The Tarakan Basin, East Kalimantan Proven Neogene Fluvio-Deltaic,

8/10/2019 The Tarakan Basin, East Kalimantan Proven Neogene Fluvio-Deltaic,

http://slidepdf.com/reader/full/the-tarakan-basin-east-kalimantan-proven-neogene-fluvio-deltaic 1/14

IPA03-G-136

PROCEEDINGS, INDONESIAN PETROLEUM ASSOCIATIONTwenty-Ninth Annual Convention & Exhibition, October 2003

THE TARAKAN BASIN, EAST KALIMANTAN: PROVEN NEOGENE FLUVIO-DELTAIC,PROSPECTIVE DEEP-WATER AND PALEOGENE PLAYS IN

A REGIONAL STRATIGRAPHIC CONTEXT

Stephen Noon*

John Harrington*

Herman Darman**

ABSTRACT

The geological history and petroleum geochemistry ofthe four Tarakan sub-basins (Tidung, Tarakan, Berau

and Muaras) are reviewed and presented in thecontext of a revised stratigraphic framework, whichdraws on recent advances in biostratigraphy,chronostratigraphy and paleoclimatology. Neogenesource rocks comprise mostly coals and organic-richshales assigned to a 'fluvio-deltaic, paralic'depositional system. Reservoired oils in shelf settingsconfirm this interpretation and point to a matureMiocene 'source facies' and to likely deep-water

prospectivity. Another prospective 'source play' isidentified, with evidence put forward forhydrocarbons being derived from Eocene or older

aquatic organic matter. This is consistent with biostratigraphic and seismic data, which suggest thedevelopment of Paleogene (and possibly older)lacustrine, brackish and marine, syn-rift sediments.An increasing body of evidence from Tarakan, andelsewhere in East Kalimantan and the MakassarStraits area, lends support to the premise that potentialhydrocarbon-source sediments extend offshore intodeep-water settings.

INTRODUCTION

The geological history of well sections drilled in theTarakan Basin has up to now been poorly understood,in part due to the diachronous nature of many of theformations encountered. Seismic correlations areoften hampered by the lack of age control acrossfaults. Without a coherent chronostratigraphicframework for the area it has not, in the past, been

possible to effectively date tectonic activity or

* P.T. Corelab Indonesia** Brunei Shell Petroleum Co. Sdn. Bhd

hydrocarbon migration. Also, the geochemicaldatabase could not be appreciated in its correctgeological context. We have tried to resolve these

problems by attempting to erect a broad sequence-

based chronostratigraphic model for the area utilizinga holistic approach, combining biostratigraphic re-interpretations and new analyses of a number of keywells, with limited re-analysis of regional seismiclines.

Basin Definition

In this paper we refer to the ‘Tarakan Basin’ as thecollection of four major depocenters of Paleogene and

Neogene age situated in northeast Kalimantan. Themain depocenters within this basin are the Tidung,

Berau, Tarakan and Muaras (sometimes known asMuara) sub-basins (e.g. Achmad and Samuel, 1984).

METHODOLOGY

Stratigraphy

It is recognized that major sequence boundaries, aswell as tectonically enhanced angular unconformities,can be identified in the Tarakan Basin (e.g. Lefort etal., 2000). In our study major sequence boundarieswere selected on the basis of regional significance.

Surfaces representing sequence boundaries weredefined, where possible, by their erosionalcharacteristics and seismic reflection terminations(such as onlap, offlap, downlap and toplap) and by

paleoenvironmental, biostratigraphic and palynofaciescharacteristics. It was not intended to carry out a full-

basin seismic stratigraphic study, but interpretation ofkey lines and integration with paleoenvironmentaland biostratigraphic data from key wells does givesufficient coverage to enable a sequence stratigraphic



framework to be constructed for the area. Theresultant sequences are numbered consecutively fromthe surface downwards, because analysis initiallyconcentrated on the shallowest events, using thefollowing procedures:

a. The available biostratigraphic database of keywells was interpreted, or re-interpreted for ageand paleoenvironments.

b. Using the paleoenvironmental signals, palynofacies events and available age-diagnosticmicrofossils, candidate sequence boundaries wereidentified and correlated between wells.

c. While these candidate sequence boundaries were being picked in the well sections, seismic analysis

was concurrently identifying sequence boundariesand seismic facies by their erosional nature and

by reflection terminations.

d. The candidate paleoenvironmental sequence boundaries and seismic picks were tested againsteach other in an ongoing parallel process.

e. Sequence boundaries between individualsequences were recognized; these are dated byreference to the latest calibrations of Wornardt(1999).

f. By correlation, even well sections with few agediagnostic mic rofossils could now be consideredin a chronostratigraphic context.

g. An improved geological history (Figure 1),including relative sea-level fluctuations, couldtherefore be put forward for the area.

