regional depositional model of south makassar basin...

J. SE Asian Appl. Geol., Jan–Jun 2012, Vol. 4(1), pp. 42–52

REGIONAL DEPOSITIONAL MODEL OF SOUTHMAKASSAR BASIN DEPOCENTER, MAKASSARSTRAIT, BASED ON SEISMIC FACIES

Rahmadi Hidayat∗, Salahuddin Husein, and Sugeng Sapto Surjono

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

Abstract

South Makassar Basin Depocenter (SMBD) islocated in Southern Makassar Strait which haspetroleum potential by the presence of oil and gasindications within the area based on Airborne LaserFluorescence survey. However, detail studies withinthis area are not developed well. One of the studieswhich can be utilized for further discoveries of oiland gas field in SMBD is a study of depositionalmodel using seismic facies method to maximizelimited seismic and well data. Interpretation ofdepositional model in Eocene (syn-rift phase) wasvaried from alluvial plain and alluvial fan complex,continued gradually to platform. In Oligocene time(post-rift phase), massive transgression caused amajor deepening in entire SMBD where the de-positional environment changed to basinal plain.In early Miocene – recent interval (syn-orogenicphase), SMBD was relatively in stable conditionat basinal plain environment. Lower Tanjung Se-quence will be the most prolific petroleum play inSMBD due to its adequate source rock, reservoirrock and seal rock as well.Keywords: South Makassar basin, depositionalmodel, seismic facies

1 Introduction

Several hydrocarbon occurrences within andsurrounding SMBD indicate potential discov-

∗Corresponding author: R. HIDAYAT, Department ofGeological Engineering, Faculty of Engineering, GadjahMada University, Jl. Grafika 2 Yogyakarta, 55281, Indone-sia. E-mail: h [email protected]

ery in the exploration point of view, suchas seepages of hydrocarbons in the offshoreMakassar Strait based Airborne Laser Fluo-rescence survey (MacGregor et al, 1991) andoil-gas seepages in onshore Sulawesi (Figure1). Other informations surrounding study areaalso give potential hydrocarbon occurrencessuch as Makassar Straits-1 gas discovery, pres-ence of oil in Pangkat-1X, existence of thermo-genic gas in the Rubi Field and non-commercialgas discovery in Sultan-1 (Pireno and Darus-salam, 2010). Hence, detailed studies of thisarea are required to be able to assist in findingnew oil or gas fields. One of them is the studyof depositional model based on seismic faciesstudy to optimize limited 2D seismic data andexploration wells.

2 Geology and Tectonic Settings

South Makassar Basin is bounded by the AdangFault Zone to the north and West Sulawesi FoldBelt (WSFB) to the east. Spermonde Platformlimits this area to the south while PaternosterPlatform becomes boundary to the west (Pirenoand Darussalam, 2010).

Generally, tectonostratigraphy of study areacan be associated with a typical basin in SouthSulawesi which is divided into pre-rift, syn-rift,post-rift and syn-orogenic phase (Garrard et al,1992). Syn-rift phase was related to extensionphase, marked by the opening of the Makas-sar Strait (Guntoro, 1999) on around 42 mil-lion years ago or in Middle Eocene (Coffieldet al, 1993). Middle – Late Eocene sediments

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REGIONAL DEPOSITIONAL MODEL OF SOUTH MAKASSAR BASIN DEPOCENTER

Figure 1: Location of Study area and distribu-tion of seepage indication of ALF survey byMacGregor et al (1991) and onshore seepages.

filled the basin, equivalent to Toraja/MalawaFormation in several basins in South Sulawesi(Coffield et al, 1993). In Sebuku Basin (Off-shore Kalimantan), this phase was representedby Lower Tanjung and Upper Tanjung For-mation (Figure 2), commonly silisiclastic sed-iments which tend to be terrestrial origin andtransitional environment in upper part (Pirenoand Darussalam, 2010).

Post-rift phase was considered as phase ofquiescence (Yulihanto, 2004), characterized bythe cessation of the opening of the MakassarStrait, thermal cooling and sagging in the EarlyOligocene or about 38 million years ago (Fraseret al, 1993). Post-rift sediments mainly consistof limestone with some sandstone, siltstone andmudstone in Oligocene – Early Miocene age. AtSengkang Sub-Basin and South Sulawesi, thissequence is represented by the Tonasa/MakaleFormation (Coffield et al, 1993; Yulihanto, 2004;Figure 2). Berai Formation of Sebuku Basin isequivalent to Tonasa Formation which consistsof coralline limestones on basement highs andon the edges of the basin (Pireno and Darus-salam, 2010; Figure 2).

Syn-orogenic phase was a development ofvolcano-plutonic complex that occurred in thewestern Sulawesi (Coffield et al, 1993) due to

collision stage in the beginning of time dur-ing Middle – Late Miocene between East Su-lawesi and the Banggai-Sula microcontinent. Itcaused compressional phase in the MakassarStrait that formed WSFB. Syn-orogenic intervalis divided into three, named Volcanic CambaFormation, Tacipi Formation and Walanae For-mation. Equivalences in the Sebuku Basin areLower Warukin, Upper Warukin and Dahor(Figure 2).

