The thermal effect is not considered in the current fracability index model. In this paper, we investigated experimentally the formation capacity of fracture networks in hot dry rocks at different temperatures, by using rock mechanics triaxial testing system and acoustic emission monitoring. A new brittleness index with consideration of thermal effect is proposed on the basis of crack volumetric strain calculated at different stress levels, which captures the following two characteristics: (1) thermal micro-crack density in the crack closure stage and (2) crack propagation, nucleation and coalescence by external stress. Then, a comprehensive fracability index model is established, which integrates the thermal effect and fracture toughness at different temperatures and confining pressures. The fracability index calculated by the new model is consistent with acoustic emission characteristic, microstructure analysis and b-value analysis, which verify that the proposed model is reliable. The results show that both temperature and confining pressure have a significant effect of formation capacity of fracture networks in hot dry rocks. This study provides new insight into improving the thermal efficiency in geothermal reservoirs.

当前的脆性指数模型中未考虑热效应。在本文中，我们通过使用岩石力学三轴测试系统和声发射监测，以实验方式研究了不同温度下干热岩石中裂缝网络的形成能力。根据在不同应力水平下计算出的裂纹体积应变，提出了一种考虑热效应的新脆性指数，该脆性指数具有以下两个特征：（1）裂纹闭合阶段的热微裂纹密度和（2）裂纹扩展外力作用下的成核和聚结。然后，建立了一个综合的脆性指数模型，该模型综合了在不同温度和限制压力下的热效应和断裂韧性。b值分析，证明所提出的模型是可靠的。结果表明，温度和围压都对干热岩石裂缝网络的形成能力有显着影响。这项研究为提高地热储层的热效率提供了新的见识。