Geochemistry

The geochemistry component of this paper comprisesan overview of a comprehensive, pre-existingdatabase of geochemical data from several studies.Source rocks were evaluated by TOC content andRock-Eval pyrolysis, supplemented by visual kerogenobservations, including vitrinite reflectance (Vr), and

pyrolysis-gas chromatography analysis. Crude oilswere characterized by bulk properties, GC/GC-MSdata and stable carbon isotope results. Computerized

burial history modeling was also conducted.

TERTIARY BASIN DEVELOPMENT

The Eocene to Early Miocene section is displayedclearly by the regional seismic sections (Figure 2) andon the evidence available we suggest the followingscenario:

(i) Sub-sequences VII and VIB were deposited in asyn-rift setting during the Middle to LateEocene (with rift inception possibly as early asCretaceous).

(ii) The regional plate re-organization, that led toocean-floor spreading in the South China Seaand subduction in northwest Borneo, causedmajor reactivation towards the end of LateEocene times, and possibly some inversion offaulted structures; this is also consistent with

the global Late Eocene/Early Oligocenecompressional pulse of Davidson (1995).

(iii) Topographic highs formed where sub-sequences VIB, VII and Basement was upliftedin response to the plate re-organization episode.

(iv) Uplift was followed by erosion, possiblyassociated with the major eustatic event at theend of the Late Eocene (SB 33.30), and the‘peneplanation’ of much of the area.

(v)

Following a marine transgression during thelatter part of the Early Oligocene, platformcarbonates of sub-sequence VIA were depositedunconformably on the peneplain surface.

(vi) The uplifted horst blocks continued to berelatively stable highs as Late Oligocene andEarly Miocene sedimentation continued undertransgressive conditions; the intra-horst areassagged and reefs developed on the positiverelief of the paleo-horsts.

STRATIGRAPHIC FRAMEWORK

Basement

There is no definite evidence that basement was penetrated in any of the study wells. In the past, theDark Blue or Purple seismic events (Figure 2) wereoften considered to be economic basement due in partto poor seismic resolution and the often angularnature of the contact below the Purple Horizon.



Possible deep structures and faulting were, however,recognized on several seismic lines and indeedregional evidence now indicates that the Tarakan rift

basins may have originated as early as the ‘mid’Cretaceous (Andreason et al., 2000).

Sequence VII (Middle Eocene)

On seismic sections this sequence is poorly imaged,although faulting is clear (Figure 2). Sequence VII is

probably time equivalent to the SembakungFormation onshore, which at outcrop consists ofsandstones, shales, siltstones, foraminifera-richlimestones and tuffs deposited under coastal to deepmarine conditions (Hidayat et al., 1995; Situmorangand Burhan, 1995). Fluvio-deltaic sandstones in thissequence are considered reservoir targets in a regional

sense. Coals are reported in what are likely to be timeequivalent lithologies on the Mangkalihat Peninsula(Core Laboratories, in-house data). There is alsotentative well evidence for lagoons, or restrictedmarine conditions, and rift-controlled lakes could

potentially be present in the more continental settings.Regionally, these syn-rift settings all potentiallycontain hydrocarbon source rocks (Andreason et al.,2000). Volcaniclastic sediments are widespread.

Sub-Sequence VIB (Late Eocene)

The Olive Green Horizon (39.07 Ma) is a markedunconformity where it is recognized on high standinghorsts. Rifting and volcaniclastic sedimentationcontinues into this sequence, which in available wellsections consists predominantly of shales andlimestones deposited in inner neritic to outerneritic/bathyal settings. Foraminiferal carbonate

banks are potential reservoir rocks. Late Eocene strataare not restricted to the Muaras sub-basin wells; atleast one proximal well in the Tarakan sub-basin also

penetrates this sequence. Late Eocene sediments are

also likely to be present in the more distal part of theTarakan sub-basin, to the east (Hemmes et al, 2001,

Nichols et al., 1998). This sequence is probably in part time equivalent to the Sujau Formation, whichonshore consists of shales, sandstones and coalsdeposited in coastal to shallow marine settings.Reduced significance of volcaniclastic sediments,compared with the underlying Sequence VII,

probably indicates that rifting intensity is reduced bysub-sequence VIB time.

