An anisotropic damage–permeability model for hydraulic fracturing in hard rock

Abstract Hydraulic fracturing is the most efficient method to exploit valued geothermal energy trapped in low-permeable hard rock, e.g. granite. Most research on hydraulic has focused its application shale gas and oil. However, performs differently reservoir, as rock properties are quite different. In this work, an anisotropic damage–permeability model developed fundament of continuum theory study reservoir. The plastic-hardening damage-softening behaviours considered model. A cubic law adopted characterize damage enhanced permeability. Its directional information converted from tensor, while effect compression stress permeability isotropic characterized by impact factor. newly calibrated validated a series stress–strain curve, axial triaxial tests cyclic test at Aspö Hard Rock Laboratory, capacity proven good matching measured injection pressure, permeability, etc. results show clearly that fracture mostly activated tensile failure case. Moreover, stimulated will be closed during flow back re-activated subsequent re-fracturing. If previous not completely, no new fractures created current re-fracturing, amasses continuously due repeated re-activation