Cooling-induced permeability enhancement for networks of microfractures in superhot geothermal environments

Abstract Recent researches have proposed the use of enhanced geothermal system reservoirs consisting dense networks microfractures, created by hydraulic and/or thermal fracturing in superhot/supercritical environments, because their suitability for energy harvesting. During and extraction, fracture are exposed to cooling due injection cold fluid into reservoirs. Previous studies showed such reservoir permeability conventional environments. However, may result a higher risk seismicity, owing decreased normal stress on fractures. Nevertheless, it is unclear whether cooling-induced enhancement seismicity occurs within microfractures which consist numerous interconnected at various orientations situ triaxial stress. Thus, no dominant fractures possibility cause enhancement/induced seismicity. In this study, results presented borehole experiments network granite, 400 °C, under true Permeability acoustic emissions were measured with decreases temperature (up ~ 90 °C). Results that increased increasing drop relatively low levels (15 20 MPa). The occurred without intensive failure, was reversible. almost constant level (65 required equivalent mean stress, so reduced near-zero, considerable amount microfractures. Additionally, microfracture can be primarily through thermo-elastic deformation (without failure), useful compensate reduction injectivity property changes.