Deep-Water Sedimentation 2001 (Fosi_deepwater)

Proceedings of FOSI 2nd Regional SeminarHotel Mulia Senayan, Jakarta, IndonesiaMay 14-16, 2001

Deep-water Sedimentationof Southeast Asia

Editors:Aris Setiawan (VICO Indonesia)

Herman Darman (Brunei Shell Petroleum)Mohammad Syaiful (Lasmo Indonesia)

F. Hasan Sidi (Conoco Indonesia)



Editors:Aris Setiawan (VICO Indonesia)Herman Darman (Brunei Shell Petroleum)F. Hasan Sidi (Conoco Indonesia)Mohammad Syaiful (Lasmo Indonesia)

PRINTED IN INDONESIA

Copyright @ 2001FOSI – Indonesian Sedimentologists Forum

ISBN 979-96438-0-5

FOSI grants permission for photocopies of all items from this book for personal and academic use. Authorization for profit-oriented copies is granted by FOSI.

About the Editors

Aris Setiawan received his BSc degree in geology from Gadjah Mada University in 1990 and joined PT ElnusaSchlumberger after graduation. Since 1991, he joined VICO Indonesia, where he worked on various field developmentin Sanga-sanga Block, East Kalimantan. He received Master of Management degree from Atmajaya University in 1996.During 1996, he was assigned to work on regional venture with PT VICO Enterprises Indonesia. He pursues his Masterdegree in geology from the Monash University - Australia, with a research on tectonic evolution and extensional basinmodeling, during 1997-1998. His research received 1997 PESA (Petroleum Exploration Society of Australia) StudentResearch Scholarship Award. Currently, he works as senior geologist for VICO Indonesia. His responsibilities rangingfrom integrated geology and geophysical interpretation for reservoir management of complex deltaic depositionalfacies. Aris is member of IPA, AAPG, IAGI and FOSI.

Herman Darman is a regional geologist of Brunei Shell Petroleum. He received his BSc from the Institute ofTechnology, Bandung (ITB) in 1991 and MSc from Aberdeen University (UK). He has worked as a field geologist forLasmo, evaluation geologist and new business development geologist for Shell Indonesia. Herman has recently edited“An outline of the geology of Indonesia” book and “Tectonics and Sedimentation of Indonesia” proceedings togetherwith Hasan Sidi. His interests are in sedimentology and tectonics of Asia Pacific region. He is now a FOSI’s bulletineditor, AAPG’s visiting geologist program, and active member of SEPM, IAS, and EAPG.

Mohammad Syaiful was graduated in geology from Bandung Institute of Technology (ITB) in 1991. He had beeninvolved for a couple years in coal exploration (field mapping) when was a student. After obtaining his B.Sc. degree, hespent more than five years doing surface geological mapping for petroleum exploration. Syaiful is currently working forLASMO Companies in Indonesia. He is also member of IAGI, IPA, and AAPG. He has been active in FOSI since late1998 as a treasurer and membership manager.

F. Hasan Sidi joined the exploration department of Conoco Indonesia in early 2000, after 8 years with VICOIndonesia in Mahakam consession. In early 1998, he finished two master degrees, in geology (emphasizing onsedimentology and stratigraphy) from Queensland University of Technology (QUT) and in technology managementfrom Griffith University, Australia. His experience is mainly as a 3D seismic interpreter with responsibilities encompasserecting sequence stratigraphic, regional structural mapping, seismic modeling, and prospect generation. Hasan haspublished several papers of his studies locally and internationally and started his interest in FOSI by being theperiodical editor and followed by helping organizing the regional seminar and guest lecturers. He is currently thegeneral secretary of FOSI and the editor-in-chief for FOSI’s Berita Sedimentologi. He is also as one of the editors forthe proceedings of IPA (Indonesian Petroleum Association) Annual Convention. Hasan is also a member of SEG,AAPG, IAS, and SEPM.

Technical Program: Oral SessionTuesday, May 15, 20018.00-8.30 Opening Ceremony8.30-9.00 FX Soejanto Deep-water Opportunities in Indonesia and Vicinity9.00-9.30 Brad Prather Controls on Reservoir Distribution and Architecture in Slope

Settings: Implications for the Global Deep-water Play9.30-10.00 A.D. Donovan Physiographic Controls on Basin-Floor Fan Development

Keyn

otes

10.00-10.30 Coffee Break10.30-11.00 Arse Kusumastuti Deep-water Petroleum Provinces of SE Asia, A High Level

Overview11.00-11.30 Greg Partyka et al. Interpretational Applications of Spectral Decomposition in Reservoir

Characterization11.30-12.00 Arnold Bouma Geological Architecture and Reservoir Characteristics of Fine-

Grained and Coarse-Grained Turbidite Systems

Conc

epts

12.00-13.00 Luncheon13.00-13.30 Koesnadi H.S. et al. Sunda Strait Ventilation Role on Sediment Transport And Primary

Productivity in Offshore South Java And Southwest Sumatera13.30-14.00 Indra Jaya et al. Permeability Distribution in Thin-Bedded Turbidites Sandstones of

Cinambo Formation, West Java14.00-14.30 Edy Sunardi et al. Facies Analysis of The Cisubuh Formation Outcrops Analogues at

Brebes-Tegal-Pemalang District, Central Java14.30-15.00 Wartono Rahardjo Depositional Dynamics of mid Tertiary Deep-water Sambipitu and

Oya Formations of Southern Mountains Area, South Central Java

Sum

atra

and

Jav

a

15.00-15.30 Coffee Break15.30-16.00 R.J.Morley et al. Biostratigraphy of Deep-water Sequences, A Holistic Approach16.00-16.30 Parada Devy Silitonga and

Dwi MartonoPetroleum systems and Evolving Seismic InterpretationTechnologies in Makassar Deep Water Exploration

16.30-17.00 Hoang Ngoc Dang & NguyenThanh Tri

Upper Miocene Turbidite Playfairway in the Nam Con Son Basin,Offshore Vietnam M

etho

ds

Wednesday, May 16, 20018.00-8.30 K. Hemmes et al. Depositional Systems of The Deep-water Tarakan Basin, Indonesia8.30-9.00 D.A.S. Ranawijaya et al. Litho-biofacies Variations of Modern Deep Water Mahakam: A

Paleoclimatological Preliminary Study on A Stable Thermo-salinityEnvironment

9.30-10.00 Jossy Inaray et al. Merah Besar and West Seno Field Discoveries: Example ofExploration Success on The Slope Environment, Confined TurbidityChannel Sand, Deep-water Kutei Basin, Indonesia

9.00-9.30 John Dunham and L.D. McKee Hydrocarbon Discoveries in Upper Miocene Unconfined SubmarineFan Facies, Deep-water Kutei Basin, Indonesia.

Mak

assa

r

10.00-10.30 Coffee Break10.30-11.00 R. Heryanto et al. Depositional Environment Of The Late Cretaceous Pitap Group,

Meratus Mountain, Southeast Kalimantan11.00-11.30 Awang H. Satyana and Imam

SetiawanOrigin of Pliocene Deep-water Sedimentation in Salawati Basin,Eastern Indonesia: Deposition in Inverted Basin and ExplorationImplications

11.30-12.00 Kuntadi Nugrahanto et al. Submarine-Fan Deposition in The Lower Steenkool Formation,Bintuni Basin, Irian Jaya, Eastern Indonesia: "Deep-water ReservoirPotential?"

East

ern

Indo

nesi

a

12.00-13.00 Luncheon13.00-13.30 Paul Crevello Turbidite and Deep-water Depositional Systems of Borneo:

Reservoir Models of Basin Floor and Slope Reservoir Fan Systems13.30-14.00 Zulkefli Abdul Hamid and

Charlie LeeSTRATAGEM Forward Stratigraphic Modelling of The NorthwestSabah Deep-water Area, Malaysia

14.00-14.30 Baharuddin and R Heryanto Cretaceous Selangkai Formation of West Kalimantan and ItsTectonic Implication

14.30-15.00 Stefan Back Deep-water Reservoirs Of NW Borneo: Evaluating PotentialOutcrop Analogs

NW B

orne

o

15.00-15.30 Coffee Break15.30-16.00 Peter King and G.H. Browne Spectacular Outcrop Analog for Turbidite Reservoirs: The Miocene

Mount Messenger/Urenui Deep-water System, New Zealand16.00-16.30 K.A.A van Noord Facies and Sequences of A Restricted, Active-Margin Submarine

Fan in A Transgressive Setting, The Devonian Mindip Formation,Eastern Australia

16.30-17.00 Chandra Suria and Meizarwin Deep-water Systems in the Campos Basin, Brazil: A Comparison tothe Makassar Strait

Oth

er A

reas

Poster Presentation• Stefan M. Luthi and Alberto Malinverno – Reservoir Modelling of Turbidites Using Well Data and Laboratory Experiments

• Patrick Allman-Ward and Abdullah – Tectonostratigraphic Controls on Turbidite Depositional Processes in Brunei

• Y. Yamada - Scientific targets of IODP -New Ocean Drilling Plan

• Malvin Bjoroy - Surface Geochemistry As An Exploration Tool in Frontier Deep Water, Areas: Case Studies from SouthEast Asia

• Sartono - Gravity Data Analysis of Ujungpangkah Area - Implication for Structural Evolution And Hydrocarbon Prospect

• Sugeng Sapto Suryono et al. - Oligo-Miocene Deep-water Clastic Sediments: Identified from Watugajah and BanyutiboStratigraphic Measured Sections Southern Mountain, Yogyakarta

• Bayu Handoko and Tigor Yuni Ardi – Depositional Environment Of Sambipitu Formation

• M. Yohannes P Koesoemo - Pliocene Deep Water Sedimentation of Mundu and Kalibeng Formations in Northeast JavaBasin

• Philippe Rabiller et al. - MRGC, A New Clustering Methods that Helps The Sedimentologists To Take Advantage of NMRand Borehole Imagery to Recognize Sedimentary Facies from Logs

Table of Contents

Preface

Keynotes

Deep-water Opportunities in Indonesia and VicinityFX Soejanto

Controls on Reservoir Distribution and Architecture in Slope Settings: Implications for the GlobalDeep-water PlayB.E. Prather

Physiographic Controls on Basin-Floor Fan DevelopmentA.D. Donovan

Deep-water Concepts

Deep-water Petroleum Provinces of SE Asia, A High Level Overview.Arse Kusumastuti

Interpretational Applications of Spectral Decomposition in Reservoir CharacterizationGreg Partyka, James Gridley, and John Lopez

Geological Architecture And Reservoir Characteristics Of Fine-Grained And Coarse-GrainedTurbidite SystemsArnold Bouma

Sumatra and Java

Sunda Strait Ventilation Role on Sediment Transport and Primary Productivity in Offshore SouthJava and Southwest SumateraKoesnadi H.S., D.A.S. Ranawijaya, Yusuf S. Djajadihardja, and M. Wiedicke

Permeability Distribution in Thin-Bedded Turbidites Sandstones of Cinambo Formation, West JavaIndra Jaya, Hartanto Hadi Saputro, and Mac Endharto

Facies Analysis of the Cisubuh Formation Outcrops Analogues at Brebes-Tegal-Pemalang District,Central JavaEdy Sunardi, Billy G. Adhiperdana, Nurdrajat, Nanang Muchsin, Tri Widyo Kunto, and RudiRyacudu

Depositional Dynamics of Mid Tertiary Deep-water Sambipitu and Oya Formations of SouthernMountains Area, South Central JavaWartono Rahardjo

Deep-water Methods

Biostratigraphy of Deep-water Sequences, A Holistic ApproachR.J.Morley, H. Pribatini, A.A.H Wonders

Petroleum Systems and Evolving Seismic Interpretation Technologies In Makassar Deep-waterExplorationParada Devy Silitonga and Dwi Martono

Upper Miocene Turbidite Playfairway in the Nam Con Son Basin, Offshore VietnamHoang Ngoc Dang & Nguyen Thanh Tri

Makassar

Depositional Systems of The Deep-water Tarakan Basin, IndonesiaKaj Hemmes, Herman Darman, Leonardus Suffendy, and Meizarwin

Litho-biofacies Variations of Recent-Subrecent Deep-water Sediment of Mahakam Delta: APaleoclimatological Preliminary Study on A Stable Thermo-salinity EnvironmentD.A.S. Ranawijaya, D. Rostyati, N. Sutisna, N.A. Kristanto, Y. Noviadi, E. Usman, N. Cahyo, J.Widodo, and S. Lubis

Merah Besar and West Seno Field Discoveries: Example of Exploration Success on The SlopeEnvironment, Confined Turbidity Channel Sand, Deep-water Kutei Basin, IndonesiaJossy Inaray, Yusak H. Setiawan, Rhys Schneider, Jesse T. Noah, and Eko Lumadyo

Hydrocarbon Discoveries in Upper Miocene Unconfined Submarine Fan Facies, Deep-water KuteiBasin, Indonesia.John Dunham and L.D. McKee

Eastern Indonesia

Depositional Environment Of The Late Cretaceous Pitap Group, Meratus Mountain, SoutheastKalimantanR. Heryanto et al.

Origin of Pliocene Deep-water Sedimentation in Salawati Basin, Eastern Indonesia: Deposition inInverted Basin and Exploration ImplicationsAwang Satyana and Imam Setiawan

Submarine-Fan Deposition in The Lower Steenkool Formation, Bintuni Basin, Irian Jaya, EasternIndonesia: "Deep-water Reservoir Potential?"Kuntadi Nugrahanto, Scott W. McFall, and Festarina Estella

Northwest Borneo

Turbidite and Deep-water Depositional Systems of Borneo: Reservoir Models of Basin Floor andSlope Reservoir Fan SystemsPaul Crevello

STRATAGEM Forward Stratigraphic Modelling of The Northwest Sabah Deep-water Area,MalaysiaZulkefli Abdul Hamid and Charlie Lee

Cretaceous Selangkai Formation of West Kalimantan and Its Tectonic ImplicationBaharuddin and R Heryanto

Deep-water reservoirs of NW Borneo: Evaluating Potential Outcrop AnalogsStefan Back

Other Areas

Spectacular Outcrop Analog for Turbidite Reservoirs: The Miocene Mount Messenger/ UrenuiDeep-water System, New ZealandP.R. King and G.H. Browne

Facies and Sequences of A Restricted, Active-Margin Submarine Fan in A Transgressive Setting,The Devonian Mindip Formation, Eastern AustraliaK.A.A van Noord

Deep-water Systems in the Campos Basin, Brazil: A Comparison to the Makassar StraitChandra Suria and Meizarwin

Poster Session

Reservoir Modeling of Turbidites Using Well Data and Laboratory ExperimentsStefan M. Luthi and Alberto Malinverno

Tectonostratigraphic Controls on Turbidite Depositional Processes in BruneiPatrick Allman-Ward, Jan Pieter Tromp and Abdullah B. Ibrahim

Scientific Targets of IODP -New Ocean Drilling PlanY. Yamada

Surface Geochemistry As An Exploration Tool in Frontier, Deep-water Areas. Case Studies fromSouth East AsiaMalvin Bjoroy

Gravity Data Analysis of Ujungpangkah Area - Implication for Structural Evolution andHydrocarbon ProspectSartono

Oligo-Miocene Deep-water Clastic Sediments: Identified from Watugajah and BanyutiboStratigraphic Measured Sections Southern Mountain, YogyakartaSugeng Sapto Suryono et al.

Depositional Environment Of Sambipitu FormationBayu Handoko and Tigor Yuni Ardi

Pliocene Deep-water Sedimentation of Mundu and Kalibeng Formations in Northeast Java BasinM. Yohannes P Koesoemo

MRGC, A New Clustering Methods that Helps The Sedimentologists to Take Advantage of NMRand Borehole Imagery to Recognize Sedimentary Facies from LogsPhilippe Rabiller et al.

Deep-water Sedimentation of Southeast AsiaThe 2nd FOSI SeminarCommittee Members

ADVISORSPatrick Allman-Ward (Brunei Shell) - Dennis Brock (ExxonMobil)

Kris Budiono (Marine Geological Inst.) - Graham Goffey (Lasmo) - Soejono Martodjojo (ITB)Dwi Martono (Pertamina) - Wartono Rahardjo (UGM) - Hans Schwing (Unocal)Martin Stauble (Shell Sabah Berhad) - Chandra Suria (BP) - Surono (GRDC)

CONVENERF. Hasan Sidi (Conoco) and Herman Darman (Shell)

SECRETARYArse Kusumastuti (Lasmo)

TECHNICAL PROGRAMAris Setiawan (VICO) – Agus Guntoro (Trisakti)

ORAL SESSIONJossy Inaray (Unocal) – Kustomo Hasan (P3G)

POSTER SESSION AND SHORT COURSEIwan Busono (Lasmo) – Kuntadi Nugrahanto (BP)

FIELD TRIPChandra Tiranda (Amerada Hess) – Deddy Sebayang (Lasmo)

LOGISTIC COORDINATORMohammad Syaiful (Lasmo)

SPONSHORSHIPMarijke Pulunggono (Santa Fe) – Nila Murti (Premier)

EVENT COORDINATORFrank Sinartio (Repsol-YPF)

REGISTRATIONSherry Pambayuning (Lasmo) - Tati M Sahea (Schlumberger) - Fajar Hendrasto (Trisakti)

List of Sponsors

• Western-Geco• Gulf Indonesia Resources Ltd• Conoco Indonesia Inc. Ltd• Amerada Hess• Lasmo• Unocal• Repsol YPF _ Southeast Sumatra• Pertamina• TotalFinaElf• Veritas• BG Indonesia• Exspan Nusantara• Santa Fe Energy Resources Ltd• Santos (Bentu No.2) Pty Ltd.• Premier Oil

DEEP-WATER SEDIMENTATION OF SOUTHEAST ASIAFOSI (Indonesian Sedimentologists Forum), 2nd Regional SeminarMulia Hotel, Jakarta 14-16 May 2001

Deep-water Sedimentation of Southeast Asia:ForewordF. Hasan Sidi1

1FOSI General Secretary INTRODUCTION

First of all, many thanks for the support of FOSI’s second regional seminar, “Deep-waterSedimentation of Southeast Asia” here in Jakarta. We rely the seminar heavily on the technicalprogram, both oral and poster presentations that have been gathered from Brunei, Malaysia,Vietnam, Australia and of course Indonesia. This focused seminar surely attracts worldwidegeoscientists’ attention, not only within the region.

As we all know, the current trend in hydrocarbon exploration is toward a greater effort to locateand produce supplementary reserves from mature basins and to explore frontier areas, deepoffshore and tectonically complex zones. Most people would agree that the goldrush ofpetroleum industry in the beginning of 21st century lies on the deep-water provinces throughoutthe world. Deep-water reservoirs in the world have been actively explored and generating largevolumes of hydrocarbon in areas like the Gulf of Mexico and the North Sea. These intense andhigh technology activities created spin-offs towards SE Asia and Indonesia with several recentdiscoveries in offshore Kalimantan during the last a couple of years.

However, the understanding of its depositional systems in relation to various types of reservoirsand various tectonic setting have not been fully understood within the entire region. Respondingto that need, this compilation of extended abstract will hopefully can unlock some of thequestions in better understand the region. At least it might serve to generate ideas, discussionsand exploration concepts within this attractive setting.

Hopefully the participants can develop the concepts and strategies of deep-water depositionalsetting throughout the two-day seminar.

Last but not least, I would like to thank all parties involved, the technical presenters who arewilling to publish their work here, the sponsors, the committee members who have spent plentyman-hours voluntarily, and all individuals that can not be mentioned here.

Have a nice seminar -

Keynote Papers

Deep-Water Opportunities in Indonesia and VicinityF.X. Soejanto 1

1PERTAMINA Upstream ABSTRACT

Deep-water exploration areas on the world are significant as it totally cover 35 million squarekilometer on the surface, within 260 basins spread out in all continents, and contribute 14 % oftoday total oil and gas reserves. The largest area with highest potential is in Mexican part ofGulf of Mexico having 250 000 sq km with 15 BBO, whereas in Indonesia there are still as largeas 10,000 sq km with 5 BBO of unexplored deep-water areas. In term of exploration, it is achallenge to search for new targets and tool improvement.

Deep-water drilling in Indonesia has been carried out since 1972 in 350 m water depth in SouthJava Sea yielding some non-economic discoveries. It reached the deepest sea of 1,224 metersin North Sumatra Basin. The advancement of exploration concept and more sophisticatedtechnology led to the first significant deep-water hydrocarbon discoveries of Merah Besar andWest Seno in Makassar Strait in 1994. In the whole Kalimantan area included in Indonesia,Malaysia and Brunei authorities there are now deep-water potential of 11 BBO + 31 TCF, and itseems that more reserves are likely present at the deeper area.

Indonesia launches the blocks of deep-water with a tamer incentive designed for frontier areasin Eastern Indonesia, and also for parts of Western Indonesia areas having similar geologicaland geographic condition. Those deep-water blocks in Indonesia are having potential of oil andgas, where the gas market is large and growing succeeding oil market. Brunei also accelerateddeep-water endeavor by offering 2 deep-water blocks in Baram delta. Similarly, India offers 8blocks of deep-water play, which reaches 30 % among the total number of 25 blocks offered.The recent activities prove that deep-water invention plays a more and more important role inthe oil and gas industry.


Controls on Reservoir Distribution and Architecturein Slope Settings: Implications for The Global Deep-water PlayB. E. Prather 1

1Shell International E&P,2280 AB Rijswijk, TheNetherlands.

ABSTRACT

Realisation that high performance turbidite reservoirs exist in continental slope environmentshas substantially changed industry’s perception of the profitability of the global deep-water play.Lessons learned from developing and producing turbidite fields show that thick, high net-to-gross sheet sands with areally extensive, well-connected aquifers typify the architecture of highperformance turbidite reservoirs. The highest-performing turbidite reservoirs (rates >10,000BOPD and EURs > 20 MMBO) are found in intraslope basins on above-grade slopes and at thebase of graded slopes. This pattern of distribution suggests there is a link between evolution ofslope systems, and the occurrence of high performance turbidite reservoirs.

Turbidite reservoir distribution and architecture across slope environments varies as a functionof accommodation space. The degree of slope substratum mobility, sediment flux and sand-mud content control the type and distribution of accommodation space across slope and base-of-slope systems. Presence of ponded-basin accommodation space and large amounts of mid-to upper-slope healed-slope accommodation space distinguish above-grade slope systemsfrom graded-slope systems. Large amounts of healed-slope accommodation space in basinfloor and toe-of-slope positions and absence of ponded-basin accommodation spacedistinguish graded-slope systems from above-grade slope systems.

Sheet sand deposition on above-grade slopes results from ponded basin "fill-and-spill"processes. Spill-and-fill dominates early phases of deposition in above-grade slopes underlainby highly mobile substrates prior to progradation of graded (unconfined) slopes. Slopes withlower substrate mobility tend to have an early graded-slope that evolves with time into anabove-grade slope. Late onset of above-grade slope conditions on these slopes results in sheetsand deposition in ponded basins that are too shallow to be prospective for hydrocarbons.Sheet sands are also found in basin floor positions and at the toes of graded (unconfined)slopes associated with stable substrates.

