Thousands of cubic meters of fluid are continuously injected for a long term to create complex fracture patterns in hydraulic fracturing of hot dry rocks. However, the physics and mechanics behind the interaction of fluid–rock are not fully understood at present. To reveal the related damage mechanisms of saturated rock samples such as damage initiation and evolution at various alternative stress levels, a series of in-house laboratory tests were performed on a TAW-series triaxial rock mechanics testing system, combined with ultrasound measurement and acoustic emission (AE) monitoring. After saturation with nano-emulsion and distilled water, ultrasound velocity of longitudinal wave was increased by 40%. Saturation weakens these mechanical parameters such as the crack damage stress ratio, fracture toughness and cohesive strength under different stress conditions. Fluid-saturated rock sample has higher AE hit rate than dry rock sample. Meanwhile, many step-like jumps appeared on the curve of cumulative AE events. Failure envelop, b-value and frequency spectrum were analyzed out to compare the mechanical difference between fluid-saturated and dry rock samples. The experimental results demonstrate that the saturation increased the pore pressure in rocks and further promoted crack propagation in hydraulic fracturing. Moreover, nano-emulsion liquid is more advantageous than distilled water for enhancing fracture complexity. This investigation provides for better understanding of the mechanisms of complex fracture formation in deep geothermal reservoirs.

长期连续注入数千立方米的流体，以在热干岩石的水力压裂中产生复杂的裂缝形态。但是，目前还没有完全了解流体-岩石相互作用背后的物理和力学。为了揭示饱和岩石样品的相关破坏机理，例如在各种不同应力水平下的破坏起始和演化，在TAW系列三轴岩石力学测试系统上进行了一系列室内实验室测试，并结合了超声测量和声发射（AE）监控。用纳米乳液和蒸馏水饱和后，纵波的超声速度提高了40％。饱和会削弱这些机械参数，例如裂纹破坏应力比，在不同应力条件下的断裂韧性和内聚强度。流体饱和岩石样品比干燥岩石样品具有更高的AE命中率。同时，在累积AE事件的曲线上出现了许多阶梯状跳跃。失败笼罩，分析了b值和频谱，以比较流体饱和和干燥岩石样品之间的机械差异。实验结果表明，饱和度增加了岩石的孔隙压力，并进一步促进了水力压裂裂缝的扩展。此外，纳米乳液液体比蒸馏水更有利于增加断裂的复杂性。这项研究可以更好地了解深部地热储层复杂裂缝的形成机理。