Molecular simulation of CH4 adsorption behavior in slit nanopores: Verification of simulation methods and models

The aim of this study is to select an appropriate method for CH4 adsorption in organic nanopores for shale-gas development. Molecular dynamics (MD) and grand canonical Monte Carlo (GCMC) simulations were performed. Three comparison studies were included: (i) comparison of the adsorption behavior in kerogen nanopores using different schemes for dispersion correction, (ii) comparison of the adsorption behavior in graphite nanopores using MD and GCMC simulations, and (iii) comparison of the adsorption behavior in kerogen and graphite nanopores using MD simulations. The result was reliable when using a particle-mesh Ewald scheme or a cut-off >= 1.5 nm without dispersion correction. The simulation results were essentially identical for the MD and GCMC simulations. The free-gas CH4 density inside the nanopores started to deviate from the bulk density at similar to 2 nm for the graphite model and at similar to 7-10 nm for the kerogen model, whereas the total CH4 density deviates from the bulk density at similar to 20 nm.