Many recent turbidite discoveries principally on the continental slope of west Africa, and a greatdeal of the remaining deep-water potential in the global play is associated with stepped orterraced above-grade slopes that lack intraslope basins with ponded-basin accommodationspace. Since reservoirs in these settings have yet to be developed, their performancecharacteristics are poorly understood. Many of them are associated with belts of highly sinuousribbon and shoestring channel sands with locally scattered, thin, ponded fans. These sinuouschannel belts and small fans occur across lower gradient portions or steps on the slopewhereas straight to lower sinuosity channels form across ridges between the steps whereseafloor gradients are higher. Highly discontinuous external and internal (subseismic)


architectures associated with these reservoir types present development challenges notencountered with sheet sand reservoirs due to poorer reservoir connectivity resulting inreservoir compartmentalization and limited aquifer support.

DistanceKftA seafloor profile across central GOM shows the distribution of accommodationspace onan typical above-grade slope profile (1) ponded basin accommodation space,(2) slopeaccommodation space, and (3) healed-slope accommodation spacePrather

0.5°

0.8°

1.0°

vertical exaggeration1:675

0.1°

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3

1600 1400 1200 1000 800 600 400 200

Distance KftFigure 2: A seafloor profile across eastern GOM shows the distribution of accommodation space on a typical gradedslope profile. The graded slope profile comes from the present-day unconfined slope of the eastern GOM where it dipsto the south at about 0.8o. Absence of ponded-basin accommodation space and large amounts of healed-slopeaccommodation space in basin floor and toe-of-slope positions distinguish graded-slope systems from above-gradeslope systems. Healed-slope accommodation space in the mid- to lower- slope position is the space above toe-of-slope deposits and below the higher angle equilibrium profile associated with landward thickening slope deposits. Theamount of head-slope accommodation space across both the mid- to lower- slope is controlled in part by the amount oftoe-of-slope deposits, and seafloor topography caused by faulting and submarine slides.

0.5°

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1600 1400 1200 1000 800 600 400 200

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slope accommodation space

healed slopeaccommodation

space

slopeabovegrade

graded slope profile

ponded basinaccommodation

space

shelf/slope break

steepest stable slopeequilibrium profile

(eastern GOM unconfined slope)

vertical exaggeration 1:675

mud-limited profileseafloor

Figure 1: A seafloor profile across central GOM shows the distribution of accommodation a typical above-grade slope profile(1) ponded basin accommodation space, (2) accommodation space, and (3) healed-slope accommodation space (Prather etal., 1988). The graded slope profile comes from the present-day slope of the eastern GOM where it dips to the south.

shelf/slope break

healed-slopeaccommodation

space: mid-slopedeposition

slopeaccommodation

space below grade

healed-slopeaccommodation

space: toe-of-slope

mud-rich slope profilemud-limited slope profilepresent-day sea floor


Cbh Facies

I. Ponding

II. Fill

Cbh Facies

Cbh Facies

Cbh Facies

Ctl Facies

III. Early healing phase

IV. S lope re-adjustment

Truncation

D Facies

V. Late healing phase

VI. Dr ape

Ponded Assemblage Evolution

A.

B(h or l) /Cbh Facies

B(h or l) /Cbh Facies

±Cbh Facies

A Facies

Bl Facies

XI. Mass- wast ing

X. Drape

IX. Slope retrogradation ? and heal ing

VIII. Slope progradation

VII. Ponding

D Facies

E Facies

Cth/Ctl Facies

Bypass Assemblage Evolution

B.

Cth/Ctl Facies

Figure 3: Idealized ponded depositional sequence (A): capture of submarine fans (I) occurs in ponded accommodationspace created by salt withdrawal; fans eventually filling the accommodation space (II). Healing of the slope occurs after theponded basin fills and gravity flows spill down-slope as the sill separating the up-slope basin from down-slope basin istopped (III). A localized truncation surface form from erosion of the up-slope basin as the equilibrium profile adjusts to thedown-slope basin (IV). Continued healing of the space above the truncation surface occurs as the down-slope basin fillsand the slope between the two basins aggrades to a local equilibrium profile (V). Muddy gravity flows and/or hemipelagicdeposits drape the basins after the slope grades to the equilibrium profile or there is a decrease in sediment influx resultingfrom either a rise in eustatic sea level or slope-system avulsion (VI). Idealized bypass depositional sequence (B): capturedsubmarine fans fill ponded accommodation space where the rate of local basin subsidence due to salt withdrawalexceeded the rate of sediment influx (VII). Progradation of the slope occurs once the ponded accommodation space filles(VIII). Retrogradational parasequences sets suggest slope progradation is followed locally by “healing phase” deposit (?)reducing the local slope gradient (IX). Muddy turbidites and/or hemipelagic deposits drape the slope after the depositionalsurface grades to the equilibrium profile and/or there is a drop in the rate of sediment influx due to rise in eustatic sea levelor slope-system avulsion (X). A really extensive mass-wasting occurs as the regional slope steepens beyond the angle ofrepose for rapidly deposited muds during slope progradation and/or basinward tilting (XI). Refer to Prather et al. (1998) forfurther explanations of seismic facies classes (modified from Prather et al., 1998).

Seismic Facies Classes:A = chaotic with rotated eventsB1 = simple-chaotic low reflectivityBh = simple-chaotic high reflectivityCbh = convergent-baselapping high reflectivityCbl = convergent-baselapping low reflectivity (not shownCtl = convergent-thinning low reflectivityCth = convergent-thinning high reflectivityD = high acoustic impedance single loop or doubleE = low acoustic impedance single loop

A B


Figure 4: A continuum exists between graded slopes and above-grade slopes that reflects an interplay betweenaccommodation space and supply. As above-grade slopes heal (i.e., as they become graded), progressively moresand is bypassed downslope. Therefore, explorationists must look for subtle features to identify reservoir instepped or graded slopes.

5kmAmpli tude

Low High

Incise dbypass channels

amalgam ation ofshallower events

1 mile

A

A'

B'

B

Ponded Subma rine Fan

N

Oil field

A

B

Figure 5: Comparison of map-view geometriesof sinuous “meander-belt” (A) with map-viewgeometry of high-performance sheet-sandreservoir (B).

Physiographic Controls on Basin-Floor FanDevelopmentA.D. Donovan1

1BP Upstream TechnologyGroup

ABSTRACT

Depositional sequences with distinct depositional relief can occur on the craton and continentalshelf, as well as along the continental margin. This depositional topography can occur alongsequence boundaries (Erosional), within sequences (Constructional), or as abandoned (Relict)physiography. Detailed analysis of the depositional topography associated with sequencesdeposited in a variety of tectonic settings reveals that neither the presence of depositional reliefor proximity to the continental margin explains basin-floor fan development within sequences.However, in the datasets studied the magnitude of the depositional relief along sequenceboundaries can be used to explain and predict basin-floor (lowstand) fan development withinsequences.

Integration of published seismic, well-log, and outcrop data from the Cretaceous and Tertiary ofthe U.S. Gulf and Atlantic coasts, offshore Australia, Norway, Russia, as well as the Triassicthrough Tertiary of the Alaskan North Slope, suggests that 3 distinct types of depositionalsequences can be defined. Low-relief sequences lack clinoform development. Thesesequences typically have slopes of less than 1/2 of a degree and depositional relief of less than50 meters (150') along sequence boundaries. Low-relief sequences, which are common incratonic basins, lack basin-floor lowstand fans. Moderate-relief sequences display distinctclinoform development, with slopes of .5 to 3 degrees and depositional relief of less than 150meters (500') along sequence boundaries. Moderate-relief sequences are common in forelandbasins and on continental shelves. They also lack basin-floor lowstand fans. High-reliefsequences display slopes of 1-5 degrees and depositional relief greater than 150 meters (500')along sequence boundaries. High-relief sequences, which typically occur along the continentalmargins, but can occur in foreland and rift basins, contain basin-floor lowstand fans.

These observed relationships suggest that there is a Critical (Erosional) Shelf Break thatcontrols slope stability or failure during relative sea-level falls. In basins where the depositionalrelief is less than the Critical Shelf Break, progradation continues during relative sea-level falls.The resulting low- to moderate-relief sequences lack basin-floor (lowstand) fans. In basinswhere the depositional relief is greater than the Critical Shelf Break, slumping, canyonformation, fluvial capture, and sediment by-pass occur during relative sea-level falls. Theresulting high-relief sequences contain basin floor (lowstand) fans. In the data sets studied, itappears that the Critical (Erosional) Shelf Break occurs with erosional depositional relief of 150-180 meters (500-600').

Deep-water Concepts


Deep-water Petroleum Provinces of Southeast Asia:A High Level OverviewA. Kusumastuti1 , A. Mortimer1, C. Todd1, E. Guritno1, G. Goffey1, M. Bennett 1, andS. Algar1

1LASMO Companies inIndonesia, Jakarta

INTRODUCTION

Deep-water (200m+) exploration is an increasingly important component in the search forhydrocarbons in SE Asia. The Kutei Basin represents the most intensively and successfullyexplored deep-water basin in the region. In addition to the Kutei basin there are other lessexplored deep-water basins in the region such as the Baram, Sandakan, Tarakan, East Java,North Sumatra and Palawan Basins. This paper describes, compares and contrasts thepetroleum systems of some of these basins.

A regional map (Figure 1) illustrates the distribution of deep-water basins in the region whilstTable 1 compares the characteristics of the individual basins reviewed. Note that we use a200m depth cutoff to differentiate deep from shallow water as this is depth cutoff employed bythe Indonesian Government for the purposes of fiscal terms.

KUTEI BASIN – INDONESIA

The Kutei Basin is one of the most prolific basins in the region, with at least 11.5 BBOEdiscovered to date onshore and offshore. However, the focus of exploration in this basin hasrecently shifted to the deep-water with a variety of oil and gas discoveries such as West Seno,Merah Besar, Gendalo and Gandang made in water depths of 500-2000 m. Preliminaryestimates suggest that these discoveries may represent 15% of Kutei reserves at present butexploration is still at an early stage and the deep-water proportion of reserves is likely toincrease.

The deep-water area of the Kutei Basin is over 60,000 km² and the basin developed as apassive margin from Eocene rifting and probable development of oceanic crust, through Oligo-Miocene thermal and sediment-loading driven subsidence. From the Middle Miocene onwardsthe basin has experienced slight inversion. The prospective structures in the main part of thebasin are largely related to this inversion, but in the deep-water areas uplift/extension-driventoe-thrusting is also important. The Kutei is dominated by the huge sediment input from theKuching uplift, focussed towards the Mahakam delta.

The reservoirs thus far proven in the deep-water acreage are Pliocene and Late Miocenesediment gravity flows, with the deep-water discoveries located in different depositionalsystems in an upper to lower slope setting. The source rocks are thought to comprise highlyunusual, re-deposited terrestrial source particles and other organic matter transported into thedeep-water by Early to Late Miocene (post-rift) sediment gravity flows and thus deposited inclose juxtaposition with reservoir sandstones at a number of stratigraphic levels. These sourcerocks are therefore very different from the terrestrial organic matter thought to be the primary


source for the fields in shallow water and onshore. Trapping geometries in the deep-water arerelated to thin-skinned extensional and contractional structures, often with a significantstratigraphic component.

Unocal’s West Seno field will be the first deep-water discovery to be developed in Indonesiawhen it comes on stream in 2003, whilst the deep-water gas discoveries are likely to bedeveloped in a timeframe dictated by capacity in the Bontang LNG plant.

BRUNEI BASIN

Brunei is another prolific hydrocarbon province in SE Asia, with total reserves of at least 7BBOE in onshore and largely offshore shallow water fields. The presence of a deep-waterpetroleum system in the Brunei area has been proven by the Merpati and Meragi discoveries inwater depths of 400-500m. These discoveries represent less than 2% of Brunei’s reserves anddeep-water Brunei is otherwise under-explored.

The Brunei deep-water acreage extends to the northeast and southwest into the Sabah andSarawak offshore sectors respectively, with a total area of around 150,000 km2, and ischaracterised by a steep slope with a relatively rapid descent into water depths greater than2,500m in the centre of the NW Borneo Trough. Similar to the Kutei Basin, structures in theBrunei deep-water are related to presumably thin-skinned, contractional toe-thrust anticlines onthe lower slope, with a much greater involvement of shale diapirism on the middle and upperslope than is the case in the Kutei.

To date, the main productive reservoirs in the shallow water Brunei Basin have been deltaicprogradational sandstones of Pliocene and Late Miocene age. Turbidite reservoirs in the verylimited number of deep-water well penetrations are reported to be thin-bedded sandstones witha relatively low net to gross. However, some of these have been interpreted as overbank orlevee deposits, with the shale-filled channel forming a lateral seal. The age and depositionalsetting of the source rock in deep-water remains unclear but, we speculate, may be similar tothat of the Kutei Basin.

An extensive offshore pipeline network in shallow water exists to transport produced liquids tothe BSP oil terminal and gas to the Lumut LNG plant. There is currently no deep-waterinfrastructure or developed deep-water hydrocarbons.

TARAKAN BASIN - INDONESIA

The deep-water area of the Tarakan Basin is under-explored with only one well drilled in waterdepths significantly greater than 200m. Some 450 MMBOE are proven onshore Tarakan. Thedeep-water petroleum system is postulated to be very similar to that of the Kutei Basin andhence success or failure and oil:gas reserve ratios in the deep-water could be very different tothose encountered onshore.

The Tarakan Basin is very similar to the Kutei Basin in that it formed as a passive margin duringEocene rifting, followed by thermal and sediment load-driven subsidence during Oligo-Miocenetimes. As with the Kutei Basin, parts of the Tarakan Basin have also been inverted and a thin-skinned toe-thrust belt is well developed. The deep-water segment of the basin is around30,000km2 in area. Water depths increase rapidly over a relatively steep slope. Consequently


there is a limited portion of the basin that can be explored in water depths of less than 2500m.

Sediment is thought to have been derived from the uplifted Kuching High to the west and recentdrilling has confirmed that significant quantities of Mio-Pliocene sand are present in the deep-water. Source rocks for the deep-water are postulated to be the same re-deposited organicmatter found in the deep-water sediments of the Kutei Basin. Although hydrocarbon discoverieshave yet to be made in deep-water, the close similarity to the Kutei Basin lendsencouragement. Trapping geometries are expected to be analogous to those in the KuteiBasin, involving thin-skinned extensional and compressional fault blocks with a stratigraphiccomponent also being likely.

NORTH SUMATRA BASIN - INDONESIA

This basin occupies a back-arc setting that extends over a large area (160,000 km2) in theIndonesian and Thai sectors (where it is referred to as the Mergui Basin). Proven hydrocarbonreserves in this basin are approximately 5 BBOE onshore and nearshore in shallow water.Only a small volume of gas has so far been discovered in deep-water.

The main proven hydrocarbon reservoirs in shallow water/onshore are Late Oligocene andEarly Miocene reefal build-ups whilst potential reservoirs of Middle Miocene deep marine,lowstand fan clastics are beginning to be explored. The syn-rift section has yet to yield materialdiscoveries despite being sand-prone. The principal source rocks are thought to be lacustrineshales and deltaic coals in the Oligocene syn-rift section. The structural style is predominantlyextensional fault blocks, locally modified by reactivation/inversion with related folding.

Production from this basin is dominated by the giant onshore Arun Field, which produces gas tothe adjacent Arun LNG plant.

EAST JAVA BASIN - INDONESIA

Similar to the North Sumatra Basin, the East Java Basin is also located in a back-arc setting.The basin contains sediments of Eocene to Recent age which were deposited in continental,shallow and deep marine environments. The current deep-water areas cover approximately40,000 km2 and the sedimentary section is estimated to exceed 5 km. The proven hydrocarbonreserves in this basin are approximately 1.4 BBOE with no commercial discoveries in therelatively under-explored deep-water area.

Several main reservoir targets are identified: Eocene-Oligocene syn-rift clastics, Early Miocenecarbonate buildups and Mio-Pliocene deep-water clastics. Of these reservoirs, the Eocenesyn-rift clastics are currently the main target in the deep-water portion of the basin. Theprincipal source rocks are Eocene shales and coals which are mixed oil/gas prone. Shallowbiogenic gas is also present. Trapping geometries tend to be inverted extensional fault blocks.

There is a shallow water and onshore infrastructure, but no deep-water infrastructure.

PALAWAN BASIN - PHILIPPINES

The Palawan Basin has a NE-SW trend and covers an area of 80,000 km2 with water depthsfrom less than 100m to greater than 3000m. Eocene-Oligocene rifting was followed by thermalsubsidence. Some compressional structuration occurred along the southeastern basin marginduring Mid to Late Miocene times. Reserves of approximately 1.3 BBOE have been


discovered although some 50% of the gas and 10%-15% of the oil is considered to beuneconomic. Production of hydrocarbons to date from this basin has come from several smalloil discoveries in water depths of less than 300m.

Unlike the other deep-water basins, this basin lacks a thick development of deep-water coarseclastics. Early Miocene age carbonate build-ups provide the main proven reservoir in the basin.Other potential reservoirs are fractured platform carbonate facies, pre and syn-rift clasticsections and post-rift turbidites. The main source rock is thought to be syn-rift Palaeogenelacustrine shales. Traps with a stratigraphic element exist in the carbonate buildups whereMiddle Miocene shales are draped over the buildup and the carbonate shales out laterally. Theother dominant trapping geometry is four-way closure generated by mid/late Miocenecompression.

The giant Malampaya-Camago gas and oil field (850m water) is due onstream in 2002 and thismarks the first significant deep-water infrastructure in this basin.

CONCLUSIONS

Despite their varied locations, most of these basins initiated through Palaeogene rifting andthen subsided relatively passively as a result of a combination of thermal subsidence and/orsediment loading. All basins appear to have experienced some degree of compression from atleast as early as the Middle Miocene, through to Recent times. This compression hasreactivated thick-skinned structures and, when combined with extensional gravitationalcollapse, has led to the development of thin-skinned structures. There is a notable difference inthe circum-Borneo basins (Kutei, Brunei, Tarakan) compared to the rest of the basins in thatthey have a much thicker post-rift sedimentary section which tends to be both more sand-proneand more prone to thin-skinned extension and contractional toe-thrust development.

The circum-Borneo basins appear to be broadly analogous, with similar depositional andstructural styles. Common deep-water features are well-developed slope to basin depositionalelements, reservoirs being deep-water sediment gravity flow deposits and the dominant role ofthin-skinned extensional and contractional tectonics in formation of structural traps. It isprobable that the transported post-rift source rock known to occur in the Kutei basin is theprevailing nature of source rock in the circum-Borneo basins, which seem to lack a single, well-developed regional source rock horizon. The other basins reviewed, whilst their tectonicsettings vary, contain both deep and shallow water reservoirs in present-day deep-water,contain exclusively lacustrine or deltaic syn-rift source rocks in a known stratigraphic intervaland thick-skinned (basement-involved) tectonics dominates structural trap formation.

The circum-Borneo basins access an extensive sedimentary provenance area with majordrainage systems focussing large clastic volumes towards the basins, whereas the other basinsreviewed tends to access smaller hinterland areas with multiple, smaller drainage routes intothe basins.

A common feature of all basins is their relatively under-explored nature.


Interpretational Applications of SpectralDecomposition in Reservoir CharacterizationGreg Partyka1, James Gridley1, and John Lopez1

1BP Upstream Technology

Previously published by theSEG in The Leading Edge:

Partyka, G., Gridley, J.,Lopez, J., InterpretationalApplications of SpectralDecomposition inReservoir Characterization,The Leading Edge, vol. 18,no. 3, pg. 353-360.

INTRODUCTION

Spectral decomposition provides a novel means of utilizing seismic data and the discreteFourier transform (DFT) for imaging and mapping temporal bed thickness and geologicaldiscontinuities over large 3D seismic surveys (Partyka and Gridley, 1997). By transforming theseismic data into the frequency domain via the DFT, the amplitude spectra delineate temporalbed thickness variability while the phase spectra indicate lateral geologic discontinuities. Thissignal analysis technology has been used successfully in 3-D seismic surveys to delineatestratigraphic settings such as channel sands and structural settings involving complex faultsystems.

Widess pioneered a widely used method for quantifying thin bed thickness (Widess, 1973).Because it uses peak to trough time separation in conjunction with amplitude, Widess’ methodis dependent on careful seismic processing to establish the correct wavelet phase and truetrace to trace amplitudes. Though similar in context, the spectral method proposed here uses amore robust phase independent amplitude spectrum and is designed for examining thin bedresponses over large 3D surveys.

The concept behind spectral decomposition is that a reflection from a thin bed has acharacteristic expression in the frequency domain that is indicative of the temporal bedthickness. For example, a simple homogeneous thin bed introduces a predictable and periodicsequence of notches into the amplitude spectrum of the composite reflection. The seismicwavelet however, typically spans multiple subsurface layers and not just one simple thin bed.This layered system results in a complex tuned reflection that has a unique frequency domainexpression.

The amplitude spectrum interference pattern from a tuned reflection defines the relationshipbetween acoustic properties of the individual beds that comprise the reflection. Amplitudespectra delineate thin bed variability via spectral notching patterns, which are related to localrock mass variability. Likewise, phase spectra respond to lateral discontinuities via local phaseinstability. Together, the amplitude and phase related interference phenomena allow theseismic interpreter to quickly and efficiently quantify and map local rock mass variability withinlarge 3-D surveys.

The frequency response difference between a long window and a short window amplitude froma long seismic trace approximates the spectrum of the wavelet, the transform from a shortseismic trace comprises a wavelet overprint and a local interference pattern representing theacoustic properties and thickness of the geologic layers spanned by the analysis window. Theshort window amplitude spectrum no longer approximates just the wavelet, but rather thewavelet plus local geologic layering.


Figure 1 Thin Bed Spectral Imaging


With a few exceptions such as cyclothems and sabkhas, long analysis windows encompass agreat deal of geological variations that statistically randomize interference patterns of windowreflectivity spectra appear white or flat. This behavior is the common premise behind multiplesuppression via deconvolution. Given a large enough window, the geological stacking ofindividual thin layers can be considered random. The convolution of a source wavelet with arandom geologic section creates an amplitude spectrum that resembles the wavelet.The response from a short window is dependent on the acoustic properties and thicknesses ofthe layers spanned by the analysis window. The shorter the analysis window, the less randomthe sampled geology. The amplitude spectrum no longer approximates just the wavelet, butrather the wavelet plus local layering. In such small windows, the geology acts as a local filteracting on the reflecting wavelet, thereby attenuating the spectrum of the wavelet. The resultingamplitude spectrum is not white and represents the interference pattern within the analysiswindow.

