Simultaneous determination of the effective stress coefficients for permeability and volumetric strain on a tight sandstone

Gas transport processes in low-permeable (tight) sandstones at elevated pore pressures involve a combination of fluid-dynamic (slip flow) and poro-elastic or rock-mechanical stress (pore and bulk compressibility) effects. To assess the interdependency of both processes, permeability experiments with gas (argon) were combined with volumetric strain measurements. The flow studies were performed under controlled effective stress (10, 20 and 30 MPa) with pore and confining pressures up to 30 and 50 MPa, respectively. The results of the permeability and strain measurements could only be described by the modified effective stress laws for apparent permeability coefficients (χ = 1.25) and volumetric strain (Biot α = 0.7), respectively. Measured apparent permeability coefficients (~10−18 m2) were implemented into a permeability model considering both gas and stress effects individually. A “clay-shell” pore structure model was used to describe the interrelated changes in permeability and bulk volume with respect to pore and confining pressure. •Simultaneous measurements of apparent gas permeability and volumetric strain on a tight sandstone.•Stress-dependencies of permeability and volumetric strain do not follow Terzaghi's principle.•Effective stress coefficients for apparent permeability (χ) and volumetric strain (Biot α) were 1.25 and 0.66–0.7, respectively.•Gas flow appears to be controlled by soft and compressible clay components in the sandstone.•Stress-dependence of permeability and bulk deformation can be described by the “clay-shell” pore-structure model.