#TITLE_ALTERNATIVE#

• Main Author: EKO PIRENO, GADJAH
• Format: Theses
• Language: Indonesia
• Subjects: Geologi, hidrologi & meteorologi
• Online Access: https://digilib.itb.ac.id/gdl/view/15745
• Institution: Institut Teknologi Bandung

Up to now, the Salawati Basin is recognized as the one of the big prolific oil basin in Eastern Indonesia with a total cumulative oil production more than 300 million barrel oil. The Klasafet shale Formation has been assumed as the main source rock for the oil in Salawati Basin deposited in the shallow restricted marine environment during Middle Miocene time. Part of the Kais Formation which contains coal layer within the limestone is also assumed as the Early Miocene source rock in the area.<p> Several wells that have been drilled in the deepest part of the Salawati Basin show the average of total organic carbon content are between 0,4-1%, therefore, it is not match with a total oil produced from the basin. The maturation model from several points in the basin is also indicated that the Klasafet Formation still in the early mature phase until present day and has not been yet generated hydrocarbon effectively. Therefore, the statement that the Klasafet Formation is the main source rock in the Salawati Basin is still questionable.<p>The new well information that indicated good oil and gas shows has been encountered in the Late Oligocene sandstones of Sirga Formation in SF-1X exploration well (2007), and also oil has been discovered in the pre-Kais sandstones in SAR-1X exploration well (2008). It indicates that the oil trapped within the Sirga sands and in the intra-Kais carbonate probably has been generated from the Sirga shales source rock, because it will be difficult to explain how the oil from the Mid-Miocene Klasafet source rock can migrate to the Late Oligocene Sirga sands by penetrating thick impermeable Lower Miocene upper Kais carbonate platform.<p>Geochemical analysis of the oil samples from the SF-1X and SAR-1X wells indicated that the oil type is waxy (3.57 wt%) with very low sulphur content (0,024-0,028 %), heavy carbon isotope (-22 to -23), pristane/phytane ratio ranges from 1,33-2,61, supported by the occurrences of oleanane as the biomarker of the Tertiary land plants and diahopane/ neohopane as the biomarker of the shallow lacustrine product. Therefore, based on the geochemical analysis mentioned above; it is assumed that the oil trapped in the lower Kais reservoir (intra-Kais) and Sirga sandstones was derived from the lacustrine source rock that usually contains very rich of organic carbon content developed during Early Tertiary time. It is agreed with total cumulative oil produced from the Salawati Basin.<p>The 2D/3D seismic data have identified that the Sirga Formation deposited in the Early Tertiary separuh-graben system that developed as the tension structure due to the uplifted of Papua area. The occurrence of the half-graben structures in Early Tertiary time is also agreed with the geochemical analysis results that mentioned the Sirga Formation source rock deposited within the lake system.<p>By integrating the geology, geophysical and laboratory analyses data mentioned above, it can be resulted that the Sirga Formation has the better potential as the main source rock in the Salawati Basin rather than the marine Klasafet Formation. However, this assumption is still a hypothesis because up to now there is no well penetrated Sirga Formation in the deepest part of the graben that expected to be rich of organic carbon.