POTENTIAL EVALUATION OF COALBED METHANE BASED ON THE GRADE AND QUANTITY OF THE COAL IN THE MANGUS SEAM, MUARAENIM FORMATION, NIBUNG REGION, SOUTH SUMATRA BASIN

摘要

Indonesia’s oil and gas reserves decrease by about 2.4% per year (Panuju, 2010). Therefore, we need sustainable energy: CoalBed Methane (CBM). CBM is simply methane found in coal seams and is mixture of hydrocarbon gases, with methane (CH4) as the dominant composition of 90-95% (Bayrak, 2010). The potential of the CBM reserves in South Sumatra, Indonesia is 183 trillion cubic feet (Steven and Hardiyanto, 2005). The amount of methane gas was evaluated using desorption tests, adsorption isotherm analysis, gas chromatography, geochemistry methods, and drilling to determine the thickness and depth of the coal. Based on the geochemistry method, the desorption test, adsorption isotherm analysis, and gas chromatography from as many as 20 coal samples tested from the Mangus seam on the Muaraenim formation, the CH4 content is about 42.21% (0.48 m3 /ton), and the total gas content is 40.10 SCF/ton (1.14 m3 /ton). For an approximate analysis, the moisture is 31.15%; volatile matter is 33.74%; and the fixed carbon content is 33.04%. Ash content in the Mangus seam is 2.07%, and the caloric value is 5542-6346 cal/g. From drilling tests at depths of 237.58-251.22 m, the thickness of coal is 13.64 m. The Mangus seam has the ability to store gas at 12.43 m3 /ton at 474 psi (Arso, 2011). Based on the geochemistry for the Mangus seam, the Muaraenim formation is categorized as sub- bituminous class A-B (USA, ASTM) that can produce CBM, while the results of drilling at depths of 237.58-251.22 m with 13.64 m of coal thickness, the derived methane content is low and the depositional environment categorized as wetlands will generate biogenic methane, so the potential of the Mangus seam to produce CBM is low.