Cui Yuan, Xu Chao, Xue Lei, Bu Fengchang, Zhu Jun
State Key Laboratory of Lithospheric and Environmental Coevolution, Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing, 100029, China.
Key Laboratory of Shale Gas and Geoengineering, Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing, 100029, China.
Sci Rep. 2025 Aug 13;15(1):29671. doi: 10.1038/s41598-025-14590-z.
Understanding the thermo-mechanical behavior of granite under high-temperature conditions is crucial for the safe and efficient development of deep geothermal resources. This study revealed the physico-mechanical properties, cracking mechanism and fracture precursor of granite via compression experiments with acoustic emission (AE) monitoring. Results indicated that 500 °C is the critical temperature for the brittle-ductile transition of granite, characterized by progressive degradation of P-wave velocity, Young's modulus, and uniaxial compressive strength (UCS) with increasing temperature, while peak strain shows an inverse trend. As the temperature and number of thermal cycles increase, the physico-mechanical parameters, AE characteristics and the failure modes show a strong temperature dependence, whereby the temperature is categorized into "slight weakening range (25-200°C)", "stable weakening range (200-500 °C)" and "significant weakening range (≥ 500 °C)". Thermally induced cracks are mainly composed of extrusion cracks from mineral thermal expansion mismatch, and intergranular cracks along weakened grain boundaries. In addition, the high energy rate AE event can be regarded as the fracture precursor, but it is significantly affected by the thermal effect. This study aims to determine the optimal temperature, cooling method, and number of thermal cycles needed for geothermal resource extraction.
了解花岗岩在高温条件下的热-力学行为对于深层地热资源的安全高效开发至关重要。本研究通过带有声发射（AE）监测的压缩实验揭示了花岗岩的物理力学性质、破裂机制和断裂前兆。结果表明，500℃是花岗岩脆-韧性转变的临界温度，其特征是随着温度升高，纵波速度、杨氏模量和单轴抗压强度（UCS）逐渐降低，而峰值应变则呈相反趋势。随着温度和热循环次数的增加，物理力学参数、AE特征和破坏模式表现出强烈的温度依赖性，据此将温度分为“轻微弱化范围（25-200℃）”、“稳定弱化范围（200-500℃）”和“显著弱化范围（≥500℃）”。热致裂缝主要由矿物热膨胀失配产生的挤压裂缝和沿弱化晶界的晶间裂缝组成。此外，高能量率AE事件可被视为断裂前兆，但它受热效应的影响显著。本研究旨在确定地热资源开采所需的最佳温度、冷却方法和热循环次数。
