Flow of Gases in Organic-Nanoscale Channels: A Boundary-Driven Molecular Simulation Study

In modeling fluid transport in organic nanopores of shale, particular attention should be paid to the gas wall interactions, specifically the adsorption phenomena, and the fact that the size of pores are comparable with the mean-free-path of the gas molecules. The objective for this work is to investigate the significance of the adsorbed gas molecules in the total mass flux of organic nanoscale channels. Molecular dynamics (MD) has proven to be a credible technique to examine dynamics of atomic-level phenomena. In this study, transport of four different gases, methane and argon (high adsorption affinity) and helium and neon (low adsorption affinity), is studied, and their velocity and mass flux profiles are analyzed using dual control volume grand canonical molecular dynamics (DCV-GCMD) simulations. DCV-GCMD simulations are performed for different pressures, pressure gradients, and channel sizes. Computed normalized velocities are close to 1 for all the gases and channel heights, which shows that the velocity profiles are plug-shaped. For all the gases, as the pressure increases, the density and normalized velocity of the molecules at the wall increase. Furthermore, as pressure increases, the local strain rate at the channel wall decreases because the viscosity of the fluids increases as the pressure increases. The contribution of the adsorbed gas to the total mass flux across the channel for methane is significant. Investigation of the effect of the channel length on the velocity profiles shows that the channel lengths have a significant impact on transport of gases through nanochannels.