Supercritical CO2 adsorption in a simulated deep coal reservoir environment, implications for geological storage of CO2 in deep coals in the southern Qinshui Basin, China

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.