Riset dan Publikasi


Fortieth Annual Convention & Exhibition, May 2016

Sedimentology and limnology of Singkarak and Toba Lakes, Sumatra, Indonesia: Depositional AND PETROLEUM SYSTEM MODEL for tropical fluvio-lacustrine and volcanic related rift basins in SouthEast Asia

Prihatin Tri Setyobudi* Purnama Ary Suandhi* Zaka Lesmana Tarigan* Andang Bachtiar** Anita Galih Ringga Jayanti*** Lamsyah Budin****

*GDA Consulting **Indonesia National Exploration Committee *** Institute of Technology Bandung **** Institute of Technology Medan


Lake Singkarak and Lake Toba are situated in Northeast – Southwest (NE-SW) trend of The Great Sumatera Fault. Lake Singkarak and Lake Toba could be ideal models for similar lacustrine sedimentary environments in Tertiary basins around Southeast Asia especially for hydrocarbon exploration. The goals of this study are to create a depositional-environment model (sedimentology), compile paleo-climate evolution information and develop a petroleum system analogue.

Research methodologies include the comprehensive field observations of sedimentology-geometry using PVC-pipe sampler, gravity coring, grabber, and outcrop observation. Bathymetry-geometry field observations have utilized the echo-sounder and strata-box multi beam, while the laboratory analyses covered the carbon dating analyses for stratigraphy, geochemistry analyses for total organic content, and pollen analyses for paleo-climate reconstruction.

Singkarak Lake is modern tropical rift basin classified as pull-apart basin related with Great Sumatra Fault. The Lake Toba is classified as subduction related basin in continental margin controlled by Great Sumatra Fault and associated volcanic activities. The sedimentary sections in the last 11,400 years at Lake Singkarak, and 28,000 years at Lake Toba have been recorded during the field observations. The depositional environment can be divided into nine facies comprising fluvial braided-meandering complex, lacustrine delta, fan delta, shoreline complex, inner shelf-middle shelf lacustrine, sub-lacustrine channel and levee complex, deep lacustrine, and sub-lacustrine fan. The development of these facieses has been strongly controlled by the present-day tectonic and volcanic activities.

Keywords: Singkarak, Toba, rift, basin





Bachtiar, A**., Suandhi, P.A.*., Setyobudi, P.T.*., Fitris, F***., Malda, O*., Lesmana, Z*

GDA Consulting* – DEN** – Chevron Pasific Indonesia***
Tebet Timur Dalam X Street No 2, Postal Code 12820 – Jakarta, Indonesia

Abstract ID: 2210852


Lake Singkarak is the biggest modern pull apart basin in Indonesia and closes modern analogue model for Central Sumatera and Ombilin Basins. This lake is situated at Solok District, West Sumatera Province. Lake Singkarak was originally developed by active transtensional tectonic regime at one of many compartment of Great Sumatera Fault. This study is aimed to give alternative sedimentology analogue model for fluvio lacustrine environment in tropical area by made similarity comparation between modern to ancient sediment.

Results of comprehensive field sedimentology work showing series of Quaternary Holocene (12,700 – 2,700 years) sediments which are distinguished by particular association of individual facies (10 defined facies) related to fluvio – lacustrine system. Alluvial fan facies was characterized by coarsening sequence pattern of intercalation gravity flow and traction sediments. Braided river facies was characterized by high energy traction sediment at steep slope river with volcanic clastic sediment supply with soil layer at top part. Meandering river facies was characterized by low sinuosity meandering belt with high traction current sediment and fining upward sequence. Fan delta facies was divided become three part, upper, medial and lower which dominantly characterized combination of gravity flow and traction current. Shoreline lacustrine facies was characterized by low energy of wave current creating wash over sediment. Lacustrine delta facies was divide become four sub-facies consisting of delta plain, distributaries channel, and mouth bar. Shallow lacustrine facies was characterized by falling out suspension creating interlaminate of clay, algae, silt and medium grain sand and poorly massive clay. Shelf slope – deep lacustrine facies is distributed from first bathymetry slope (25-35 meter) to the basin floor or deepest part of lacustrine (267 meter). Results of strata box measurement which is integrated with bathymetry survey, gravity coring and sediment grabbing on systematic mechanism showing that this depositional was divided becomes four sub-facies consisting of sub-lacustrine channel and levee complex, sub-lacustrine fan, shelf turbidity and pelagic facies. Shelf – deep lacustrine facies was characterized by high density turbidity and falling out of suspension sediment.