Sub-Sequence VIA (Early Oligocene)

Sub-sequence VIA overlies the Purple Horizonmarker (dated 33.30 Ma) where seismic data showevidence for a distinct angular unconformity, withtilted fault blocks below. Well evidence suggests that

the Purple Horizon event is coincident with the basalOligocene global low sea-level event at 33.30 Ma.Deposition of limestones and shales in this sequencemay have been controlled in part by post-rift sag anderosion surfaces that were left following the period ofuplift. Reefal limestones formed on slight positiverelief (seen as mounds on seismic surrounded bydebris slopes), and these are potential reservoir rocks.This sequence is probably time equivalent to theclastic Mangkabua Formation and carbonate SeilorFormation onshore (van de Weerd and Armin, 1992)and has been penetrated by well sections in the

Muaras sub-basin, Berau sub-basin and the Tarakansub-basin.

Sub-Sequence VB (Early to Late Oligocene)

The base of sub-sequence VB is a regionalunconformity that apparently coincides with globalsequence boundary 29.40 Ma. This is a mostlytransgressive sequence, which onlaps on to the basinedges and emerging reefs. These limestone reefs are

potential reservoir rocks, especially where low-standevents may have resulted in local karstification. Sea

levels rose rapidly in the Late Oligocene withconcomitant warming climates (e.g. Zachos et al.,2001), but this sequence apparently also represents anearly phase of subsiding basin fill. Reefs continuedforming on paleo horst blocks as accretion kept pacewith sea-level rise. While limestones in this sequenceare probably time equivalent to the lower part of thediachronous Taballar Formation, the calcareousshales are considered equivalent to the BirangFormation in the south and Naintupo Formation in thenorth.

Sub-Sequence VA (Early Miocene)

The sequence boundary at the base of this section isthe marine low-stand event of global significance atthe Oligocene/Miocene boundary (23.80 Ma), which

punctuates what is otherwise a long-termtransgressive interval. Sag basin-fill deposits, withincrementally rising sea levels, characterize this sub-sequence. Onlap is evident at basin margins.Lithologies consist of shales, calcareous shales,



limestones and occasional volcaniclastics. Noorganic-rich facies were encountered in the wellsavailable. As in the underlying section, the clasticsare probably equivalent to the Birang Formation ofthe Berau and Muaras sub-basins and the NaintupoFormation of the Tarakan sub-basin. The carbonate

reefs are equivalent to the diachronous TaballarLimestone, which this study reveals to have beenalmost continuously accreted during the trangressiveinterval from the Late Oligocene to Middle Miocene.The Taballar Limestone reefs formed during the later(and more quiescent) sag phase of the extensionalregime. There are numerous equivalents to theTaballar Formation throughout Indonesia, many ofwhich produce hydrocarbons, and it is a potentialreservoir rock in the Tarakan Basin.

Sequence IV (Early to Middle Miocene)

The Dark Brown Horizon (dated 17.30 Ma), at the base of this sequence, is a regional event which mayhave been in part associated with plate re-organization, the cessation of ocean-floor spreadingand the collision of the Palawan Terrane with Borneo;although final closure of the proto-South China Sea isdated by Hall (2002) at circa 15 Ma. According towell data within this sequence there is a ‘pivotal

point’ in basin evolution where a shift fromdominantly transgressive to dominantly regressiveenvironments of deposition also appears to represent a

change from an extensional to a compressive tectonicregime. Some eustatic control is also likely becausethis ‘pivotal point’ coincides with the global sea levelmaximum of around 14 to 15 Ma. The net result is anincremental lowering of relative sea levels from theMiddle Miocene to the Late Pliocene (Figure 1), andeventual uplift and erosion of the onshore Tidung andBerau sub-basins as deposition shifted to the east. Inwell sections, Sequence IV generally consists ofshales, sandstones, limestones and rare coals. Delta

progradation is present in the Tarakan, Tidung andBerau sub-basins, with local reservoir potential,

which extends also to deep-water low-stand settings.These Sequence IV lithologies are probably timeequivalent to the Latih Formation of theMuaras/Berau sub-basins and the Meliat Formation ofthe Tarakan sub-basin. The onset of major

progradation enabled coal formation in deltas in theTidung, Tarakan and Berau sub-basins and a slightincrease in organic input into the Muaras sub-basin.Seismic facies in the Muaras sub-basin exhibitvariable thickness indicating local differences in basin

subsidence or sediment supply; unfortunately in theTarakan sub-basin this sequence is poorly imaged dueto the thickness of overlying sediments.

Sequence III (Late Miocene)

The base of this sequence is a marked regionalerosional event: the Orange Horizon sequence

boundary (dated 11.30 Ma). Lithologies includeclaystones, sandstones, limestones and minor coals.Coals are only present in the Tarakan sub-basin andare often likely to be allochthonous. Sequence III is

probably time-equivalent, at least in part, to theDomaring and Santul Formations. Distinct episodesof lower relative sea levels in this sequence led toerosion of Sequence IV (Middle Miocene) and/orolder sediments from the Berau and Tidung sub-

basins and redeposition in deep-water to the east.

