Flow of Multicomponent Gases in Carbon-Based Organic Nanopores

Abstract

Abstract In the study of transport of gases in shale reservoirs, a special attention should be paid to gas transport in organic nanopores due to their nano-scale pore sizes and adsorption phenomena at the pore surfaces. Most of current studies are focused on the transport of single component fluids, mainly methane. The objective for this work is to investigate transport of multicomponent gases in carbon-based organic pores. In this study, adsorption and transport of multicomponent gas systems in identical setups of graphite channels with rough surfaces are investigated using non-equilibrium molecular dynamics simulations (NEMD). Simulations are performed for two gas samples with different compositions for channel heights of 2 and 4 nm. For each simulation, the velocity, density, and mass flux profiles are computed. Moreover, the selectivity values of heaviest molecule (hexane) over other gas components are determined. Finally, diffusion coefficients of each gas component are computed and compared. Based on MD simulation results, most of heavier gas components are adsorbed to the wall. Hexane, which is the heaviest gas component, has a higher tendency to be adsorbed to the channel walls compared to lighter gas components. Therefore, in real systems, most of the heavier components may stay in reservoir in adsorbed state. Furthermore, in contrary to previous studies in which plug-shaped flow profile were observed, parabolic-shaped velocity profile are observed due to presence of rough channel surfaces and heavier gas components. Based on the simulation results, heavier gas components have lower diffusion coefficients compared to lighter components. This work is one of the few in-depth investigations of the transport of natural gas systems in organic pores. The results in this study can potentially modify the multiscale formalism of fluid flow in shale resources.