Coalbed methane sorption related to coal deformation structures at different temperatures and pressures

Coal methane adsorption capacity is related to coal deformation structures. Due to different deformation properties and deformation degrees, tectonically deformed coals have different adsorption isotherms and adsorption capacities. In this work, adsorption capacity investigations are performed using three types of tectonically deformed coal (weak brittle deformed coal, strong brittle deformed coal and strong ductile deformed coal) with vitrinite reflectance of about 0.9% at different temperatures and pressures. The results indicate that the methane adsorption capacity in coal has a decreasing relationship with temperature. At a constant temperature, the methane adsorption of different tectonically deformed coals also varies. For example, the strong-ductile deformed coal has a significantly higher adsorption capacity than the weak-brittle deformed coal and the strong-brittle deformed coal at a constant temperature of 30 °C. At low pressures, the strong-brittle deformed coal has a higher adsorption capacity than the weak-brittle deformed coal; as the pressure increases, the adsorption capacities of both types of coal become equal. The findings show that the methane adsorption capacity of different types of tectonic coal is mainly affected by temperature and pressure. At high temperatures (i.e., 50 and 70 °C), the coal samples do not show significant differences in coal methane adsorption capacity, and their adsorption isotherms are similar.