The short window phase spectrum is also useful in mapping local rock mass characteristics.Because phase is sensitive to subtle perturbations in the seismic character, it is ideal fordetecting lateral acoustic discontinuities. If the rock mass within the analysis window is laterallystable, its phase response will likewise be stable. If a lateral discontinuity occurs, the phaseresponse becomes unstable across that discontinuity. Once the rock mass stabilizes on theother side of the discontinuity, the phase response likewise stabilizes.Iand-rich sections in the submarine fan are interpreted as ramp channel sandstone,


WEDGE MODEL RESPONSE

Spectral decomposition and the thin bed tuning phenomenon can be illustrated by a simplewedge model . The temporal response consists of two reflectivity spikes of equal but oppositemagnitude. The top of the wedge is marked by a negative reflection coefficient, while thebottom of the wedge is marked by a positive reflection coefficient. The wedge thickens from 0ms on the left to 50 ms on the right. Filtering the reflectivity model (using an 8-10-40-50 HzOrmsby filter) illustrates the tuning effects brought on with a change in thickness. The top andbottom reflections are resolved at larger thicknesses, but blend to become one reflection as thewedge thins.

A short window amplitude spectrum was computed for each reflectivity trace. These are plottedwith frequency as the vertical axis. The temporal thickness of the wedge determines the periodof the notches in the amplitude spectrum with respect to frequency.

Pf = 1/t

Where:

Pf = Period of notches in the amplitude spectrum with respect to frequency (Hz), andt = Thin bed thickness (seconds).

Examination from another viewpoint illustrates that the value of the frequency component


determines the period of the notches in the amplitude spectrum with respect to thin bedthickness:

Pt = 1/f

Where:

Pt = Period of notches in the amplitude spectrum with respect to temporal thickness (seconds),andf = Discrete Fourier frequency.

Even a relatively low frequency component such as ten hertz quantifies thin bed variability.

This wedge model illustrates the application of this approach to a very simple two-reflectorreflectivity model. Increasing the complexity of the reflectivity model will in turn complicate theinterference pattern.

THE TUNING CUBE

Amoco’s most common approach to characterize reservoirs using spectral decomposition is viathe “Zone of Interest Tuning Cube”. The interpreter starts by mapping the temporal and verticalbounds of the seismic zone of interest. A short temporal window about the zone of interest isthen transformed from the time domain into the frequency domain. The resulting “Tuning Cube”can be viewed in cross-section or plan view (common frequency slices). The frequency sliceform is typically more useful because it allows the interpreter to visualize thin bed interferencepatterns in plan view, thereby drawing on experience in identifying textures and patternsindicative of geologic processes. Amplitude or phase versus frequency behaviour/tuning is fullyexpressed by animating through the entire frequency range (i.e., through all frequency slices).

REMOVING THE WAVELET OVERPRINT

Removing the Wavelet Overprint The Tuning Cube consists of three components: thin bedinterference, wavelet overprint and noise. Since the geologic response is the most interestingcomponent for the interpreter, it is prudent to balance the wavelet amplitude without degradingthe geological information. In doing this, the tuning cube is reduced to thin bed interference andnoise.

Common spectral balancing techniques used in seismic data processing rely on sparseinvariant stationary statistics. If we assume that the geologic tuning varies considerably alongany flattened horizon, then we balance the wavelet spectrum by equalizing each frequencyslice according to its average amplitude. After whitening to minimize the wavelet effect, thetuning cube retains two main components: thin bed interference and noise.

In frequency slice form, thin bed interference appears as coherent amplitude variations.Random noise speckles the interference pattern in a similar fashion to poor quality televisionreception. At dominant frequencies, the relatively high signal to noise ratio results in clearpictures of thin bed tuning. Movement away from dominant frequency causes the signal tonoise ratio to degrade. At frequencies beyond usable bandwidth, the poor signal to noise ratioresults in a noise map.


EXPLORING BEYOND THE LOCALIZED ZONE-OF-INTEREST

Whereas the Tuning Cube addresses the tuning problem on a local zone-of-interest scale,larger seismic volume characterization requires a different approach. For decompositionbeyond the single reflectivity package or zone of interest, we recommend using “DiscreteFrequency Energy Cubes” or with different data organization, the “Time-Frequency 4-D Cube”.

“Discrete Frequency Energy Cubes” are computed from a single input seismic volume intomultiple discrete frequency amplitude and phase volumes. Computation is done via runningwindow spectral analysis which calculates the amplitude or phase spectrum for each sample inthe seismic volume. The spectral components are then sorted into common frequencycomponent cubes. This method is typically done only after scoping the zone of interest, horizon

Figure 5: Thin-bed tuning of amplitudes versus frequency (a)with respect to frequency and (b) with respect to thin-bedthickness.

xy

z

xy

z

xy

z

xy

freq

xy

freq

Interpret

3-D Seismic Volume

Subset

Compute

Animate

Interpreted3-D Seismic Volume

Zone-of-InterestSubvolume

Zone-of-InterestTuning Cube

(cross-section view)

Frequency Slicesthrough Tuning Cube

(plan view)

Figure 6: Zone-of-interesttuning cube.


based Tuning Cube. For the case of a “Time-Frequency 4-D Cube”, the spectral decompositionis also computed using a running window approach. The results are sorted into commonsample with increasing frequency. This volume allows the interpreter to exploit conventionalinterpretive workstation software and navigate through the volume at any depth slice for anyfrequency. The output is many times the size of the input but allows the interpreter to navigateand visualize in space, time, and frequency (x, y, t, and f).

GULF OF MEXICO DATA EXAMPLE

A Gulf of Mexico 3-D seismic example illustrates the use of spectral decomposition to imagethe Pleistocene age equivalent of the modern day Mississippi River delta (Lopez et al., 1997).The Tuning Cube frequency slices capture the subtleties of inherent tuning and reveal thevarious depositional features more effectively than full bandwidth amplitude and phaseextractions. For example, compare the north-south delineation extent for Channel A. It issignificantly better imaged by 26hz energy than by 16hz energy. On the other hand, Channel Bis better imaged by 16hz energy than by 26hz energy. Any single frequency however, does nottell the full story; the strength of this technique lies in the ability to animate through the entireTuning Cube to reveal subtle acoustic variations. Neither Channel A nor B is adequatelydelineated by conventional, full-bandwidth energy. The strength of the phase component lies indetecting discontinuities. The 16hz phase response and 26hz phase response are stable awayfrom the faults, but become unstable crossing discontinuities such as faults. These spectralphase maps provide sharper definition of faults than conventional full-bandwidth responsephase.

CONCLUSIONS

Spectral decomposition is a powerful technique which aides in the imaging and mapping of bedthickness and geologic discontinuities. Real seismic is rarely dominated by simple blocky,resolved reflections. In addition, true geological boundaries rarely fall along fully resolvedseismic peaks and troughs. By transforming the seismic data into the frequency domain withthe discrete Fourier transform, short-window amplitude and phase spectra localize thin bedreflections and define bed thickness variability within complex rock strata. This technologyallows the interpreter to quickly and effectively quantify thin bed interference and detect subtlediscontinuities within large 3D surveys.

REFERENCES

Bracewell, R. N., 1965, The Fourier transform and its applications: McGraw-Hill Book Co.

Dilay, A. and Eastwood, J., 1995, Spectral analysis applied to seismic monitoring of thermalrecovery: The Leading Edge, 11, No. 6, 1117-1122.

Partyka, G.A., Gridley, J.M., Interpretational Aspects of Spectral Decomposition, Abstract,Istanbul ‘97 International Geophysical Conference and Exposition, July 7-10, 1997.

Widess, M.B., 1973, How Thin is a Thin Bed?, Geophysics, vol. 38, pg 1176-1180.ranges from 5 to rarely 10 feet. Further works are needed in order to assess its potentiality asproducing reservoir.


Multiply

Tuning Cube

xy

freq

xy

freqx

y

freqx

y

freq

Seismic Wavelet NoiseThin Bed Interference++Add

Figure 7: Prior to balancing the spectrum, the tuning cube consists of thin-bed interference, theseismic wavelet, and random noise.


xy

freq

xy

xy

xy

xy

xy

xy

xy

xy

xy

xy

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Split Spectral Tuning Cubeinto Discrete Frequencies

Tuning Cube

Spectrally BalancedTuning Cube

Gather Discrete Frequenciesinto Tuning Cube

Independently NormalizeEach Frequency Map

Frequency 1 Frequency 2 Frequency 3 Frequency 4 Frequency n

Frequency 1 Frequency 2 Frequency 3 Frequency 4 Frequency n

Frequency Slicesthrough Tuning Cube

(plan view)

Spectrally BalancedFrequency Slices

through Tuning Cube(plan view)

Figure 8: Removing the wavelet overprint (balancing the spectrum) without removing the reflectivity tuning characteristics.

Figure 8: Removing the wavelet overprint (balancing the spectrum) without removing the reflectivity tuningcharacteristics.

Compute

3-D Seismic Volume

xy

freqxy

freqx

yfreq

xyfreqxy

freqx

yfreq

xyfreq

xy

zz = 1

z = n

z = n

z = 3z = 4z = 5z = 6

z = 1z = 2

xy

zz = 1

z = n

Subset

xy

zz = 1

z = n

xy

zz = 1

z = n

xy

zz = 1

z = n

xy

zz = 1

z = n

4-D Spectral Decomposition

Discrete FrequencyEnergy Cubes

Frequency 1 Frequency 2 Frequency 3 Frequency 4 Frequency m

Figure 9: Discrete frequency energy cubes.


North-South ExtentNorth-South Extentof Channel “A” Delineationof Channel “A” Delineation

Channel “A”Channel “A”

Channel “B”Channel “B”

Fault-Controlled ChannelFault-Controlled Channel

Point BarPoint Bar

10,000 ft

N

1

0

Amplitude

analysis window length = 100ms

North-South ExtentNorth-South Extentof Channel “A” Delineationof Channel “A” Delineation




Point BarPoint Bar

10,000 ft

N

1

0

Amplitude


Figure 10: Gulf of Mexico (a) 16-Hz energy map, (b) 26-Hz energy map


FaultsFaults

10,000 ft

N

180

-180

Phase


FaultsFaults

10,000 ft

N

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-180

Phase


Figure 10: Gulf of Mexico (c) 16-Hz phase map, (d) 26-Hz phase map.





Point BarPoint Bar

10,000 ft

N

1

0

Amplitude

FaultsFaults

10,000 ft

N

180

-180

Phase

Figure 11: Gulf of Mexico full-bandwidth (a) conventional energy envelope extraction, (b)conventional response phase extraction.

Geological Architecture and ReservoirCharacteristics of Fine-Grained and Coarse-Grained Turbidite SystemsArnold Bouma1

1Lousiana State University ABSTRACT

Exploration and production of oil and gas from deep-water turbidite systems is of high interestto most companies. Several models have been developed, emphasizing the architecture andseveral aspects of reservoir characterization. Application of a non-suitable model can result indry holes, bypassed oil, and other frustrations. Of all general models available the mostimportant ones are the coarse-grained and the fine-grained turbidite systems.

The coarse-grained turbidite systems are called canyon-fed fans. They are prograding into thebasin and constructed by non-efficient transport systems. They thin downdip and theirsediments become finer. In many cases the sediments are immature.

The fine-grained systems are delta-fed bypassing fan types with well-developed leveedchannels and significant depositional lobes or sheet sands on the outer/lower fan. They aretypical for passive margins but are also rather common in foredeeps and some trenches,depending on the distance from the sediment source and the fluvial gradient. Fine-grained fanscommonly contain mature sediments. Calculations on the Mississippi Fan and Tanqua Karoofans in South Africa indicate that 75% or more of all the sand in fine-grained fans is stored inthe outer fan sheet sands. Therefore, just to indicate that coarse-grained turbidite systems arerelated to active margins and fine-grained ones to passive margins is only partially correct. Theterms active and passive margins should not be used to identify turbidite system types.

A general understanding of the types of transport and depositional processes responsible forthe distribution and characteristics of the sands and shales is essential and makes it mucheasier to predict sand distribution and reservoir characteristics. The factors (tectonics, climate,sediment, and relative sea level fluctuations) that influence basin setting, transport, deposition,and timing interact rather variably with one and another.

The coarse-grained turbidite systems are rather well understood because those deposits arecommon in outcrop, often adjacent to productive fields. Fine-grained turbidite systemscommonly do not outcrop. That makes it very difficult to determine architectural changes indowndip and lateral direction, as well as reservoir continuity. The non-tilted Permian TanquaKaroo fan systems in South Africa are the only ones known to make it possible to conduct suchobservations.

Sumatra and Java


Sunda Strait Ventilation Role on Sediment Transportand Primary Productivity in Offshore South Java andSouthwest SumateraKoesnadi H.S.1, D.A.S. Ranawijaya1, Yusuf.S.Djajadihardja2, and M.Wiedicke3

1Marine GeologicalInstitute of Indonesia (MGI)Jl. Dr.Junjunan 236Bandung-40174INDONESIA

2Agency for theAssessment andApplication of Technology(BPPT) Jl. MH.Thamrin 8Jakarta-10340 INDONESIA

3Bundesanstalt f�rGeowissenschaften undRohstoffe (BGR)Stilleweg 2, D-30655Hannover, GERMANY

ABSTRACT

There are three important reasons for studying paleocirculation-paleooceanography inIndonesian waters due to paleoclimatic cycles: first, Indonesian archipelago is the transitionregion between Indian Ocean monsoon and Pacific monsoon, although the study area is moreinfluenced by Indian monsoon. Second, it is also the region of upper layer return water fromPacific to Indian Ocean (Gordon,1980) and third, it is commonly known that the region has highenough rate of sedimentation because close to the islands creating high resolutionsedimentation cycles. Those factors might influence the variations of integrated sedimentarysignals whether global (climatic, sea level change) or local (sediment flux, monsoon, oceancirculation) signal.

The carbonate composition fluctuation could illustrate the integrated signal above to describethe sedimentary cycle. The result of carbonate curve reconstruction and carbonate lateraldistribution analysis of deep sea piston cores of study area (South Java and SouthwestSumatera Indian Ocean) explained the modern distribution model and interpret thesedimentation history of unconsolidated sediment during subrecent due to paleoclimatic cycle.By the key word: “primary productivity”, the assemblage of planktonic microfauna, mainlyforaminifera, indicate vertically the variations of the integrated signal; and the benthicassemblage variations correlated with the fluctuation of mostly global signal. When we subtracteach other, the fluctuated carbonate curve is correlated with the variations of global signal likethe sea level change and ocean circulation. Finally, by that phenomena we try to calculate theapproximately rate of sedimentation.


Permeability Distribution in Thin-Bedded TurbiditesSandstones of Cinambo Formation, West JavaIndra Jaya1, Hartanto Hadi Saputro 1 and Mac Endharto2

1 Lemigas

2 Geological Research andDevelopment Centre

ABSTRACT

Permeability distribution for thin-bedded turbidites facies of Cinambo Formation (UpperOligocene – Lower Miocene) exposed at Cinambo River, Sumedang, West Java are presentedin this paper. The outcrop is about 150 m thick and 15 m wide. Vertical and horizontaltransects were sampled from the sandstone succession comprising several number ofbeds/bedsets which range from 10 to 75 cm in thickness. Small to medium scalespermeability/porosity measurements and sandstones lithofacies counterparts were spatiallycorrelated. Additionally, both sedimentary structures and petrographical properties of studiedsamples were examined in order to show the potential effect of these variations on flowbehaviour. The expected outcome of this study is to model the fluid-flow simulation inanalogous reservoirs.


Facies Analysis of The Cisubuh Formation OutcropsAnalogues at Brebes-Tegal-Pemalang District,Central JavaEdy Sunardi1, Billy G. Adhiperdana1, Nurdrajat1, Nanang Muchsin2, Tri Widyo Kunto2, andRudi Ryacudu2

1Department of Geology,Faculty Of Mathematicsand Natural SciencesUniversity of Padjadjaran,Bandung

2Pertamina E & P, Jakarta

ABSTRACT

Seismic data evaluation of line 99 BBS and line 74 BBS, Brebes Areas has revealed a rocksequence in the level, identified as an equivalent to Cisubuh Formation, forming plan viewedfan-shaped geometry. Their origin is suggested as a sediment of submarine turbidite system.The study area severely faulted and consists of many thrust sheets showing northwardstepwise propagation.

Some measured sections traverses are performed to examine the lithologic data along someoutcrop distribution that is considered to represent the analogues of Cisubuh Formation, suchas the sections of: 1). Banjarharja areas-Brebes; 2). Lebaksiu areas-Tegal; and the sections of3). Karanganyar areas-Pemalang. Rock sequence along these sections furthermore subdividedinto several facies, whereby their lithologic, lateral distribution and the vertical stacking pattern,indicating a development of a sedimentation pattern.

The facies model, their association and facies distribution could be attributed to depositionaland erosional turbidite elements. The elements of turbidite system signify the setting ofchannel-levee complex, including channel fill element, channel lag, overbank, basin plain,channel-lobe transition, a limited number of major erosional features, and shelfal sandstonelobe.

Elemental approach through mapping, facies correlation, and profiles comparison, e.g. in termsof the erosional and depositional elements, provides depositional pattern characterization. Thepattern indicates sedimentary system development from shelf sedimentation towards basinalsedimentation as a response to breaks in the equilibrium between shelfal and basinalsedimentation. This change is shown by the profile types of Lebaksiu-Karanganyar sections forthe former, and the sections of Banjarharja, and part of Karanganyar as well, for the latter


630

'o

700

'o

630

'o

700

'o

10830'o

10900'o

10930'o

10830'o

10900'o

10930'o

1:500.000

Fig. 1 Studied Area within simplified Regional Geological Framework Map of the Geol. Surv. of Indonesia, 1989

Figure 1: Studied area within simplified regional geological framework map of theGeological Survey of Indonesia, 1989.


Fm. Tapak

Fm. Kumbang

EndapanVolkanik

EndapanAluvialN 23

N 22N 21

N 20N 19

N 18

N 17

N 16N 15

N 14

N 13N 12

N 11

N 10N 9

N 8

N 7

N 6

N 5

N 4

P 21

P 20

P 19

P 18

P 22

BA

WA

HTE

NG

AH

ATA

S

PLIOSEN

HOLOSEN

Fm. Halang

Fm. Rambatan

Fm. Gabon ?

Fm. Pemali

Fm. Rambatan

Fm. Halang

Fm. Kumbang

Fm. tapak

Fm. Kalibiuk

Fm. Kaliglagah

Fm. MenggerFm. Linggopodo

Volkanik G. Slamet

Aluvialdan

Endapan VolkanikAluvial of Young Slamet

Linggopodo BrecciasGintung BedsMengger Horizon

Kaliglagah Beds

Kalibiuk Beds

Kumbang Beds

Tapak Beds

Halang Beds

Lawak Beds

Rambatan Beds

Pemali Beds

Fig. 2 Summarized regional surface lithostratigraphic framework of Western and Northern part of Central Java

Figure 2: Summarized regional surface lithostratigraphic framework of western and northern part of Central Java.

LithofaciesEquivalent

Mutti&

Ricci Lucchi (1972)

OccurrenceInterpretationDescription

Mostly composed of alternating thin bedded sandstone, siltstone, and claystone;moderately-good bed lateral continuity, subordinate crude bedded thin sandstone,occasional amalgamation; individual bed have commonly subtle lateral grain sizevariation,distinct to poorly defined Tb-e; commonly high clay/sand ratio, sand sizeranging from coarsed to very fined, overall finer-up bed, rarely sharp flat sandstonebasal contact, non erosive sandstone bottom marks more common, vertical successive relation to associations 2, 4, and association 5.

closed

Process/Mechanism:Low density turbidites, Channel abandoned, and suspension,flow deccelerationTurbidite Element/Environment:Interchannel, Overbank fines,levee facies

Common, elsewheremainly within lower andmid interval section ofBrebes and Tegal area

D, E, (C)

D, G, (E)

A, B, (C)

A, C, (E)

A, B, F,(C, E)

Mostly composed of interbedded thin to thick claystone, siltstone and minor finedsandstone; moderate bed lateral continuity, shaly texture commonly present, physicalstructures are undiscernible to poorly defined laminations, may frequently passed intovery fined sandstone downward, claystone occassionally massive, reddish brown topale grey coloured,absent to very low sand/clay ratio poorly defined Td, subtle planarto wavy laminations are due to compositional segregation, pelagic mud are common,frequently calcareous, very thin-thin sandstone intercalations occasionally lenticulair,very closed successive vertical relation to association 1.

Process/Mechanism:Low density turbidites, Channel abandoned, and suspended from flow lofting whenflow deccelerateTurbidite Element/Environment:Interchannel, Overbank fines,levee facies

Common, mainly withinmost lower section ofBrebes and Tegal area

Only present in mostlower part section ofPemalang and upperinterval section of TegalArea (Lebaksiu)

Only present in lowerand upper part sectionof Brebes and Tegal,may present in upperinterval of Pemalangsection

In most sectionof Brebes and mostupper of Tegal interval,common in upperinterval of Pemalangsection

Most common in sectionof Brebes and mostupper of Tegal interval,common in upperinterval of Pemalangsection

Fig. 3 Description, interpretation and occurences of common facies associations, facies term and association is used here in the sense of Walker (1992), and the earlier term that provides a quite similar implication in the sense of Middleton (1978)

CommonFacies

Asscociation Formation

Mostly

inHalang Fm.

as intercalation

Rambatan Fm.common

1.L-, L- ,

(L- )I v

III

2.L- , L-v vI

3.L- , L-IIb v

4.L- , L- ,(L- L )

IIa IIIIV, -VII

5.L- , L- ,

(L-)IIa V

I

6.L- L-

L-L-))

IV VIIIX

I

, ,(L- , )

((VIII

MostlyPemali and

inHalang Fm.

as intercalation

Rambatan Fm.present

Rambatan Fm.

Halang Fm.

Halang Fm.

Halang Fm.

Mostly composed of interbedded very thick sandstone , occassionally up to 4 ms.thick with alternating thin to thick bedded siltstone and claystone, frequently with verythick bedded claystone or shale, moderate to excelent bed lateral continuity; typicalsedimentary structure in vertical order are: lag pebble alignment, coal chips or claypellets are frequently found, passed upward into more massive interval, but still showoverall finer up, before change abruptly upward into gently undulating interval ofparalel lamination, or quite flat laminations, ripple laminations, while the uppermost ofbeds characterized by convolutions, and commonly hummocky like cross stratificationform and cross stratification related to storm wave modification.

beds Process/Mechanism:Low density turbidites, fall out combined with traction,modified by storm or normal waveactionDeposition Element/Environment:offshore bar and shelf mudstone,shelf progradation system

Mostly composed of very thick bedded sandstone, with randomly oriented mudstone ripped up clasts,

amalgamation are common, rarelygradded stratified, massive divisions are more common, sharp erosive basal surface,no persistent thickness, , closed vertical association withpebbly sandstone,poorly defined coarsed tail grading, may occassionally show faintplanar subhorizontal lamintaion in upper divisions,lateral transition between massiveand bedded sandstone, Bouma divisions generally not applicable, though Ta, Tab is alikely representation, moderate to high sand/mud ratio, overall finer up are common.

to poorlydefined paralel orientation sandstone ranges from mediumto very coarsed grain, moderate to poorly sorted,

poor beds lateral persistence

Process/Mechanism:High density turbidites, grain flows, freezing fromliquefied flow, or cohesive debrisflowsTurbidite Element/Environment:channel/valley fill sequence

Mostly composed of thick to very thick bedded sandstone, with randomly oriented mudstone ripped up clasts,

amalgamation are common,occassionally with claystone/mudstone parting, sharp-flat to erosive basal surface,may show semi-persistent thickness, moderate to good

, closed vertical association with L-V and L-I. Bouma-divisions may present, moderate to high sand/mud ratio, overall finer up are common.

topoorly defined paralel orientation sandstone ranges frommedium to very coarsed grain, moderate to poorly sorted,

beds generally show lateralpersistence Ta, Tab (Tabc ?)

