Molecular simulation of gas adsorption under coupled temperature–pressure conditions in shale reservoirs

The interfacial properties of clay mineral nanopores strongly control methane occurrence and gas–water transport in shale reservoirs, making them crucial for evaluating shale gas recoverability. In this study, molecular dynamics simulations were carried out to explore the competitive adsorption and transport characteristics of CH4/H2O in kaolinite pores with distinct surface arrangements (G-G, S-S, and G-S). The results indicate that methane uptake decreases in the sequence of S-S pore > G-S pore > G-G pore, while water adsorption shows a reverse tendency. In heterogeneous pores, CH4 preferentially accumulates near the siloxane surface, while H2O is mainly concentrated on the hydroxyl surface, indicating pronounced interfacial segregation. Increasing temperature and pressure enhances the mobility of both species, with a more significant promotion observed in hydrophobic pores. These results demonstrate that surface heterogeneity of kaolinite plays a decisive role in controlling shale gas storage capacity and transport behaviour.