Inducing shear failure in reservoir rocks is a critical strategy for enhancing hot dry rock resource exploitation, as it promotes the development of an extensive fracture network. In this study, granite was subjected to direct shear tests under three distinct temperatures and five thermal cycling treatments. Utilizing acoustic emission (AE) and digital image correlation (DIC) techniques, the shear failure traits and the evolutionary patterns of cracks in granite under diverse thermal cycling treatments were probed. Experimental results reveal that the direct shear strength of granite initially decreases, subsequently rebounds with increasing thermal cycles, and exhibits a steady decrease with temperature increase. Effects of thermal shock provoke a surge in AE counts and energy during the initial half of the shearing process, steering the failure mode of the samples from brittle to plastic. Furthermore, the macro crack morphology changes from a singular shear crack to a pair of parallel shear cracks, becoming intricately complex at elevated temperatures (600 °C). Additionally, the initiation of the main shear crack in granite consistently manifests a mixed tensile-shear failure, with the proportion of shear action displaying a positive correlation with temperature. In contrast, the proximal secondary cracks are purely tension-initiated. Finally, a competitive mechanism between rock strengthening and weakening induced by thermal cycles treatment was proposed to explain the remarkable rebound in direct shear strength following thermal cycling treatment. The current work provides insights for the mechanism of shear failure in rocks under different thermal cycling conditions in geothermal reservoir stimulation.

中文翻译：

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热循环与直剪加载路径耦合作用下干热岩破坏机制

诱发储层岩石剪切破坏是加强干热岩资源开发的关键策略，因为它促进了广泛的裂缝网络的发育。在这项研究中，花岗岩在三种不同的温度和五种热循环处理下进行了直接剪切测试。利用声发射（AE）和数字图像相关（DIC）技术，探讨了不同热循环处理下花岗岩的剪切破坏特征和裂纹演化模式。实验结果表明，花岗岩的直剪强度最初下降，随后随着热循环的增加而反弹，并随着温度的升高而稳定下降。在剪切过程的前半段，热冲击的影响会引起声发射计数和能量激增，从而将样品的失效模式从脆性转变为塑性。此外，宏观裂纹形态从单一剪切裂纹变为一对平行剪切裂纹，在高温（600°C）下变得错综复杂。此外，花岗岩中主剪切裂纹的萌生始终表现为混合拉剪破坏，剪切作用的比例与温度呈正相关。相反，近端二次裂纹纯粹是由张力引发的。最后，提出了热循环处理引起的岩石强化和弱化之间的竞争机制，以解释热循环处理后直剪强度的显着反弹。目前的工作为地热储层改造中不同热循环条件下岩石的剪切破坏机制提供了见解。