Laboratory Simulation of Injection-Induced Shear Slip on Saw-Cut Sandstone Fractures under Different Boundary Conditions
Laboratory Simulation of Injection-Induced Shear Slip on Saw-Cut Sandstone Fractures under Different Boundary Conditions
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DOI：
10.1007/s00603-021-02689-4
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发表时间：
2021-11
影响因子：
6.2
通讯作者：
Nao Shen;Lei Wang;Xiaochun Li
中科院分区：
文献类型：
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作者：
Nao Shen;Lei Wang;Xiaochun Li
人们普遍认为，诱发地震可能与流体以重新激活原有的自然断层的方式注入地下有关。为了更好地了解构造边界条件对诱发断层滑动行为的潜在影响，我们对临界应力锯齿砂岩样品进行了在围压为10 Mpa和15 Mpa的恒活塞位移(CPD)和恒剪切应力(CS)条件下的注入诱导剪切滑移实验。在流体增压速率为0.1兆帕/分的情况下，人工裂缝(断层)在CPD试验中表现出较慢的滑动速度(<； 0.1μm/S)并伴有线性的剪应力下降，而在随后的css试验中观察到较快的滑动速度(<； 5μm/S)和较大的滑动距离。我们的实验结果表明，在实验测量的速率和状态摩擦参数和线性稳定性分析的支持下，在两次测试中，实验室裂缝对流体超压的响应是稳定的。随着围压从10 Mpa增加到15 Mpa，裂缝表现出相当大的水力扩散率下降。此外，在两种围压下的CS试验中，流体压力的非均质性也受到滑移速度的影响。我们将其解释为局部流体降压的结果，这种降压可能发生在远离注入端的地方，这是由于快速剪切增强的膨胀。此外，在CPD和CS测试的背景下，分别对与流体诱发的裂缝滑动相关的完整的能量平衡部分进行了定量评估。我们的实验观察表明，注入引起的破裂滑移行为不仅与所施加的有效正应力密切相关，而且与构造边界条件密切相关。
It is widely acknowledged that induced earthquakes may be linked to the fluid mass injection into the subsurface in a manner of reactivating preexisting natural faults. To better understand the potential effect of tectonic boundary conditions on induced fault slip behavior, we performed injection-induced shear slip experiments on critically stressed saw-cut sandstone samples under the conditions of constant piston displacement (CPD test) and of constant shear stress (CSS test) at confining pressure of 10 MPa and 15 MPa, respectively. In response to the low fluid pressurization rate of 0.1 MPa/min, the artificial fractures (faults) show a slow slip velocity (< 0.1 μm/s) accompanied by a linear drop of shear stress in CPD tests, whereas a faster slip velocity (< 5 μm/s) and a larger slip distance are observed in the subsequent CSS tests. Our experimental results indicate that the laboratory fractures slide stably in response to fluid overpressure during the two tests, supported by the experimentally measured rate-and-state frictional parameters and linear stability analysis. As the confining pressure applied increases from 10 to 15 MPa, the fractures show a considerable decrease in hydraulic diffusivity. Also, the fluid pressure heterogeneity is found to be affected by slip velocity in CSS tests at both confining pressures. We interpret this as a result of the local fluid depressurization that potentially occurs far away from injection end due to the rapid shear-enhanced dilation. In addition, the complete energy budget components associated with fluid-induced fracture slip in the context of CPD and CSS tests, respectively, have been quantitatively evaluated. Our experimental observations highlight that injection-induced fracture slip behavior is closely related not only to the applied effective normal stress, but also to tectonic boundary conditions.