Geochemistry and habitat of oil and gas in the East Java Basin: Regional evaluation and new observations*
Awang H. Satyana** and Margaretha E.M. Purwaningsih***
** Badan Pelaksana Kegiatan Usaha Hulu Minyak dan Gas Bumi, Jakarta; ***Department of Geology, Institute of Technology Bandung
* 31st Annual Conference Indonesian Association of Geologists, Surabaya, September 30 – October 2, 2002
A regional oil and gas geochemistry study was conducted recently based on geochemical data from around 100 wells and seeps of the East Java Basin. Geologic setting of the oil and gas occurrences were evaluated to derive their habitats. Most oils were derived from sub-oxic and oxic terrestrial to marginal marine source facies. Offshore oils are more terrestrial than those of onshore. Three genetic types of natural gases are found : thermogenic, biogenic, and mixed gases. The Paleogene Ngimbang, Lower Kujung, and Lower Tuban shales and coals are the sources of the oils and thermogenic gases. Biogenic gases were sourced by the Neogene Tawun to Lidah shales and coals. The study also evaluated the CO2 gas accumulations and found that significant high CO2 gas content are associated with thermal degradation of the Paleogene Kujung carbonates. Four trends of habitats are recognized: Ngimbang, Kujung, Ngrayong, and Mundu Trends.
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