The hydrated shales under cyclic loading and unloading conditions are common for the shale reservoir development; corresponding mechanical properties and permeability evolution are very significant and should be deeply researched. Firstly, the experiments of the hydrated shales under the above conditions are discussed, showing that the peak strength is lower and corresponding permeability is higher for more days of hydrating treatment. Secondly, the damage theory is proposed to analyze the shale permeability evolution due to hydromechanical damage and get permeability variation under initial loading and unloading conditions, observing that the permeability in the loading process decreases with increasing confining pressure and increases in the unloading process with decreasing confining pressure; however, the former changes much greater than the latter considering the same confining pressure, indicating that the irreversible damage for the hydrated shales in this cyclic condition has resulted in obvious difference of the permeability. Furthermore, the curves between the permeability and confining pressure based on the experimental data are fitted as negative exponential functions under initial loading conditions and power functions under more cyclic loading conditions, showing that more loading process will change the permeability evolution model. However, the permeability while unloading changes smoothly and can be fitted as a power function with the confining pressure. And in addition, the loss ratio and recovery ratio of the permeability have been deeply researched under five cyclic loading and unloading conditions, thoroughly explaining the permeability decreasing variation with more cyclic processes. Finally, the sensitive coefficients of the permeability have been investigated to observe the largest coefficients under initial cyclic conditions and less and less with more cyclic processes, especially the coefficients while loading which are more sensitive to lower confining pressure and smaller while unloading, which is in accordance with the shale permeability loss and recovery variation, revealing the permeability evolution of the hydrated shale under complex extracted environment.

中文翻译：

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循环加载和卸载条件下水合页岩的渗透率

循环装卸条件下的水化页岩是页岩储层开发的常见现象；相应的力学性能和渗透率演化意义重大，值得深入研究。首先讨论了上述条件下水化页岩的实验，结果表明，水化处理天数越多，峰值强度越低，相应的渗透率越高。其次，提出损伤理论分析流体力学损伤引起的页岩渗透率演化，得到初始加载和卸载条件下的渗透率变化，观察到加载过程中渗透率随着围压增加而减小，卸载过程中渗透率随着围压减小而增加。压力; 然而，在围压相同的情况下，前者的变化远大于后者，说明水化页岩在这种循环条件下的不可逆破坏导致渗透率存在明显差异。此外，基于实验数据的渗透率与围压曲线拟合为初始加载条件下的负指数函数和更多循环加载条件下的幂函数，表明更多的加载过程将改变渗透率演化模型。然而，卸载时的渗透率变化平稳，可以作为围压的幂函数拟合。此外，深入研究了五种循环装卸条件下渗透率的损失率和恢复率，彻底解释了随着更多循环过程渗透率下降的变化。最后考察了渗透率的敏感系数，观察了初始循环条件下系数最大，循环次数越多，系数越小，尤其是加载时的系数对低围压更敏感，卸载时的系数更小。根据页岩渗透率损失和恢复变化，揭示复杂开采环境下水化页岩渗透率演化规律。