Distribution of CO2-CH4 in a nanoslit medium and the efficiency of displacement of CH4 by CO2

The replacement of CH 4 with CO 2 in reservoirs is crucial for natural gas exploitation and sequestration of CO 2 . Therefore, the states and distribution patterns of coexisting CO 2 and CH 4 and the dynamic patterns of CH 4 displacement by CO 2 in mineral slits must be understood. Here, we simulate the molecular dynamics and displacement efficiency of CH 4 in gypsum, quartz, and illite mineral slit models. The results demonstrate that gas density is not uniform throughout the slits and prove that gypsum and quartz have a greater adsorption capacity for CO 2 than for CH 4 and illite has a greater adsorption capacity for CH 4 . We find that (1) the application of the same force to different mineral slits leads to dissimilar CH 4 displacement efficiencies, whereas an increase in the applied force in the same mineral slit is positively correlated with the CH 4 displacement efficiency; (2) the main factor affecting CH 4 displacement efficiency is CO 2 adsorption; (3) the greater the adsorption capacity of mineral slits for CO 2 (such as for gypsum), the more difficult it is to displace the CH 4 in the slit despite large applied force; and (4) CH 4 displacement efficiencies of illite, quartz, and gypsum decrease under the same conditions. These results provide a reference for theoretical research and industrial applications related to geologic carbon sequestration.