Process/Mechanism:High density turbidites, grain flows, freezing fromliquefied flowTurbidite Element/Environment:uppermost interval of channel fillor channel margin sequence

Mainly composed of very thick unbedded-crudely bedded pebbly sandstone/mudstone,and occassionally breccia, disorganized fabric arrangements, mostly matrix supported,

amalgamation, crudely gradded stratified, sharperosive basal surface, with pebble lag, slump-soft sediment deformation and stratifiedblocks may present,no persistent thickness, , closedvertical and lateral association with L-VIII and L-IIa, may show poorly defined coarsedtail grading and inversed grading, Bouma divisions generally not applicable, indistinctoverall finer up are occassionally present.

poorly sorted, may generally show

poor beds lateral persistence

Process/Mechanism:Grain flows, debris flow/mudflows,and slumpingTurbidite Element/Environment:channel lag, basal division ofchannel fill sequence/slope relateddebris flow deposits

Figure 3: Description, interpretation, and occurences of common facies associations, facies term andassociation is used here in the sense of Walker (1992) and the earlier term that provides a quite similarimplication in the sense of Middleton (1978).


NWSE

?

?Broad Shallow Valley System

Channel Filled-Complex

Shelf/Lower Shoreface System

Minor Channel Filled Sandstones

Abandoned Channel System(Interchannel/Overbank ?)


Lobe/Channel Upper Interval (?)

?

Channel-Levee System


Minor Channel-Levee System

?

Fig. 4 Representative summary of depositional model for Brebes sections showing lateral and vertical relationship of turbidite and associated facies

Figure 4: Representative summary of depositional model for Brebes sections showing lateral and verticalrelationship of turbidite and associated facies.


N

?

?

Channel Filled-Complex

Shelf/Lower Shoreface System

Abandoned Channel System(Interchannel/Overbank ?)

Lobe/Channel Upper Interval (?)

?Channel-Levee System

Amalgamated Channel Fill System

Minor Channel-Levee System

SE S

Fig. 5 Representative summary of depositional model for Pemalang sections showing lateral and vertical relationship of turbidite and associated facies

Figure 5: Representative summary of depositional model for Pemalang sections showing lateral and verticalrelationship of turbidite and associated facies.


Depositional Dynamics of Mid Tertiary Deep-waterSambipitu and Oya Formations of SouthernMountains Area, South–Central JavaWartono Rahardjo1

1Department of GeologicalEngineering, Gadjah MadaUniversity, Jl. Grafica 2,Yogyakarta 55281Phone/Fax: 0274-513668

ABSTRACT

Sambipitu and Lower part of Oya Formations are known as deep-water deposit of Middle toearly Late Tertiary of Southern Mountains, Central Java. Sambipitu consists predominantly ofsiliciclastic non carbonate turbidite beds on the lower part, followed by a more carbonatesandstones at the top. Oya Formation begins as carbonate turbidite composed of packstonesand wackestones, with marls and tuffaceous marls interbeds of deep-water setting, overlain byplaty to thick-bedded limestones, indicating of shallowing environments.

Benthonic formaniferal study on both formations revealed that several swallowing periodsoccurred during their deposition of the deep-water sediments. Intercalation of redbed inSambipitu event indicates that subaerial exposure may have been occurred. This oscillatingconditions are supported by the frequency changes of total population of microfossil content, aswell as the occurrence of barren zones.

Detailed planktonic studies are now underway to determine the accurate age of the fossilfrequency shifts, which eventually led to determination of whether the changes were caused bylocal tectonics or global event of sea level fluctuations.

Deep-water Methods


Biostratigraphy of Deep-water Sequences, A HolisticApproachR.J.Morley1, H. Pribatini1, A.A.H.Wonders2

1Palynova, 1 Mow Fen Rd,Littleport, Cambs, UK

2StrataData, 14, LakelandDrive, Frimley, Surrey, UK

ABSTRACT

Understanding biostratigraphic signatures in deep-water settings requires an approach thatchallenges a number of the traditional concepts in biostratigraphy. This review, based on anextensive database drawn from four low latitude petroleum provinces from Southeast Asia andWest Africa, emphasises that the three biostratigraphic disciplines of micropalaeontology,nannopalaeontology and palynology each have a major role to play in deep-water sequenceevaluation. The basis of our approach is that the fossil record is an output signal of climaticchange, which affects sea level, oceanic water masses, sedimentary processes on continentalmargins and terrestrial and coastal vegetation.

Micropalaeontology has been the traditional tool for stratigraphic and environmentalassessment of such facies, but often provides misleading results in cases where age restrictedplanktonics and calcareous benthonic tests are removed by dissolution, common at bathyalwater depths. Also, large-scale downslope transport of foraminifera from the shelf commonlyresults in the in situ assemblages being overwhelmed by shallow water forms, leaving little hintof the true deep-water environmental setting. Furthermore, only a few foraminiferal abundanceand diversity maxima truly reflect maximum flooding surfaces. Identification of such floodingsurfaces is often possible only through the integration of foraminiferal data with nannofossil,palynological and lithological data.

Primarily we use foraminiferal assemblages to characterise various deep-water facies and todifferentiate phases of sediment transportation through the differentiation of transported shallowwater forms from the autochthonous fauna. Planktonic foraminifera play a role in ageinterpretation.

The nannofossil record tends to be a little more resilient to dissolution in deep-water settings,and hence nannofossils may still be common in some facies where calcareous foraminiferahave been removed by dissolution. Their primary role is in age interpretation, and ‘sequencefingerprinting’. As with foraminifera, nannofossil abundance and diversity maxima onlyoccasionally reflect maximum flooding surfaces; many nannofossil abundance maxima reflectsecondary condensed sections within the lowstand systems tract.

The majority of the palynomorphs found in deep-water slope settings within the areasconsidered are derived from terrestrial sources rather than being from the marine environment,being transported into this setting mainly by gravity flow processes. For sequence stratigraphicinterpretation, the palynomorph record is very valuable, for it gives information about processestaking place on the shelf, such as sediment sequestration, retrogradation and progradation. It isin the shelf setting that the processes that determine sequence architecture primarily takeplace, and so in a deep-water setting, far from the effects of interaction of sea level change in


relation to the continental shelf, such information is critical. Palynological data also providesevidence for climate change. Intermittently cooler and drier tropical climates coincide withphases of low sea levels and result in major fluctuations of vegetation. These changes arereflected in the palynological record and their differentiation helps to differentiate lowstanddeposits from those sequestered on the shelf.

Palynology is thus primarily of value in the differentiation of systems tracts on the basis ofevidence for changing coastal plain geomorphology and changing climate; it has a secondaryrole in age interpretation.

Each discipline therefore provides a different aspect of deep-water sequence evaluation. If abiostratigraphic evaluation is envisaged as giving information on sequence age, sedimentaryfacies and water depth, and systems tract interpretation, all three disciplines should be used inconjunction. In all three disciplines, quantitative evaluation is crucial for a proper interpretationof results.


Petroleum Systems and Evolving SeismicInterpretation Technologies in Makassar Deep-waterExplorationDwi Martono1, Parada D. Silitonga1, Richard H. Tamba1 and Djoko N. Imanhardjo1

1PERTAMINA –Exploration Division

ABSTRACT

Oil discoveries in deep-water have increased the oil industry’s attention on the potential ofpassive margin petroleum systems worldwide. The key elements of the system are an effectivesource rock and a progradational clastic sediment supply to provide reservoir, the overburdenmaters, and the structural deformation. The Miocene to recent progradation of the Mahakamriver provides the clastic sediment supply, creating toe thrust and anticlines structures in thedeep-water area.

The 2D Regional Seismic lines and 3D Seismic data which covered the studied area detectingthe presence of large structure. Some of these structures have associated hydrocarbonindicators and will be displayed as a confined reservoir. Large stratigraphic features are alsoevident on the seismic in Mahakam deep-water area, indicating the possibilities of anunconfined reservoir geometry. Using some of the seismic attributes and incoherency from 3DSeismic data with the observed algorithm and techniques could determine the lateraldistribution of these stratigraphic features. High amplitude reflection packets are visible in 2Dseismic data, showing that the process of channel incision, levee building and channel stacking,associated with turbidities flows, have operated throughout the deposition of the sediments andthroughout the lower slope region.

The clearly imaged flat spot/flat-based amplitude anomalies also provide the most compellingevidence for active petroleum systems within the deep to ultra deep-water province of theMahakam Delta.

“GEOBODY “

Figure 1: Reflection Magnitude could determine a real “Geobody” from 2D Seismic Data

FEEDERCHANNEL

SANDYFAN SHAPELOWER

SLOPE

BASINFLOOR

PONDEDBASIN

Figure 2: An example of deep sea stratigraphic features performed from variance cubes 3D-seismic data


Upper Miocene Turbidite Playfairway in The Nam ConSon Basin, Offshore VietnamHoang Ngoc Dang1 and Nguyen Thanh Tri1

1BP Exploration Vietnam ABSTRACT

The Nam Con Son Basin in offshore Vietnam is a large Tertiary extensional basin, formed asthe result of extrusion of SE Asia due to the collision of India and Eurasia and stronglyinfluenced by the South China Sea spreading.

The basin evolution comprises two rifting phases in Oligocene and Middle Miocene and a post-rift phase since Late Miocene onward. Marine transgression began from Early Miocene,reaching maximum at end of Middle Miocene. The Middle Miocene rifting together withmaximum marine transgression at the time have established a typical marine environment inthe basin, ranging from shelf, slope and deep-water during Late Miocene. In such conditions, adeep-water turbidite sandstone system has been well developed in the basin center.

The geometry of turbidites depends on several factors, but was strongly controlled by seabedmorphology and therefore it was changing from more channeling-like at lower stratigraphic levelto more fan-like at upper stratigraphic level. Seismic attributes are used as good tool todescribe the distribution and characteristics of these turbidite sandstones.

Gas and condensate have been discovered and the turbidite play became an importantexploration objective of the basin.

Makassar


Depositional Systems of The Deep-water TarakanBasin, IndonesiaKaj Hemmes1, Herman Darman1, Leonardus Suffendy1, and Meizarwin2

1Shell E&P Companies inIndonesia, Jakarta,Indonesia

2Atlantic RichfieldIndonesia Inc, Jakarta,Indonesia

ABSTRACT

Exploration activity in the Tarakan Basin spans more than a century. Numerous oil and gasdiscoveries have been made onshore on the Tarakan and Bunyu structural highs. Offshore,only the shallow water deltaic sequence has been tested so far.

Recently, 2000 km of modern 2D seismic data were acquired over the deep-water area andused to develop reservoir depositional models for oil and gas exploration.

The Tarakan Basin constitutes a passive continental margin with Late Eocene-Recentsediments on continental to oceanic crust, created during the Middle-Late Eocene opening ofthe Celebes Sea. Rifting ceased during the early Oligocene with quiet marine conditionsprevailing until the Middle Miocene uplift of the Borneo hinterland. The latter uplift triggered amassive influx of turbidites in the deep-water area, deposited as unconfined toe of slope fansahead of the outbuilding Tarakan delta. During Plio-Pleistocene delta outbuilding, this sequencewas buried by rapidly prograding slope deposits, which triggered gravity-driven toe thrusting.Small basins were formed between thrust ridges and filled by slope deposits. In the southernpart of the delta, westward dipping normal faults limited progradation, resulting in excessivethickening of the Pliocene-Pleistocene deltaic sequence and limiting sediment influx into thedeep-water area.

Several potential reservoir systems are recognized in the deep-water area. These include 1)unconfined toe of slope fans, 2) confined intra-slope fans, and 3) intra-slope channel (-levee)systems. Further seismic and exploratory drilling will be required to confirm the lateral extentand sand proneness of the deep-water plays.


Bathymetrynot mapped

500

119°00'E118°00'E

4°00'N

3°00'N

2°00'N

117°00'E

TIDUNGSUB-BASIN

NEOGENEEXTRUSIVE

NEOGENE CARBONATECOMPLEX

QUARTENARY

NEOGENE

PALAEOGENE

CRETACEOUS

IGNEOUS ROCK

Sub-Basin Boundary

WITH SOME IGNEOUS ROCKS

NW-SE ANTICLINAL

ARCHES

LEGEND

PRETERTIARY SEDIMENTS

NMUARASUB-BASIN

INTRUSIVE

BERAUSUB-BASIN

- - -- - - -

- - - - - -- - - - - - -- - - - - - -- - - - - -

- - - - - -

BunyuArch

TarakanArch

LatihAnticline

MangkalihatPeninsula

SempurnaPeninsula

Folding, Thrusting & Shale Diapirism

0 100km

Maratua Fault Zone

TARAKANSUB-BASIN

MAJOR FAULT ZONE

Figure 1: Location map of Tarakan Basin.


Figure 2: Regional tectonic framework of Kalimantan and Sulawesi

20 (47 MY)

19 (46 MY)

Middle-Late EoceneSpreading

18 (43 MY)

N. SULAWESI TRENCH M-U Miocene (15-10 MY)Active Subd uctionM INAHASA BAS IN

GORO NTALO BASIN

TARAKANBASIN

MUARABASIN

KUTEI BASIN

KALIMANTAN

SARAWAK

BRUNEI

SABAH

MINDANAOSULU SEA

SOUTH CHINA SEA

CELEBES SEA(SULAWESI SEA)

MAKASSAR STRAIT

SULU ARCHIPELAGO

PALAWAN

NEGROS

SULAWESI

5°N

10°N

0°

125°E120°E115°E

0 300 KM

Cross section


?

?

??

0

5000

10000

0

5000

10000

Hol oce ne

Upper Eocene-Mio cene

Pl io-P leist ocene

Oceanic Crust

TARAKAN DELTA SULAWESI SEA NORTH SULAWESI TRENCH

SEBAWANG II PSC BUKA T PSC

T ERRACED SLO PE BASIN F L OOR

AMB AL AT PSC

Accretiona ry wedge

rece nt subd ucti on42-33 Ma?Spreading Axis?

TWT in ms TWT in ms

0 50 km

Plio-Pleistocene

Miocene

DEEP WATER PLAYS

Plio-Pleistocene intra slope channels and channel leveecomplexes

Pliocene intra s lope confined/ponde d fa ns

Mioce ne toe of slope unconf ined fans

Figure 3: Regional cross section and schematic play concept in the deep-water Tarakan Basin


Litho-Biofacies Variations of Recent-SubrecentDeep-water Sediment of Mahakam Delta:A Paleoclimatological Preliminary Study on A StableThermo-Salinity EnvironmentD.A.S. Ranawijaya1, D. Rostyati1, N. Sutisna1, N.A. Kristanto1, Y. Noviadi1, E. Usman1, N.Cahyo1, J. Widodo1, and S. Lubis1

1Marine GeologicalInstitute of Indonesia(MGI); Jl. Dr. Junjunan 236Bandung-40174Phone: 022.6078303,6032020, 6032201E-mail :[email protected]

ABSTRACT

There is no influence of sea surface current layer (Wyrtki, 1961) at the study area even that isvery correlated with monsoonal intensity. The possible cause is the deep-water thermohalinecurrent (Gordon, 1980), that responsible for most of all phenomenal variations. Thecombination of monsoon-global climate-thermohaline oceanic circulation would be a veryprecise solution to answer the study area .

The result of unconsolidated sediment core analysis of offshore Mahakam Delta illustrates thatthe fluctuations of lithology and microfaunal composition are correlated with the variations ofoceanic current due to thermohaline and monsoonal intensity. Based on planktonic microfaunaassemblage analysis, we can also interpret that there were some fluctuations signal due tovariations of primary productivity and sedimentation cycles or continental erosion.

Correlation between litho-facies variations curve and high resolution oxygen isotop curve canbe interpretated as a combination of a local-global climatological signal. Therefore it mightdetermine correlatively the age of each litological layer, so then we can calculate the rate ofsedimentation.


Merah Besar and West Seno Field Discoveries:Examples of Exploration Success on The SlopeEnvironment, Confined Turbidity Channel Sand,Deep-water Kutei Basin, IndonesiaJossy C. Inaray1, Yusak H. Setiawan1, Rhys Schneider1, Jesse T. Noah1, and Eko Lumadyo2

1Unocal Indonesia Co.,Balikpapan, Indonesia

2Unocal Corporation,Sugar Land, Texas.

ABSTRACT

Exploration on the Kutei Basin has indicated that abundant Pliocene and Miocene sand wasdeposited on the shelf-platform environment of the active Mahakam delta. Seismicinterpretation showed that a number of low areas so-called mini basins, which were formed byshelf-edge listric-normal faulting, was identified on the slope environment. Several wells drilledon the upper slope environment and seismic data along with the present day bathymetri profilesled us to the interpretation that during Miocene lowstands significant sand transported byturbidity currents through deeply incised slope canyons should have been confined in thesecontinental slope mini basins. Merah Besar field discovery in 1996 and West Seno fielddiscovery in 1998 proved this interpretation and significantly provided inputs to the explorationof Upper Miocene, slope environment, confined turbidite sand, deep-water Kutei Basin.


Hydrocarbon Discoveries in Upper MioceneUnconfined Submarine Fan Facies, Deep-water KuteiBasin, IndonesiaJohn B. Dunham1 and L.D McKee1

1Unocal Indonesia Co.,Balikpapan, Indonesia

ABSTRACT

Exploration on the Ganal PSC has led to several significant gas discoveries. The key elementsof the hydrocarbon system are simple anticlinal four-way closures that contain thick laterallyextensive sand bodies. Most significantly, the sands were deposited prior to structural growth,with the result that the sands do not thin over the crests of the structures. Initial explorationwas based on a relatively coarse 2 x 2 km grid of 2D seismic data. This 2D grid revealednumerous large anticlines at 4500’ to 7000’ water depth. Since it was known that abundantPliocene and Miocene sand existed on the Kutei shelf, it was interpreted that significant sandshould have been deposited in the basin during Miocene lowstands, prior to Pliocene structuralgrowth. We did not need 3D data to interpret presence of reservoir.

Hydrocarbon charge was predicted along deep-penetrating faults, sourced from terrestrialkerogen carried into the basin by turbidity currents, with top seals formed by thick hemipelagicclaystone sections. All the elements of a working hydrocarbon system were present, and welllocations were chosen directly from the 2D grid.

Our exploration philosophy was that if sands were present in the closures, then 3D would beacquired to delineate and develop the discoveries. In fact, excellent reservoir-quality gas sandswere discovered in several Ganal anticlines. 3D seismic data subsequently acquired over theGendalo discovery shows a large unconfined submarine fan covering at least 20000 acres, withan internal architecture of broad laterally continuous overlapping fan lobes.

MDT data demonstrate continuous pressure communication within the fan over a lateraldistance of 3.7 km. Additional gas discoveries were also made in the Gandang, Gula, andGada structures, and reserves are estimated to be in the multiple TCF range. There are twosignificant lessons to be learned from this successful exploration program. First, we did notneed a 3D structural/stratigraphic seismic interpretation to drill these structures. Our 2D gridwas adequate to define large anticlines that would have been drilled 50 years ago if they werein shallow water. Second, the presence of abundant sand on the Kutei shelf clearly pointed tothe high probability of significant deep-water sands in the basin. It was not necessary to coverthe entire 5050 sq. km. area of the Ganal PSC with 3D data in order to make these discoveries.However, 2 km x 2 km 2D seismic data is not adequate to guide development of thesediscoveries. That will take 3D data.

Eastern Indonesia

Depositional Environment Of The Late CretaceousPitap Group, Meratus Mountain, SoutheastKalimantanR. Heryanto1, P. Sanyoto 1, H. Panggabean1 and K. Hasan1

1Geological Research andDevelopment Centre,Bandung

ABSTRACT

The Pitap Group in Meratus Mountain is divisible into Pudak, Keramaian and ManunggulFormations. These formations have inter-fingering relationships one to each other. The lowerpart of the Pudak Formation is an olistostrom with olistolith such as Orbitolina Limestone andvolcanic rock, bounded within the matrix of volcanic sandstone. They were deposited in acontinental slope. The upper portion of Pudak Formation comprises medium- to coarse-grainedvolcanic sandstone interbedded with gravity and mass flows conglomerate/breccia, and wasdeposited as an upper submarine fan.

The Keramaian Formation consists of typical fine- to medium-grained turbidite sandstone whichwas deposited as a lower submarine fan. The Manunggul Formation consisting ofconglomerate, sandstone and mudstone was deposited in a middle submarine fan environment.

Volcanic activity has produced volcanic rocks of the Haruyan Group deposited coinciding withthe deposition of the Pitap Group, where their relationships are interfingering. They have beendeposited during Late Cretaceous time directly above the imbricated basement consisting theBatununggal Limestone, Paniungan Mudstone, ultramafic, metamorphic and granitic rocks.They are also acted as a source rocks for the Pitap Group. The Tertiary sedimentary rocksunconformably overlie both Pitap and Haruyan Groups.


Origin of Pliocene Deep-water Sedimentation inSalawati Basin, Eastern Indonesia : Deposition inInverted Basin and Exploration ImplicationsAwang H. Satyana1 and Imam Setiawan1

1Exploration - PertaminaMPS (Management ofProduction Sharing)

ABSTRACT

Salawati Basin is a foreland basin located at the frontal edge of the Indian-Australiancontinental plate. Sorong Fault, a major strike-slip fault in Eastern Indonesia and terminatingthe basin to the north, has inverted the basin’s polarity in the Late Pliocene by subsiding thewhole northwestern part of the basin. Before this inversion, the Salawati Basin had a southerndepocenter.

The newly formed northwestern depocenter has subsided rapidly since the inversion as anisostatic compensation to the southern and eastern uplifts. This condition resulted in theaccommodation space for northwestern deep-water sedimentation. Sediments were erodedfrom the uplifted areas and deposited rapidly into the subsiding basin as debris flow deposits ofPliocene Klasaman sediments within bathyal depositional environment. The depocenter wasincreasingly subsided by tectonic loading of the contemporaneous Upper Klasaman multiplethrust sheets.

