Shale gas transport mechanisms in inorganic and organic pores based on lattice Boltzmann simulation
Peng Hou, Feng Gao, Jian He, Jia Liu, Yi Xue, Zhaopeng Zhang
Abstract
A better understanding on the mechanism and difference of shale gas transport through inorganic and organic pores is critical to accurately predicting shale gas recovery. Due to the complicated gas flow dynamics in such narrow pores, traditional experimental methods or simulation methods is difficult to accurately describe these processes. Here, a regularized lattice Boltzmann (LB) model coupled with the slippage boundary condition and gas adsorption effect is employed to simulate shale gas transport in the inorganic and organic pore. The adsorption parameters of shale gas in the LB model are obtained from the molecular dynamics (MD) simulations. Effects of the adsorption effect, pore size, pore wall roughness and gas rarefaction effect on the shale gas transport are studied. The simulation results show that the shale gas transport mechanism heavily depends on the pore size. Basically, in the nano-scale pore, the gas slippage and Knudsen flow are the dominated transport mechanism, but the gas transport is dominated by the surface diffusion in the organic pore width with less than 5 nm owing to the gas adsorption effect. The surface roughness effect plays an important role in the gas transport, and this effect significantly increases with the decreasing of the Knudsen number. At the same time, the gas adsorption effect can also cause a significant increase of the friction factor and a slight decrease of the mass flow rate, which indicates that the gas adsorption effect must be considered in the organic roughness pores.