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

TL;DR

This study combines molecular dynamics and lattice Boltzmann simulations to explore how methane adsorption influences fluid flow and permeability in shale matrices, revealing the interplay of slippage and adsorbed layers.

Contribution

It introduces a multi-scale simulation approach that accounts for methane adsorption effects on flow in shale, highlighting the importance of adsorbed layer thickness in permeability analysis.

Findings

Adsorbed layer thickness depends on pressure and pore size.

Slippage and adsorbed layer effects jointly influence shale permeability.

Permeability trends vary with the balance of slippage and adsorption effects.

Abstract

Methane adsorption and its effect on fluid flow in shale matrix are investigated through multi-scale simulation scheme by using molecular dynamics (MD) and lattice Boltzmann (LB) methods. Equilibrium MD simulations are conducted to study methane adsorption on the organic and inorganic walls of nanopores in shale matrix with different pore sizes and pressures. Density and pressure distributions within the adsorbed layer and the free gas region are discussed. The illumination of the MD results on larger scale LB simulations is presented. Pressure-dependent thickness of adsorbed layer should be adopted and the transport of adsorbed layer should be properly considered in LB simulations. LB simulations, which are based on a generalized Navier-Stokes equation for flow through low-permeability porous media with slippage, are conducted by taking into consideration the effects of adsorbed layer. It is found that competitive effects of slippage and adsorbed layer exist on the permeability of shale matrix, leading to different changing trends of the apparent permeability.