Molecular insights into supercritical methane sorption and self-diffusion in monospecific and composite nanopores of deep shale

•Montmorillonite, kerogen and MMT-kerogen composite slit nanopores with desirable pore sizes are constructed;•GCMC and EMD simulations are conducted to study the sorption and self-diffusion behaviors of methane in various nanopores;•Pore surface roughness can impede the diffusion of gases, especially in smaller pores.