(1. Technology Innovation Center for In-situ Stress，Ministry of Natural Resources，Chinese Academy of Geological Sciences， Beijing 100081，China；2. State Key Laboratory for Geomechanics and Deep Underground Engineering，China University
of Mining and Technology(Beijing)，Beijing 100083，China；3. Department of Civil Engineering，Tsinghua University，
Beijing 100084，China；4. Department of Civil and Environmental Engineering，Cornell University，Ithaca，New York
14853，USA；5. Department of Mechanical Engineering，Tsinghua University，Beijing 100084，China；
6. Beijing Research Institute of Uranium Geology，Beijing 100029，China)
Abstract：The multi-stage hydraulic-acid stimulation has become a key technology for permeability enhancement of geothermal reservoirs. In this study，the artificial fracture samples were artificially produced from the granite collected from Gonghe Basin，China，direct shear tests were performed on each fracture sample for six times after different acid immersion treatments. The results show that the shear behavior of rock fractures changes from brittle failure to ductile failure after during the previous five shear tests. The peak shear strength significantly reduces，but the residual shear strength does not change significantly during the previous five shear tests. After acid immersion treatment，the shear behavior of the rock fractures still exhibits ductile failure，but the peak and residual shear strengths significantly reduce. Based on wear theory，a formula of calculating shear-induced damage volume of rough fractures is developed，which is in good agreement with the experimental results. After acid immersion treatment，the differential dissolution rates of different minerals increase the fracture surface roughness，but the acid corrosion is further promoted by the large number of micro-cracks in the fracture surfaces induced during the previous five shear tests，which in turn degrades the mechanical properties of fracture asperities. Because the latter mechanism is dominant，rock fractures exhibit weakening effects after acid immersion treatment.
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2023, Vol. 42 
