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

The carbon dioxide (CO2) sequestration combined with enhanced natural gas recovery is a promising technology. Injecting CO2 into hydrocarbon reservoirs induces a competitive adsorption process between CO2 and CH4, which not only facilitates significant CO2 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 CO2/CH4 binary mixtures on clay minerals with different structures, specifically kaolinite and montmorillonite. Van der Waals forces predominantly govern the interaction of CO2 and CH4 with clay surfaces. The cations located between the isomorphously substituted montmorillonite layers exert stronger electrostatic interactions with CO2, leading to an increased adsorption selectivity of montmorillonite for CO2/CH4. 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 H2O 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.