Abstract The fracture characteristics of fine-grained granite were examined for a potential geothermal-energy reservoir. The granite was thermally cycled in a furnace between 100 °C and 300 °C and its mechanical behavior and meso-crack characteristics were analyzed. The results indicate that thermal cycling leads to decreased fracture toughness (Keff), absorbed energy (U), longitudinal wave velocity (Pv), and increased permeability (K) in granite. These changes can be explained using the thermal fatigue accumulated damage. The ability of granite to resist fracturing is greatly reduced in the first five thermal cycles. Thermal cycling is more conducive to inducing intergranular cracks. The interconnection of intragranular and intergranular cracks causes the structure of granite to become fragmented and more likely to fail. Thus, thermal cycling deteriorates the mechanical stability of fine-grained dense granite, and allows crack networks to form more easily. The correction of crack propagation critical radius (rc) can improve the accuracy of the modified maximum tangential stress (MMTS) predictive fracture.

中文翻译：

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热循环对地热能储层花岗岩断裂特征的影响试验研究

摘要 研究了细粒花岗岩的断裂特征，作为潜在的地热能储层。将花岗岩在 100°C 至 300°C 的炉子中进行热循环，分析其力学行为和细观裂纹特征。结果表明，热循环导致花岗岩的断裂韧性 (Keff)、吸收能 (U)、纵波速度 (Pv) 和渗透率 (K) 降低。这些变化可以用热疲劳累积损伤来解释。花岗岩的抗压裂能力在前五个热循环中大大降低。热循环更有利于诱发晶间裂纹。晶内和晶间裂纹的相互连接导致花岗岩的结构变得支离破碎，更容易失效。因此，热循环会降低细粒致密花岗岩的机械稳定性，并使裂纹网络更容易形成。裂纹扩展临界半径（rc）的修正可以提高修正后的最大切向应力（MMTS）预测断裂的准确性。