Extensive turbidites were deposited at this time asunconfined, toe-of-slope fans ahead of the outbuildingTarakan deltas (Darman, 2001) and these areimportant potential deep-water plays. This erosion isalso evident from the reworking of microfossils insome well sections. According to Daly et al. (1991)the main collision of the Australasian Plate with theBanda Arc occurred within the Late Miocene at circa 8 Ma and this may have been in part responsible forcompression causing uplift and erosion ofTidung/Berau sediments. Regional palynologicalevidence, however, suggests that the collision was an

ongoing process dating back to at least 21 Ma(Morley, 1999) and this is consistent with Hall(2002). There is a tectonic event of varying intensitydated in the region by biostratigraphy at around 7 Ma(e.g. Lunt et al., 1996), which may be due to a pulsein this ongoing collision. At about this time (7-8 Ma)there is also a global vegetation change, possiblylinked to a lowering of atmospheric carbon dioxidelevels (Ocean Drilling Program, unpublished data).

Sub-Sequence IIC (Early Pliocene)

The base of this sequence is the Blue Horizonsequence boundary (5.70 Ma), which is a distinctregional unconformity that is likely to have resultedin the deposition of extensive, prospective, lowstandfacies in deep-water to the east of the Tarakan sub-

basin. This is a markedly transgressive, but relativelythin sequence, of claystones, sandstones, limestonesand coals. Limestones are most significant in theMuaras sub-basin, but reefs also formed in theTarakan sub-basin. Coals are only present in the



Tarakan depocenter, where they may beallochthonous. In lithostratigraphic terms thissequence is probably equivalent to part of the SadjauFormation in the Muaras sub-basin and the TarakanFormation in the Tarakan sub-basin. Seismic and wellevidence indicate major uplift and volcanic activity at

the Maratua basement ridge and onshore duringdeposition of this sequence, although there are alsodistinct periods of regional subsidence. According toour interpretations the uplifted area trends north-westto south-east. The Vanda reef formed during this timeand may also be a response to local tectonics(Netherwood and Wight, 1992). Seismic evidence inthe northwestern part of the Tarakan sub-basinindicates that this phase of uplift may have continueduntil the Brown Horizon (0.96 Ma). These Plio-Pleistocene sediments extend into deep-water whereintra-slope channels and channel levee complexes are

potential plays (Darman, 2001).

Sub-Sequence IIB (Early to Late Pliocene)

The base of this distinctly regressive sequence isdefined by the Dark Green Horizon sequence

boundary (3.95 Ma). Lithologies are similar toSequence IIC in the Tarakan sub-basin. In both theMuaras and Tarakan depocenters, however,limestones are much less significant than in SequenceIIC. Uplift continued onshore and on the MaratuaHigh.

Sub-Sequence IIA (Late Pliocene)

The 3.21 Ma event at the base of this sequence cannot be carried around the basin on seismic, and so is notcolor-coded, but it is identified in most wells on

paleoenvironmental evidence. The sequencecomprises a distinct lowstand facies ofclaystones/shales, sandstones and coals, probablyassignable to part of the Sadjau and TarakanFormations. Some wells yield palynological evidenceinferring input from fluvio-lacustrine settings. The

presence of lacustrine algae and coals probably reflectthe erosion and reworking of high-stand deposits intothese dominantly low-stand sediments.

Sub-Sequence ID (Late Pliocene)

Sequence ID rests on the Light Green Horizon (2.56Ma) sequence boundary. In the Tarakan depocenterthis sequence represents the onset of higher sea levelsor transgressive conditions following the dominantly

regressive Sequences IIC to IIA. This sequenceattains greatest thickness in the southeast of theTarakan sub-basin, on the downthrown side of theeast-dipping Mayne Fault and over the Bunyu Arch(implying later uplift).

Sub-Sequence IC (Late Pliocene to Pleistocene)

The base of this interval is the Beige Horizonsequence boundary (2.09 Ma). This sequence is

probably time equivalent to the lowermost part of theWaru Formation in the Muaras sub-basin and theBunyu Formation in the Tarakan sub-basin. Tectoniceffects may have been severe because complicatederosional events and missing sections are evident onseismic data between the Beige and Brown markers ina number of wells.

Sub-Sequence IB (Pleistocene)

The base of this interval is defined by the BrownHorizon high-stand (0.96 Ma), which, when pickedon paleoenvironmental characteristics, is a distinctflooding event. Seismic, however, sometimes shows aclear erosional event. This sequence apparentlyonlaps the Brown Marker in the Tarakan sub-basin,(see seismic profile A-A' in Figure 2). In the Muarassub-basin well sections, this sub-sequence isrelatively thin and cannot be clearly differentiatedwithin Sequence I as a whole. Following the abrupt

rise in sea-level at the base, this sequence is seen to be generally regressive with prograding deltaicsediments of sandstones, claystones and coalsdominating. In the Muaras sub-basin some wellsections show evidence for similar progradation anddeltaic lithologies, while others were subject toshallow marine carbonate accretion.