Thirty-Ninth Annual Convention & Exhibition, May 2015


Integrated Study of The Depositional Environment, Structural Geology, Diagenesis, and Petroleum System of The Tertiary At The Southern Border of The Upper Kutai Basin

Andang Bachtiar* Prihatin Tri Setyobudi*  Muhammad Rozalli *  Elly Guritno**  Ari Subekti**  Purnama Ary Suandhi*  Andi Kriyunianto*

*GDA Consulting  ** Salamander (West Bangkanai) Energy Ltd


 The southern border of the Upper Kutai Basin is a semi-mature exploration area in Central Kalimantan which has proven producing hydrocarbons. In 1982, a significant gas and condensate accumulation was discovered in Oligocene Carbonates in Kerendan Field. Most of the seismic data in this area have poor-fair quality. So an integrated study of the surface and sub-surface was needed to get a better petroleum system component potential oversight.

Surface geological mapping and measured oucrop stratigraphy were integrated with well correlations and seismic facies to obtain the depositional environments and overall stratigraphic framework. Burial history analysis from source rock maturity and petrographic analysis were conducted to understand the diagenesis or burial effects within the reservoir and source rock quality. Detailed surface structural geology investigations were integrated with image/landsat and seismic interpretations to valididate structure occurrences and possible reconstruction of the traps.

Syn-rift sediments were developed during Middle to Late Eocene with terrestrial to deltaic environments A bounding fault (southern area), transitions to a marine environments which developed in a flexural margin (northern area). Post-rift sediments were developed during Early to Late Oligocene which were dominated with a marine environment, isolated reefs commonly occur in the northern area, and platform carbonates occur in the southern area. Inversion sedimentation developed in Early to Late Miocene which was dominated with deltaic sediments, where the paleo-shoreline changed from a E-W to a N-S direction. A Post-Inversion stage is developed during Plio-Pleistocene which is composed of mollasic sediments and NE-SW thrust faults.

The primary source rocks are Eocene, fluvial-deltaics (Type II, III, II & III, and matured) and Oligocene marine source rocks. The best reservoirs are Miocene & Eocene fluvial deltaic sandstones and Oligocene carbonates with secondary porosity (fracture and dissolution). Regional seals are Late Oligocene offshore-bathyal shales and intra-formational seals of Eocene and Miocene deltaic sediments. The predominate traps are a combination of stratigraphy and structure which are controlled by NE-SW thrust faults or fold propagated faults.




Thirty-Ninth Annual Convention & Exhibition, May 2015


Ari Yusliandi*, Bambang Dodi Hari Sasmita*, Muhammad Arifai*, Muhammad Alfatih Syaifurrohman*, Prihatin Tri Setyobudi*, Andang Bachtiar*, Purnama Ary Suandhi*, Andi Krisyunianto (* GDA Consulting)


Marine deposits make good reservoirs. Cibulakan Formation in Northwest Java Basin is one example of productive reservoir. Teluk Naga and Parang Tritis beach deposits are good example of modern analogue to compare characteristics between the tertiary and recent beach deposits.

This study reviews Cibulakan Formation characteristics based on previous studies including an assessment of sediment composition, texture of material and stratigraphy based on core and outcrops data compared with modern beach sands at Teluk Naga and Parang Tritis.

Cibulakan Formation can be divided into two members, Upper Cibulakan Member and Lower Cibulakan Member. In this study, Upper Cibulakan Member comprises poorly consolidated greenish grey claystone to consolidated shale, containing dispersed silt, quartz sand, pyrite, glauconite, lignitic plant remains, foraminifera and shell fragments. Upper Cibulakan Member was deposited in shallow inner-outer neritic environment.

Parang Tritis is a beach located in southern part of Java Island exactly at Yogyakarta province, Teluk Naga is a beach located in northern part of Java Island exactly at Banten province. Observation of modern sediments on both beaches used pipe coring methods. Data were collected from different places. Characterization of Parang Tritis beach shows more indications of wave dominated deposits than Teluk Naga sedimentological characteristics. The results of this study can be applied to hydrocarbon exploration based on the analogue between recent sediment and Tertiary formation.

