Geomechanical evaluation of natural shear fractures in the EGS Collab experiment 1 test bed

Natural fractures can have a significant influence on hydraulic stimulation. One must estimate the peak and residual geomechanical strengths, hydraulic conductivity, and in-situ stress state for the exiting natural fractures in a site in order to identify those natural fractures that are prone to hydraulic opening and/or shear. We apply a triaxial direct-shear method to measure these fracture properties in the Poorman's schist for the EGS Collab project's Experiment 1 test bed at the Sanford Underground Research Facility. In addition, we measure rock matrix density, matrix permeability, and acoustic velocity anisotropy. Using this data, we identify that south-east striking foliation-parallel fractures in this test bed are vulnerable to shear stimulation and can be hydrosheared at in-situ stress conditions. However, natural infilled fractures which are relatively easy to locate and are ubiquitous at the site were found to be too strong and high-friction for hydroshearing, with exception for those parallel to the foliation of the rock.