Mechanisms controlling fracture permeability enhancement during injection-induced and natural dynamic stressing remain unresolved. We explore pressure-driven permeability (k) evolution by step-increasing fluid pressure (p) on near-critically stressed laboratory fractures in shale and schist as representative of faults in sedimentary reservoirs/seals and basement rocks. Fluid is pulsed through the fracture with successively incremented pressure to first examine sub-reactivation permeability response that then progresses through fracture reactivation. Transient pore pressure pulses result in a permeability increase that persists even after the return of spiked pore pressure to the null background level. We show that fracture sealing is systematically reversible with the perturbing pressure pulses and pressure-driven permeability enhancement is eminently reproducible even absent shear slip and in the very short term (order of minutes). These characteristics of the observed fracture sealing following a pressure perturbation appear similar to those of the response by rate-and-state frictional healing upon stress/velocity perturbations. Dynamic permeability increase scales with the pore pressure magnitude and fracture sealing controls the following per-pulse permeability increase, both in the absence and presence of reactivation. However, initiation of the injection-induced reactivation results in a significant increase in the rate of permeability enhancement (dk/dp). These results demonstrate the role of frictional healing and sealing of fractures at interplay with other probable processes in pore pressure-driven permeability stimulation, such as particle mobilization.

中文翻译：

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断层再激活对注入诱导渗透率演化动态触发的影响

在注入诱导和自然动态应力过程中控制裂缝渗透率增强的机制仍未得到解决。我们通过逐步增加页岩和片岩中近临界应力实验室裂缝上的流体压力 (p) 来探索压力驱动的渗透率 (k) 演化，这些裂缝代表沉积储层/密封件和基底岩中的断层。流体以连续增加的压力脉冲通过裂缝，首先检查亚再活化渗透率响应，然后通过裂缝再活化进行。瞬态孔隙压力脉冲导致渗透率增加，即使在尖峰孔隙压力恢复到零背景水平后，渗透率仍会持续增加。我们表明，裂缝密封在扰动压力脉冲的情况下是系统可逆的，压力驱动的渗透率增强即使在没有剪切滑移的情况下也可以在非常短的时间内（几分钟）重现。压力扰动后观察到的裂缝密封的这些特征看起来与应力/速度扰动时速率和状态摩擦愈合的响应相似。在不存在和存在再活化的情况下，动态渗透率增加与孔隙压力大小和裂缝封闭控制以下每脉冲渗透率增加。然而，注入诱导再活化的启动会导致渗透率增强率 (dk/dp) 显着增加。