GEOCHEMICAL ANALYSIS AND GENERATED HYDROCARBON VOLUME ESTIMATION FROM ACTIVE SOURCE ROCK OF ASRI BASIN

• Main Author: YUMANSA, ANDRI
• Format: Theses
• Language: Indonesia
• Subjects: Geologi, hidrologi & meteorologi
• Online Access: https://digilib.itb.ac.id/gdl/view/14900
• Institution: Institut Teknologi Bandung

Asri Basin is located inside of China National Offshore Oil Company (CNOOC) SES Ltd. concession block. There are two Tertiary sedimentary basins inside this block namely Asri and Sunda Basins. These back arc basins are located about 150 km to the south east offshore of Sumatra Island, at 04°30’ S - 06°00’ S and 106°00’ E – 107°00’ E. Even though Asri Basin does not has the depocenter as deep as Sunda Basin, Asri Basin is also a prolific basin. These basins have similar tectonic backgrounds, then impact to the similar basin geometry and stratigraphy. The difference is the hydrocarbon produced, Sunda Basin generally produces oil and gas, while the Asri Basin oil only. <br /> <br /> <br /> <br /> <br /> Asri Basin is known as one of the large oil-producing basin in the western part of Indonesia with major oil fields in the basin which has estimated reserves around 1.2 billion barrels of oil and cumulative production has reached more than 500 million barrels oil. Generally, the producing oil fields in the Asri Basin is located on the western flexural margin. The oil produced from the fields is almost the same type, the black oil type with 33-34° API. But, until now the active source rock intervals that contribute and potentiality of active source rocks to generate hydrocarbons is still poorly understood. Eocene Banuwati lacustrine shale is the only active source rock which is known to produce hydrocarbons in Asri Basin. Present oil window is estimated to be at 11,500 feet below sea level. <br /> <br /> <br /> <br /> <br /> With the new evidence from several recent exploration drillings, research has focused to analyse the geochemistry of sedimentary rocks in the Talangakar Formation and Banuwati Formation to identify in more detail the potential source rock. Allegedly, the Banuwati Formation is not the only source rock which contributed as producer of hydrocarbons in the Asri Basin. Lower Zelda Member of Talangakar Formation is also expected to contribute producing hydrocarbons in Asri Basin. <br /> <br /> <br /> <br /> <br /> Banuwati Formation shows TOC ranging from 0.5-12.3% (fair-excellent), hydrogen index value up to 902, kerogen type I with mix algae and minor terrestrial content in deep lacustrine. While geochemical analysis in Lower Zelda Member of Talangakar Formation shows TOC ranging from 0.5-3.4% (fair-excellent), hydrogen index value up to 769, kerogen type I with mix algae and terrestrial content in shallow lacustrine. Maturation evaluation by Tmax and Ro shows Lower Zelda Member of Talangakar Formation and Banuwati varies from immature to early mature. Banuwati also varies from immature to peak mature. Oil window from these parameters is predicted at 8,000 feet SSTVD or rise about 3,500 feet from the previous study. This research gives <br /> <br /> <br /> <br /> <br /> greater exploration opportunities in the Asri Basin, especially from Talangakar active source rock which has not been considered before. <br /> <br /> <br /> <br /> <br /> Using the Schmoker method, potential generated oil by active source rocks in Asri is 22.6 billion barrels. With present day oil reserves about 518 million barrels or equivalent to 70 billion kilograms, Asri Basin is classified as “Significant Petroleum System”. With the generation accumulation efficiency (GAE) ratio 5.3%, Asri Basin is classified as “Moderately Efficient System”. This low efficiency might be caused by several reasons, one of them is possibly caused by some hydrocarbons trapped stratigraphically, especially in Lower Zelda Member of Talangakar Formation.