Sub-Sequence IA (Pleistocene)

The top of sub-sequence IB is marked by the PinkHorizon sequence boundary (tentatively dated at 0.5

Ma), which is defined by a marked increase in marineinfluence across the area. This is consistent withobservations made by Caratini and Tissot (1985) whorecognized a general increase in marine influencewithin the later part of the Pleistocene (certainly

before 0.3 Ma based on radiocarbon dating) in theMahakam delta area. This relative rise in sea-level isalso apparent in the Muaras sub-basin. According toseismic, this sub-sequence attains great thickness inthe depositional troughs of the Tarakan sub-basin, but



thins towards the arches and basin margins. It alsothickens on the downthrown side of a number ofeasterly dipping growth faults. On seismic data, thissub-sequence could be divided into many para-sequences, but biostratigraphic resolution is difficultdue to persistent reworking (including older

Pleistocene taxa) and the scarcity of short-rangingmarker taxa. The identification of climate trendsusing high-resolution palynology and palynofaciestechniques should resolve this issue. Apparently, latePleistocene uplift led to the formation (or re-activation?) of the north-west to south-east trendingarches (e.g. the Bunyu Arch and Tarakan Arch, whichwere described by Lentini and Darman, 1996) and

possibly concomitant uplift in the hinterland of EastKalimantan. This uplifted terrain was then rapidlyeroded and re-deposited in sub-sequence IA. The

presence of Pleistocene reworking within this

sequence, where nannofossil evidence suggestsreworking of material from sub-sequences IB and IC,is indicative of the late date of this renewed uplift.This is locally a very thick sequence.

GEOCHEMISTRY

Source Rock Potential

a. Tarakan and Tidung sub-basins

Sequences I and II (Pleistocene - Pliocene) coals and

shales are the most organic -rich sedimentary packages in the area, but are invariably immature foroil generation on structure (Figure 3); howevermaturity is achieved in the troughs. Sequence III(Late Miocene) has moderate to good source potentialin supra-littoral coals and shales and is also immature,except in the northern part of the Tarakan sub-basinwhere it is early mature; these Late Miocene coalsare, however, a potential source facies when reworkedinto deep-water turbidites which were extensive atthis time (Darman, 2001). Sequence IV (Early toMiddle Miocene) is of moderate organic richness and

displays hydrocarbon generating potential, chiefly inthe Tarakan sub-basin. On available evidence,Sequences V, VI and VII (Middle Eocene to EarlyMiocene) generally show poor source potential andare primarily gas-prone. Significantly greater source

potential exists in the Tarakan sub-basin compared tothe Berau and Muaras areas to the south, in particularin the Bulungan Delta where most gas/oil sourcematerial has been identified. This latter area onlyreaches early maturity at the base of Sequence III and,

where present, in Sequence IV. Narrowing iso-rankgradients and embayed iso-reflectance contourssuggest that advancing thermal maturity would beencountered deeper within the Tarakan sub-basin andin a more easterly direction. Hence data tend to high-grade the prospectivity of deep-water deposits.

Similar ‘prospectivity’ was recognized in theMahakam Delta, which was later supported by deep-water discoveries (Peters et al., 2000).

b. Berau and Muaras sub-basins

No highly prospective hydrocarbon source rock unitshave yet been encountered in wells drilled in theBerau and Muaras sub-basins. Drilled sections reachthe base of the oil window in Sequences VI and VIIand only minor hydrocarbon generation may haveoccurred. The existence of migrated oil stains plus

additional corroborative evidence of ‘live’hydrocarbons, however, highlight the occurrence ofmature, prospective source rocks (unpenetrated) in thesubsurface. This is consistent with the work ofCuriale et al. (2003) who discuss the possibility ofhypersaline and lacustrine source rocks in thePaleogene of this region.

c. Coals

In general, coal-occurrence diminishes withincreasing stratigraphic age throughout the Tarakan

Basin, therefore with advanced thermal maturity ofhydrocarbons, there is an obvious expectation ofincreased source contribution from argillaceoussediments and lesser input from coal. More extensivesampling and subsequent analysis of Eocene ‘coaly’facies (known to outcrop onshore in the MangkalihatPeninsula area), would be required to test the exact

potential of the Paleogene graben sequences. Thecoals analyzed to date are mainly humic in character,

but oil and gas-prone. No cannel or boghead coalswere analyzed. The individual oil-source contributionof the coals and interbedded carbonaceous/organic-

rich shales is difficult to predict, but the argillaceoussediments are not thought to be preferred over the‘coalier’ horizons.

