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Swelling response of anthracite coal during CH4-CO2 competitive adsorption by molecular simulation

Adsorption-induced swelling is a major concern for gas injection to promote recovery of coalbed methane, especially in the CH4-CO2 competitive adsorption process because it directly determines the permeability of the reservoir. In this work, adsorption isotherms and the swelling response of anthracite coal during CH4-CO2 competitive adsorption are investigated through molecular simulation. The results show that the adsorption capacity of CH4 is suppressed due to the preferential adsorption of CO2 on anthracite coal. The increase in the mole fraction of CO2 can increase the total adsorption capacity of the binary mixture. Moreover, as the fugacity increases from 0.1 to 10.1 MPa, the volumetric strain dominated by adsorption-induced swelling gradually increases. Also, the increase in the mole fraction of CO2 can increase the volumetric strain of the binary mixture. This research can provide guidance for coalbed methane recovery. GRAPHICAL ABSTRACT