Simulation of microscale gas flow in heterogeneous porous media based on the lattice Boltzmann method

A microscale multi-relaxation-time lattice Boltzmann model with the regularization procedure is adopted to simulate gas flow in different porous media. The diffuse reflection boundary condition is used to deal with the random solid boundaries. Because of the complex geometry of the pores, the characteristic length is no longer a constant but a function of the pore locations for the porous media. A rational method is proposed to obtain the local characteristic lengths of the porous media for the microscale gas flow simulations. The simulation results show that gas flow characteristics in different flow regions are notably different. In the continuum flow region and slip flow region, the gas flow abilities in different pores are quite different. The effect of heterogeneity of the porous media on gas velocity distribution is very obvious. As the Knudsen number increases, the differences of gas flow abilities in different pores decrease. For gas flow in the strong transition flow region and free molecular flow region, the gas flow abilities in small pores are similar to those in large pores and the effect of heterogeneity becomes small. Such phenomena are mainly caused by the different gas flow mechanisms in different flow regions. In addition, two commonly used apparent permeability calculation models are evaluated by the simulation results and a better coefficient for the Klinkenberg model is proposed according to the simulation results.