Maturation and Burial History

Moderate thermal and Vr rank gradients are observedin the onshore areas of the Tarakan and Berau sub-

basins, while low geothermal gradients prevail in theoffshore Tarakan and Muaras sub-basins (Figure 4).



Some well sections show higher rank gradients in thePlio-Pleistocene intervals, which is probably due tohydrodynamism. Increasing Plio-Pleistocenesedimentation in the more offshore parts of thesouthern Tarakan sub-basin makes this area a possiblesource kitchen for gas/condensate generation. On the

evidence available for the Muaras sub-basin, lowthermal maturity in the Miocene and accompanying

poor source potential in older sections generally precludes substantial oil generation. No conclusiveevidence for adverse vitrinite reflectance suppressionhas been found. The overpressure zone is not thoughtto be an insurmountable barrier to maturation andsubsequent migration of oil and gas in the TarakanBasin. Burial history modeling generally indicates agood correlation between measured vitrinitereflectance data and mathematically generatedmaturity profiles. Within the Tarakan sub-basin

depths to effective oil generation lie between circa 3100 m and 4250 m in wells penetrated. Modelingindicates intense oil (and gas?) generation fromSequence IV units in the past 3 million years, whileSequence III has been oil-generative since 2 Mawithin the Kantil Trough. In the south Tarakandepocenter Sequence II has been mature for oilgeneration from 1.5 Ma up to the present-day. Depthto effective oil generation in the Tarakan sub-basindepocenters is at or below circa 5000 m.

Sequences I to IV, where drilled, are generally pre-oil

generative within the Muaras sub-basin. Modelingsuggests only Sequences V to VII have been oil-generative i.e. since Late Miocene for the wells, andover the period Late Oligocene through to the presentday for specific depocenters. Effective oil windowsoccur at or below circa 3000 m in the structurally lowareas within this sub-basin.

Migration

Oil-charge from organic-rich ‘Miocene’ sediments isessentially vertical for the produced light oils and

waxy crudes from the onshore Tarakan sub-basinareas, although certainly some lateral component isinvolved. Burial history suggests significantexpulsion since 5 Ma. Gas/condensates originate fromthe offshore areas where appreciable amounts of gasmay have been generated in the past 2 to 3 millionyears. High maturity hydrocarbons are probablymigrating vertically and westwards from the deeper,south Tarakan sub-basin depocenter. Lower maturityoils are migrating more vertically from west of this

area. Fractionation of liquid hydrocarbons may have been an active phenomenon.

Crude Oils and Gases

a. Tarakan and Tidung sub-basins

Multiple crude oil types are reservoired throughoutthe Miocene to Pleistocene section of the Tarakansub-basin, but all apparently belong to one geneticallyrelated family. This group of oils is classified as non-marine, waxy (in part), paraffinic, liquidhydrocarbons, which are the mature products of faciesdeposited in fairly oxic conditions (e.g. continentalswamps/brackish water settings or marine embay-ments, plus possibly minor ephemeral lake input).Most crudes are unaltered or only mildly altered.Source rock extracts from across the Tarakan sub-

basin indicate an organic facies high in vegetal waxesand resins which is equivalent to Type III, plussecondary Type II kerogen assemblages. Thesemacerals are identified as being the main precursorsfor many of the oils reservoired in the area; most arein the marginal to early mature stage within facies ofMiddle to Late Miocene age. A marine algaloverprint has not been established for any of thesereservoired liquid hydrocarbons in these sub-basins.

Reservoired natural gases have been encountered invarious wells throughout the Tarakan sub-basin, and

one large gas field exists on Bunyu Island (BunyuTapa). Limited data confirm a thermogenic origin forthese relatively sweet gases with low carbon dioxidelevels.

b. Berau and Muaras sub-basins

Non-commercial oil shows from the Muaras sub- basin exhibit a distinctly different geochemicalfingerprint compared to the crude oils and migratedoil stains from the productive Tarakan sub-basin to

the north (Figure 5). Gas chromatography patternsand biomarker fingerprints bear characteristic traits,which are diagnostic of a more aquatic/algal sourcefacies for the residual oils recognized. Advanced GC-MS data point to a marine component in the oil-extract from the Muaras sub-basin, which is perhaps

partly analogous to the recent regional indications ofaquatic sources in the Paleogene (Curiale, et al.,2002). The precursor source facies of the Muaras area‘migrant oils’ is believed, however, to be a mixture of



terrestrial and marine debris deposited in a near shoreor (restricted?) marine setting.

