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The objective for this work is to investigate the contribution of the adsorbed phase to the mass flux and comparing transport of gases with different adsorption affinities in organic nano-scale channels. In this work, force-driven Non-Equilibrium molecular dynamics (NEMD) simulations are used to compare the transport of gases with high adsorption affinity (Methane and Argon) with the ones with low adsorption affinity (Helium), for channel heights of 2, 4, 6, and 8 nanometers at two Knudsen numbers of 0.1 and 0.2. Velocity and mass flux profiles across the channel for Argon, Methane, and Helium are compared. Transport diffusion coefficients and molecular flux of these gas are also calculated. Furthermore, adsorption properties are analysed using Grand Canonical Monte Carlo simulations.For all the gases studied, plug-shaped velocity profiles are observed irrespective of the channel size and Knudsen number. Mass flux profiles of Argon and Methane across the channels demonstrate a significant contribution of adsorbed molecules to the total mass flux. Furthermore, as Knudsen number increases, the contribution of the adsorbed phase to the total mass flux becomes higher. Molecular flux of Helium is smaller than that of Argon and Methane for all channel sizes. The calculated diffusion coefficients of Methane are higher than those for Argon for all the channel sizes and they decrease as the channel size increases. For Argon and Methane, the diffusion coefficients become smaller as Knudsen number increases. For Helium, the diffusion coefficients are weak functions of the channel size and Knudsen number. Based on the results, contribution of the adsorbed molecules can be more than 50% of the total mass flux of the channel. For the pressure ranges studies, transport diffusivity of Helium is less sensitive to pressure and Knudsen number compared to Argon and Methane.This study shows that the transport through organic nano-scale conduits is essentially diffusive. Therefore, to have a realistic model for predicting the recovery of fluids from unconventional resources, the transport equations in organic nanopores should be replaced by the diffusive transport equations.

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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.