REV-scale simulation of gas transport in shale matrix with lattice Boltzmann method

Shale gas reservoirs have obscured transport properties owing to the complex micro-porous structure and extremely low permeability. In this study, a lattice Boltzmann (LB) model at representative elementary volume (REV) scale has been proposed to simulate gas transport in a 2-dimensional (2D) micro-porous media reconstructed by optimized quartet structure generation set (QSGS) method. The velocity distributions and apparent permeability of gas transport inside the reconstructed porous media are demonstrated and analyzed, and the gas flow mechanisms such as slippage, gas adsorption and surface diffusion have been investigated. The simulation results indicate that gas displays considerable different flow behaviors due to the effects of gas slippage, and the apparent permeability is significantly related to the Knudsen number (Kn). Moreover, the increasing adsorbed gas concentration in the pore surface has great impact on the gas transport behaviors, which is accounting for the decreasing apparent permeability. Surface diffusion can strongly affect the apparent permeability, but the strength of this effect is subject to the adsorbed gas concentration. It is hoped that this study can provide some novel insights into the investigation of gas transport in shale gas reservoirs.