Fracture propagation in shale under conditions is a critical but poorly understood mechanical process in hydraulic fracturing for deep shale gas reservoirs. To address this, hydraulic fracturing experiments were conducted on hollow double-wing crack specimens of the Longmaxi shale under conditions simulating the ground surface (confining pressure =0, room temperature ()) and at depths of 1600 m (=40 MPa, =70 °C) and 3300 m (=80 MPa, high temperature =110 °C) in the study area. High stress was found to significantly increase fracture toughness through constrained microcracking and particle frictional bridging mechanisms. Increasing the temperature enhances rather than weakens the fracture resistance because it increases the grain debonding length, which dissipates more plastic energy and enlarges grains to close microdefects and generate compressive stress to inhibit microcracking. Interestingly, the fracture toughness anisotropy in the shale was found to be nearly constant across burial depths, despite reported variations with increasing confining pressure. Heated water was not found to be as important as the environment in influencing shale fracture. These findings emphasize the need to test the fracture toughness of deep shales under coupled stress and temperature conditions rather than focusing on either stress or temperature alone.

中文翻译：

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模拟不同埋深应力与温度耦合条件下页岩水力压裂行为


在某些条件下页岩中的裂缝扩展是深层页岩气藏水力压裂中一个关键但人们知之甚少的机械过程。针对这一问题，在模拟地表条件（围压=0，室温（））、深度1600 m（=40 MPa，=70）的龙马溪组页岩空心双翼裂缝试件上进行了水力压裂实验。 ℃）和3300 m（=80 MPa，高温=110 ℃）。研究发现，高应力可通过约束微裂纹和颗粒摩擦桥接机制显着提高断裂韧性。提高温度会增强而不是减弱断裂抗力，因为它增加了晶粒脱粘长度，从而耗散更多塑性能并增大晶粒以闭合微缺陷并产生压应力以抑制微裂纹。有趣的是，尽管据报道随着围压的增加而变化，但页岩中的断裂韧性各向异性在整个埋藏深度上几乎是恒定的。研究发现，热水对页岩破裂的影响不如环境那么重要。这些发现强调需要在应力和温度耦合条件下测试深层页岩的断裂韧性，而不是单独关注应力或温度。