Investigation of methane adsorption and its effect on gas transport in shale matrix through microscale and mesoscale simulations

摘要

Methane adsorption and its effect on fluid flow in shale matrix areinvestigated through multi-scale simulation scheme by using molecular dynamics(MD) and lattice Boltzmann (LB) methods. Equilibrium MD simulations areconducted to study methane adsorption on the organic and inorganic walls ofnanopores in shale matrix with different pore sizes and pressures. Density andpressure distributions within the adsorbed layer and the free gas region arediscussed. The illumination of the MD results on larger scale LB simulations ispresented. Pressure-dependent thickness of adsorbed layer should be adopted andthe transport of adsorbed layer should be properly considered in LBsimulations. LB simulations, which are based on a generalized Navier-Stokesequation for flow through low-permeability porous media with slippage, areconducted by taking into consideration the effects of adsorbed layer. It isfound that competitive effects of slippage and adsorbed layer exist on thepermeability of shale matrix, leading to different changing trends of theapparent permeability.