The Stress‐Memory Effect of Fracture Stiffness During Cyclic Loading in Low‐Permeability Sandstone

The hydraulic performance and mechanical stability of open fractures are crucial for several subsurface applications including fractured geothermal reservoirs or nuclear waste repositories. Their properties (fluid flow fracture stiffness) both strongly dependent on the geometry. Any change in effective stress impacts aperture thus ability to promote flow. Here, we carried out experiments with shear displaced tensile pre-loaded, low-permeability sandstones two different cyclic loading scenarios up 60 MPa hydrostatic confining pressure. During “constant loading” (CCL) experiments, was repeatedly loaded same peak (up MPa). “progressive (PCL) pressure progressively increased each cycle 15, 30, 45, matrix deformation monitored using axial circumferential LVDT extensometers obtain stiffness. geometry before after experiment compared by calculating distribution from 3D surface scans. Initial leads a linear specific stiffness evolution. For any subsequent cycles shifts nonlinear behavior. transition is shown be related memory effect, similar “Kaiser Effect” acoustic emissions. Progressive possibly less permeability reduction continuous loading.