This article is summary of the paper published in “International Journal of Rock Mechanics and Mining Sciences” (Ishibashi et al., 2023a). To provide key parameters and constitutive laws essential for field-scale multiphysics simulations that accurately predict fracture network structures in enhanced geothermal systems (EGS) and resultant energy extraction, we investigate the comprehensive spectrum of hydraulic shear processes in granite fractures and reassess the connection between hydraulic and mechanical properties during shear slips. Key results from our novel laboratory experiments include the following: (1) Fracture permeability of granite increases due to hydraulic shear slip even at an effective normal stress exceeding 50 MPa, (2) Shear slip and stress drop are proportional, and the increase in fracture permeability correlates with the total shear slip displacement, and (c) although hydraulic shear slip tends to make fracture surfaces slightly smoother, the factual characteristics of surface are maintained after slip. By integrating our experimental results with seismological analysis, we first examine the energy balance during the hydraulic shearing of preexisting rock fractures and highlight the critical role of the elastic potential energy stored in the surrounding bulk rock masses. Subsequently, we derive a constitutive model that relates to the permeability change of granite fractures during hydraulic shearing under typical crustal stress conditions of EGS, estimating that the maximum change in fracture permeability due to shear dilation is approximately 20-fold, though scale effects are not considered. In summary, we successfully demonstrate novel and advanced insights into hydro-mechanical coupled processes during hydraulic shearing, aiming to improve the accuracy of fracture network designs in EGS technology.
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