Stress-dependent fluid dynamics of shale gas reservoirs: A pore network modeling approach

Abstract

In this study, the pore network modeling approach is implemented to study the flow behavior of the methane gas in shale reservoirs in the presence of slip flow and gas desorption under different effective stress conditions through the effect on apparent permeability. A single pore and a pore network are constructed using a down-scaled Berea sandstone image. The compressible Stokes is applied with proper boundary conditions to capture slip flow and gas desorption effects. To include the effect of stress, poroelasticity principles are applied to describe the interaction between fluid flow and solid deformation. The model performance is verified against an experimental data taken from the literature. Both models show a negative effect of stress on gas flow when slip flow and desorption mechanisms are activated in the models. In the single pore model, slip has a positive and complementary effect on desorption at a specific stress value when their coupled contributions are summative. However, the results of pore network model show that slip has a destructive effect on desorption contribution specially at low effective stress values. That is, the changes in pore pressure induced by the slip mechanism act to limit the desorption contribution. This is clearly noted with the consideration of stress effects. At high effective stress values, the slip effect is limited due to the increase in pore pressure by compression, hence a closer matching between the permeability enhancement produced by the desorption mechanism alone and the coupled effect of desorption and slip can be noticed. Stress acts to limit the slip flow and also the desorption mechanism as they both are a function of pore pressure, however, as stress increases the contribution of desorption no longer would be reduced by slip flow. This study provides insights into stress role in multiphysics gas flow in shale reservoirs.