Keywords: Marine reservoir, Cibulakan Formation, Northwest Java Basin, Teluk Naga, Parang Tritis, Reservoir Characteristics, Modern Analogue.


(ICGES 2014)

Proceeding of 2014 3rd International Conference on Geological and Environmental Sciences

(ICGES 2014)

Singapore, 6-7 August, 2014

Sedimentology and Petrography of Selected North Sumatra Pre-Tertiary Formations: Anticipating New Petroleum Systems in Western Indonesia

 Andang Bachtiar (1), Prihatin Tri Setyobudi (1), Siti Asyiah (2), Armein Suleiman(2), Purnama Ary Suandhi(1), Andi Kriyunianto (1)

Affiliation (“1” PT. Geosain Delta Andalan; “2” PT. Paleopetro)


This research is focused on studying the depositional system and petrographic characteristics of petroleum system that form in North Sumatera, Indonesia to reveal the diagenesis, metamorphism, alteration indicators related to reservoir and source rock potential. Field work was integrated with paleontology analysis and comprehensive petrographic study of selected thin sections. Paleozoic and Mesozoic Stratigraphy of North Sumatra can be divided into Tapanuli Group (Alas Fm, Kluet Fm, Bohorok Fm) and Peusangan Group (Pangururan Bryozoa Bed, Batumilmil Fm, Kaloi Fm, Kualu Fm). Pre-Tertiary Rocks were variously deposited in deep marine (ie: Sibaganding Limestone) with Radiolarian Limestone; shallow marine (ie: Batumilmil Fm, Kaloi Fm) with Limestone and dolomitic limestone; moraine glacier and till (ie: Bohorok Pebbly Mudstone); and shallow water (ie: Kualu Mudstone, Pangururan Bryozoa Bed). Batumilmil Fm can be divided into Dolomitic red limestone, Light-grey Limestone, Dark-grey Limestone, and Carbonaceous Claystone. Reservoir potential was formed by farctures, disslutions and dolomitization (ie: Kaloi and Batumilmil Dolomitic Limestone). Further more, source rock potential was found in Batumilmil and Kualu Mudstone.

Keywords: petroleum system, North Sumatera, diagenesis.




Thirty-Eighth Annual Convention & Exhibition, May 2014


Andang Bachtiar*, Jaafar B Unir**, Amin Bunyamin**, Hendra Iriansyah Darmawan**, Fithra Harris Darmawan**, Frederick Herbert Korah**, Bobby Mazmur Sihole**, Lismawati***, Prihatin Tri Setyobudi****

* Institute of Technology Medan, GDA Consultingand Exploration Think Tank Indonesia, ** Petronas Carigali West Glagah Kambuna Ltd., *** Institute of Technology Medan, ****GDA Consulting


The offshore area of North Sumatra Basin is believed to have good hydrocarbon accumulation potential and is considered challenging for hydrocarbon exploration. Several exploratory wells had been drilled in this area with major discoveries mainly in Tertiary age reservoirs such as the Baong and Belumai Formations. The Pre-Tertiary plays of the North Sumatra Basin are still underexplored and are believed to have an important role in future successful hydrocarbon exploration in the area.

The Pre-Tertiary play is the main exploration target in West Glagah Kambuna in offshore North Sumatra Basin. Previous regional studies suggested that the basements in this area are mainly the Tampur Formation of Eocene – Early Oligocene age. Based on present study however, the basement of the West Glagah Kambuna area mainly consists of the Batumilmil, Kaloi and Kualu Formations of Permian – Triassic age that are parts of the Peusangan Group.

The offshore seismic data clearly indicate angular unconformity contact between the Pre-Tertiary and the Tertiary stratigraphy.  In addition to the clearly defined Tertiary sedimentary-fills section, the seismic also shows good images of the Pre-Tertiary packages which can be differentiated based on their internal-external reflection characteristics and reflectivity.

By correlating the pre-rift seismic section with onshore geology which is based on outcrop data, it is interpreted that the Pre-Rift stratigraphy found in offshore area belongs to Mesozoic Peusangan Group. The Peusangan Group in the offshore area can be divided into three different formations; from the oldest to the youngest are the Batumilmil, Kaloi, and the Kualu Formations. The Batumilmil Formation is represented by chaotic seismic character; the Kaloi Formation is represented by high amplitude seismic reflection, while the low amplitude seismic reflection above the Kaloi Formation is interpreted as the Kualu Formation. The good match between seismic and well data in WGK block and surrounding area strongly support the interpretation.

