Biogenic Gas has become an economic target of exploration and exploitation in Indonesia due to increasing gas demand and the consequent increased in gas prices. It can be reliably identified from seismic data, is widespread, shallow and is of good quality with >98% CH4 and minimal H2S and CO2. The Bentu PSC and the Korinci Baru PSC in the Central Sumatra Basin contain Biogenic Gas fields containing up to 350 bcf of biogenic gas reserves. This biogenic gas for formerly considered a drilling hazard in the search for oil in deeper formations. But now, the Baru, Baru West Baru and Korinci gas fields in the Korinci Baru PSC are in production, with a combined peak gas rate around 30 MMscfd, and the Segat and Seng gas fields in the Bentu PSC are under development. This paper summarises the integration of Geology, Geochemistry, Geophysics and Reservoir to assess the biogenic gas resources of the Binio Formation in the Bentu PSC and the Korinci Baru PSC. The main gas-bearing sand reservoirs are in the Late Miocene to Pliocene Binio formation. The sands were deposited in coastal environment that reflects the onset of marine regression. The gas is trapped along a NW-SE anticlinal system related to reverse faults. The gas reservoirs are 600-2000 feet below sea level, are 7-25 feet thick, and have excellent porosity and permeability. The seismic data shows strong amplitude anomalies or “bright spots” which in this area are usually associated with gas sands. However, the bright spots are sometimes associated with coals and thin stacked water-filled sands. The reliability of the interpretation of gas sands is increased with advanced geophysical analysis such as amplitude-verse-offset (AVO). The biogenic gas origins were shown by gas composition and carbon isotope analysis with 13C CH4
value -62 to -66 ‰.
Author : R. W. Yuwono, B. S. Fitriana, P. S. Kirana, S. Djaelani, B. A. Sjafwan