Methane/Carbon Dioxide Adsorption and Diffusion Performances at Different Mineral Compositions and Buried Depth Conditions

This study employed the molecular dynamics (MD) and grand canonical Monte-Carlo (GCMC) methods to investigate the adsorption and diffusion performances of methane and carbon dioxide in illite, montmorillonite, and calcite and to explore their molecular dynamic properties under different buried depths. The results suggested that, in the adsorption simulation, with the increase in buried depths, the adsorption capacities and adsorption heats of illite and montmorillonite for methane and carbon dioxide at the buried depths of 0-6 km first showed an increase and then a decrease, while those of calcite showed a continuous decreasing trend. The adsorption capacity for methane conformed to the following order: montmorillonite > illite > calcite, while that for carbon dioxide followed the order of montmorillonite > calcite > illite. The adsorption capacities of these three minerals for carbon dioxide were superior to those for methane. In the diffusion simulation, at the buried depths of 0-6 km, the self-diffusion coefficients of methane and carbon dioxide first showed a decrease and then an increase. In the mixed adsorption, methane was more susceptible to competitive adsorption, and the competitive adsorption between methane and carbon dioxide was more obvious in montmorillonite.