The outcrop study in Aceh and North Sumatra Province has confirmed that the pre-Bampo/Bruksah section of the  North Sumatera Basin comprising  not only the Dolomite Tampur Formation, but also several formations from Meureudu and Peusangan Groups which are Pre-Tertiary in ages. The study also suggested that the pre-rift dolomitic carbonate are not just belong to the Tampur Formation since the Peusangan Group also shown similar lithology, particularly in Batumilmil and Kaloi Formations. The extensive tectonic and subaerial exposure has promoted fractures and caving in those formations. Beside the dolomitic carbonate, the study also found clastic rock within the Pre-Tertiary stratigraphy. The clastic rocks are black shale in Batumimil and mudstone in Kualu Formation. Several fossils could still be found in Batumilmil carbonate and Kualu mudstone. The outcrop sedimentology characteristic are still showing sedimentary rock character where bedding and layering is clear and common.

The Pre-Tertiary formations that developed in WGK block and surrounding area are parts of the Peusangan Group, which based on our field observation and laboratory analysis of Kaloi, Kualu, and Batumilmil Formation, they show good reservoir properties and also with high carbon content in their shales in some places. It shows a possibility of the Pre-Tertiary formations to have its own petroleum system, separated from the Tertiary formations. This promotes new exploration opportunity in southern part of North Sumatera Basin, particularly in WGK block.



Thirty-seven Annual Convention & Exhibition May 2013


 Purnama Ary Suandhi*, Andang Bachtiar**, Prihatin Tri Setyobudi*, Muhammad Rozalli*, Yudi Satria Purnama**

* GDA Consulting, ** Exploration Think Tank Indonesia


North Barito Shelf is one of the most potential exploration area in Central Kalimantan which is proven producing hydrocarbon in border of Upper Kutai – North Barito Basins. Significant gas condensate accumulation has been discovered in Oligocene Carbonates in Kerendan Field, Teweh Permit by Union Oil in 1982. Paleogene petroleum system play is one of the main target in this area including reservoir target. Integrated stratigraphy, sedimentology features, facies and potential reservoir information from outcrops samples of Paleogene Sediments Units should be a guide line to explore the potential of petroleum system. Data is derived from outcrops and laboratory analyses results. Studied area covers area of  Bintang Ninggi – Gunung Purai – Muara Teweh (Central and East Kalimantan).

Comprehensive stratigraphic measurement in the North Barito area showing 6 (six) sediments units (chronostratigraphy), consisting of Pre-Tertary, Middle Eocene, Late Eocene, Early Oligocene, Late Oligocene, and Miocene Sediment Unit. The pre tertiary basement rocks are consisting mica schist and quartzsite. Middle Eocene Sediment Unit are consisting of 5 (five) facies unit, i.e; Alluvial Fan, Fluvial Braided and Meandering River, Fluvial to Upper Delta Plain,Lower Delta Plain – Delta Front,Prodelta/Offshore. Late Eocene Sediment Unit are consisting of  3 (three) facies units, i.e; Lower Delta Plain – Delta Front, ProDelta/Offshore, Offshore – Bathyal. Early Oligocene Sediment Units are consisting of 4 (four) facies units, i.e; Tidal Flat/Barrier Bar, Shoreface, Carbonate Complex, Offshore – Bathyal. Late Oligocene Sediment Unitsare Consisting 5 (five), i.e: Shoreface, Carbonate Complex, Offshore – Bathyal, Tidal Flat/Barrier Bar, Fluvial – Delta Plain – Delta Front Facies. Miocene Sediment Unit are consisting of 5 (Five) facies units, i.e Lower Delta Plain – Delta  Front, Delta Plain – Delta Front, Delta Front – Prodelta, Pro Delta/Offshore, Fluvial – Delta Plain – Delta Front.