Thick deep Klasaman deposits became burial sediments for the Miocene source rocks oncedeposited in the lagoonal environment to attain a depth of oil window. Rapid Klasamandeposition triggered overpressuring and shale diapirism. The deposition was too fast for thesediments to compact and dewater in normal way. Overburden pressure and lack of permeableconduits caused the overpressuring. The Klasaman overpressuring presents a drilling hazardas undergone by all wells drilled in the area. Low densities of overpressured Klasaman shalescaused the shales flowed upward as diapirs. Sorong Tectonism controlled these diapirs asshown by their parallel trends with the Sorong Fault. The Klasaman diapirism may relate withhydrocarbon traps of faulted domal structures, dragged beds below the diapirs’ overhangzones, faulted beds in the peripheral sinks, and turtle structures.


INTRODUCTION

Recent success of exploring hydrocarbons in deep-waterreservoirs throughout the world has enhanced theunderstanding of deep-water sedimentation. Concepts withinseismic sequence stratigraphy have contributed verysignificantly to this success. However, understanding of thedepositional system relating to various tectonic setting hasnot been fully understood. This paper contributes someconcepts to this understanding by addressing the case in theSalawati Basin, Eastern Indonesia.

The Salawati Basin, Eastern Indonesia, based on our recentregional evaluation, is a poly-history basin with the history ofbasin’s polarity inversion during its evolution. Sorong FaultTectonism bordering the Salawati Basin to the north andwest has strongly controlled the basin since the Pliocene.The Sorong Fault has inverted the basin’s polarity from theold pre-Pliocene southern depocenter to the new Pliocenenorthwestern depocenter. Within the Pliocene, the newdepocenter has subsided rapidly forming a deep-water basin.The Pliocene Klasaman sediments eroded from the southernand eastern uplifted areas were deposited very rapidly intothe subsiding deep basin. The rapid Klasaman depositiontriggered overpressuring and shale diapirism. Explorationimplications of this Pliocene deep-water sedimentation arealso addressed in the paper.

GEOLOGIC SETTING

The Salawati Basin is an east - west trending asymmetricforeland basin located on the northern margin of the Indo-Australian Plate. The deformed zone of the left-lateralSorong Fault presently bounds the basin to the north andwest. The present structural style of the basin is dominatedby NNE - SSW normal faults formed as conjugates of theSorong Fault. The Sorong Fault has also developed enechelon folds and synthetic left-lateral faults with normal slipin the Salawati Island. (Figure 1).

The Salawati Basin records the stratigraphic and tectonichistory from Paleozoic time to the Recent (Figure 2). Theoldest stratigraphic sequence of the basin is the continentalbasement rocks of the Siluro-Devonian Kemum metamorphicand Carbo-Permian Aifam sediments. Overlying thebasement are Mesozoic sediments (Tipuma andKembelangan groups). Tertiary sediments of the SalawatiBasin began with the Late Eocene to Early Oligocenetransgressive carbonates of the Faumai Formation. Overlyingthe carbonates, is the Late Oligocene shallow marine clastics

of the Sirga Formation. Thick carbonates of the Miocene KaisFormation cover this formation. The thick Kais carbonatedeposition was contemporaneous with the Klasafet lagoonaldeposits. The Pliocene Klasaman clastics ended the Tertiarystratigraphic sequences composing the thickest sediments inthe Salawati Basin. This paper discusses these sediments.Molassic deposits of the Pleistocene Sele conglomeratesend the stratigraphy of the basin.

ORIGIN OF PLIOCENE SALAWATI DEEP-WATER BASIN

The Sorong Fault presently bounding the Salawati Basin tothe north has strongly controlled the evolution of the basin.Regionally, this fault is part of a large global transcurrentzone that separates the westward moving Pacific oceanic(Caroline and Philippine Sea) plate from the relatively stableAustralian continental plate. The fault trends east-west asleft-lateral (sinistral strike-slip) fault.

Based on the thickness of the formations, it is known that theSalawati Basin has had a long history of dipping southwardinto which sediments from the Late Paleozoic to the Miocenethickened (Figure 3). Some formations onlapped to the north.However, this basin’s polarity was disturbed significantlywhen the Sorong Fault Tectonism strongly controlled thebasin’s configuration.

At the Middle-Late Miocene time, the Salawati Basin startedtilting southwestward possibly due to initial platesreadjustment around the Northern Irian Jaya and SouthwestPacific. This had shifted the depocenter slightly to thesouthwest and consequently, the eastern part of the basinwas uplifted. At the Mio-Pliocene, the Salawati Basin startedto undergo significant tectonic changes. This was possiblyrelated with the changes in plates movement around thenorth of Irian Jaya and the Southwest Pacific. The SorongFault was formed to accommodate the oblique convergencebetween the Philippine Sea Plate and northern AustralianContinental Plate. The southern, southeastern, eastern andnortheastern parts of the basin were increasingly uplifted.Consequently, the western, northwestern, and northern partsof the basin were subsided. This configuration resulted in thecondition of reversed basin's polarity as compared to theconditions of the pre-Miocene periods.

In the end of mid-Pliocene, the Salawati Basin started to tiltsignificantly to the north, northwest and west providing largespace of accommodation for depositing sediments erodedfrom the uplifted areas (Figure 4). Upper Klasaman


sediments were rapidly deposited into this new basin whichwas contemporaneously subsiding. In this area, the UpperKlasaman reached its maximum thickness constituting morethan two third of the basin's strata. The new basin,consequently, was more subsiding due to very thick burialloads. The basin also subsided due to tectonic response ofisostatic compensation to the southern and eastern uplifting.Contemporaneously, the Sorong Tectonism was also takingplace to deform the Upper Klasaman during the LatePliocene. This has also subsided the new basin due totectonic loading of the contemporaneous Upper Klasamanmultiple thrust sheets.

Thus, there are at least three mechanisms which caused theinversion/reversal of the Salawati Basin’s polarity resulting ina deep-water basin. They are : (1) subsidence due toisostatic compensation to uplifting, (2) subsidence due tovery thick burial sediments, and (3) subsidence due totectonic loading of multiple thrust sheets. These threemechanisms are related to each other and triggered by theSorong Tectonism.

DEEP-WATER SEDIMENTATION OFKLASAMAN

Uplifted areas in the southern, eastern, and northeasternparts of the Salawati Basin became the provenances of thePliocene Klasaman sediments deposited in the subsidingnorthern and western basin. These provenances were : (1)to the south and east were the uplifted Miocene Kaiscarbonates of the Misool-Onin Geanticline and the AyamaruPlatform respectively and (2) to the northeast was continentalbasement, metasediments, oceanic fragments, and someKais/Klasafet sediments of the Kemum High.

Klasaman sedimentation was started by the deposition of theEarly Pliocene Lower Klasaman in inner to outer sublittoralenvironments with lagoonal facies developed in some areas.This formation mainly consists of calcareous shales withlimestone and siltstone stringers indicating provenances ofuplifted Klasafet and Kais carbonates. The Lower Klasamanslightly thickens to the north revealing the first emergence ofthe northern depocenter. Before this, all pre-Lower Klasamanformations thickened to the south. This indicates that theinversion of the Salawati Basin’s polarity initially occurred inthe Early Pliocene.

Significant deep-water sedimentation took place when theLate Pliocene Upper Klasaman sediments were deposited.

This period was contemporaneous with the initiation of majorepisode of the Sorong Tectonism. The Kemum High at thenortheastern part of the basin contributed most of thesediments. Huge volume of the Upper Klasaman sedimentswas deposited into the basin mostly as turbiditic debris flowwithin bathyal setting. Marly clays with a more or less siltsand sands dominate the deep-water sedimentation in thenorthwestern area (Figure 5). The sediments close to theprovenance (in the Sele Strait area) are characterizeddominantly by coarse sands with significant lithic content.More to the west and northwest, the depositionalenvironment was increasingly deeper since the basin wasmore tilting. In this area, the bathyal condition was reachedand the sediments obtained their highest rate ofsedimentation (Figure 6). Three wells penetrating thesediments in this region generally consist of rapid alternationof clays, siltstones and sandstones.

KLASAMAN SHALE DIAPIRISM

Shale-dominating Lower Klasaman and coarser rapiddeposits of Upper Klasaman triggered the Klasamanshale/mud diapirism. Mud diapirism is mostlikely to developin clay sequences underneath the thick, rapidly depositedregressive sandy sequences (Allen and Allen, 1990).Subsidence of the Salawati Basin is approximately equaledby the rise of the Klasaman diapir. The deposition of theUpper Klasaman was too fast for the Lower Klasaman claysto compact and dewater in normal way. Low densities ofoverpressured Klasaman clays caused the clays flowedupward as diapirs. Doming and piercing of diapiric materialsoccur primarily because the density of the plastic materials islower than that of the overlying sediments (O’Brien, 1968;Lemon, 1985). This density inversion causes gravitationalinstability or tectonic vertical stress.

The distribution of the Klasaman diapirs shows an alignmentwith the major structural element (Figure 7), indicating thatthese diapirs were triggered tectonically by the horizontalstress of the Sorong Fault Tectonism.

Seismic sections (Figures 8,9 ) show that the Klasamandiapirs had passed through all stages of diapiric development: (1) pillow, (2) diapir, and (3) post-diapir stages. Structuresassociated with these three stages are observed. Rimsynclines were formed right to the diapirs and areincreasingly steeper towards the younger section. Theperipheral sinks immediately adjacent to the rim synclineswere the sites of active subsidence and therefore the sitesfor considerable thickening of the sediments being deposited


at that time. At the upper section, reverse and thrust faultswere formed within the peripheral sinks. The faults generallyverge to the south. Turtle structure is also observed to form.Underlying the diapirs, the Klasafet and Kais formations aredeformed by normal faults down to the north. These faultsare compensating faults due to the basin subsidence to thenorth. Overlying the diapirs, the uppermost section of theKlasaman was deformed as surface anticlines or faults,partly forming the fold and thrust belts of North Salawati.

EXPLORATION IMPLICATIONS

Deep-water Klasaman sedimentation have some implicationson hydrocarbon exploration. Three aspects are discussed :presence of diapiric traps, maturation of hydrocarbonsources, and drilling hazard due to overpressuring.

The Klasaman diapirism may relate with hydrocarbon traps(Figures 8, 9). The flowing and doming of plastic materials atdeep levels play an important role in the formation of oil andgas traps in overlying strata (Wang Xie-Pei et al., 1982).Evidence that the Klasaman diapirism is closely related withthe hydrocarbon accumulation is shown by numerous oil andgas seeps at the fold and thrust belts of North Salawati.These fold and thrust belts partly represent the faulted domalstructures overlying the diapirs. The dragged Intra-Klasamansand beds against the walls of the diapirs and below theoverhang zones of the diapirs also provide the diapiric traps.Faulted beds in the upper sections of the KlasamanFormation and turtle structures within the peripheral sinks arepotential hydrocarbon traps as well. Reservoir quality ofIntra-Klasaman sands and the presence of faults for verticalmigration conduits connecting mature Lower Klasaman,Klasafet and Kais sources with the Intra-Klasaman trapsseems to hold the keys for hydrocarbon accumulation. In theabsence of these conduits, then the interbedded Intra-Klasaman shales should be mature and have generativecapacity to make the accumulation possible.

Miocene Klasafet/Kais shales and carbonates are the provenmain source rocks of the Salawati Basin. The sedimentswere deposited in lagoonal environment at the northern areawhen the basin still tilted to the south (Figure 10). As thebasin’s polarity inversion took place, the area subsided to thenorth and was immediately deeply buried by the Klasamansediments to attain a such depth of the oil window.Hydrocarbons were generated and started to migrate updip.Thermal modeling revealed that 3.8 Ma (mid-Pliocene time)as the initiation of major oil generation from the Klasafet/Kaisand this was contemporaneous with the commencement ofthe basin’s polarity inversion. The Early Pliocene Lower

Klasaman shales are also proven source rocks and they alsobecame mature when very thick Upper Klasaman sedimentsburied these sources.

Klasaman overpressuring presents a drilling hazard. Threewells drilled in this area : Waipili-1 (1956), Waibu-1 (1957),and West Island Reef (WIR) -1 (1993) all encountered drillingproblem due to penetrating overpressured Klasaman shales.Waipili-1 found gas activity and a blowout in the shallowUpper Klasaman sediments. Waibu-1 and WIR-1encountered severe technical difficulties in the overpressuredKlasaman shales and each well was sidetracked into foursidetrack holes due to pipe sticking. Later seismic data(1991) show that both Waipili-1 and Waibu-1 wells arelocated at the diapiric surface anticlines.

CONCLUSIONS

• The Salawati Basin, Eastern Indonesia, records thedeep-water sedimentation of the Late Pliocene UpperKlasaman sediments. This deep-water basin was formedby the inversion of the basin’s polarity and was stronglycontrolled by the Sorong Tectonism.

• The Upper Klasaman sediments were deposited veryrapidly into the subsiding basin and the sedimentationhas triggered the diapirism within the deep basin.

• Rapid deposition of the Upper Klasaman sediments hasthree exploration implications : (1) to subside theSalawati Basin to the depth of oil window, (2) to providediapiric hydrocarbon traps, and (3) to present drillinghazard due to diapiric overpressuring.

ACKNOWLEDGMENTS

This paper roots from the regional studies conducted by theSalawati Exploration Group of the Pertamina and Santa FeEnergy Resources. The first author joined the Group in 1997-2000. Isnaini from Santa Fe Salawati is thanked for providingseismic supports. Sartono and Sugiri from Santa Fe Salawatidrafted most of the figures. The management of the JOBPertamina-Santa Fe Salawati and the ExplorationDepartment of the Pertamina MPS (Management ofProduction Sharing) is acknowledged for the supports to thispaper.


REFERENCES

Allen, P.A. and Allen, J.R., 1990, Basin analysis : principlesand applications, Blackwell Scientific Publications, Oxford,451 ps.

Lemon, N.M., 1985, Physical modeling of sedimentationadjacent to diapirs and comparison with Late PrecambrianOratunga breccia body in Central Flinders Ranges, SouthAustralia, The AAPG Bulletin, V. 69, No. 9, p. 1327-1338.

O’Brien, G.D., 1968, Survey of diapirs and diapirism inBraunstein, J. and O’Brien, G.D., eds., Diapirism and Diapirs: AAPG Memoir No. 8, The AAPG, Tulsa, p. 1-9.

Satyana, A.H., 1999, Basin polarity reversal and rotation ofthe Salawati Island : implications on petroleum system andnew potential reserves of the Salawati Basin, Irian Jaya,Proceedings Lomba Karya Tulis Direktorat EP Pertamina, p.9-38.

Wang Xie-Pei, Fei Qi, Zhang Jia-Hua, 1985, Cenozoicdiapiric traps in Eastern China, The AAPG Bulletin, V. 69,No. 12, p. 2098-2109.


Submarine-Fan Deposition in The Lower SteenkoolFormation, Bintuni Basin, Irian Jaya, EasternIndonesia: “Deep-water Reservoir Potential?”Kuntadi Nugrahanto 1, Scott W. McFall2, and Festarina Estella3

1Geologist, BP Indonesia,Arkadia D-5, Jl.TBSimatupang Kav.88,Jakarta 12520, Indonesia

2Geophysical Specialist,BP Indonesia, Arkadia D-5,Jl.TB Simatupang Kav.88,Jakarta 12520, Indonesia

3Geophysicist ExplorationBP Indonesia, Arkadia D-5,Jl.TB Simatupang Kav.88,Jakarta 12520, Indonesia

ABSTRACT

It is commonly recognized that the transpressional motions associated with the evolution of thenorthern Australian margin and Pacific plate have been active since the Miocene time. In theearly stage of this tectonic phase (Early-Middle Miocene), sub-aerially exposed local high areasoccurred on the remnant Oligocene-aged ridges (Ubadari, Sekak, Wiriagar) and on the northernmargin (Kemum) of the Bintuni Basin. While to the east, the Lengguru orogenic belt was still inthe early folding stage. Later in the Late Miocene to Early Pliocene, these emergent areasshed sediments to the south depositing the Steenkool Formation, which initiated the terminationof the Miocene carbonate sedimentation in the area. The subsequent Plio-Pleistocenecompressional tectonic event initiated the overthrusting phase of the Lengguru fold belt, whichoccurred in association with the subsidence of the adjacent deep Bintuni Basin.

The scope of this study is the clastic interval that was deposited post Kais deposition during theLate Miocene to Pliocene. It is in part conformably and unconformably overlain the Kaislimestone. An overall upward coarsening strata characterizes the vertical change from theKlasafet to Steenkool Formations. The depositional environment changes from deep-waterKlasafet (outer shelf to upper bathyal) to deltaic to deep-water Lower Steenkool.

Although only a limited grid of 1970’s vintage 2D seismic data image the Bintuni Basin in thisdifficult rain forest environment, the data quality are sufficient to recognize seismic stratigraphicsignatures corresponding to deep-water depositional features. Early Lowstand Wedge (ELW)that consists of basin floor and slope fans, and Late Lowstand Wedge (LLW) that exhibitsprogradational complexes with clinoformal and shingled geometries have been interpretedwithin the Lower Steenkool interval.

The ELW feature has dimension of 30-70 ms TWT in thickness (130-300 feet), 30 km in length,and 40 km in width. Two prograding complexes (PGC) in the LLW are clearly identified on theseismic. The PGC has dimension of 100-370 ms TWT in thickness (450-1,650 feet), 20 to 40km in length, and 30 to 40 km in width. Shingled-turbidite fan features within the PGC, calledST, has dimension of ~24 to 30 ms TWT in gross thickness (~135 feet), 15 to 20 km in length,and up to 35 km in width.

Sand-rich sections in the submarine fan are interpreted as ramp channel sandstone, while therewere no sand-rich sections penetrated in the ramp lobe fan. The coarsest grains penetratedranges from very fine to fine-grained sandstone, while the individual thickness of the sandstoneranges from 5 to rarely 10 feet. Further works are needed in order to assess its potentiality asproducing reservoir.


INTRODUCTION

The Arguni blocks consist of two Production SharingContracts (PSC): the West (3,489 km2) and East (4,865 km2)Arguni. These blocks are located just southeast of theTangguh field, east of the Babo PSC, and south of the MuturiPSC. They lie from 100 feet water depth and swampy areasin the northern portion, to lowland forest in the west, andsteep ridges that can reach an elevation of up to 4,000 feetin the eastern part (Figure-1).

The Bintuni Basin is bounded to the west by the Oninanticline, to the northwest by the NW-SE trend anticlinoriums(Ubadari, Sekak, and Wiriagar). The Ayamaru Plateau andKemum highs are considered as the northern edge of thisbasin. The N-S Lengguru fold and thrust belt is found as theeastern boundary. This basin is limited to the south by theW-E Tarera Aiduna left-lateral fault zone, the southern pair ofthe Sorong left-lateral fault zone to the north (Figure-1).

Generalized stratigraphic succession in the Bintuni Basin issimply divided into four major intervals: Permian toPaleocene clastics, carbonate section of the Eocene toMiocene, the Late Miocene to Pliocene and Plio-Pleistoceneto present day clastic intervals.

The West and East Arguni were awarded to ARCO (now BP)and Inpex in 16 November 1998 for a 30 years term ofexploration and production, including 10 years explorationprogram. There were ten wells drilled from 1948 to 1983. In1948, Shell (NNGPM) did not reach their primary target, Kaislimestone, as the Steenkool-1 well had stuck pipe problemand TD in the Klasafet Fm. During the 1970 to 1980,Sunoco, Gulf, Esso, and Marathon unsuccessfully tested theKais reef carbonate build-up, the producing reservoir in theSalawati and Mogoi fields. The last dry hole (Suga-1) drilledby Trend in 1983 penetrated repeated Mesozoic sections inthe Lengguru fold belt.

The aim of this study is to preliminary investigate the deep-water reservoir potentiality within the Pliocene section in theArguni blocks. Wells and 2D seismic data were utilized inthis assessment. The study mainly evaluates the WestArguni PSC because most of the 1970’s onshore 2D seismicdata were acquired in this part. It is clearly defined in theseismic that there is a series of low stand deep-waterphysiography. It consists of basin floor and slope fans in theEarly Lowstand Wedge (ELW), and prograding complexassociated with shingled-turbidite stratas in the LateLowstand Wedge (LLW).

TECTONIC ELEMENTS

The Bintuni Basin is bounded to the west by the Onin-Kumawa highs that emerged during the Plio-Pleistocenetectonic event. These highs are predominantly New GuineaLimestone (NGL) outcrops. To the northwest, this basin islimited by the Oligocene-aged and NW-SE trendanticlinoriums (Ubadari, Sekak, and Wiriagar). Theseanticlinoriums separate the Bintuni Basin to the smallerBerau Basin to the west. The Ayamaru Plateau and Kemumhighs are considered as the northern edge of this basin,where the sedimentary section is thinning and outcroppingalong the southern edge of the high. The N-S Lengguru foldand thrust belt is found as the eastern boundary. This foldand thrust belt is variably composed by the NGL to Mesozoicoutcrops from west to the east, respectively. Thecontinuation of the deepest portion of the basin beneath thefrontal edge of this fold and thrust belt is considered. Thisbasin is limited to the south by the W-E Tarera Aiduna left-lateral fault zone, the southern pair of the Sorong left-lateralfault zone to the north (Figure-1).

The transpressional motions associated with the evolution ofthe northern Australian margin to the north and the Pacificplate to the west have been active since the Miocene time.In the early stage of this tectonic phase (Early-MiddleMiocene), sub-aerially exposed local high areas occurred onthe remnant Oligocene-aged ridges (Ubadari, Sekak,Wiriagar) and on the northern margin (Kemum) of the BintuniBasin. While to the east, the Lengguru orogenic belt was stillin the early folding stage. Later in the Late Miocene to EarlyPliocene, these emergent areas shed sediments to the southdepositing the Steenkool Formation, which initiated thetermination of the Miocene carbonate sedimentation in thearea. The subsequent Plio-Pleistocene compressionaltectonic event initiated the overthrusting phase of theLengguru fold belt, which occurred in association with thesubsidence of the adjacent deep Bintuni Basin.

STRATIGRAPHY

Generalized stratigraphic succession in the Bintuni Basin issimply divided into four major intervals: (1) predominantlyPermian to Paleocene clastic, (2) carbonate section of theEocene to Miocene, (3) clastic interval from the Late Mioceneto Pliocene, (4) clastic interval from Plio-Pleistocene topresent day.


The overall upward transgressive succession is applied tothe Permian-Paleocene clastic interval. Continental todeltaic sequences in the Permo-Triassic is unconformablyoverlain by the shallow to deep marine Mesozoic andPaleocene intervals. A period of broad carbonate depositionwas begun in the Eocene, when the deep carbonate Faumailimestone was deposited. Following the Oligocenecompressional event that associated with angularunconformity, a broad platform carbonates Kais Fm.developed throughout the Salawati, Bird’s Head, Bintuni, andto the south to the Lengguru and Kaimana regions.

The Late Miocene Klasafet and Pliocene Lower SteenkoolFormations have been suggested as deep-water facies. Thisinterpretation is mainly based on biostratigraphic andlithostratigraphic analyses of the well penetrations within theBintuni Basin. The Klasafet Fm., which conformably overliesthe Miocene Kais Formation carbonate strata through-outmost of the basin, consists of a fine to very fine-grainedclastic sequence deposited in an outer shelf to upper bathyalenvironment. An overall upward coarsening characterizesthe vertical succession from the Klasafet Fm. to LowerSteenkool Fm, Figure-1A. The depositional environment ofthe overlying Lower Steenkool Fm. varies from shallow waterto deep marine (turbiditic) depending on the location withinthe basin.

