Confirmation of the Paleogene Source Rocks in the Northeast Java Basin, Indonesia, Based from Petroleum Geochemistry
Danis A. Wiloso1, Eddy A. Subroto2, and Eddy Hermanto3
1Geology, Institute of Technology Adhi Tama Surabaya (ITATS), Surabaya, Indonesia
2Dept. of Geology, Bandung Institute of Technology (ITB), Bandung, Indonesia
3BPMIGAS, Jakarta, Indonesia
Northeast Java Basin is one of the biggest hydrocarbon producers in Indonesia. Significant oil and gas accumulation has been discovered in this basin both offshore and onshore. Despite the recent significant discoveries, there are still many uncertainties concerning aspects of petroleum geochemistry in the basin, especially in determining source rock(s) at the western part of this basin. It has been speculated that Ngimbang Formation is the hydrocarbon source rock in the whole basin. This speculation was mainly based by geological interpretation since only two wells drilled in the eastern part of the basin that penetrated up to the formation. It should note that the samples condition for the formation in the two old wells are poor. In 1999, a well, namely Rembang-1, was drilled in the western part of the basin. This well has a total depth of 2134 meters and penetrated the Ngimbang Formation.
Sediment samples from five old and new exploration wells, which include the Padi-1 whose total depth is 1296 meters (drilled in 2004) and also penetrated the Ngimbang Formation and four oil seepages were used during this study. They were subjected to detailed geochemical analyses comprising organic carbon determination, maturity assessments based on pyrolysis and vitrinite reflectance techniques, and kerogen typing for the sediments and isotope study and biomarker assessments for both sediment and crude oil samples. Then, source rocks assessment and oil to source correlation were done. The results indicate a positive correlation between the crude oils and the Ngimbang Formation. Beside, the Ngimbang Formation is relatively rich in organic matter and mature. Therefore, this study is a milestone in the Northeast Java Basin exploration history.
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