Keywords: Paleogen, Facies, North Barito



HAGI-IAGI Joint Convention Medan 2013

28 – 31 October

Litofasies studies and Maturity Levels of Ngrayong Deltaic Sandstone, Tawun Formation Jamprong Region, Kenduruan District, Tuban and Its Implications for Reservoir Quality

Bhaskara Aji1) Prihatin Tri Setyobudi1) Rizqi Syawal1) Aveliansyah1)

1) Forum Geosaintis Muda Indonesia (FGMI)


 Ngrayong Sandstones member of Middle Miocene Tawun Formation, is one of the main reservoir in the North East Java Basin. Currently depositional environment of Ngrayong Member is still being debated, because in Cepu area and surrounding sediments with relatively similar characteristics can be interpreted into two different environments are deltaic and deepwater turbidite. The difference being the object of interest to be discussed related to hydrocarbon reservoir potential.

The integrated research methods are surface geological mapping, measured stratigraphic column, granulometry analysis (spericity, roundness, composition, grain size and sorting variations), petrography, porosity and permeability measurements.

Litofacies unit in the mapping area are Facies of Shale with Sandstone Intercalation, Coal and Gypsum Fragments, Sandstone Facies, Siltstone Facies, Interbeding Sandstone – Siltstone Facies, and Red Sandstone Facies. Sedimentary structures such as bedding fisillity, bedding, bicurrent crossbedding, oscillation ripplemark, flaser, lenticular bedding, coarsening upward. Petrographic analysis of red sandstone shows types of sandstone such as Arenite Quartz, arkosic Wacke until Sub Arckose. Granulometri analysis shows sortation ranged from poorly – moderately, level of roundness and sphericity are low sphericity with a little clay content, showing a level of maturity from submature until mature which was deposited with medium energy. Porosity and permeability test of Sandstone facies  result porosity 32% -44% with permeability-833 mD –  0.015 mD, and Porosity and permeability test of Red Sandstone facies result porosity 32% -41% with 90 – 404 mD permeability. Based on an integrated analysis of sedimentology known that many facies was deposited in Pro-delta environment and Delta Front. The most excellent reservoir quality are the Red Sandstone facies and sandstones  facies with good porosity and permeability which are interpreted as part of mouth bar from deltaic system.

Keywords: Ngrayong, Delta, Sandstone



HAGI-IAGI Joint Convention Medan 2013

28 – 31 October

Sedimentology of Fluvial-Deltaic Coal Formation in Kutai Basin Based on Various Outcrops, Previous Geological Study and Modern Mahakam Delta Analogue

Prihatin Tri Setyobudi1) Purnama Ary Suandhi1) Andang Bachtiar1) Achmad Miri1)

1) GDA Consulting (PT. Geosain Delta Andalan)


Kutai Basin is Tertiary basin which is the largest coal producers in Indonesia. Basic sedimentology knowledge, regional geology controlled and modern environment analogue are needed to support coal exploration activity specially coal seams correlation framework in the fluvial – deltaic environment in Lower Kutai Basin.

The methods of this research are spot mapping in several coal outcrops in Samarinda – Tenggarong areas (Lower Kutai), comprehensive stratigraphic measurement in the Muara Teweh – Kutai Barat areas (Upper Kutai Basin) and modern Mahakam Delta sedimentology observation in the Samarinda area as modern analogue reference for fluvial – deltaic depositional environment.

There are several coal bearing formations which is famous in the Kutai Basin, start from the oldest is Middle – Late Eocene coal (equivalent to Tanjung Formation), Late Oligocene – Early Miocene coal (equivalent to Pamaluan Formation), Middle Miocene coal (equivalent to Balikpapan Formation). Middle to Late Miocene coal formation is the most productive formation which is exploited in Kutai Basin.

Middle to late Eocene deltaic coal characters are black, platy and blocky cleavage, vitreous luster, vitrain to clarain lithotype, thickness 20 to 30 cm. Late Oligocene – Early Miocene delta plain coal is characterized by black, blocky cleavage, hard to medium hard, thickness 30 to 70 cm. Middle to Late Miocene delta front coal is characterized by oyster bed coal, high gamma ray. Middle to Late Miocene fluvial coal character is coal sandwiching sandstone.

Modern Mahakam delta observation are showing several depositional environment which has potential become coal bearing environment. The first is fluvial flood plain environment, upper delta plain, lower delta plain, tidal distributary bar, delta front mouth bar and back spit / back lagoon.