The subsequent major uplift, resulting from a Plio-Pleistocene compressional tectonic event, created anunconformity which partially removed Steenkool, Klasafet,Kais and, in some locations, Pre-Tertiary stratas from thesurrounding high areas. This tectonic event initiated theemerging and overthrusting phases of the Lengguru foldbelt,which occurred in association with the subsidence of theadjacent Bintuni Basin. The subsequent erosion associatedwith this event resulted in the deposition of a regressivesequence known as the Sele Fm. This formation thatconformably, and in some areas unconformably, overlie theSteenkool strata, consists of more coarse-grained proximalclastics from paralic to alluvial flood plain sediments

DEEP-WATER INDICATIONS: AT GLANCE

Lithology description of the Klasafet and Lower SteenkoolFormations based on cuttings, sidewall core, andconventional core data lead us into a deep-water lithologyvariation. All of eight wells indicate the presence ofpredominantly light to dark grey calcareous claystone andshale that interbedded with thinly bedded siltstone,

argillaceous limestone, marl, and minor fine to very fine-grained sandstone. The claystone and shale areoccasionally pyritic and very rich in planktonic and deep-water calcareous benthonic foraminiferas.

Supporting evidence from the biostratigraphy analysis in theMonie-1, South Jarua-1 and Terie-1 wells confirms thepresence of the foraminifera assemblages. It characterizesthe marine environments from deep inner-outer shelf by thepresence of Textularia sp. and Discoaster pentaradiatus, toupper bathyal by the increase in abundance of diverseGloborotalia sp. Deep inner-outer shelf ranges from 300-600feet (Berggren, 1983) or 225-450 feet (Boersma, 1983), whileupper bathyal ranges from 600-1,800 feet (Berggren, 1983).

SEQUENCE STRATIGRAPHY OF THESUBMARINE FAN

Early Lowstand Wedge (ELW)

Early Lowstand Wedge (ELW) consists of basin floor andslope fans (BFSF), Figure-2. The BFSF is underlain by type-Isequence boundary (SB-1). The other terminology of thebasin floor fan (bff) is lowstand fan (lsf), Posamentier andVail (1988). The bff is onlapped/downlapped onto asequence boundary (Mitchum, Sangree, Vail, Wornardt,1993) in basinward position, laterally continuous, usuallysand-rich deposits, and described as type-1 turbidite stage(Mutti, 1985). The sequence boundary where the bff lies ischaracterized as type-I sequence boundary or SB-1 (Vail,1987; Posamentier and Vail, 1988; Weimer andPosamentier, 1993).

The slope fan (sf) is onlapped/downlapped onto the bff orsequence boundary (Vail, 1987). It is described as type-3turbidite stage (Mutti, 1985), consists primarily of channel-levee systems (Mutti, 1985; Vail, 1987) or channel overbankdeposits (Vail, 1987; Weimer and Posamentier, 1993).

The bff or lsf was deposited during the rapid relative meansea-level drop from its highstand’s position, while the sf wasformed during the phase when relative mean sea-level dropto the lowest point (Weimer and Posamentier, 1993).

The development of the lowstand wedge in the study areacan be tied to the transpressional motions associated withthe evolution of the northern Australian margin to the northand the Pacific plate to the west. The early stage of this


event resulted uplift on the Kais platform at AyamaruPlateau, northwest of the study area. The uplift event wassubsequently followed by the seaward shoreline shift, whichin turn, could deliver sediments further outboard to the distalportion. Deep incision features that relative to the upliftevent are clearly identified on top of Kais carbonate throughto the seismic data in the Bintuni Bay area. The deepest partof the incision features ranges from 40 to 50 ms TWT (180-250 feet) in thickness. This is interpreted to be theequivalent to a type-1 sequence boundary (SB-1), a markerthat separate Klasafet to the Lower Steenkool Formations(Figure-4 and 5). In the Arguni area, this process can bedescribed in most of the wells if looking at the vertical changefrom the finer-grained Klasafet to the coarser-grained LowerSteenkool Formations, see Figure-1A.

The bff typically consists of a massive sand body thatinterbedded with thin pelagic shales. At the outer edges ofthe sand body interbedded shales may become common andform local vertical barriers. Unfortunately, the BFSF part inthe study area is seismically difficult to differentiate the bffand sf (Figure-4 and 5). Based on well penetrations, this partis rich in pelagic claystone with very fine to fine-grainedcalcareous sandstone, siltstone, and thin limestone layers,which originally sourced from the eroded Kais carbonate.

The BFSF or ELW feature has dimension of 30-70 ms TWTin thickness (130-300 feet), 30 km in length, and 40 km inwidth, Figure-6.

Late Lowstand Wedge (LLW)

According to deep-water models that have been proposed byMutti (1985), Vail (1987), Posamentier and Vail (1988),Posamentier et al. (1991), Weimer and Posamentier (1993),the clinoform features seen in the seismic can be interpretedas the prograding complex (PGC).

The PGC is onlapped onto the sequence boundary updip,and downlapped onto the sf downdip. It primarily consists ofprograding clinoforms, while turbidite systems may developat toe of those clinoforms as shingled-turbidites (ST), Vail,1987; Mitchum et al., 1993. Seismic feature analogs aretaken from the Permian Basin in West Texas and theExmouth Plateau offshore Australia (Figure-3)

The PGC formed between phases of the lowest relativemean sea level and the first phase of relative mean sea-levelrise. Therefore, Posamentier and Vail (1988) described thePGC as the Late Lowstand Wedge (LLW). It is subsequentlyoverlain by a transgressive surface, a first flooding surface

above the maximum regression (Weimer and Posamentier,1993).

Shew (1997) subdivided stratal criteria for PGC into: (1)simple PGC, when the base of the unit downlaps directlyonto the top of the underlying sf or older PGC, (2) PGC withclimbing-downlap pattern that downlaps onto surfaces ofsuccessively younger shingled turbidites. Based on thissubdivision, the PGC in the study area is categorized as thesimple PGC, Figure-4.

There is two recognized prograding complexes (PGC) in theLLW: PGC-1 and 2. The PGC-1 has dimension of 130-370ms TWT in thickness (580-1,650 feet), 40 km in length, and40 km in width. Shingled-turbidite fan feature within thePGC-1, called ST-1, has dimension of ~30 ms TWT in grossthickness (~135 feet), 15 km in length, and up to 35 km inwidth, Figure-7. Several N-S seismic lines show the PGC-1is eroded by the PGC-2. This erosion is considered assubmarine erosion, Figure-8.

The PGC-2 has dimension of 100-220 ms TWT in thickness(450-1,000 feet), 20 km in length, and 30 km in width.Shingled-turbidite fan feature within the PGC-2, called ST-2,has dimension of ~24 ms TWT in gross thickness (~130feet), 20 km in length, and up to 30 km in width, Figure-7 and9.

DEEP MARINE CLASTIC SYSTEM

According to one of the model that proposed by Reading andRichards (1994, in Shew, 1997), mixed-sand mud deepmarine clastic system can be divided into slope aprons, fans,and ramps. In relation with this model and well-logsignatures in the study area, Wami-1 and Aroba-1 wells aresuggested to be in the shelf setting (in PGC/ST-2) and themedial ramp lobes (in PGC/ST-1). The Terie-1 and SouthJarua-1 are considered to be located in the proximal tomedial ramp lobes (in BFSF) and medial ramp channels (inPGC/ST-1) and the medial-ramp-inter channels (in ST-2).South Monie-1 is interpreted to be in the medial ramp inter-channels area, both in PGC/ST-1 and 2. Mandala-1 issituated in the medial ramp lobe (in PGC/ST-2) to the distalramp setting (in PGC/ST-1), see Figure-10, 11, and 12.

The log signatures of the proximal-medial ramp channels arecharacterized by the upward fining succession, where thecoarser grained is deposited earlier than the finer one underthe gravity process along the restricted levee channel, Morevariable log signatures characterize medial ramp lobe, which


varies from blocky to upward fining/coarsening successions.This is suggested due to widely spread and unlimitedreceiving area on the distal ramp plain. Medial ramp interchannels and distal ramp plain, are determined by themonotonous shaly sections with occasionally presence of thelimestone streaks.

RESERVOIR POTENTIAL

Cuttings description of the medial ramp lobe sandstonewithin the BFSF section in the South Jarua-1 is white-lightgray, very fine to fine-grained, very calcareous, moderatelywell sorted, and interbedded with limestone streaks andshale. This sandstone package has a gross thickness of 135feet, while individual sandstone is 5 feet in average, Figure-10. Based on well penetrations the average net to grossratio (N/G) is 0.2 and sparse vertically.

Cuttings description of the ramp channel sandstone withinthe PGC-1 or ST-1 in the South Jarua-1 is gray-white, veryfine to fine-grained quartz, friable, calcareous, and abundantmicro forams, poor visible porosity, grading or interbeddedwith pelagic shale. It has a gross thickness of 105 feet, whileindividual sandstone is usually 5 feet to rarely 10 feet. It issuggested to have up to 25% neutron-log porosity, Figure-11. Based on well penetrations the N/G is 0.4 and sparsevertically.

Unfortunately, the Mandala-1 and Aroba-1 did not penetratethe sand-rich interval within the medial ramp lobe system,Figure-11 and 12. This well encountered the interbeddedsiltstone and claystone, where the siltstone is gray-dark gray,argillaceous, calcareous, abundant micro forams, minor shellfragments, and grading to very fine-grained-calcareous-quartz sandstone in part. This fact leads us to come up withtwo interpretations: (1) that the whole medial ramp lobe-fan isnot necessary to contain sand-rich section. It is becausethere are actually channeling process in this lobe-fangeometry that only allows sand-rich accumulation in theparticular channels. (2) less sedimentary supply of coarse-grained materials from the proximal direction.

CONCLUSIONS

• Sand-rich section is commonly found in the PGC, and isinterpreted as ramp channel sandstone. Using current

2D seismic data, it is difficult to define these individualchannel geometries within the submarine fan deposit.

• Sand-rich section in the ramp lobe fan is suggested asanother reservoir potential, despite there were no sand-rich sections penetrated. It may be due to inappropriatewell location in the tributary channels within the lobe fan,and/or less coarse-grained supply.

• The grain size of the sand-rich sections range from veryfine to fine-grained sandstone, while individual thicknessranges only from 5 to rarely 10 feet. By looking at thegrain size and thickness variation, this sandstone shouldbe further evaluated before it can be categorized aspotential producing reservoirs.

• Further evaluations on the effective porosity-permeability, trap and source rock/charge need to beimplemented to justify the overall risk of this interestingpetroleum system.

REFERENCES

Berggren,W.A.,1983, Marine Micropaleontology AnIntroduction, in B.U. Haq, and Anne Boersma, eds.,Introduction to Marine Micropaleontology, Elsevier,4th.edition, p. 3.

Boersma, A., 1983, Foraminifera, in B.U. Haq, and AnneBoersma, eds., Introduction to Marine Micropaleontology,Elsevier, 4 th.edition, p. 42-44.

Mitchum, R.M., Jr., J.B. Sangree, P.R. Vail, and W.W.Wornardt, 1993, Recognizing Sequences and SystemsTracts from Well Logs, Seismic Data, and Biostratigraphy:Examples from The Late Cenozoic of the Gulf of Mexico, inP. Weimer, and H.W. Posamentier, eds., SiliciclasticSequence Stratigraphy: AAPG Memoir 58, p. 163-167.

Mutti, E., 1985, Seismic Stratigraphy InterpretationProcedure, in A.W. Bally, ed., AAPG Studies in GeologyNo.27, v.1, p. 1-10.

Posamentier, H.W., R.D. Erskine, and R.M. Mitchum, Jr.,1991, Models for Submarine Fan Deposition within aSequence Stratigraphic Framework, in P. Weimer, and M.H.Link, eds., Seismic Facies and Sedimentary Processes ofSubmarine Fans and Turbidite Systems: Springer-Verlag,New York, p. 127-136.


Posamentier, H.W., and Vail, P.R., 1988, (?), in PaulWeimer, course instructor, Course#6 Petroleum Geology ofRift and Passive Margin Turbidite Systems: Brazilian andWorldwide Examples, Part-1: Petroleum Geology of TurbiditeSystems, 1998 AAPG International Conference andExhibition, Rio de Janeiro, Brazil.

Shew (?), 1997, Gulf of Mexico Reservoir Performance, inPaul Weimer, course instructor, Course#6 PetroleumGeology of Rift and Passive Margin Turbidite Systems:Brazilian and Worldwide Examples, Part-1: PetroleumGeology of Turbidite Systems, 1998 AAPG InternationalConference and Exhibition, Rio de Janeiro, Brazil.

Vail, P.R., 1987, Seismic Stratigraphy InterpretationProcedure, in A.W. Bally, ed., AAPG Studies in GeologyNo.27, v.1, p. 1-10.

Weimer, P., and Posamentier, H.W., 1993, RecentDevelopments and Applications in Siliciclastic SequenceStratigraphy, Ch.1, in Siliciclastic Sequence Stratigraphy,Recent Developments and Applications, AAPG Memoir 58,Weimer, P., and Posamentier, H.W., eds., Fig.1, p.9.

Accre te d

Ter ra i n s

Pacif ic Pla teSorong Fau l t

A y a m aruP la teau

Sa lawat i

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in A

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Sc a le

W e s t A r g u n i

S e b y a r - 1

Vorwata - 5

S u ga - 1

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S. Jarua-1

Ter ie -1

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Kasur i -1

Bin tun i

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ng

gu

r u

Fo

l d

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r us

t

E a s t A r g u n i

K e m u mB l o c k

Figure-1. Location and Simplified Tectonic Element Maps.

Figure-2. Model for Submarine-Fan Deposition (Posamentier et.al., 1991).

Submarine Fans in The Permian Basin, West Texas, after Sarg (1989), in Posamentier and Erskine (1991)

Submarine Fans in Exmouth Plateau, offshore Australia, afterErskine and Vail (1988), in Posamentier and Erskine (1991)

Figure-3. Submarine-Fan Analogs from West Texas and Offshore Australia.

CLICK

SEISMIC ANALOGS FOR SUBMARINE FAN

Maximum RegressionSurface

ShingledTurbidite-2 (ST-2)

ShingledTurbidite-1 (ST-1)

SB-1KAIS SHELF

PGC-1PGC-2

UNINTERPRETED SECTION

KLASAFET

LOWER STEENKOOL

EARLYLSW

S N

Shew (1997)

Figure-4. Submarine-Fan Subdivision with Major Surface Boundaries.

BINTUNI BAY

Terie-1

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THICK

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Figure-6. Early Lowstand Wedge (ELW): Basin Floor and Slope Fans (BFSF).

ISOTWTST-2

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Mandala-1

Aroba-1

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20 km

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Terie-1S. Jarua-1

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ERODEDBY PGC-2

Figure-7. Late Lowstand Wedge (LLW): Prograding Complex (PGC) with Shingled Turbidites (ST).

Note: color scales for PGC and ST maps are not similar

KAIS

PGC-1 PGC-2

KLASAFET

SB-1

after Mutti (1985)

Figure-8. Submarine Erosional Surface between PGC-1 and PGC-2.

BABO BINTUNI BAY

20 km

Shew (1997)

Figure-9. Composite Map of the ST-1 and ST-2 on Top Kais Time Structure Map.

ISOTWTST-2

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Terie-1Aroba-1

Mandala-1

S.Jarua-1 S.Jarua-1 Terie-1Mandala-1

Aroba-1

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after Reading and Richards (1994), in Shew (1997)

SB-1

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Figure-10. The Gross Depositional Facies and Log Responses: in BFSF Section.

ISOTWTBFSF

Terie-1Aroba-1

Mandala-1

S.Jarua-1 S.Jarua-1 Terie-1

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-1

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Figure-11. The Gross Depositional Facies and Log Responses: in PGC/ST-1 Section.

ISOTWTST-1

Terie-1Aroba-1

Mandala-1

S.Jarua-1 S.Jarua-1 Terie-1

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ISOTWTST-2

Figure-12. The Gross Depositional Facies and Log Responses: in PGC/ST-2 Section.

Northwest Borneo


Turbidite and Deep-water Depositional Systems ofBorneo: Reservoir Models of Basin Floor and SlopeReservoir Fan SystemsPaul Crevello1

1Petrex Asia Reservoir andStratigraphy Consultants1032 Muria 2 / Pujut 2BMiri 98000, Sarawak,[email protected]

This talk is a shortenedversion of the 2001 AAPGDistinguished Lecture,Funded by the AAPGFoundation in honor of RoyM. Huffington.

ABSTRACT

Turbidites are relatively new exploration targets in deep-water plays of Southeast Asia, viz., theMahakam and Baram deltas and the NW Sabah shelf, where recently discovered reservoirsands flow at rates approaching 10k bpd. Discoveries of hydrocarbon-charged sands in theseactive tectonic basins have meet with mixed success. Imaging of pay sands and predictingsand fairways are complicated by shifting basin receptacles associated with foreland thrustsystems, which include deformation of basin floor turbidite fans by thrust ridges and byprogressive growth in ponded slope basins. Knowledge of the hinterland source area, shelfstaging area and sand influx are poorly constrained because of the complicated tectonic andprolonged turbidite basin history of Borneo. Outcrop and subsurface data sets will bepresented in this talk that will provide examples to elucidate turbidite models for the pan-Borneobasins.

The oldest turbidite systems of Borneo, the Cretaceous-Eocene Rajang and Embaluh groups,extend well over 1000 km along the backbone of Borneo. The younger West Crocker,Temburong and Setap Formations occur in outcrop and offshore NW Borneo, and importanthydrocarbon-bearing turbidite sequences occur in offshore regions of the Miocene-PlioceneKutei, Baram and NW Sabah basins. Not all turbidite systems contain prospective reservoirs,however, because of burial, tectonic history or poor reservoir attributes.

Two principle turbidite systems were deposited north central Borneo: the West Crockersubmarine basin floor fan and the Neogene Setap basin floor and slope turbidite systems:these range from middle Late Oligocene to Middle and Late Miocene in outcrop to Miocene-Pliocene in the offshore hydrocarbon provinces.

The Crocker Formation is a classic, unconfined basin-floor submarine fan complex. The fandeveloped in a foredeep accretionary trough, which extended over 500 km along the Borneotrench. Sand-rich channel-sheet complexes exceed 300 m in thickness, with 80% net sand.Individual channel axis sands rarely exceed 3-5 m, while channel and sheet sands occur inamalgamated sequences of 30-60 meters thick multistory sands, proximal and distal levees andchannel margin facies successions. The lateral and strike extent of the fan system supports anextensive complex of off-lapping unrestricted channel-sheet lobe fans. The Crocker reservoirsare poor quality because of low permeability and moderate burial depths. These sands wererecycled into the Neogene turbidite basins during uplift of the heart of Borneo.


The Neogene turbidite systems formed in ponded slope basins and unconfined basin floor fansof the pan-Borneo basins. These systems formed during inversion of the Borneo backbone andclearly record linkage between sedimentation and tectonics. Turbidite channel sands and lobesthin and onlap or are truncated along active sea floor structures, faults and shale diapirs.Depositional cycles contain mega-slumps, olistoliths and debris flows alternating with channeland sheet/lobe sands. Individual channel and lobe sands rarely exceed 3 m, whileamalgamated multistory sands are typically between 10-30 m. Subsurface fans approach 50 min thickness and may stack to form 300 m thick reservoir systems. The linkage of lowstandshelf-edge deltas and tectonic episodes with optimum reservoir sands, input and shelf bypassis recorded in these Neogene systems. To date, turbidite systems have been discovered inPliocene and Miocene fan systems.


STRATAGEM Forward Stratigraphic Modelling Of TheNorthwest Sabah Deep-water Area, MalaysiaZulkefli Abdul Hamid 1 and Charlie Lee1

1PETRONAS Sabah ShellPetroleum Co. Ltd(Currently in Shell Deep-water Services – Houston)

ABSTRACT

A STRATAGEM model (an interactive modelling program for integrated stratighraphicevolution), based on regional 2D deep-water seismic lines from the Northwest Sabah deep-water area, adequately modelled the stratigraphic and structural geometries of the continentalmargin and deep-water basins. The modelling allows geoscientist to complete the circle fromsubsurface seismic and wells interpretation through forward stratigraphic modelling togeneration of syntethic seismic and wells for comparison with real data.

Good match between modelled and observed stratigraphy based on seismic and well data hasdeveloped and quantified concepts of deep-water basin evolution, predicted deep-waterfacies/reservoir distribution and architecture, constructed interpretation of deep-watersubsurface data and performed sensitivity test that evaluate the fundamental controls on theobserved deep-water basin stratigraphy.

Tectonically induced subsidence and eustatic sea level changes are found to be the two maincontrolling factors on the deep-water reservoir evolution and distribution. Thrust-sheet piggy-back basins and associated thrust ridges form an ideal trap for the ponding of turbidites on theshelf, slope and basin by the fill-and-spill mechanism. Changes in eustatic sea level have majorimpact on the rate of the deep-water sediment supply, accommodation space and environmentof deposition.


Figure 1: Time section (reflectivity) of regional seismic line BGR8616, showing the major structural features andseismic horizons used for STRATEGEM modelling.

Figure 2: STRATAGEM model for regional seismic line BGR8618, showing the environment of deposition. The modelcorrelates well with the control well.


Figure 3: STRATAGEM model for regional seismic line BGR8618 showing the sand distribution. The model correlateswell with the control well.


Cretaceous Selangkai Formation of West KalimantanAnd Its Tectonic ImplicationsBaharuddin1 and R. Heryanto 1

1Geological Research andDevelopment Centre

ABSTRACT

Data collected during the 1982-1984 regional geological and geophysical mapping in westKalimantan emphasizing the Cretacesous Selangkai Formation have fed us to reassess theexistence of flysch type deposits in order to understand the tectonic development of the area.

The Selangkai Formation is well exposed in 1:250.000 scale map of Sintang Quadrangle. Itbelongs to a deformed flysch type deposit, which has deposited in a submarine fanenvironment. Lithologically, the formation consists of calcareous mudstone with intercalations ofbouldery to pebbly mudstone, graded sandstone, rare limestone and conglomerate. Theconglomerate unit, which is known as the Belakai Conglomerate, is interpreted as a basalconglomerate of the lower Selangkai a total thickness of the Selangkai formation in exceeds of3000 m. Several stratigraphic stages are occupied by classical turbidite Bouma sequence orother mass flow deposits. Fossils assemblages discovered within the formation indicate agesranging from Early to Late Cretaceous.

The Cretaceous Selangkai Formation (including Embalugh Group in eastern region) and BoyanMelange are possibly parts of an accretionary complex of southerly dipping subduction zone ineastern part of West Kalimantan during the Cretaceous time. This subduction activity has alsoresulted the Cretaceous Schwaner magmatic belt.


