GAS CONTENT APPRAISAL OF SHALLOW COAL SEAMS IN THE SOUTH PALEMBANG BASIN OF SOUTH SUMATRA

Abstract

The gas content of coal seams in the South Palembang basin has been assessed using well log data and core analysis. The seams are stratigraphically exposed at shallow levels (<300 m), and present in the Late Miocene-Early Pliocene Muara Enim sequence. The coal thickness of single bed in each well varies between ~7 m and ~14 m. All samples analyzed are low rank coals, suggesting subbituminous and high volatile bituminous. Vitrinite reflectance (VR) measurements vary from 0.49-0.59%, but there appears an increase in the VR value with depth. The coals contain predominantly huminite (56-86 vol. %), whereas liptinite and inertinite are less abundant, ranging from 0.2-12.2 vol. % and 4.2-19.2 vol. % respectively. These low rank coals comprise a small number of minerals (6-11 vol. %), high moisture content of 2.4-12.6 wt. %, volatile matters of >39 wt. %, and fixed carbons of >43 wt. %. The amount of gas within individual coal layer varies from 4.1-5.3 m3 /t, but the gas content tends to increase with deeper burial. The sum of the estimated gas-in-place is approximately 3,019x106 m 3 . In addition, the onset of gas generation within these near surface coals may occur due to biogenic controls during the coal-forming processes, as a result of sedimentation of the overburden in Pliocene time prior to the subsequent basin inversion commencing in the Plio-Pleistocene.