Gas Competitive Adsorption on Clay Minerals and Its Impact on CO 2 Sequestration and Methane Recovery

The carbon dioxide (CO 2 ) sequestration combined with enhanced natural gas recovery is a promising technology. Injecting CO 2 into hydrocarbon reservoirs induces a competitive adsorption process between CO 2 and CH 4, which not only facilitates significant CO 2 storage underground but also enhances hydrocarbon recovery. Clay minerals, which are abundant in oil- and gas-rich strata, provide numerous gas adsorption sites. This study employs a combined Grand Canonical Monte Carlo (GCMC) and Molecular Dynamics (MD) approach to investigate the competitive adsorption behavior of CO 2 /CH 4 binary mixtures on clay minerals with different structures, specifically kaolinite and montmorillonite. Van der Waals forces predominantly govern the interaction of CO 2 and CH 4 with clay surfaces. The cations located between the isomorphously substituted montmorillonite layers exert stronger electrostatic interactions with CO 2, leading to an increased adsorption selectivity of montmorillonite for CO 2 /CH 4 . As pore size, pressure, and temperature increase, the selectivity of binary mixtures decreases, but adsorption sites undergo temperature-dependent redistribution. Under higher hydration conditions, selectivity improves, primarily because gases adsorbed between layers are mainly captured by H 2 O molecules rather than by the surfaces of clay minerals. Within the pores of two hydrated clay minerals, in addition to the competitive adsorption mechanism, the “water-mediated synergistic adsorption” mechanism predominates in the adsorption of gases.