CO₂ sequestration in deep, unmineable coal seams has been proposed as a method for offsetting increasing anthropogenic CO₂ emissions, while increasing natural gas production. Through laboratory experiments on gaseous/supercritical CO₂ adsorption using a manometric procedure, we investigated anomalies in supercritical CO₂ adsorption and determined CO₂ density‐temperature effects on adsorption capacity, which are closely related to the CO₂ storage potential in deep coal reservoirs. Results indicate that the revised Dubinin‐Radushkevich (D‐R) model can fit supercritical CO₂ adsorption data well, and there is a significant difference between excess and absolute adsorption capacity as CO₂ density increases. In the supercritical isochore, a rapid change in CO₂ density results in a transition from Langmuir‐like monolayer adsorption to multilayer adsorption, and there is an unsaturated multilayer system during this transition. Above the temperature at the cross point, the increasing of density decreases, and a negative dependence on temperature causes a gradual decrease in adsorption capacity. Coal reservoirs near the boundary between the supercritical isochore stage and fully supercritical CO₂ stage should be the prime target for geological storage of CO₂. In order to better understand supercritical CO₂ adsorption behavior and identify target coal seams, further supercritical CO₂ adsorption experiments are needed in the southern Qinshui Basin.

The relationship between the pore structure characteristics and methane adsorption behavior evolution during coalification is vital for elucidating coalbed methane (CBM) storage and the impact on gas production. The middle-high rank coals collected from the Western Guizhou were analyzed by the full-scale pore structure characterization and methane adsorption isotherms. The evolution of pore, including pore type, structure, and fractal dimension, and gas adsorption behavior were established. Based on the quantitative characterization of coal samples' desorption, diffusion, and permeability capabilities, the impact of the gas storage mechanism on the gas production at the microscale and the geology-adapted technologies for gas recovery was elucidated. The results show that as the coal rank increases, the methane adsorption spaces and sites within coal undergo a substantial expansion primarily due to the enhanced development of micropores. During this process, the quantity of mesopores remains low, but their proportion increases while macropores gradually diminish. Coal petrographic and quality parameters related to the pore structure parameter exhibit a strong correlation with saturated adsorption capacity (SAC), with micropores playing a dominant role in controlling methane molecule adsorption. Coalification, on the one hand, increases the methane adsorption site, coupled with an increase in gas-solid interaction due to the condensation of macromolecular structures, leading to an increase in SAC. On the other hand, it results in a reduction in the micropore diameter and an intensification of monolayer molecular adsorption, causing a significant decrease in average adsorbed molecular layers (AAML). Therefore, the increase in SAC accompanies a decrease in AAML. Although high-rank coals exhibit higher methane desorption volume, desorption efficiency, and diffusion capacity, their low permeability characteristics hinder fluid seepage. To facilitate efficient development of high-rank CBM, it is imperative to implement geological compatibility techniques aimed at reducing solid-gas interactions within coal reservoirs and enhancing the connectivity of the pore network.