Study area

NATUNA

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S A R A W A K

East

K A L I M A N T A NWest

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J A V A S E A

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BELITUNG

BALIKPAPAN

BANJARMASIN

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Putusibau

SanggauPONTIANAK

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Figure 1 : Location of study area

Sintang

Prominent Sandstone BedsBelakai ConglomerateSelangkai Formation

0 50 Km

1 1 2 0 0 E0 0

500

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Figure 2: Distribution of Selangkai Formation and Belakai Conglomerate, Sintang 1:250.000 sheet area.


+++

+ ++

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B LateCretacaous

CEarlyTertiary

. . . .... ... .. . .. ... ....

+ + + +

+ + + +

Modern coastline

Modern coastline, not stabilised

Strike-slip fault inferred

Extensional area

Inferred compressional area

Crustal fragments of China and Indochina origin

Present day north

Yunnan-Malay geosyncline

Active

Inactive

Inferred subduction zone

Southeast Asiamagmatic belt

Figure 3 : Paleogeographic recontructions showing a major N-W transform fault during the Late Cretaceous and Early Tertiary in NW Borneo, modified from Taylor and Hayes (1983.)

Figure 3: Paleogeographic reconstructions showing a major NW transform fault during the LateCretaceous and Early Tertiary in NW Borneo, modified from Taylor and Hayes (1983).


Deep-water Reservoirs of Northwest Borneo:Evaluating Potential Outcrop AnalogsS. Back1 and J.J. Lambiase1

1Department of PetroleumGeoscience, UniversitiBrunei Darussalam

ABSTRACT

Deep-water reservoirs offshore NW Borneo are currently an important target for hydrocarbonexploration. Data used to evaluate potential reservoir geometries and quality includequantitative reservoir models from outcrop analogs. An evaluation of several Oligocene andMiocene turbidite outcrops in Brunei and southern Sabah with respect to offshore reservoirsindicate that a number of key parameters influencing turbidite development differ significantlyfrom those of the prospective Late Miocene/Pliocene deep-water targets.

Turbidite outcrops in Brunei include a Middle Miocene succession of >50m interbedded sandsand shales (individual sand beds 0.02-1.3m thick). Sedimentary structures match divisions A-Cof the Bouma sequence indicating turbidity current deposition. Foraminiferal assemblagesindicate a shelf setting and pollen analyses suggest close proximity to a coast. The associationof exclusively shallow-water microfossil assemblages with turbidites is interpreted to reflectsedimentation in a delta-front setting. Depositional system analysis shows that the turbiditesoccur amongst slumps and storm sands in thin detached lowstands (offshore sands) not farfrom a deltaic feeder system. Lateral and vertical scale, as well as the stratal architecture,match that of a prograding shelf delta on a ramp margin. This setting is fundamentally differentfrom the offshore deep-water area with target reservoirs located on the slope of a >80km widegrowth-fault margin.

A re-evaluation of previously described Oligocene/Middle Miocene turbidite outcrops of Sabahand Labuan also indicates major differences in their structural and stratigraphic settingcompared to the Late Miocene/Pliocene offshore successions. This suggests a limited value ofthe outcrops as offshore reservoir analogs.


Other Areas


A Spectacular Outcrop Analog For TurbiditeReservoirs: The Miocene Mount Messenger/UrenuiDeep-water System, New ZealandP. R. King1 and G. H. Browne1

1Institute of Geological andNuclear Sciences Ltd, P.O. Box 30 368, LowerHutt, New Zealand

ABSTRACT

A Late Miocene deep-water submarine fan and overlying progradational slope succession issuperbly exposed in coastal cliffs in north Taranaki Basin, New Zealand (Figures 1&2; King etal. 1993, 1994; Browne et al. 2000). The fortuitous orientation of the present-day coastline withrespect to the gentle regional dip of strata and the paleo-seabed profile provides a semi-continuous exposed transect through one 3rd-order order (c. 5 m.y. duration) progradationalsystem, from basin floor to uppermost slope-outermost shelf.

The section is characterised by fresh (wave-washed) exposures and only moderatelyconsolidated rocks. It is becoming recognised as a “classic” turbidite succession worldwide forexamining a variety of deep-water facies types, stratal geometries, and stacking patterns, atscales ranging from seismic to microscopic. The section is useful for developing conceptsrelating to sequence stratigraphy and depositional processes, and is ideal for developingreservoir analogues and comparing and correlating outcrop and subsurface data. In particular,the different sedimentology and morphologies of sheet fan and lobe sandstones (Figure 3),base-of-slope fan aprons (Figure 4), and slope channels/canyons (Figure 5) are clearly evident.A variety of industry and research data acquired along or near the coastal transect are availableto supplement the excellent exposures, including: exploration and shallow stratigraphic welldata (core, log), 2-D regular and high-resolution seismic reflection data, outcrop data(poroperm, bed thickness and continuity, rock mechanical), paleontological data.

These deep-water sediments were deposited in a complex foreland basin/intra-arc setting onthe northwestern margin of proto-New Zealand (Australian Plate) and above the west-dippingsubducting Pacific Plate. The exposed succession forms part of an extensive regressive systemresulting from a huge influx of sediment produced by hinterland uplift and erosion to the eastand southeast. Laterally-equivalent successions in subsurface Taranaki Basin are evident onseismic reflection profiles as a spectacular series of offlapping clinoforms. As well, laterally-equivalent intervals constitute the main reservoir units in two producing oilfields located c. 50km from the coastal section. The outcrop succession can be correlated into the subsurface asfar as the producing fields using seismic reflection profiles and SP logs.

The overall succession extends for tens of kilometres, and is around 2000 m thick. It is sand-dominated at the base, and mud-dominated at the top. Microfaunal assemblages indicate aprogressive shallowing up-section from mid- to upper bathyal paleo-water depths. A number ofstacked, 4th-order depositional cycles have been identified at various locations along theoutcrop section. The base of each cycle is marked by an erosional disconformity. In lowermostcycles deposited in deepest waters, the disconformities have little erosional relief and are


inferred to pass basinwards into correlative conformities. The degree of channelling andincision at cycle bases increases dramatically upsection. Lithofacies, bed geometry andstacking patterns also change along the transect, and although no single exposed cycledisplays all facies types and bed forms, a composite picture of the internal architecture of ageneric cycle can be predicted. The lowermost cycles seen all fine upwards (contrary toWalker-type models), and comprise thick-bedded massive sandstones, overlain by thinlyinterbedded sandstones and mudstones, then mudstones, and finally slumped mudstones.These are inferred to be mid-fan deposits. Immediately overlying cycles with basal, clastconglomerate-infilled scours and channels, are inferred to represent more proximal submarinefan deposits. Successions deposited at the base of the advancing slope are characterised bydramatically interleaving channels, infilled with minor conglomerates, thin-bedded turbiditesdisplaying near-'classical' Bouma sequences, and mudstones. Overlying slope deposits aremud-dominated, but are punctuated at regular intervals by spectacular canyons and channels.These features are variously infilled with, or their margins onlapped by, thick conglomeraticdebris flow deposits, thick-bedded and massive sandstones very similar to the mid- andproximal-fan sandstones, thin-bedded and ripple-laminated sandstones, and mudstones.Mudstones at the top of these cycles are generally slumped, indicating some form of slopeinstability prior to the next channelised debris flow.

From the perspective of recognising or predicting reservoir type and quality, the mainparameters that vary within the overall succession include sand-mud proportions, sandstonebedding thickness and style, and degree of channelling. One interesting observation is thatBouma-type turbidite sequences with thick climbing-ripple portions are prevalent in base-of-slope settings, where sedimentation was rapid, but are virtually absent in deeper-water fandeposits, which generally appear massive. Amalgamated thick-bedded basin-floor sandstonesare relatively continuous, whereas associated thin-bedded lobe sandstones pinch and swelldramatically. Scouring markedly reduces the lateral continuity of slope fan units, and individualbeds show marked lateral and vertical variation in permeability. Coarse-grained reservoir facieson the slope are entirely confined within large channels or canyons.

From observed and predicted stratigraphic relationships and lateral facies variability within thesuccessive offlapping 4th-order cycles, we have elucidated constituent system tractcomponents, and their genetic relationship to changing relative base level. The proportionalthickness of various lowstand (and possible highstand) components changes upsection withinthe overall 3rd-order progradational system exposed.

REFERENCES:

Browne, G.H.; Slatt, R.M.; King, P.R. 2000: Contrasting styles of basin floor fan and slope fandeposition: Mount Messenger Formation, New Zealand. Chapter 13 in: Bouma, A. H.; Stelting,C.E; Stone, C.G. ed.: Fine-grained turbidite systems. AAPG memoir 72. American Associationof Petroleum Geologists, Tulsa, Oklahoma. p.1-10.

King, P.R.; Scott, G.H. and Robinson, P.H. 1993: Description, correlation and depositionalhistory of Miocene sediments outcropping along north Taranaki coast. Institute of Geologicaland Nuclear Sciences Ltd. monograph 5. 199 p.

King, P.R.; Browne, G.H.; Slatt, R.M. 1994: Sequence architecture of exposed late Miocenebasin floor fan and channel-levee complexes (Mount Messenger Formation), Taranaki Basin,New Zealand. p. 177-192 In: Weimer, P.; Bouma, A.H.; Perkins, B.F. (eds.) Submarine Fans


and Turbidite Systems. Proceedings Gulf Coast Section Society of Economic Paleontologistsand Mineralogists Foundation fifteenth annual research conference, Houston. 440 p.

Dip slope within basinfloor fan interval

Figure 1 Aerial view north along coastal outcrop section

Slope fan thin-bedded turbidites

Depos itio nal bas e line

SW

4R

egional dip

O

Coastal clifftransect

Not to s c aleVE= 15

NE

NE

NW

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Figure 3: BASIN FLOOR FAN: mid cycle (thin-beds) and upper cycle (muds)

Toe of slope, debris flow conglomerate

Coalescing scour and fill packages

Figure 4. Slope fan succession, upper Mount Messenger Formation

Paramoudra

SLOPE CANYON MARGIN: URENUI FORMATION

Slope msts

Canyon margins

1

2

Thin-bedded ssts(canyon fill)

Figure 5. Similar feature at same stratigraphic level on seismic profile, about 10 km inland

500 m_____

Person


Facies and Sequences of A Restricted, Active-MarginSubmarine Fan in A Transgressive Setting, TheDevonian Mindip Formation, Eastern AustraliaK.A.A. van Noord 1

1School of NaturalResource Sciences,Queensland University ofTechnology, 2 George St,GPO Box 2434, Brisbane,QLD, Australia 4001.Current address: BakerAtlas GEOScience, 2ndlevel Adelaide House, 200Adelaide Terrace, EastPerth, WA, Australia 6001.

ABSTRACT

The Mindip Formation is the youngest of five formations that developed in an ancient intra-oceanic island arc during the mid-Cambrian to Late Devonian. Together these formations areknown as the Silverwood Group, a sequence that forms one terrane within the New EnglandFold Belt along the eastern margin of Australia (Figure 1a). The Mindip Formation is unique forit represents one of the few ancient examples of a restricted, sand-rich submarine fandeposited in an overall transgressive regime. The inclined exposures of the unit allows itsvertical and lateral succession to be compared against equivalent deep-marine explorationplays.

The late Devonian Mindip Formation consists of the basal Long Mountain Breccia Member(LMB) and six overlying sub-units labelled A to F. The LMB is a massive cohesive debris flowwith a rigid central plug of block and boulder material. The member shows overall lateralcoarse tail grading, from blocks and boulders in the centre of the deposit, to pebbles 1-2 kmaway. The member has an angular unconformable contact with the Ormoral Volcanics andBald Hill Formation and is postulated to represent the product of sector collapse from asubaerial basaltic-andesitic stratovolcano. The debris avalanche resulting from the collapsewas transformed into the mass transport complex upon entering the sea.

Overlying the LMB are the tuffaceous cohesive debris flows and proximal high density turbiditesof Unit A, which represent erosional and mixed erosional-depositional inner-fan channelturbidites. These inner-fan turbidites formed as a series of braided channels emplaced withinlevee facies turbidites, such as those in Unit C. Similar coarse grained tuffaceous facies arefound in Unit D, which also represents a series of erosional and mixed erosional-depositionalinner-fan channels. Like Unit A, inner-fan channels of unit D are braided and were emplacedwithin levee facies turbidites (Unit C).

Units B and E overlie Units A and D respectively and consist of very thick bedded, high density,sandy turbidites which form a system of braided channels on the mid-fan (suprafan lobes).These suprafan lobes conformably overlie the inner-fan channel turbidites and are convex-upward in shape. Unit C consists of very thin to medium bedded 'classic' Bouma turbiditeswhich form levee, channel-margin and crevasse splay elements. Unit C is present as a wedgeof exposure beneath Unit E (Figure 1b). Unit F overlies Unit E and consists of thin bedded'classic' Bouma Tbcde, Tcde, Tde and Te turbidites that were deposited on the outer-fan (lobe-fringe).


All together, the LMB and six sub-units described above constitute a single point-sourcesubmarine fan equivalent to the Type II fan of Mutti (1985), the submarine fan model of Walker(1978), and the sand-rich point-source fan of Reading and Richards (1994). The fan wasinitiated by deposition of a mass transport complex (the LMB), and subsequently developed astwo repetitive stages of retrogressive sedimentation, in which channel-levee elements (Units A,C and D) are overlain by suprafan lobe elements (Units B and E) and eventually by outer-fandeposits (Unit F). Both inner-fan channels and suprafan lobes show centralised stackingpatterns with limited lateral migration (Figure 1b). This sedimentation pattern is consistent withvertical aggradation of 4th order elements, like channel-levee complexes, as a result of lateralrestrictions on sedimentation (e.g. perhaps by submarine ridges). The characteristics of theformation are typical of an active margin fan that formed by a combination of tectonic stageinitiation, followed by eustatically-controlled retrogradation.

REFERENCES

Mutti E. 1985. Turbidite systems and their relations to depositional sequences. In Zuffa G.G.(ed.), Provenance of Arenites, pp. 65-93. D. Reidel Publishing Company, Dordrecht.

Reading H.G. and Richards M. 1994. Turbidite systems in deep-water basin margins classifiedby grain size and feeder system. Bulletin of the American Association of Petroluem Geologists,78, 792-822.

Walker R.G. 1978. Deep-water sandstone facies and ancient submarine fans: models forexploration for stratigraphic traps. Bulletin of the American Association of PetroluemGeologists, 62, 932-966.

Figure 1. a) Location map of study area in relation to eastern Australia. Also shown on thefigure is the distribution of the youngest orogen of the Tasman orogen, the New England FoldBelt (hachured area). b) Geological interpretation map of the Mindip Formation. Features tonote from this figure include the vertical stacking of the various architectural elements (MTCand Units A to F), the steep dips of the exposures (up to 80� to the east), and theunconformable contact at the base of the formation beneath the LMB. Of the remainingformations shown, the Connolly Volcanics, Bald Hill Formation and Ormoral Volcanics also formpart of the Silverwood Group, while the Eight Mile Creek beds are part of an overlying Permiansuccession. The Connolly Volcanics represents the oldest formation shown on the figure(middle or late Silurian to Early Devonian). It is overlain by the Bald Hill Formation (EarlyDevonian), which is subsequently overlain by the Ormoral Volcanics (Early to MiddleDevonian). The small arrows within the figure represent younging direction.

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Deepwater Systems in the Campos Basin, Brazil:A Comparison to the Makassar StraitChandra Suria1 and Meizarwin1

1BP Indonesia ABSTRACT

Brazil offers world class oil and gas reserve potential from more than 20 sedimentary basins.Industry estimates indicate that Brazil contains over 12 billion barrels of undiscovered oilreserves, with much of this potential in deep to ultra deepwater. In the last ten years,exploration in deepwater (>1000 ft) has discovered a total of 5 billion barrels of oil. Gasreserves are significantly under explored. Proven reserves are only 5.5 tcf, due primarily to thelack of gas exploration. Published reports indicate undiscovered reserves ranging from 25 to50 tcf.

In February 1997, Brazil offered more than 150 exploration and production opportunities to theindustry after more than 12 years monopoly by Petrobras in Brazil’s oil and gas industry. Morethan 10 project agreements had been signed in Brazil’s deepwater exploration and productionopportunities, mostly in the Campos basin, part of the East Brazil Rift System.

The rift was formed in Jurassic to Early Cretaceous time and led to the opening of the Atlantic.The non-marine Lower Cretaceous Lagoa Feia Formation was deposited on Neocomianbasaltic extrusives, which in turn is overlain by the Aptian terrigenous and evaporate sequence.Inaugurating the drift stage, a marine carbonate platform sequence, grading into fluvial-deltaicsediments along the landward margin of the basin (the Albian Macae Formation) overlies theevaporates. Continuous subsidence and concomitant seaward tilting of the basin led todeposition of transgressive deepening marine shales that, in turn, are overlain by a regressiveprogradational shallowing sequence of sandstones, limestones, and shales. The entirepackage of sediments is the Turonian-Quartenary Campos Formation. The main deepwaterreservoirs are the Late Cretaceous-Paleocene Carapebus member and the Oligocene-MioceneUbatuba member (Guardado et al., 1989, Falkenhein et al., 1981, Carozzi and Falkenhein,1985, Barros et al., 1980). The sediment source for the deepwater reservoir systems isbelieved to be the interior mountain ranges, which were exhumed in the Cretaceous andEocene times (Meisling et al., 2001, Cobbold et al., 2001.).

The prospective deepwater systems in the Campos Basin were deposited from Late Aptian toMiocene time in diverse physiographic settings, in response to the complex interplay of salttectonics uplift and progradation of the continent margin. The Late Aptian turbidites occur asextensive blankets deposited on a flat sea floor and can be seismically correlated over wideareas. The Cenomanian-Turonian turbidites show rapid lateral thickness variations and areconfined to narrow troughs formed in response to deeper salt movement and erosion. Bothtypes of turbidites consist predominantly of medium to coarse massive sandstones withaverage net pay of 30 meter, porosity 17% and permeability 100 mD. Oligocene and Mioceneturbidites are the main reservoirs in the deepwater of the Campos basin. During the Oligocenethere was intense progradation of the continental margin. Large area of the continental shelfwere exposed, several submarine canyons developed, and extensive deepwater fans formedoffshore. The sand reservoirs occur as tabular bodies 30 to 100 meters in thickness and coverareas as large as 300 sq. km. The range of net pay is 15 to 45 meter, porosity 20-30% andpermeability of 200 to 5,000 mD. Oligocene sands are the sole reservoirs in the giant Marlimfield (2.1 bbo and 2.2 tcfg), whereas Albacora (1.1 bbo and 2.3 tcfg) produces from deepwater

sand reservoirs ranging in age from Albian to Miocene, but Miocene is by far the most important(Guardado et al., 1990, Bacoccoli and Toffoli, 1988, Moraes and Bruhn, 1988).

In Makassar Strait deepwater systems, the basin was initiated in the Middle Eocene as a resultof rifting in the North Makassar Straits. This episode was followed by regressive style ofsedimentation during late Oligocene-Miocene. Middle Miocene to Pliocene interior tectonicuplift in the western part of the basin Margin initiated the redeposition of the Upper Kutei deltasystem into the Lower Kutei system and eventually the Makassar deepwater area (Moss &Chambers, 1999, Malecek et al., 1993). This Middle Miocene to Pliocene recycled sandstonedeposits appear to be the most prospective reservoir interval for hydrocarbon accumulation inthe deepwater area (IHS). In the northwestern part of the Makassar Strait area, the majorturbidite reservoirs occur as amalgamated channels and interbedded overbank-levee depositsin a confined setting (Readhead et al., 2000). To the east and southeast, the sand reservoirswere deposited in an unconfined setting such as moderate to high sinuosity leveed channels,distributary channels/frontal splays, overbank wedges (levees), overbanks splays/sedimentwaves and debris flow deposits (Posamentier et al., 2000). The reservoir has porosity valuesin the range of 22 to 32% and permeabilities are in the 150 to 1500 mD range with a 40 to 360feet of net pay (IHS, Readhead et al., 2000). Published reports indicate the total reserves of thedeepwater discovery fields to date are in the range of 1 – 1.6 BBOE from about 9 fields.

The petroleum systems of the Campos basin depend on the syn-rift Lagoa Feia lacustrinesource rock with a TOC up to 9%. The high prospectivity of the basin is explained by theadequate timing of hydrocarbon migration and entrapment, associated with salt tectonics.Large volumes became trapped after the Eocene/Oligocene, by which time the EarlyCretaceous sediments are believed to have reached their peak maturation level and the basinwas characterized by a high sedimentation rate. Hydrocarbon migration pathways exist wherefaulting is transmitted, from reactivated sub-salt transfer zones, through salt windows, intosupra-salt sediments. Deposition of the Tertiary deepwater reservoir systems was associatedwith the eastward progradation of the continental shelf, at times interrupted by periods oferosion and deformation by salt tectonics. Correspondingly, reservoir distribution had animportant stratigraphic control on the trap capacity of several accumulations (Guardado et al.,1989, Meisling et al, 2001, Cobbold et al, 2001).

In the Makassar Strait, source rocks in the deepwater are believed to be transported organicmaterials derived from the lower delta plain, with mixed oil and gas potential. The pre-MiddleMiocene to Late Miocene section is potentially within the oil window, depending on the localheat flow and Plio-Pleistocene sediment load. Peak generation is quite recent. Faults,associated with sediment loading and tectonic event, are interpreted to be the vertical migrationpathways from source kitchen to the reservoirs (Peters et al. 2000, Readhead et al. 2000).Rollover anticlines as well as toe thrust belt seems to be the successful exploration target inMerah Besar and West Seno area (Malecek et al., 1993, Readhead et al. 2000, Johansen2000).

Poster Session


Reservoir Modeling of Turbidites Using Well Data andLaboratory ExperimentsStefan M. Luthi1 and Alberto Malinverno2

1Delft University ofTechnologyDepartment of AppliedEarth Sciences2628 RX Delft, TheNetherlands

2Schlumberger-DollResearch, Ridgefield, CT06877, USA

ABSTRACT

When a sequence of turbidite beds is crossed by the wellbore of an oil well, one fundamentalquestion is how these beds extend away from the wellbore. In the first place, an accuratemeasurement of the turbidite beds, down to the very thinnest layers, has to be carried out. Thena three-dimensional reconstruction of the layer geometry around the wellbore can beperformed. Several approaches can be taken here, but we discuss only two: A statistical one,based on the power-law distribution of the bed thicknesses, and an object-based 3-modelingapproach using a basic geometric template obtained from experimental turbidites. In bothcases, the true bed size distribution (as opposed to the apparent bed thicknesses observed inthe wellbore) is obtained, and bed extents and volumes of the beds connected to the wellboreis obtained.

These approaches were applied to a case study from the Gulf of Mexico where over 4500 bedswere found in a single well. The resulting estimations of the hydrocarbons in place that can bedrained by the wellbore were similar for both models, but substantially smaller than from alayer-cake model using a typical drainage radius.


