Fracture Transmissivity in Prospective Host Rocks for Enhanced Geothermal Systems (EGS)

We experimentally determined the hydraulic properties of fractures within various rock types, focusing on a variety Variscan rocks. Flow-through experiments were performed slate, graywacke, quartzite, granite, natural fault gouge, and claystone samples containing an artificial fracture with given roughness. For slate samples, transmissivity was measured at confining pressures, pc, up to 50 MPa, temperatures, T, between 25 100 °C, differential stress, σ, acting perpendicular surface 45 MPa. Fracture decreases non-linearly irreversibly by about order magnitude increasing pressure slightly stronger influence pc than σ. Increasing temperature reduces only high pressures when aperture is already low. An increase in roughness three times yields initial almost one higher. Fractures similar display highest quartzite granite whereas granitic gouge material several orders lower. The reduction stress room varies composition uniaxial strength, where deduction lowest for rocks fraction strong minerals associated brittleness strength. Microstructural investigations suggest that induced compaction matrix crushing asperities. Our results roughness, as example target reservoir unconventional EGS, comparable other hard rocks, e.g., highly altered and/or clay-bearing poor potential extracting geothermal energy from discrete fractures.