The 41st IAGI Annual Convention and Exhibition


 Prihatin Tri Setyobudi 1*, Bambang Wisnu Handono2

 1 Geologist of Geosain Delta Andalan (GDA) Consulting, Jakarta, 2 Chief Geologist of PetroChina International Jabung, Jakarta

*Corresponding author:


Area studi batuan dasar granit Eosen (34.30 ± 0.91 Juta Tahun Lalu) adalah berlokasi pada tinggian di sebelah utara dari Cekuangan Sumatra Selatan. Selama Jurasik sampai Kapur, batuan dasar Cekungan Sumatra Seltan berkembang dipengaruhi rezim tektonik kompresi. Setelah fase kompresi, fase rifting Cekungan Sumatra Selatan berlangsung selama Eosen. Disamping itu intrusi terjadi di beberapa zona sesar. Aktivitas tektonik, iklim dan perubahan muka air laut dan air permukaan di daerah penelitian mempengaruhi karakteristik dari granit sehingga memiliki potensi sebagai reservoir dan sebuah test laju alir sumur menunjukkan aliran 1044 BOPD.

Melalui observasi petrografi, kita dapat mendapatkan informasi tentang mineralogi, porositas terlihat dan alterasi mineral pada granit. Disamping itu, karakteristik reservoir granit dapat diketahui dari pengujian laboratorium porositas dan permeabilitas dan uji laju alir (drill stem test). Sehingga kita dapat mengetahui pengaruh alterasi mineral dan pelarutan terhadap porositas dan permeabilitas reservoir.

Berdasarkan pengamatan 10 sampel sayatan tipis, mineral primer granit adalah kuarsa 21,20%-32%, Alkali Feldspar 34,40%-41,20% dan Plagioklas 0-19.2%, dan mineral primer lainnya seperti mika, apatit, dan zirkon. Mineral sekundernya sekitar 5.60%-32.00%, yaitu terdiri dari dolomit, siderit, kaolinit, serisit/illit atau paragonit, dan pirit. Granit memiliki intensitas alterasi lemah sampai sedang, dengan tingkat alterasi selectively pervasive. Tekstur granit yang teramati adalah perthitik, mikrografik dan granopirik. Porositas sekunder yang berkembang pada granit adalah porositas pelarutan dan porositas rekahan, nilai porositas terlihat adalah berkisar 1.60%-8.80%. Berdasarkan uji laboratorium pada kondisi NOB, porositas pada kedalaman disekitar sampel petrografi adalah berkiasr 1.2%-19.2% dan permeabilitas horizontalnya 0.001-122.0 md. Proses pelarutan memiliki peran penting dalam peningkatan nilai porositas, tetapi dilain sisi kaolinit dan siderit dapat mengisi rekahan dan memiliki pengaruh buruk terhadap porositas dan permeabilitas.

Katakunci: Petrografi, Karakteristik, Reservoir, Eosen, Granit, Jambi



The 41st IAGI Annual Convention and Exhibition


 Prihatin Tri Setyobudi 1, Dini Andriani 2, Prakosa Rachwibowo 3

 1 Geologis Geosain Delta Andalan, 2 Geologis Patra Nusa Data, 3 Dosen Teknik Geologi Universitas Diponegoro


Secara administrasi, daerah penelitian terletak di Kecamatan Kemusu, Kabupaten Boyolali, Jawa Tengah. Sedangkan menurut pembagian fisiografi Jawa, daerah penelitian termasuk ke dalam zona Kendeng. Zona Kendeng atau Cekungan Kendeng ini merupakan cekungan belakang busur. Litologi di daerah Kendeng dikontrol oleh sedimentasi dari tinggian di sekitarnya, perubahan muka laut dan aktivitas vulkanik. Litologi di Zona Kendeng sangat intensif terdeformasi dan banyak sesar dan lipatan yang terbentuk.

Tujuan dari penelitian ini adalah mengetahui karakteristik litologi dan hubungan stratigrafi antar unit litologi Formasi Kerek serta mengetahui umur dan lingkungan pengendapan dari Formasi Kerek. Sedangkan metodologi yang digunakan untuk memahami pengendapan litologi Formasi Kerek ini adalah pemetaan geologi, analisis petrografi dan analisis foraminifera.

