Abstract Thermal cycling induced micro-cracks can change the physical and mechanical properties of geothermal energy reservoir, which may influence the heat and mass transfer performance as well as the stability of the reservoir. In this study, thermal cycling treatment was carried out on granite over the temperature range of 20–300 °C with 1–20 thermal cycles. The results show that thermal cycling promotes the initiation and propagation of intergranular and intragranular cracks, which are evenly distributed in all directions. With increase in the number of thermal cycles, the crack density (Pl) increases, resulting in increased permeability (K). The path of seepage passage is mainly between the mineral particles. Moreover, the critical crack propagation radius (rc) of rock decreases with increasing cracking degree, which leads to the decrease in rock fracture resistance. In particular, the fracture toughness (Keff) of granite decreases most when it is subjected to 1–5 thermal cycles. Water-cooling thermal cycling and cooling rate can significantly affect the micro-crack evolution, permeability and ability of granite to resist fracture. The changes in mechanical and physical properties observed in this work can provide basic theoretical reference for the rational selection of geothermal energy mining methods and process parameters, as well as the study of reservoir stability evaluation.

中文翻译：

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热循环相关裂纹对强化地热系统花岗岩物理力学性能的影响

摘要 热循环引起的微裂纹会改变地热能储层的物理力学性质，进而影响储层的传热传质性能和稳定性。在这项研究中，在 20-300°C 的温度范围内对花岗岩进行了热循环处理，并进行了 1-20 次热循环。结果表明，热循环促进了沿各个方向均匀分布的晶间和晶内裂纹的萌生和扩展。随着热循环次数的增加，裂纹密度（Pl）增加，导致渗透率（K）增加。渗流通道主要在矿物颗粒之间。此外，岩石的临界裂纹扩展半径（rc）随着开裂程度的增加而减小，从而导致岩石抗裂性降低。特别是，花岗岩的断裂韧性 (Keff) 在经受 1-5 次热循环时下降得最多。水冷热循环和冷却速率可显着影响花岗岩的微裂纹演化、渗透性和抗断裂能力。该工作观测到的力学物理性质变化可为地热能开采方法和工艺参数的合理选择以及储层稳定性评价研究提供基本的理论参考。花岗岩的渗透性和抗断裂能力。该工作观测到的力学物理性质变化可为地热能开采方法和工艺参数的合理选择以及储层稳定性评价研究提供基本的理论参考。花岗岩的渗透性和抗断裂能力。该工作观测到的力学物理性质变化可为地热能开采方法和工艺参数的合理选择以及储层稳定性评价研究提供基本的理论参考。