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| Experimental research on permeability of fractured-subsequently-filled granite under high temperature and triaxial stresses |
| YIN Weitao1，2，ZHAO Yangsheng1，2，FENG Zijun1，2 |
| (1. College of Mining Engineering，Taiyuan University of Technology，Taiyuan，Shanxi 030024，China；2. Key Laboratory of In-situ Property Improving Mining of Ministry of Education，Taiyuan University of Technology，Taiyuan，Shanxi 030024，China) |
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Abstract The permeability of the parent rock(type I granite)，hydrothermal fluid backfill(type II granite)，A-type fractured-subsequently-filled granite(cementation interface between the backfill and the parent rock laterally positioned through the specimen，type III granite) and B-type fractured-subsequently-filled(granite cementation interface between the backfill and the parent rock longitudinally positioned through the specimen，type IV granite) under high temperature and triaxial stresses was studied in this paper. The threshold temperatures of permeability change of types I，II，III and IV granite are 300 ℃，200 ℃，300 ℃ and 250 ℃，respectively. When the temperature is lower than the threshold，the permeability of four kinds of granite almost unchanged. When the temperature exceeds the threshold，however，the permeability of four kinds of granite increases rapidly by 1，3，2 and 3 orders of magnitude respectively，and the permeability magnitude of types II and IV granites reaches 10－1 mD at above 450 ℃. The micro-structure and thermally induced fracture number of fractured-subsequently-filled granite under the action of high temperature were observed by a microscope. It is found that the permeability of types I and III granite increases because of the penetration of fractures with a length greater than 200 μm after 300 ℃，and that the low strength and deteriorated mechanical property of the backfill due to dissolution are the main reasons for the permeability of types II and IV granite to be significantly higher than that of types I and III granite. Through the analysis of the model of convection heat transfer between water and rock mass，it can be seen that the reservoir construction in fractured-subsequently-filled granite can greatly reduce the construction cost，increase the water-rock heat exchange area and improve the heat exchange efficiency. The research work provides a new technical and theoretical thinking for deep HDR geothermal exploitation.
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2020, Vol. 39 
