Contribution quantification of nanoscale gas transport in shale based on strongly inhomogeneous kinetic model

Abstract

The small pore sizes and intense intermolecular interactions among gas-gas and gas-solid particles lead to complex gas transport in shale nanopores. The strong non-linear flow mechanics, e.g. viscous flow, slippage effect, surface diffusion, adsorption and desorption, may occur in such systems. In this study, a kinetic model for strongly inhomogeneous fluid systems is employed to quantify the contribution of different flow mechanisms to total mass flux in a nanoscale pore considering dense gas effect and pore confinement effect. It is shown that the overall mass flux is dominated by slip flow in bulk region and enhanced surface diffusion in adsorbed region in organic pores. But in inogranic pores, no slip is observed. Then, the contributions from the bulk flow and (enhanced) surface diffusion in organic and inorganic nanopores are quantified. The adsorption and desorption characteristics under different pressure and temperature conditions are consistent with previous studies, and the density and velocity profiles are validated by molecular dynamics simulations. Results show that the flow enhancement effect is significant in organic nanopores due to the large slip velocity and high adsorbed gas density. This study provides a quantitatively multi-scale approach to clarifying various gas transport mechanisms in shale gas reservoirs.