CONCLUSIONS

The re-interpreted stratigraphy has shown that

deposition of rift sediments in the Tarakan Basin waslikely to have been already underway by 43 Ma(Middle Eocene) and may have begun in theCretaceous. These graben sediments have reservoir

potential and may extend into the Celebes Sea. Themost pronounced rifting continued until a majortectonic event at, or close to, the Eocene/Oligocene

boundary. Basin sag and eustasy then controlleddepocenters until the Middle Miocene. An episodiccompressional regime, punctuated by eustatic events,characterizes the Middle Miocene to Recent. Thisresulted in sediments being eroded and reworked into

reservoir and potential reservoir systems in shelf anddeep-water depocenters of the Tarakan sub-basinwhere syn-depositional faulting was a factor. Thecarbonate-rich Muaras sub-basin depocenter has beenrelatively stable tectonically since the Late Oligocene,

but reservoir potential exists in carbonates.

Geochemical data and interpretations have benefitedfrom the context of improved stratigraphic resolution.Moderate to good oil/gas potential exists in post-EarlyMiocene sediments within the Tarakan sub-basin.Plio-Pleistocene coals/shales are generally immature

on-structure, but there are prospective source kitchensoffshore, including deep-water areas. Syn-rift,Paleogene source facies may be present at depth andcould extend across into the Celebes Sea. Crude oilsand extracts from the Tarakan sub-basin areterrestrially-derived. In the Berau and Muaras sub-

basins generally poor source potential is indicated.Potential source rock units, however, are expected toexist in unpenetrated rifts and basinal depressionsidentified on seismic. Data for oil stains in the Muarassub-basin indicate marine algal influence.

ACKNOWLEDGEMENTS

The authors wish to thank PT Corelab Indonesia andBP-Migas without whom the Tarakan Basin Study, onwhich this paper is based, would not have been

possible. Particular thanks also to Michael de Smet,Martin Evans, Chandra Tiranda, Jopie Adhidjaja,Mikael Odum, Michael Lentini, JohannesGoeyenbier, Ralf Hoffman and especially JohnBarrett, for their involvement in 1996.

REFERENCES

Achmad, Z. and Samuel, L., 1984. Stratigraphy anddepositional cycles in the N.E. Kalimantan Basin.Proceedings Indonesian Petroleum Association, 13

th

Annual Convention, Jakarta, Vol. 1, p. 109-120.

Andreason, M.W., Chatfield, F., Curiale, J.A.,Filewicz, M.V., Eko D. Lumadyo, E.D., Seeley, T. P.and Sutiyono, S., 2000. Deepwater exploration in anEocene petroleum system, Salayar Basin, Indonesia.AAPG Bulletin, V. 84, No. 9, p. 1398-1518.

Bissada, K.K., Elrod, L.W., Darnell, L.M., Szymczyk,H.M. and Trostle, J.L., 1992. Geochemical Inversion- A modern approach to inferring source-rock identityfrom characteristics of accumulated oil and gas.Proceedings Indonesian Petroleum Association, 21

st

Annual Convention, Jakarta, Vol. 1, p.165-199

Blow, W.H. (1979). The Cenozoic Globigerinidae.Vol I-III, pp. 1-1413.

Caratini C. and Tissot C., 1985. Le sondageMisedore. Etude Palynologique. CEGET. DomaineUniversitaire de Bordeaux. No. 3. 49 p.

Curiale, J.A., Decker J., Caughey C.A., and SchwingH.F., 2003. Oil-prone lacustrine source-rock potentialin central Indonesia. AAPG Annual Meeting 2003.

Abstract.

Curiale, J.A., Lumadyo E., and Rui Lin, 2002.Petroleum and source-rock geochemistry of theSalayar Basin (Offshore Sulawesi), Indonesia. AAPGAnnual Meeting 2002. Abstract.

Daly, M.C., Cooper, M.A., Wilson, I., Smith, D.G. &Hooper, B.G.D., 1991. Cenozoic plate tectonics and

basin evolution in Indonesia. Marine and Petroleum

Geology, 8, p. 2-21.

Darman, H., 2001, Turbidite Plays of Indonesia: Anoverview, Berita Sedimentologi #15.

Davidson, J.K., 1995. Globally synchronouscompressional pulses in extensional basins:implications for hydrocarbon exploration. Jour.Australian Petroleum Exploration Association, Vol.35, No. 1, p. 169-188.



Hall, R., 1996. Reconstructing cenozoic S.E. Asia.In: Hall R. and Blundell D. (eds.) 1996. Tectonicevolution of Southeast Asia, Geological SocietySpecial Publication no. 106, p. 153-184.

