Adsorption Thermodynamic Property of Deep Coal Reservoirs and Adsorption Capacity Prediction under Different Temperature and Pressure Conditions

Predicting methane adsorption capacity under different temperature and pressure conditions is important for evaluating deep coalbed methane (DCBM) resources. In this study, 17 deep coal samples from three wells in the Benxi Formation, eastern Ordos Basin, were analyzed using proximate analysis, CO 2 adsorption, and high-temperature/high-pressure (HTHP) methane adsorption experiments. The relationships among coal quality, micropore structure, Langmuir adsorption parameters, and methane adsorption capacity were investigated. A semiempirical model based on the isosteric heat of adsorption was used to estimate temperature-dependent adsorption behavior, and regression models incorporating pore structure and proximate composition were developed to estimate adsorption capacity under different pressures. The results show that ash content is generally negatively correlated with micropore volume and methane adsorption capacity, whereas fixed carbon content and micropore volume are positively correlated with Langmuir volume. Methane adsorption capacity decreases with increasing temperature but increases with pressure, and the temperature effect becomes more evident at higher adsorption pressure. The initial isosteric heat of adsorption may indicate methane adsorption affinity and shows a possible positive relationship with R o,max . The proposed semiempirical models can reproduce methane adsorption behavior within the investigated samples and experimental conditions, but further validation is required before application to other coal seams or wider temperature–pressure ranges.