  Gas flow in shale is associated with both organic matter (OM) and inorganic
matter (IOM) which contain nanopores ranging in size from a few to hundreds of
nanometers. In addition to the noncontinuum effect which leads to an apparent
permeability of gas higher than the intrinsic permeability, the surface
diffusion of adsorbed gas in organic pores also can influence the apparent
permeability through its own transport mechanism. In this study, a generalized
lattice Boltzmann model (GLBM) is employed for gas flow through the
reconstructed shale matrix consisting of OM and IOM. The
Expectation-Maximization (EM) algorithm is used to assign the pore size
distribution to each component, and the dusty gas model (DGM) and generalized
Maxwell-Stefan model (GMS) are adopted to calculate the apparent permeability
accounting for multiple transport mechanisms including viscous flow, Knudsen
diffusion and surface diffusion. Effects of pore radius and pressure on
permeability of both IOM and OM as well as effects of Langmuir parameters on OM
are investigated. Moreover, the effect of total organic content and
distribution on the apparent permeability of the reconstructed shale matrix is
also studied. It is found that the distribution of OM and IOM has a negligible
influence on apparent permeability, whereas the total organic content and the
surface diffusion play a significant role in gas transport in shale matrix.
