COAL AND COALBED METHANE CHARACTER COMPARISON IN MANGUNJAYA AREA MUARAENIM FORMATION SOUTH SUMATRA BASIN WITH AMPAH AREA WARUKIN FORMATION BARITO BASIN

• Main Author: Ibnu Suhada, Dede
• Format: Theses
• Language: Indonesia
• Online Access: https://digilib.itb.ac.id/gdl/view/47304
• Institution: Institut Teknologi Bandung

Indonesia has significant coal deposit (155 Btons resources in 2019). Coal may contain economic methane gas (Coalbed methane/CBM) that can be used as source of energy equal to conventional gas. Research have shown that Indonesia coal contain significant amount of CBM (86 Tcf in 2019). This study aims to characterize coal and its CBM from two different areas, which are Mangunjaya in South Sumatra Basin and Ampah Area in Barito Basin. Both areas have low rank coal deposit. The data analyzed is derived from 4 boreholes coring samples of MJ01, MJ02 in Mangunjaya area, and JWT-01, JWT-02 in Ampah area. Coal was characterized using chemical (ultimate and proximate) and organic petrogragphy (vitrinite reflectance and maceral) analysis while CBM was characterized using desorption analysis for coal gas content and gas chromatograph for coal gas composition. Coal in Mangunjaya area belongs to Muaraenim Formation South Sumatra Basin. Regionally, the coal of Muaraenim Formation has wide lateral continuity. Sixteen coal seams were found with thickness vary from 0.36 meters to 14.35 meters Megascopic examination shows hard to fragile black to brownish coal, with dull lustre and black scratch, subconcoidal, rare cleat and gradation to clear contact. The coal contain resin and pirit, rootlet, coalyclay and coarse sandstone as parting. Mangunjaya coal has calorivic value ranges from 4,711 cal/gr to 5,938 cal/gr (adb basis). Coal ranks are lignite which have vitrinite reflectance of 0.24% to 0.36%. Gas content range from 0.23 scf/ton to 33.33 scf/ton with methane composition range from 1.9% to 85.78%. Ampah area belongs to Barito Basin. Coal bearing formation in the area is Warukin Formation. Thirteen coal seams with thickness ranged from 0.5 meters to 15.35 meter were found in the area. The coal are black to brown, dull lustre, brown scratch, fragile to soft with some wood structures on it. Coal rank are lignite, having vitrinite reflectance of 0.23% to 0.34% and calorivic value ranged from 5,041 cal/gr to 5,532 cal/gr (adb basis). Coal gas content ranged from 1.73 scf/ton to 4.39 scf/ton with methane composition ranged from 60.43% to 82.44%. Data shows that the coal calorivic value, coal vitrinite reflectance as well coal gas content in the areas increase with depth. Organik material types identified by van Krevelen (1961) diagram showed that the coal in the area dominated by kerogen tipe III for which is gas prone. Maceral composition analysis is conducted to determine the composition of maceral group huminite, liptinite, inertinite as well mineral matter in the coal of the area. Analysis were done on 62 Mangunjaya coal samples. The results show that Mangunjawa coal consist of 68.4% to 92.4% huminite, 0.2% to 8.4% of liptinit, 2.2 to 26.6 % of inertinit and 0.4% to 13,20% of mineral matter. While 29 Ampah coal samples show huminite content ranges from 65% to 92.6%, liptinite content of 0.2% to 9.2%, inertinite content of 4% to 25.8% and mineral matter of 0.40% to 9.60%. In general, although the rank of Mangunjaya and Ampah coals are similar, but the gas content of Mangunjaya coals are higher than Ampah coals. The coal seam target in Mangunjaya area are 260 meter and 389 meter while coal seam target in Ampah area are 135 meter and 224 meter. Petrographic analysis reveals that the maceral composition of the coal from the two areas are different with variation in each well. Macerals and gas contents showed positive correlation values. Based on the analysis results, this study suggests that the differences of coal gas content between Mangunjaya and Ampah coals is due the differences in their coal maceral composition. Huminite in Mangunjaya coals are higher than in Ampah coals. Micropori is the largest of gas storage in coal. Huminite group or vitrinite contains more of micropori compared with other macerals. The position of the research area on the basin and the difference in time of inversion are the causes of differences in coal maturity.