Impact of time-dependent deformation on fluid transport properties of sandstone

This study deals with the impact of time-dependent deformation on fluid transport properties of Berea sandstone under triaxial loading conditions. A series of stress-stepping experiments, incorporating hold periods at constant axial load, is conducted on cylindrical specimens instrumented for precise deformation, permeability, and acoustic emission measurements. During each period, subcritical crack growth appears to lead to progressive damage, which is monitored through accumulation of volume and shear strain. The results demonstrate an exponential decrease in both bulk and shear viscosities as deviatoric stress increases, highlighting the role of time-dependent deformation in subcritical stress regime. Notably, intrinsic permeability decreases despite the formation of microcracks, suggesting that crack closure due to external confinement outweighed any pore network connectivity enhancements. Application of lower effective mean stresses is found to accelerate these changes, leading to more pronounced permeability reductions. Overall, this study highlights the importance of incorporating subcritical time-dependent deformation in geomechanical models, as it significantly influences fluid flow and reservoir performance in subsurface operations.