Hemmes, K., Darman, H., Suffendy, L., &

Meizarwin, 2001. Depositional systems of the deepwater Tarakan Basin, Indonesia, in: Deep WaterSedimentation of Southeast Asia: eds: Setiaan et al.,Proceedings of FOSI 2nd regional seminar, Jakarta.

Hidayat, S., Amiruddin and Satrianas, D. 1995.Geological map of the Tarakan and Sebatik sheet,Kalimantan. Geological Research and DevelopmentCentre, Bandung.

Peters, K.E., Snedden J.W., Sulaeman A., Sarg J.F.,and Enrico R.J., 2000. A new geochemical-sequence

stratgraphic model for the Mahakam Delta andMakassar Slope, Kalimantan, Indonesia. AAPGBulletin, V.84, No. 1, p. 12-44.

Lefort, J.J., Thiriet, J.P., Le Quellec, P., Bailey, J.B.2000. Sequence stratigraphy of the offshore Tarakan.AAPG, V.84, p. 1395-1518.

Lentini, M.R., Darman H., 1996. Aspects of the Neogene tectonic history and hydrocarbon geology ofthe Tarakan Basin. Proceedings Indonesian PetroleumAssociation, 25

th Silver Anniversary Convention,

Vol. 1, p. 241-253.

Lunt, P., Schiller, D. and Kalan, T. 1996. East JavaGeological Field Trip Guide Book. IndonesianPetroleum Association.

Martini, E., 1971. Standard Tertiary and Quaternarycalcareous nannoplankton zonation. In: Farinacci,A. (ed.), Proc.II Plankt. Conf., Rome, 1970,

p.739-785.

Morley, R.J., 1999. Origin and evolution of tropicalrain forests. Wiley, New York, 362 p.

Netherwood, R.E. and Wight, A.W.R., 1992.Structurally-controlled linear reefs in a Pliocene

delta-front setting, Tarakan Basin, NortheastKalimantan. Indonesian Petroleum Association.Carbonate Core Workshop.

Nichols, G.J., Cloke, I.R. and Hall, R. 1998. Eoceneextensional basin formation, eastern Borneo:Proceedings Indonesian Petroleum Association, 26

th.

Annual Convention. Abstract only.

Situmorang, R.L. and Burhan, G. 1995. GeologicalMap of the Tanjung Redeb Quadrangle, Kalimantan.Geological Research and Development Centre.

Bandung.

Sofer, Z., 1984. Stable carbon isotope compositionsof crude oils : Application to source depositionalenvironments and petroleum alteration. AAPGBulletin, V. 68, p. 31-49.

Van der Weerd, A.A. & Armin, R.A., 1992. Originand evolution of the Tertiary hydrocarbon-bearing

basins in Kalimantan (Borneo), Indonesia, AAPG, V.76, p. 1778-1803.

Wornardt, W. Jr., 1999. Revision of sequence boundaries and maximum flooding surfaces: Jurassicto Recent. Offshore Technology Conference, Texas,OTC 14072, p. 1-18.

Zachos, J., Pagani M., Sloan L., Thomas E., andBillups K. (2001). Trends, rhythms, and aberrationsin global climate 65 Ma to Present. Paleoclimate,Science, Vol. 292, p. 686-693.



Figure 1 - Tarakan Basin sequences, ‘events’ (key stratal surfaces) and source facies shown in the context of global and regional biochronostratigraphy. The local relative sea-level curve is a diagrammatic presentation combining paleoenvironmental trends

observed in key wells and seismic stratigraphy.

P

L I O C E N E



Figure 2 - Seismic profiles. A-A’ illustrates extensive growth faulting in Middle Miocene and younger sediments of the Tarakan sub-basin. B-B’and C-C’ show that in the Muaras sub-basin the Eocene and older section is in general more extensively faulted, than the Oligocene

and younger. Note uplift and erosion to the west of both sub-basins.



Figure 3 - Summaries of source rock quality comparing effective hydrocarbon potential of sequences I, II,

III and IV.



Figure 4 - Thermal maturity cross-sections for the Tarakan Basin.A) West to East Section from onshore Sembakung to offshore deep area;B) Transect from Berau sub-basin through to Muaras sub-basin;

C) South – North transect through Tarakan Basin.



Figure 5 - a) Ternary plot of source-specific biomarker distributions indicating differentiation of‘Miocene’ play oils and potential ‘Paleogene’ oil stains.

b) Stable Carbon Isotope cross-plot indicating commonality between the majority ofTarakan crude oils and ‘Mahakam – type’ oils.

Date post:	02-Jun-2018
Category:	Documents
Upload:	laluhendra
View:	218 times
Download:	1 times

The Tarakan Basin, East Kalimantan Proven Neogene Fluvio-Deltaic,

Documents