Tectonostratigraphic Controls on TurbiditeDepositional Processes in BruneiPatrick Allman-Ward1, Jan Pieter Tromp1 and Abdullah B. Ibrahim1

1Brunei Shell PetroleumCompany, Seria, BruneiDarussalam

ABSTRACT

Brunei Shell Petroleum and its competitors have drilled 22 wells in Brunei waters to date whichhave penetrated turbidite reservoirs (Figure 1). These have been both in deep-water sensustricto and in shallower waters on the shelf targeting the underlying, deeper turbidite objectives.Exploration success rate has been high, over 70% of the tests having discovered hydrocarbonsbut commercial success rates have been relatively low (14%).

All of the wells drilled to date have been in the slope or by-pass environment. The results havehighlighted that the key element in commercializing turbidite discoveries in Brunei in this settingis adequate reservoir development (Figure 2). One of the most important challenges istherefore to identify where the turbidite sands are best developed prior to exploration drilling.

The late Tertiary depositional system offshore Brunei is strongly progradational (Figure 3). Thesedimentation history has been dominated by the Baram Delta to the southwest and the“Champion Delta” to the northeast (Figure 4). The shelf profile is characterized by a steep slope(up to 10 degrees in places) with a relatively rapid descent into extreme water depths (>2500m)in the centre of the NW Borneo Trough (Figure 5). The potential for turbidite reservoirdevelopment in Brunei has been related to three controlling mechanisms: source material,delivery system and accommodation space.

The sand prone nature of turbidites in NW Borneo is determined by the quantity of sand in thecatchment area and the energy and distribution of the erosional system. The nature andmaturity of the source sediments in the Borneo Highlands control sand quantity. The energyand distribution of the erosional system is linked to the river profile and whether the sedimentsupply is linear or occurs as discrete point sources. In addition, the quality of the sourcematerial can be enhanced by the action of longshore currents driven by monsoonal weatherpatterns leading to a comprehensive redistribution of sand out to the shelf edge.

The greatest likelihood of forming sand rich turbidites occurs during periods of large relative sealevel fall when the shelf is exposed and river systems may be captured directly into the head ofthe submarine canyon system allowing bypass of sediment directly into the deep-water. Adetailed time-rock synopsis of the Brunei depositional system is made possible bycomprehensive 3D seismic data coverage and high resolution (bio-) stratigraphy. It clearlyshows a correlation between intervals of better reservoir development in the deep-water andperiods of major lowstands, which in the case of Brunei, have been enhanced by tectonism(Figure 3). Large incised valleys were developed in the pro delta area and formed the conduitsbetween the source area and the areas where turbidite sedimentation took place (Figure 6).


Turbidite currents deposit their load when they reach the base of their graded (slope) profilewhich is usually the basin floor. However, in Brunei, this setting is occurs either in extremepresent day water depths or very deep in the section in shallower present day water depths andis probably undrillable due to overpressures (Figure 7). Turbidite sediment can be trapped onthe slope if accommodation space is created by either locally raising the datum or througherosion or slumping (Figure 8; Prather, 2000). The development of accommodation space inBrunei is related to gravity gliding (toe thrusted anticlines) on the lower slope and to shalediapirism on the middle and upper slope. In slope settings dominated by shale diapirism (e.g.Nigeria, Trinidad, NW Borneo) the amount of vertical relief generated is much less than in saltdominated sedimentary systems due to the slower kinetics of shale versus salt diapirism(Figure 9; Prather, 2000). Generally these mini-basins are subtle with low vertical relief andtend to be linearly confined by the shale ridges. The nature of the objective turbidite reservoirsin Brunei is therefore determined by their position on the slope and the development ofaccommodation space through time (Figure 10).

REFERENCES CITED

Prather, B. E., 2000, Calibration and visualization of depositional process models for above-grade slopes: a case study from the Gulf of Mexico. Marine and Petroleum Geology, in press.


Scientific targets of IODP - New Ocean Drilling PlanY. Yamada1

1OD21 Program Office(Japan Marine Science andTechnology Center)

ABSTRACT

The Integrated Ocean Drilling Program (IODP) is an international scientific research endeavorscheduled to begin in October 2003. This program will use both the new Japanese riser drillingvessel now under construction and an U.S. non-riser vessel. Opportunities for scientists toparticipate will clearly expand.

Through and following the CONCORD (1997) and COMPLEX (1999) meetings, three majorscientific themes have been identified for IODP: 1) the Deep Biosphere & the Sub-SeafloorOcean, 2) Environmental Change & Its Impact on Life, and 3) Solid Earth Cycles &Geodynamics. These core themes are closely linked to studies of biotechnology, climatechange, earthquake hazards, natural resource potential, sea level change, and volcaniceruptions, which are of societal relevance. Direct examination of the seismogenic zone is one ofthe prime targets of the IODP, which has been planned for practical purpose and to satisfy longheld scientific ambitions.

By drilling deeper into the crust, and to depths where plate interactions occur, we aim toapproach closer to understanding the total earth system covering from climate changes tomantle convection with a unified perspective. A drill hole provides us core samples and variousexperimental environments. This requires harmonious relationship between scientists andengineers. We also need cooperation amongst scientists from widely different disciplines, suchas seismologists, biologists, and chemists, among others. Our approach must be innovativeand synergetic, aiming for creation of a new field of science. IODP will be a proposal-drivenscience and there will be many ways to participate in the program.


Surface Geochemistry As An Exploration Tool inFrontier Deep-water Areas: Case Studies fromSoutheast AsiaMalvin Bjoroy1

1Geolab Nor AS, P.O.Box5740, Trondheim, 7437,Norway, phone:4773964000,[email protected] andGeir Hansen, SurfaceGeochemical Services AS,P.O.Box 1257, Vika, Oslo,N-0111, Norway.

ABSTRACT

Surface geochemical prospecting involves the search for near-surface or surface anomalies ofhydrocarbons, which could indicate the occurrence of petroleum accumulations in the sub-surface. The methodology, as applied in offshore basins, covers a range of techniques, fromobservation of visible oil seepages at the surface, to detection of micro-seeps, in near surfacesediments, using sensitive analytical techniques.

Since most rock types are not totally impervious to hydrocarbons, both light and heavyhydrocarbons will migrate upwards, from either mature source rocks or reservoirs, to nearsurface sediments. While the methodology for surface geochemical surveys is the subject ofcontinuous development, the current, most favoured practice is to detect possible migrationpathways from the deep to the near-surface with the aid of seismic data, often together withremote sensing data (satellite imaging etc). The expression of such pathways at the surface isthen the focus of surface geochemical prospecting grids.

This methodology has been applied in several surveys in the relatively unexplored deep-waterbasins of the western North Atlantic Margin, West Africa and South East Asia. In this paper wewill present studies from West Africa and Southeast Asia, where we will discuss the planning,sampling and analytical results. The analyses include analysis of both gas and liquidhydrocarbons in sediment samples. The results vary significantly in the different basins, fromshowing only micro-seepage to showing a combination of micro-seepage and macro-seepage(with biodegradation of the seeped hydrocarbons in specific areas). Our studies clearly showthat marine surface geochemical prospecting can be used to determine whether or nothydrocarbons have been generated in a basin, and whether these are oil or gas related. If oilrelated hydrocarbons are detected, then information on the types and maturities of source rockswhich have generated these hydrocarbons can also be determined.


Gravity Data Analysis of Ujungpangkah AreaImplication for Structural Evolution and HydrocarbonProspectSartono1

1Geological Research andDevelopment Centre, Jl.Diponegoro 57, Bandung,West Java, INDONESIA

ABSTRACT

Based on physiographic setting, the northern region of East Java is divided into 3 zones. Thereare Rembang-Madura zone in the north, Randublatung depression zone as dividing zone toKendeng zone in the south.

Ujungpangkah area belongs to Rembang-Madura zone, situated 40 km to the north ofSurabaya, characterised by a range of Bouguer anomaly between 20 to 45 mgal in the north.The area is interpreted as an epicontinental basin. The basin is filled by detritus material fromthe Bawean high to the north. Further on the upper of terrestrial deposit is covered by chalkylimestone and porous (karren) reef limestones.

Randublatung depresion zone is characterised by a range of gravity anomaly of 20 to -10 mgaland showing a steep gravity gradient, it is interpreted that the basement fault occured at depth.The deepest basin, the Kendeng zone, it is characterised by Bouguer anomaly with a rangefrom -10 to -40 mgal. The basin is filled by clastic sediment and volcanic origin.

The fault block processes at the northern region of East Java created a basinal deep Kendengzone, depresion Randublatung zone and a basement high Ujungpangkah area. This processcaused the sediment layer on the basement would be folded and faulted. The anticline ofsedimentary rock was created on the upper of Ujungpangkah basement high and the faultedstructure can act as a good hydrocarbon entrapment.

Within the Ujungpangkah area, calcareous sandstone from Tawun Formation and quartzsandstone also reef limestone from Watukoceng Formation have all promoted as ahydrocarbon reservoir rocks.


Oligo-Miocene Deep–water Clastic SedimentsIdentified from Watugajah and BanyutiboStratigraphic Measured Sections Southern Mountain,Yogyakarta.Sugeng S. Suryono1, Jarot Setyowiyoto 1, and Marno Datun1

1Geological EngineeringDepartment, Faculty ofEngineering, Gadjah MadaUniversity. Jl. Grafika 2,Bulaksumur Yogyakarta,Telp./Fax.:0274 513668,[email protected]

ABSTRACT

The study area is located at Watugajah village, in the northern escarpment of SouthernMountains block faulting, in Gunungkidul Regency which is approximately 40 kilometers to theeast of Yogyakarta. The research was conducted when the new road that cuts the escarpmentwas under construction. Sedimentary rocks and measured section was observed along theroad that has distance approximately 3 kilometers. The shorter distance of other measuredsection was observed at Banyutibo traverse which is located about 2.5 kilometers to the east ofWatugajah traverse.

The sedimentary section is included in Kebo-Butak Formation which is the lowest Formationcomposing the Southern Mountains. This formation composed mainly of sandstone, siltstoneand claystone intercalation in the lower part and interbedded conglomerate sandstone and clayor silt in the upper part. The lower part of this formation was intruded by sill-type igneous rocks(Bothe 1929), meanwhile the igneous rocks were interpreted as lava flows (Rahardjo, 1983).Sedimentary rocks that compose this formation is interpreted as sediment which is deposited inthe submarine fan environment (Rahardjo, 1983). The total thickness of this formation reaching800 meters with the age of late Oligocene (N2-N3)– early Miocene (N4-N5).

By making measured sections at Watugajah and Banyutibo traverses, details on the lithologyand sedimentology from the lowest to the top part of Kebo-Butak Formation could be identified.The lithology of the two detail stratigraphic measured sections can be divided into two units thatare Sandstone-Shale Unit and Pebbly Sandstone Unit.

THE SANDSTONE-SHALE UNIT

This unit is generally composed by well gradational bedding sandstone to clay on the bottom,followed by interbedded sandstone – shale and some massive sandstone bedding. The upperpart comprised of gradational pebbly sandstone to medium sandstone or clay then changes tointerbedding sandstone – shale. The upper part of this unit is intruded by igneous rock.

In details, the lowest part of this unit is composed by gradational coarse sandstone to clay,massive sandstone which is 2 – 10 meters thick and on the several layers show interbedding ofsandstone-shale which is 0,2-0,5 meters thick. The color of the bedding is light brown togreenish brown, the composing materials are andesite, plagioclase fragments, tuff and clay-


size mineral with normally graded bedding, massive or amalgamated structures. To the upperpart, fine sandstone – shale interbedding with the thickness of 0.2 – 0.5 meters more oftenappears. Among the interbeddings are composed gradational sandstone – clay from classicturbidite series which is 1-3 meters thick, or massive sandstone which reaches up to 6 metersthick. At the classic turbidite series often be found sandstone-shale normally gradational,parallel lamination and slump structures (Ta – Tc Bouma series). The sediment structures areproduced by turbidity current process.

In the middle part of this unit is dominated by gradational pebbly sandstone – mediumsandstone, or massive sandstone with 4-5 meters in thickness. Erosional base is shown at thebottom contact due to fast sedimentation of grain flows. In some layers can be found sandstoneclastic fragments with the dimension more than one meter floating in it.

In the upper part of this unit shows classic turbidities as interbedding sandstone – shale whichis 0.5 – 1 meters thick and also gradational coarse sandstone – fine sandstone which reachesup to 5 meters of thickness in several layers. Two igneous rock intrusive bodies can be found inthis part. In the field, the igneous rocks concordantly contacts the top and bottom layers andshowing baking effect on the contacts like found at the point of 325 meters Watugajahmeasured section and on the surrounding area of Banyutibo. Intrusion contacts can be seenwell on the faulting escarpments. Based on the field data, the kind of intrusion is sill. Theigneous rocks are black, porphyro-aphanitic , composed by plagioclase, pyroxene andmycrolites which are hyalo-ophitic texture. The present of igneous rocks body which enteredthe sandstone bedding at Banyutibo went to prove that the igneous rocks intruded thesandstone while the stack of sandstone was built and had not lithified perfectly yet.

The total outcrops thickness of this unit is 385 meters, which is measured from Watugajahtraverse. Fossils are really rare, however on the clay sample can be found benthonic fossilsthat show Oligocene – early Miocene age and deep marine environment (abyssal).

The petrographic analysis show that the sandstone have wacke texture. The texture mightoccurred when sandstone was deposited quickly without grain sorting. Based on the sedimentstructure, fossils and thin section, the deposition environment of this unit is interpreted as outer– middle part fan of deep ocean fan environment (Walker, 1984) by low density turbiditycurrents– grain flow (Lowe, 1982, Mutti, 1993). According to lithological component andsedimentary structure, the facies stack thickness and the other components of stratigraphicappearances, this unit can be grouped in lower parts of Kebo-Butak Formation.

THE PEBBLY SANDSTONE UNIT

The pebbly sandstone unit is generally composed of gradational pebbly sandstone – mediumsandstone, interbedded sandstone – shale and pockets breccia. This sequence was observedat Watugajah traverse. Detail description of the sequence show that the grain-size trends arecoarser to the upper layers until the breccias is formed, then become finer to the top unit. Theearly appearance is started by repeating gradational yellow greenish thick bedding pebblysandstone to clay. To the upper part, the gradational pebbly sandstones are thicker althoughinterbedded shale and fine sandstone still present. Each gradational facies is 7-8 meters inthickness, sometimes up to 15 meters. The first appearance of gradational pebbly sandstone inthe study area usually is found not too far from igneous rocks on the previous unit.


The sediment structure are bedding, amalgamated and lamination of fine-grained sand. Theerosional contact are usually occur at base of gradational pebbly sandstone which is producedby fast depositional process. Another sediment structure is traction carpets on the breccialayers.

On the middle part of this unit, the appearance of intercalation breccia has started. It is browngreenish polimix breccia or brown blackish andesite breccia, which form erosional contact oras pockets breccia among the gradational coarse sandstone body. Intercalation of sandstoneand shale occasionally is found among gradational pebbly sandstone. The composing materialsare andesite fragments, plagioclase, and tuff.

On the upper part of pebbly sandstone unit are deposited repetition of thick breccia up to 30meters. The breccias are generally blackish brown with cobble-boulder fragment, openingfabrics, poor sorting, consists basalt and andesite. The matrixes are grain supportedsandstones, composing andesitic rocks of fragment, plagioclase and a little glass volcanic. Thebeddings thickness reach up to 8 – 10 meters with gradational or massive structure. Thevarious kinds of composing lithology are basaltic or andesitic breccia which interbedding withgreenish coarse sandstone or greenish gradational polimix beccia. The bedding contacts at thebottom of layers are sharp or erosional. The unsorted fragments are probably caused by debrisflow. The fragments become finer to the upper part and sometimes show parallel fragmentsediment structure of F2-F4 Mutti’s facies. The age of this unit is difficult to identifie due toabsent of the fossil, however it can be correlated with pebbly sandstone unit that equal to lowerpart of Middle Miocene. We consider that this breccias are sub-unit of pebbly sandstone unit.The breccias are deposited at the braided channel of deep sea fan by debris flows or grainflows (Walker, 1984).

Interbedding sandstone – shale more often appears, mostly greenish, tufaceous, with 0,5 – 1meters in thickness and develop between gradational pebbly – sandstones above the breccia.In the sandstone – shale interbeddings can be found polimix breccia which are igneous, clay,sandstones and corral fragments. The existence of corral fragments pointed out that there isanother provenance beside volcanic. The greenish color of this unit is occurred due to alterationof plagioclase and tuff become chlorite or greenish clay-size minerals.

The total thickness of this unit by measured section at Watugajah traverse is 350 meters. Thefossil is very rare, some of the were observed are Globigerinoides altialperturus planktonicforamminifera index fossil which suggested that the unit’s age is the lower part of LowerMiocene (N5-N6). The depositional environment is interpreted as the mid fan of the deep seafan. This unit is part of upper part Kebo-Butak Formation.

CONCLUSIONS

Two detail stratigraphic measured sections of 750 meters thick of Watugajah and 250 metersthick of Banyutibo traverse have been performed in order to determine its sedimentology anddepositional environment. The sequence can be divided into two units: sandstone–shale unitand pebbly sandstone unit. The sedimentary structure is dominated by graded bedding, parallellamination or convolute lamination, amalgamated and sharp or erosional base contacts whichcorrespond to classic turbidite series of Ta – Td Bouma sequence.The benthonic fossilanalysis suggested that these sequence were deposited in the deep sea environment (abyssal)at lower (outer) – mid fan with intercalation of braided channel of deep ocean fan. Thedepositional mechanism is dominated by low – high density turbidity currents and minor debrisflow.


Depositional Environment of Sambipitu FormationBayu Handoko1 and Tigor Yuni Ardi1

1Student of GeologicalEngineering Department,University ofPembangunan NasionalVeteran Yogyakarta -INDONESIA

ABSTRACT

Sambipitu Formation outcropped on the base of the South Baturagung mountain range ,Wonosari, Yogyakarta. Based on our research, the Sambipitu Formation consists of five mainfacies association: 1) Classical Turbidite, 2) Pebbly Sandstone, 3) Conglomerate, 4) Pebblymudstone, debris flow, slumps and slide.

The Classical Turbidite is characterized by monotonous alteration of sharp-based sandstoneand interbedded mudstone. The classical term implies that most people would quickly identifythis sediment as typical turbidite today. This association contains two main facies: thin-beddedand thick-bedded turbidite. The thin-bedded turbidite can be separated into two distinct type:the first is characterized by one row of current ripples with rare convolute lamination and thesecond is characterized by climbing ripples.

The Pebbly Sandstone tends to be well graded, internal stratification is fairly abundant andconsists of a rather coarse horizontal stratification or a well-developed trough or planar-tabularcross bedding. Pebbly Sandstone beds are commonly channeled and laterally discontinuouswith uncommon inter-bedded shale.

The lower part of Sambipitu Formation is Conglomerate that is characterized by gradedbedding (normal and inverse). The most important feature is the imbrication, which is typified byclasts whose long axes lie parallel to flow and dip upstream.

Pebbly mudstone consists of pebbles and distorted clasts of sandstone and mudstone,disposed in silty mudstone matrix. The origin for such texture is the rapid deposition of sandand gravel on top of very watery, uncompacted mudstone. Alternatively, some pebblymudstone may be resulted from debris flow deposit.


Pliocene Deep-water Sedimentation of Mundu andKalibeng Formations in Northeast Java BasinM. Yohannes P. Koesoemo1

1Oil and Gas ManpowerDevelopment Centre (PPTMigas), Jl. Sorogo No. 1,Cepu, Central Java,INDONESIAPhone: 0296-421888Fax: 0296-421891Email:[email protected]

ABSTRACT

The study area is located in the Northeast Java Basin. The tectonic evolution can be tracedfrom Late Cretaceous to Recent. During Paleogen, the tectonic tension was active andcontinued by Neogene tectonic compression, resulting in folding and faulting structure in thestudy area.

During Pliocene (N18-N20), transgressive system tract was occurred in the Northeast JavaBasin and the 100-m thick of massive marl facies deposited in the deep-water environment,indicated by 99% planktonic foraminifera shells in the massive marl.

In the northern part of the study area (Remban Zone), massive marl facies recognized asMundu Formation. The massive marl facies also known as Kalibeng Formation in the KendengZone that located in the southern part of the study area.

The Upper Pliocene (N21) sea level drop of 2.0 Ma in the Rembang Zone producedforaminiferal sand of Selorejo Formation that act as gas reservoir in the Cepu area and as oilreservoir in Surabaya area. In the Kendeng Zone (7 km north of Ngawi), the reefal limestone ofKlitik Member developed in the upper part of Kalibeng Formation.

The marl facies of Kalibeng Formation possibly developed as caprock in Gunung Nongko(northern part of Jombang area) that located in the eastern part of Kendeng Zone. Based onthe distribution of marl facies in the study area, can be concluded that deep-water depositionalenvironment developed in the Northeast Java Basin during Pliocene.


MRGC, A New Clustering Method that Helps TheSedimentologists to Take Advantage of NMR andBorehole Imagery to Recognize Sedimentary FaciesFrom LogsPhilippe Rabiller1, J.P. Leduc1, B. Mathis1, and Shin-Ju Ye2

1TOTALFINAELF

1Halliburton EnergyServices

ABSTRACT

In 1981, Serra and Abott proposed the concept of electrofacies as a geological substitute forpartial or missing core information. Since then several methods were proposed to make thisconcept practical. However, none of them proved successful in dealing with the rich informationthat can be obtained through NMR or Borehole Imagery logging.

Amongst the numerous potential geological applications of NMR, recent examples of deepoffshore wells drilled using Oil Based Mud have shown that in appropriate logging conditions,the NMR T2 distribution can be used to recognize the presence of very thin sand and shalelaminae alternation in complex turbiditic environment, and characterize their grain size andsorting thus making NMR logging a very valuable log for the sedimentologist.

MRGC, a new clustering method published at the 41st SPWLA symposium in Houston, allowsto use the full NMR T2 distribution to define electrofacies in combination with conventionalelectric logs and Borehole Imagery Automatic Texture analysis as proposed by Ye et al. (39SPWLA symposium, Keystone 1998). The simplicity and speed of the process allows the userto rapidly set up electrofacies models for stratigraphic intervals and whenever needed to definespecific models for hydrocarbon and water bearing reservoirs within the same stratigraphicinterval. The method can be used on single well or multi-well data sets, and provision is madeto use core calibration as input. Additionally, a model defined on a data set can be propagatedto other wells with confidence as an index is calculated that controls whether or not the modelcan be applied to the new data set.

Field examples, from different sedimentary environments, are proposed to illustrate the methodand how most significant sedimentary facies can be recognized from their log characteristics.

ISBN 979-96438-0-5

supporting organizations:

Indonesian PetroleumAssociation

International Association ofSedimentologists

Society of Sedimentary Geology American Association of PetroleumGeologists

Courtesy of Greg Partyka

Documents

Deep-Water Sedimentation 2001 (Fosi_deepwater)