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 m 3 /t, but the gas content tends to increase with deeper burial. The sum of the estimated gas-in-place is approximately 3,019x10 6 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.

Coal properties and cleat attributes at Tanjung Enim coalfield in South Palembang Sub-basin, South Sumatra

“…Other constituents, including liptinite <10%, inertinite <20%, and mineral matters <10% are apparently minor. These results are similar to the previous works reported by several workers [14], [16], [17]. The recent maceral analysis suggests that the studied coals likely belong to a humodetrinite assemblage [18].…”

“…The ash content for all samples varies slightly, with average ranging from 1.77-3.98 adb.%. In general, the ash constituent for the Air Laya coal tends to be similar laterally along strike, varies vertically at different stratigraphic levels, and increases towards the intrusion [17]. Inherent moisture varies slightly among the sampled coals, but tends to be relatively high with average ranging from 10.64-14.42 adb.%, similar to the studied results of [16], [17].…”

“…In general, the ash constituent for the Air Laya coal tends to be similar laterally along strike, varies vertically at different stratigraphic levels, and increases towards the intrusion [17]. Inherent moisture varies slightly among the sampled coals, but tends to be relatively high with average ranging from 10.64-14.42 adb.%, similar to the studied results of [16], [17]. However, the yields are different, showing lower moisture content for most given samples [17].…”

“…These include ash content, total moisture, fixed carbon (FC), and volatile matter (VM). In order to better understand the coal properties in the region, each parameter here is compared to the results of proximate analysis reported elsewhere in the published studies [16], [17], [19].…”

Coal Bed Methane Properties Modeling Using Improved Seismic Resolution for Estimating Gas Reserves: A Case Study of East Kalimantan Field, Indonesia

“…Therefore, the deeper coal layers at depths greater than 400 m will be very promising, since the coal rank and gas content are much higher. This means that knowledge of the gas content of the coal reservoir will be very important in CBM exploration [3].…”