Geological and microstructural characterisation of coal seams for methane drainage from underground coal mines

Methane drainage from coal seams is a complex process. Quantification of the geological and microstructural characteristics of the coal matrix is of utmost importance to assess the migration of methane for the success of methane drainage from coal seams. This research makes a comprehensive assessment of the methane drainage potential of two gassy coal seams of the Moonidih colliery of the Jharia coalfield. Various geological and microstructural characteristics of the coal seams, viz. chemical and petrographical compositions, pore structure, cleat morphology, and permeability, have been investigated. Both the coal seams are identified as type III kerogen, which fall within the gas-prone range reaching the thermogenic methane generation peak. The vitrinite, inertinite, and liptinite content varied in the range of 78.35-84.78%, 13.82-17.88%, and 0-0.47% for the XV seam, and 55.76-68.45%, 29.65-37.53%, and 0.8-0.89% for the XVI seam, respectively. The micropore specific surface area (SSA) and micropore volume, respectively, are determined as 17.084 m(2)/g and 0.0252 cm(3)/g for the XV seam and 15.141 m(2)/g and 0.0216 cm(3)/g for the XVI seam. The Brunauer-Emmett-Teller (BET) surface area and Barrett-Joyner-Halenda (BJH) mesopore volume are determined as 0.75 m(2)/g and 0.00307 cm(3)/g, respectively, for the XV seam and 0.66 m(2)/g and 0.003273 cm(3)/g, respectively, for the XVI seam. The XV seam coal was found to be less porous (13.92%) than the XVI seam (15.76%). SEM image analysis revealed that the cleats are more developed in the XV seam; consequently, it possesses greater permeability (0.896 mD) than the XVI seam (0.274 mD). Owing to its favourable geological and microstructural properties, the XV seam is more suitable for methane drainage.