The research area is situated in the northwestern side of South Sumatra Basin, which is a part of Muara Bungo Regency, Jambi Province. The Oligocene Sinamar Formation consists of shale, claystone, mudstone, sandstone, conglomeratic sandstone, and coal-seam intercalations. This research was focused on fine sedimentary rock of Sinamar Formation, such as shale, claystone, and mudstone. Primary data were collected from SNM boreholes which have depths varying from 75 m up to 200 m, and outcrops that were analyzed by organic petrographic method, gas chromatography-mass spectrometry (GC-MS) of normal alkanes including isoprenoids, and sterane. The dominant maceral group is exinite, composed of alginite (3.4 -18%), and resinite (1.6 -5.6%), while vitrinite maceral consists of tellocolinite 0.4 -0.6%, desmocollinite 0.4%, and vitrodetrinite 8.4 -16.6%. Organic petrography and biomarker analyses show that organic materials of shales were derived from high plants and algae especially Botrycoccus species. Botrycoccus and fresh water fish fossil, found in the shale indicate a lacustrine environment. Keywords
Indonesia contains many Paleogene and Neogene basins which some of them have been proven to be a very prolific producer of oil and gas. A study on the result of Rock-Eval pyrolysis and biomarker undertaken on the Eocene Mandai Group was able to assess hydrocarbon potential of the Paleogene fine sediments in the frontier basin, especially West Kalimantan area. East Ketungau Basin is located in the western Kalimantan, bounded with Melawi Basin by the Semitau High in the south and West Ketungau Basin in the west. The Mandai Group was deposited in the East Ketungau Basin during Eocene, consisting of sandstone and mudstone facies. Mudstone facies comprises shale, claystone, and coal. Seven samples of Eocene fine sediments collected from East Ketungau Basin were analyzed by Rock-Eval pyrolisis and three samples for biomarker to evaluate their hydrocarbon potential. The Rock-Eval pyrolisis result of Mandai Group shows that TOC value of this facies ranges from 0.34 % to 5.16 %, Potential Yield (PY) between 0.06 and 4.78 mg HC/g rock, and Hydrogen Index (HI) from 12 to 89. Based on that result, the fine sediments of Mandai Group are included into a gas prone source rock potential with poor to fair categories. Moreover T max values vary from 426 o C to 451 o C. The Eocene fine sediments of Mandai Group fall under kerogen type III. Based on T max and biomarker analyses, the maturity of the sediments is situated within immature to mature level. The fine sediments of Mandai Group were deposited in a terrestrial to marine environment under anoxic to sub-oxic condition.
Hidrokarbon serpih merupakan sumber energi minyak dan gas bumi non-konvensional yang terperangkap dalam formasi batuan serpih kaya akan kandungan material organik, akan tetapi memiliki porositas dan permeabilitas yang sangat rendah. Penyelidikan ini memiliki tujuan untuk menjelaskan proses karakterisasi serpih Formasi Kelesa yang berpotensi sebagai pembawa hidrokarbon serpih berdasarkan perbedaan kondisi geologi, struktur, petrofisika, geokimia, dan geomekanika. Penyelidikan ini dilakukan pada Formasi Kelesa di Cekungan Sumatra Tengah, Provinsi Riau. Penyelidikan ini menggunakan data hasil analisis laboratorium geokimia, data log sumur, dan data seismik 2D. Data log sumur digunakan untuk analisis petrofisika yang menghasilkan nilai property batuan pembawa hidrokarbon serpih, yaitu kandungan serpih, TOC, dan indeks kegetasan. Data hasil analisis laboratorium geokimia digunakan untuk kalibrasi hasil analisis petrofisika. Interpretasi seismik dengan melakukan penarikan horizon Formasi Kelesa menghasilkan peta struktur kedalaman. Pemodelan statis property kandungan serpih, TOC, dan indeks kegetasan dilakukan dengan mengintegrasikan hasil interpretasi seismik dan analisis data sumur. Selain itu, analisis sejarah pengendapan atau burial history dilakukan untuk membuat pemodelan kematangan. Integrasi dari semua hasil pengolahan data menentukan daerah menarik (sweet spot) dari serpih Formasi Kelesa di daerah penyelidikan.Katakunci : Daerah menarik, Formasi Kelesa, hidrokarbon serpih, petrofisika.
Biomarker analyses can provide information about the source of organic matter, depositional environment, and maturity of source rock that is very useful for basin evaluation and understanding the petroleum system. In this paper, the study focuses on biomarker characterization of the Kelesa Formation that is situated in the Central Sumatra Basin, one of the petroliferous basins in Indonesia. This Eocene formation is equivalent to the Pematang Formation that is well known as acting as source rock in the Central Sumatra Basin. Thirty fresh outcrop samples were taken for biomarker analysis, with specification fourteen samples for gas chromatography and sixteen samples for gas chromatography-mass spectrometry. The gas chromatography analysis was done with a Perkin Elmer Clarus 600 type instrument while the mass spectrometry was done using a Perkin Elmer Clarus SQ 8C instrument. The results show that the organic matter dominantly comes from terrestrial plants with minor input from planktonic algae. Moreover, possible Botryococcus braunii input in the sediment suggests that the Kelesa Formation has been deposited in a lacustrine environment. Since the Kelesa Formation was deposited in a lacustrine environment, this formation is expected to be highly oil-prone source rock. The maturity biomarker indicators suggest that the formation does not reach appropriate maturity to expel hydrocarbon. However, the formation still has very good potential for oil shale resources. This study supports the previous study in the Kelesa Formation, and improves the understanding of the depositional history of the Kelesa Formation and the potential of the Kelesa Formation as oil shale resources. Moreover, the authors hope that this study can support recent basin evaluation and improve the understanding of the petroleum system in the Central Sumatra Basin.
-The Oligocene Sinamar Formation consists of shale, claystone, mudstone, sandstone, conglomeratic sandstone, and intercalation of coal seams. The objective of study was to identify the hydrocarbon source rock potential of the Sinamar Formation based on geochemichal characteristics. The analyses were focused on fine sediments of the Sinamar Formation comprising shale, claystone, and mudstone. Primary data collected from the Sinamar Formation well and outcrops were analyzed according to TOC, pyrolisis analysis, and gas chromatography -mass spectometry of normal alkanes that include isoprenoids and sterane. The TOC value indicates a very well category. Based on TOC versus Pyrolysis Yields (PY) diagram, the shales of Sinamar Formation are included into oil prone source rock potential with good to excellent categories. Fine sediments of the Sinamar Formation tend to produce oil and gas originated from kerogen types I and III. The shales tend to generate oil than claystone and mudstone and therefore they are included into a potential source rock.
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