An integrated study on the geochemical, geophysical and geomechanical characteristics of the organic deposits (Coal and CBM) of eastern Sohagpur coalfield, India

Abstract

Coal mining, especially the underground mines are often encountered with several types of geological constraints, where massive-hard roof and trapped gas are the most serious threats leading to catastrophic (fatal) effects in form of roof falls, mine explosion and gas contamination. Thus, for enhancing the safety of underground coal mines, identification of aforesaid constraints during detailed exploration is very essential. The minable seams of Sohagpur Coalfield are often associated with rich Coal Bed Methane (CBM) content, which enhances their economical importance, but the gas content along with the presence of stable sandstone roof parallely induces challenges during their extraction. CBM also acts as an environmental hazard having twenty-one times more greenhouse effect than carbon dioxide (CO2). Therefore, the present paper attempts to investigate the depositional environment of the high-quality methane-rich sub-bituminous reserves of eastern Sohagpur Coalfield through integration of geochemical, geophysical and geomechanical analysis of the drilled boreholes along with their respective gas content. The results showed that the six major Barakar coal seams possessed nearly consistent distribution in terms of reserve distribution and chemical properties. These seams consisted of good quality reserves (Grade: G5-G8) with high heat values and organic content, and had less impurity content. These coal seams are overlain by stable roof having lower cavablity in form of thick hard medium-grained sandstone beds with moderate elasticity and strength. The seam structures showed a stable profile without any abrupt discontinuity except Bahmni-Chilpa fault in southern part of block. Some of the higher rank coal seams also contained potential CBM content. Statistical analysis was also carried out for understanding the distribution of reserve properties and monitored their interdependence using suitable fitting tools. Thus, the present study helped in summarizing different aspects related to reserve quality, roof properties and gas content for understanding the geology and working environment of coal reserves of less explored but economically important Central Indian coalfields.