Molecular simulation study of CO2/CH4 adsorption on realistic heterogeneous shale surfaces

Molecular simulation enjoys a high preference for use in adsorption studies. However, modeling and preparing a realistic shale topology remains a constraint. Majority of studies are performed using a single component, such as kerogen or montmorillonite, to represent shale surface. Where more than one component is used, they are not mixed but are at different ends of the nanopores. These surfaces do not bear similitude to actual shale surfaces in terms of heterogeneity and multiplicity of minerals. Moreover, disparities have been observed between simulation and experimental results. In this work, we propose a molecular shale model prepared from montmorillonite, type IID kerogen, quartz, and illite clay minerals. The results from the adsorption simulation studies on the shale model show that the model has higher adsorption capacity and surface area than the individual molecular models of kerogen, illite, or quartz. It was also observed that the proposed model had less free gas than adsorbed gas which is the actual situation in shale formations. The current model shows increased adsorption capacity up to about 48% more than other models used in this study. This new realistic model can serve to enhance the accuracy of adsorption simulations and thus present a better understanding of adsorption behaviors. Such improvement can also lead to increased accuracy in estimating the gas in place.