Apparent permeability study of rarefied gas transport properties through ultra-tight VORONOI porous media by Discrete Velocity Method

Accurate prediction of the apparent permeability relies on deep understanding of unconventional gas transport mechanism in microscale. To achieve this goal, it is necessary to develop a controllable generation method for low porosity porous media with shale characteristics and explore advanced numerical method to study non-equilibrium phenomena in porous media. Based on the VORONOI tessellation and its topological relationship, a new method for the generation of controllable low porosity porous media is proposed. Two numerical simulation methods are adopted to study gas flow in VORONOI porous media systematically, including Multiple-Relaxation-Time Lattice Boltzmann Method for the intrinsic permeability and Linearized BGK equations via the Discrete Velocity Method for the apparent permeability influenced by the non-equilibrium effect. The results show that the effective porosity is the decisive factor affecting the intrinsic permeability. Porous media with low porosity and high tortuosity are more affected by the rarefied gas effect. The velocity contours show that velocity gradually increases in the throats perpendicular to the pressure gradient direction due to the rarefied throttling effect, which reduces the mass flow rate and apparent permeability significantly. Furthermore, by considering the influences of both porosity and tortuosity, a high-order apparent permeability correction model is proposed to fit porous media with different structures.