Based on well information, formation lithol-ogy as well as nomenclature in study area tendsto have certain similarity with the regionalstratigraphy of Sebuku Basin (Figure 2). Thusstratigraphy of Sebuku Basin will be used as ref-erence of formation nomenclature in this study.

3 Methods

This study used 68 2D seismic data as well asthree exploration wells (MAK-1, TT-1 and TT-2). Analysis of this study was carried out us-ing SMT Kingdom 8.6 software and modulesin Geological Engineering Department, Univer-sitas Gadjah Mada. Quality of seismic datawere checked and corrected such as navigation,mis-tie analysis and balance amplitude in SMTKingdom 8.6. Next stage was Well Seismic Ties(WST) which can be performed in all wells us-ing SynPAK. After finishing WST, each of faciesmarkers were picked and extracted based onseismic facies method, such as reflection charac-teristics, internal reflection configurations, ter-mination reflections, external shapes and geo-logical structure analysis. In the last stage, de-positional models were built on each sequenceand then modeled to representative seismiccross-sections and maps using 2d/3dPAK andEarthPAK.

4 Depositional Model

Based on the seismic facies analysis, it con-cludes that there are several sequences in theSMBD which can be differentiated. These se-quences are Lower Tanjung, Upper Tanjung,Berai, Lower Warukin and Upper Warukin.Characteristics of each sequence can be seen inFigure 3.

c© 2012 Department of Geological Engineering, Gadjah Mada University 43

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Figure 2: Stratigraphy column of South Makassar Basin Depocenter (red box) and surrounding area.

4.1 Lower Tanjung Sequence

In the pre-Middle Eocene, southern Kaliman-tan to Sulawesi western part was connected toeach other. The process of rifting occurred dur-ing the Makassar Strait Middle Eocene, as de-position of Lower Tanjung, caused variationsof non-marine and marine environment start-ing from fluvial, delta, shallow marine carbon-ate clastic to a deeper marine environment (Wil-son and Moss, 1999).

Lower Tanjung shows typical of rifting sedi-ments, which form terrestrial environment withtwo main facies, which are facies TB-B as allu-vial plain complex (fluvial floodplains and me-andering channels) on the hinge side of grabenand facies TB-A as alluvial fan complex on theside of the graben fault (Figure 4).

Lacustrine deposits and coal layers are alsoexpected to exist in the study area based on theindication of both at the bottom of the GrabenMakassar (Pireno and Darussalam, 2010) adja-cent to the MAK-1 wells. Rift succession contin-ued to have transgression phase and depositionof vertical facies change towards transitional-transgressive shelf.

The pattern of alluvial fan is dependent onthe relative position of major graben faultswhich have fairly complex direction. This phe-

nomena is caused by existence of two main riftstructures which are NE-SW of Taka Talu FaultZone and NNW-SSE of Adang Fault Zone.

4.2 Upper Tanjung Sequence

Massive transgression in the end of rift phase(Late Eocene), probably caused by sudden sub-sidence, is responsible in changing the environ-ment into marine as a deposition of Upper Tan-jung. At this time, the influx of clastic materialwas reduced as well (Pireno and Darussalam,2010).

The study area was dominated by facies TA-A as platform carbonates area (Figure 5). TT-1 and TT-2 bathymetry information in LowerTanjung indicate neritic zone with calcareousshale and limestone intercalation which reflectthe platform area.

Distribution of the platform facies (facies TA-A) as well as its limit were significantly influ-enced by rift structure, especially to the west,northwest and south of the SMBD. This evi-dence suggests that the rifting structure werestill active at Upper Tanjung deposition.

4.3 Berai Sequence

In Oligocene time, rifting of Makassar Strait hasstopped (Fraser et al, 1993) and has transformed

44 c© 2012 Department of Geological Engineering, Gadjah Mada University


Figure 3: Composite cross-section of facies seismic (upper figure) and depositional model (lowerfigure).


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Figure 4: Depositional model of Lower Tanjung Sequence.



Figure 5: Depositional model of Upper Tanjung Sequence.


HIDAYAT et al

into a quiet phase (Yulihanto, 2004). Thiscondition changed entire tectonostratigraphicphase of South Makassar Basin into the post-riftphase.

Transgressive phase caused deepening ofthis sequence, especially in SMBD. Deposi-tional model of Berai Sequence (Figure 6) showslateral changes (from NW to SE) in the environ-ment from platform (facies B-A) and reef (faciesB-B) to the slope (facies B-C), and basinal plain(facies B-D). Basinal plain mostly covers entireSMBD.

Intepretation of platform carbonates area isconfirmed by the biostratigraphic record of TT-2 and MAK-1 which shows the development oflimestone reef complex in neritic zone. TT-1 in-dicates limestone conglomerates of submarineslope area (sub-neritic).

