Geochemistry of Totogan Formation as potential source rock and its relationship with oil seepage manifestations in the Banjarnegara areas, Central Java, Indonesia.

Abstract

The Central Java area, especially the North Serayu Basin, has the potential to accumulate hydrocarbons, as evidenced by the many manifestations of oil and gas seepage on the surface. This research in the Banjarnegara area, part of the North Serayu Basin, aims to determine the geochemistry characteristics of potential source rock of the Totogan Formation and existing oil seepage, as well as their genetic relation. Fifteen surface rock samples were analysed for the total organic carbon (TOC) content and Rock-Eval pyrolysis. Then, several samples were selected to examine the biomarker composition using GC. and GC-MS analysis. Meanwhile, the biomarker data of oil seepage data was obtained from previously published data. The identified terpanes and steranes biomarkers of potential source rock and oil seepage samples were performed to determine the relationship of oil seepage to its potential source rock. The research reveals that the Totogan Formation was deposited under suboxic to oxic conditions that can be distinguished into the estuary or bay deposit composed mainly of higher plant organic matter and the open marine deposit with input mainly from algae organic matter. Another important finding is a positive oil-to-source rock correlation between existing oil seepage and the Totogan Formation based on biomarker data. Thus, the findings of this research suggest that the Totogan Formation is the source rock of the existing oil seepage in this research area.