surfaces (fs-6 and fs-7) at Late Jurassicand (5) E. Torynum marker at the end of UpperPlover as unconformity boundary at Late Juras-sic age (Figure 5).

Six parasequence is defined from flooding


SURJONO & ARIFIANTO

Figure 4: Core #1 description and interpretation of A-1 well.



Figure 5: Sequence stratigraphy correlation from well logs in study area.

surface boundary (Van Wagoner et al., 1988)indicates vertically regressive with thinnerparasequence. Laterally, to the northward, de-positional environment tends to deeper due toincreasing sand-shale ratio (Figure 2).

Rock type identificationTwo methods have been applied to identifyrock types (RT) that are Windland R-35 (Wind-land, 1972) and Hydraulic Flow Unit (Amae-fule et al., 2003), in order to get the best re-sult. RT identification by Windland R-35 is car-ried out by plotting all value of porosity ver-sus permeability from RCAL to define iso porethroat curve. In this study, four different isopore throat curve was identified, which are 0.1micron, 2 micron, 15 micron and 40 micron (Fig-ure 6a left side). Iso pore throat curve representone rock type (RT) that consist of certain faciesassociation, therefore four RT are also definedfrom this methods.

Hydraulic Flow Unit (HFU) methods forgrouping characters rock types has a similarway to the “Windland R-35” methods. RT byHFU method is identified by value of FlowZone Indicator (FZI) or cross plot ReservoirQuality Index value (RQI) versus Matrix Pore

Ratio (PMR) or φz (Figure 6b). From FZI cal-culation and crossplot log RQI versus φz, theUpper Plover Formation is can be divided intofour HFU.

Final RT identification is taken from thehighest number of coefficient correlation (R) oftransform permeability. Four RT is identifiedfrom this final result (Figure 6a, right side).

Reservoir characterizationThe reservoir quality classification refers to theclassification of reservoir established by Slattand Hopkins, 1991 (in Slatt, 2006). Parame-ter used to distinguish reservoir classification ispermeability, porosity, matrix grain size, porethroat, minimum water saturation and litho-fasies (Table 2. Based on those parameter, Up-per Plover Formation can be divided into fourclasses of reservoir, that are:

A Class dominantly consists of the FS andUSF facies association, has the most ex-cellent quality reservoir porosity that is6.5–19 % with permeability ranging from100–1300 mD.

B Class dominantly consists of USF, FS andLSF facies association, have good quality


SURJONO & ARIFIANTO

Figure 6: Rock Typing by Windland R-35 methods (b) Rock Typing by Hydrolic Flow Unit (HFU)methods. To get the best result, transform permeability has been utilized.



Table 2: Upper Plover Formation reservoir classification.

reservoir with porosity of 7–17 % and per-meability of 10 to 200 mD.

C Class dominantly consists of LSF dominantfacies association, ME and OT facies asso-ciation, have poor reservoir quality witha porosity of 1-13 % and permeability ofabout 0.1–2 mD.

D Class consists of LSF, USF and OT facies as-sociation, with experiencing diagenetic ce-mentation, porosity 1–14 % with perme-ability 0.001–0.08 mD. This class is consid-ered not a reservoir type due to unable toflow the reservoir fluid.

5 CONCLUSIONS

The Upper Plover Formation in the study areaconsist of alternating sandstones and shales toform coarsening upward sedimentary succes-sion deposited mainly within marine to coastalenvironment of foreshore – offshore. The suc-cession can be divided into 7 parasequences,ranges from Middle to Late Jurassic age.

The reservoir of Upper Plover Formation candivided into four classes: A class has excellentquality, B class with good quality, C class withpoor quality and D class with very poor quality.

ACKNOWLEDGEMENTS

Authors would like to express the deepestthanks to Directorate General Oil and Gas ofRepublic Indonesia for permission in using subsurface data within the study area. Thanks alsoto member of G and G Study team for fruitfuldiscussion during preparing the manuscript.

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