Biogenic Gas Exploration and Development in Bentu PSC, Central Sumatra Basin, Indonesia*

Biogenic gas has become an economic target of exploration and exploitation, due to the high demand for gas. Its geological occurrence is easily interpreted; it is significantly widespread and shallow; gas is of good quality of gas with >98% content of CH4, low S and CO2 content. Production tests from this block resulted in a production rate peak of 50 MMscfd at Segat field. This article presents a summary of geology, geochemistry and geophysical aspects in order to assess biogenic gas accumulation in Bentu Block. Biogenic gas origins were shown by carbon isotope analysis to be of  13 C CH4 value -62 to -66 ‰. The main gas-bearing reservoir is a 7-25 foot thick sand layer over the upper Miocene to Pliocene Binio Formation, at a depth of 600-2000 feet below sea level. The Binio Formation was deposited in a coastal environment that reflects the onset of marine regression. The gas is trapped along a NW-SE anticlinal system, related to a reverse fault. Seismically, existing data clearly exhibits strong amplitude anomalies or a ― bright spot‖ as a Direct Hydrocarbon Indicator. Furthermore, advanced geophysical analysis, AVO, seismic attribute and LMR methods, were carried out to confirm gas presence. The result of this analysis has been helpful to distinguish between coal and gas-bearing reservoirs, where coal revealed a similar appearance in the seismic data. Seismic data were also important in delineating lateral gas distribution and exploring prospects and leads in Bentu Block.