Adsorption characteristics of CH4 and CO2 in organic-inorganic slit pores

It is very meaningful to study the adsorption characteristics of CH4 and CO2 in shale pores in the context of CO2 sequestration and enhanced gas recovery. However, as far as the authors' knowledge, the study of gas adsorption in organic - inorganic pores is blank. The graphene - montmorillonite (MMT) pore is proposed as a model for shale matrix, and the effect of heterogeneous surface on the adsorption behavior of CH4 and CO2 in slit pores was studied by molecular dynamics (MD) method. More reasonable criteria have been adopted for the definition of free zones and adsorption zones. The adsorption characteristics and adsorption isotherms of CH4 and CO2 were analyzed, and the microscopic mechanism of gas adsorption was revealed from the molecular perspective. It was found that the heterogeneous surface caused the density distribution of the gas within the slit pores to be asymmetrical. The graphene surface shows a significantly stronger adsorption capacity than MMT, and this adsorption advantage decreases with increasing pressure. Compared with CH4, the effect of heterogeneous surface on CO2 adsorption behavior is more significant. As the pressure increases, the adsorption layer of CO2 shows a tendency to gradually become saturated. This work provides a theoretical basis for optimizing the exploitation of shale gas and geological storage of carbon dioxide.