STUDY OF SOURCE ROCKS IN THE WESTERN NORTHEAST JAVA BASIN

• Main Author: AGOES WILOSO , DANIS
• Format: Theses
• Language: Indonesia
• Subjects: Geologi, hidrologi & meteorologi
• Online Access: https://digilib.itb.ac.id/gdl/view/7532
• Institution: Institut Teknologi Bandung

Research area is located at western part of Northeast Java Basin where highly significant oil and gas accumulation has been discovered in this basin both offshore and onshore areas. Despite the recent significant discoveries, there are still many uncertainties concerning aspects of petroleum geochemistry in the basin especially at western part this basin. During the study geochemical data of oil and source samples comprising physical to molecular properties from five wells and four seeps of the onshore areas of the Northeast Java Basin were interpreted using various geochemical crossplots and methods. The oil and the source rock data from wells and seeps were tested according to their availability of n-alkanes including their isoprenoids, triterpanes data, steranes data, and carbon isotope. The biomarker data that have been used in this research is limited only on common mass ion such as triterpanes (m/z 191) and steranes (m/z 217). Based on those data, the oil – source rock correlation is made to determine source rock that produced hydrocarbon. According to the source rock richness and maturity analysis, The Ngimbang clastic Formation in Rembang-1 is known for having a good to excellent degree of richness as a source rock. The Ngimbang clastic Formation in the research area is on the stage of early mature and has a preference to produce oil and gas which comes from Type II and Type III kerogen. The oil – oil correlation in the research area has divided the oil samples into two oil groups. The first oil group is the oil group in which the organic material comes from the mix of high plants and algae where the depositional environment of the source rock for this oil group is more headed for shallow marine (deltaic?) environment. The specific characteristics of this oil group are the bimodal peak iv shape of n-alkanes distribution at C17 and C27, the low ratio of phytane/pristane, the subordinate portion of C23 and C26 tricyclic triterpanes, the presence of nonhopanoid like oleanane, gammacerane and resins on pentacyclic triterpanes, a dominant portion of C27 steranes, and the value of carbon isotope is smaller than -5. The second oil group is the oil group in which the organic material comes from more of the high plants where the depositional environment of the source rock for this oil group is more headed for terrestrial environment. The specific characteristics of this oil group are the one peak shape of n-alkanes distribution at C27, the lower ratio of phytane/pristane, the abundance amount of oleanane and resins on pentacyclic triterpanes, a dominant portion of C29 steranes, and the value of carbon isotope is bigger than +4. According to the C27-C28-C29 ternary plots from four oilseeps and extract source rock from three wells there is positive correlation about oil from terrestrial and Ngimbang clastics Formation, based on a visual comparison of triterpane (m/z 191) and sterane (m/z 217) distributions shows close similarities between Kedung Jati oilseep and extract source rock (Ngimbang clastics Formation) in Rembang-1 well, this is suggestive of Kedung Jati oilseep being generated from the Ngimbang clastics Formation. The oil – source rock correlation in the research area shows that Eocene Ngimbang Formation as a source rock that produced the terrestrial-shallow marine (deltaic?) oil group.