GEOCHEMICAL ANALYSES AND VOLUME ESTIMATION OF HYDROCARBON GENERATED FROM ACTIVE SOURCE ROCK IN YANI SUB-BASIN, SUNDA BASIN

• Main Author: Irfree P, Baharianto
• Format: Theses
• Language: Indonesia
• Subjects: Geologi, hidrologi & meteorologi
• Online Access: https://digilib.itb.ac.id/gdl/view/41525
• Institution: Institut Teknologi Bandung

Yani Sub-basin is currently under China National Offshore Oil Company (CNOOC) SES Ltd. production sharing contract (PSC) concession. Located 140 km north of Jakarta, this sub-basin is one of five Tertiary sub-basins that forms greater Sunda Basin. All of them have the same geological setting, so all of it has similar geometry and stratigraphical presence. Yani Sub-basin is hydrocarbon prolific eventhough the sediment package is thinner and shallower compare to Seribu Sub-basin that assist most of the oil fields in Sunda Basin. Currently, Yani Sub-basin is known as the smallest productive sub-basin in Sunda Basin. There are only 58 million barrels of proven oil reserve, while cumulative oil production from 2004-2014 is as low as 2.2 million barrels of oil. The only producing field is Yani Field, with reservoir from Middle Banuwati Sandstone interval. The type of the oil produced is black oil with API gravity range of 30-35o API. Study of source rock is far from definitive, hence the estimated volume of hydrocarbon generated remains unknown. The petroleum system concept of Sunda Basin still applied here with active source rock comes from Upper Banuwati Shale and window of oil generation at depth 9,500 ft SSTVD. Combining new data from recent well exploration and geochemical analyses, research for source rock identification is focussed in Talangakar (Zelda member) and Banuwati Formation (Upper Banuwati and Middle Banuwati member). There are more than one interval of active source rock estimated in Yani Sub-basin. Zelda member consist of shale, sandstone and coal. Zelda member shale has total organic content (TOC) range from 0.8-5% with fair-very good for source rock potential. Hydrogen index (HI) in Zelda member shale is ranging from 113-600 with mixed kerogen type I and II. Kerogen comes from algae and terrestrial material that deposited in fluvial-lacustrine environment. Shale from Upper and Middle Banuwati member hold the same characteristic, with hydrogen index up to 596 and kerogen type I that comes from lacustrine algae. With total organic content 1-4%, both of them are good-very good source rock potential. Source rock maturity is analyzed by three different parameters which are vitrinite reflectance (Ro), Tmax, and Spore Colour Index (SCI). Geochemical analyses result showed that window of mature source rock started at 7,500 ft SSTVD, while peak maturity started at 8,300 ft SSTVD. These results show that maturity window is 1,200 feet shallower than previous petroleum system concept and may hold the key for future exploration in Sunda basin. iv Volume of hydrocarbon generated from active source rock is estimated by Schmoker method. The result showed that 1.4 billion of barrels oil is estimated to have been generated from three different source rock intervals. With total of hydrocarbon proven reserve 58 million barrels, the generation accumulation efficiency of hydrocarbon number is only 4.1%, so there are more exploration potential to find the remaining hydrocarbon resources.