Effect of Surface Coverage of Water Molecules on Methane Adsorption on Muscovite and Pyrophyllite: Molecular Dynamics Study

To gain a better understanding of the effect of surface coverage of water (H2O) on methane (CH4) adsorption on shale, we performed molecular dynamics simulations. The interactions of H2O with minerals play a key role in the surface coverage of H2O; hence, two representative minerals were investigated: muscovite, which has a high layer charge, and pyrophyllite, which has a net zero layer charge. On the muscovite surface, the amount of CH4 adsorption decreases due to the formation of a structured adsorption layer of H2O, which increases the free energy barrier of CH4 adsorption. On the pyrophyllite surface, the amount of CH4 adsorption decreases due to the spread of a H2O droplet on the surface, which reduces accessible adsorption sites for the CH4 molecules. These insights from an atomic-scale viewpoint are expected to improve our interpretation of the results from the core analysis and modeling of the adsorption amount on shale reservoirs.