Formasi Kerek yang terdapat di daerah penelitian ini dibagi menjadi dua unit litologi, yaitu Batupasir Karbonatan turbidit yang berumur Miosen Tengah (N9-N12) dan Perselingan Batulempung Karbonatan dan Batulanau Karbonatan yang berumur Miosen Tengah (N9-N13). Kedua unit litologi tersebut mempunyai hubungan yang menjari (interfingering). Berdasarkan foraminifera bentik, lingkungan pengendapan dari Formasi Kerek ini adalah middle bathyal. Selain itu, keterdapatan Slump dan Sekuen Bouma (Tb-Te) pada Batupasir Karbonatan mengindikasikan berkembangnya sistem turbidit.

Kata Kunci: Formasi Kerek, Saling Menjari, Turbidit




The 36th HAGI and 40th IAGI Annual Convention and Exhibition

Makassar, 26 – 29 September 2011


 Prihatin Tri Setyobudi1, Bambang W. H.3, Banu A.3, Krisputranto W. N. 3, Hadi N.2, Sudaryo B.2

 1Mahasiswa Program Studi Teknik Geologi, Universitas Diponegoro, Semarang, 2Staf Pengajar Program Studi Teknik Geologi, Universitas Diponegoro, Semarang, 3 Geologist Petrochina International Jabung Ltd, Jakarta



Lapangan PT berada di Sub-Cekungan Jambi, Cekungan Sumatra Selatan yang batuan dasarnya berstruktur tinggian. Kompleksitas tektonik yang terjadi serta proses pelapukan menjadikan batuan dasarnya berpotensi menjadi reservoir hidrokarbon.

Tujuan studi ini untuk mengetahui karakteristik dan jenis batuan dasar yang menjadi reservoir serta sebaran lateralnya di Lapangan PT.

Karakteristik reservoir diketahui dengan melakukan evaluasi log kualitatif, deskripsi megaskopis dan petrografis, analisis porositas dan permeabilitas inti pemboran, serta analisis uji laju alir. Selanjutnya korelasi log dan interpretasi seismik 3-D dilakukan untuk mengetahui sebaran lateralnya.

Granit di Lapangan PT berumur Eosen Akhir, terekahkan, serta dalam kondisi lapuk dengan intensitas ubahan mineral lemah sampai sedang dengan komposisi mineral ubahan 5,60%-32,00%. Jenis batuan dasar granitik yang menjadi reservoir hidrokarbon di Lapangan PT adalah Granit terekahkan dan Granite wash. Nilai log rata-rata pada interval Granit Terekahkan  untuk GR 235-406API, LLD 16,1-80ohm-M, densitas 2,25-2,54gr/cc, dan porositas neutron 0,058-0,201npu. Adanya rekahan ditunjukan oleh defleksi spektral uranium ke angka tinggi, pergerakan kurva MSFL yang cepat, separasi antara LLD dan LLS, serta anomali sonik yang mengalami peningkatan secara tajam. Hasil pengukuran full diameter sample core dalam kondisi NOB porositasnya 11,8%-20,7% atau cukup sampai baik sekali, dan permeabilitas horizontal 1,19-46,4md atau ketat sampai baik. Hasil DST minyak terbaik pada granit terekahkan pada sumur PTD-2 sebesar 1044 BOPD, sedangkan DST minyak dan gas terbaik pada sumur PT-2 sebesar 928,0 BOPD dan 0,712 MM CFGPD. Apabila dibandingkan dengan Granit terekahkan, secara relatif Granite wash memiliki nilai gamma ray hampir sama, namun porositas neutron lebih kecil serta densitasnya lebih besar. Nilai log rata-rata tiap sumur untuk GR 360-386API, LLD 5,39-166ohm-M, densitas 2,36-2,38gr/cc, porositas neutron 0,162-0,185npu. Satuan ini terbukti mengalirkan hidrokarabon 23,8 BOPD di Sumur WPT-2. Dari data seismik, top satuan reservoir batuan dasar granitik jatuh pada peak di antara sedimen yang onlap dan batuan dasar fresh yang bertekstur reflection free. Satuan Granit terekahkan terdapat di seluruh area Lapangan PT dan pada lereng tinggian lebih berpeluang untuk terakumulasinya hidrokarbon. Di atas Satuan Granit terekahkan pada lereng sampai puncak bukit intrusi berkembang Satuan Granit terlapukkan yang semakin ke atas intensitas pelapukannya semakin tinggi. Di dasar lereng barat daya dari bukit intrusi berkembang Granite wash.

Kata Kunci: Reservoir, Batuan Dasar, Granit Terekahan, Granit Terlapukan Granite Wash


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