Direct-Simulation Monte Carlo Investigation of a Berea Porous Structure

Shale-gas and tight gas reservoirs consist of porous structures with pore diameter in the range of 1 to 200 nm. At these scales, the pore diameter becomes comparable to the gas mean free path. Flows in these structures fail often in the transition and slip flow regimes. Standard continuum fluid methods such as the Navier-Stokes- Fourier (NSF) set of equations fail to describe flows of these regimes. We present a direct-simulation monte carlo (DSMC) study of a 3D porous structure in an unlimited parallel simulation. The 3D geometry was obtained with microcomputed-tomography (micro-CT). The gas considered is CH4 (100%), and the gas intermolecular-collision model for the simulation is the variable hard sphere (VHS). Simulations were carried out for three different Knudsen (Kn) numbers within the transition and slip flow regimes. The results demonstrate some of the significant differences that appear in gas-flow properties depending on the Kn number and the flow regime. In addition, the velocity profile appears to depend on the Kn number. At the inlet of the porous structures, more-uniform velocity profile occurs for the three Kn numbers. At the outlet, the velocity profile varies depending on the Kn number. For Kn approximate to 0.037, a parabolic shape is observed for the velocity profile, whereas a more-uniform shape is observed for Kn approximate to 3.7.