4.4 Lower Warukin Sequence

Early Miocene was the beginning of syn-orogenic phase of volcano-plutonic complexoccurrence in the western Sulawesi (Coffieldet al, 1993). At this phase, Kalimantan also ex-perienced early series of deltaic progradation(Moss and Chambers, 1999). In this interval,Lower Warukin were deposited in study area.

Depositional model of Lower Warukin Se-quence at the age of Early - Middle Miocenewas relatively similar to Berai Sequence, show-ing gradual facies changes from platform (faciesWB-A) to the slope (facies WB-B) and basinalplain (facies WB-C) towards southeast (Figure7). Basinal plain covers mostly the entire SMBDat this level.

Relative position of each facies are slightlyprograde towards study area. This indicatesthat delta progradation of Kalimantan and therelative sea level drop affects the increasingsupply of sediment to the basin. The presenceof facies WB-D at the end of the Lower WarukinSequence is interpreted as debris flow whichis derived from Kalimantan (northwestern ofstudy area) as a consequence of increasing sed-iment supply to the basinal area.

All well informations show that LowerWarukin Sequence consists of shale with lime-stone intercalation on neritic to sub-neritic

bathymetry. This evidence is suitable to inter-pretation of platform area in those wells.

4.5 Upper Warukin Sequence

Late Miocene Upper Warukin Sequence wasstill part of the syn-orogenic phase (volcanismof West Sulawesi) and Kalimantan. Thus, de-positional model was not significantly changedcompare to Lower Warukin Sequence.

Upper Warukin Sequence indicates lateral fa-cies changes from platform (facies WA-A) tothe slope (facies WA-B) and basinal plain (fa-cies WA-C) within SMBD or study area (Figure8). This sequence exhibits slight progradationcompared to the Lower Warukin. Three wellsalso indicate neritic to sub-neritic bathymetrywhich is correlable to the interpretation of plat-form in northwest of the study area.

5 Significance in Petroleum Exploration

Pireno and Darussalam (2010) informed thatthe Lower Tanjung is a proven source rock inMAK-1 well, consists of lacustrine shale andfluvio-deltaic shale. Indication of Lower Tan-jung source rock in the SMBD can also be iden-tified by the intepretation of alluvial plain com-plex environment. Development of alluvialplain complex in ”sub-basins” within SMBD as-sociated with rift structure is potential to formfluvial and lacustrine shale as prolific sourcerock.

Potential reservoir in SMBD is expected fromLower Tanjung Sequence as the meanderingfluvial in the alluvial plain complex. This fa-cies generally have strong amplitude, mostly lo-cal, possibly in form of isolated fluvial channelsandstones. Pireno & Darussalam (2010) alsostated that the sandstones in the Lower Tan-jung Sequence is potential reservoir and provenin the Barito Basin. Existence of Berai reeflimestone reservoir in Paternoster (including inMAK-1) was not found within SMBD. SMBD istruly a deepest area of basin so that reef cannothave optimum growth in certain areas. Mas-sive trangression at that time also decreased thepossibilities of reef growth. Alternative reser-voir inside of SMBD are basin floor fans inthe Lower and Upper Warukin Sequence which



Figure 6: Depositional model of Berai Sequence.


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Figure 7: Depositional model of Lower Warukin Sequence.



Figure 8: Depositional model of Upper Warukin Sequence.


HIDAYAT et al

generally exhibit mounded seismic with a highamplitude character.

Seal rocks are numerous and scattered in al-most all sequences in the SMBD. Floodplainfacies with low amplitude character on theLower Tanjung Sequence can be very good forlateral seal to fluvial channel reservoir. Re-gional seal rocks can also be provided by basi-nal plain sediments of Berai, Lower and UpperWarukin Sequence which contain thick deepwater hemipelagic shale. This typical shaleshows seismic parallel configuration with lowamplitude character.

6 Conclusion

First phase was the syn-rift that occurred in theEocene with deposition of Lower and UpperTanjung Sequence. The depositional model atthat time was highly variable, in form of allu-vial plain and alluvial fan complex, graduallychanged into platform environment. The sec-ond phase was occurred in Oligocene time asa post-rift phase. This phase was the deposi-tion of Berai Sequence. Rapid transgression oc-curred in this interval, forming a basinal plainenvironment in SMBD. In the Early Miocenetime – recent, there was a regional syn-orogenicphase. However, SMBD was relatively stableand not affected so that the conditions remainin basinal plain environment.

Alluvial plain complex of Lower TanjungSequence is the most prolific petroleum playwithin SMBD. This sequence is expected tohave adequate lacustrine and fluvio-deltaicsource rock, fluvial channel reservoir rock andfloodbasin shale as lateral and vertical sealrock. Additional play can be derived frombasin floor fan reservoirs in Lower and UpperWarukin Sequence.

Acknowledgements

The authors are very grateful to Ditjen MIGASand LKFT UGM for allowing to use seismic andwell data as a Joint Study Research. Authorswould also wish to thank to IHS Kingdom forSMT Kingdom 8.6 software donation for Uni-versitas Gadjah Mada.

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