Thermal Alteration Effects on Shale and Coal: Insights into Porosity Evolution, Hydrocarbon Potential, and Carbon Sequestration Capacity

With rising global energy demands, shale gas and coal bed methane are increasingly recognised as essential unconventional hydrocarbon sources offering lower carbon emissions and reducing dependence on conventional fossil fuels. These unconventional sources are generated through the thermal maturation of organic matter, influenced by geothermal gradient, burial depth, and heat exposure duration. In certain cases, coal and shale formations are even subjected to igneous intrusions, causing localised thermal metamorphism. The proximity to these intrusions elevates the thermal maturity of organic matter and significantly modifies the porosity of these formations, which differs from burial-induced maturation. To investigate these effects, a comparative analysis was conducted on two heat-altered and two non-heat-altered samples comprising both coal and shale from the Raniganj basin. An integrated approach of Rock-Eval analysis and low-pressure gas adsorption (LPGA) techniques reveals advanced thermal maturity, increased micropore volumes and enhanced adsorption capacities due to thermal stress caused by intrusions. Such changes suggest an improved capacity for carbon dioxide storage in heat-altered samples, making them viable candidates for carbon sequestration projects. These findings provide valuable insights into thermally altered sedimentary sequences, contributing to carbon emission mitigation and sustainable carbon management strategies.