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Abstract:
Induced seismicity associated with fluid injection into underground formations jeopardizes the sustainable utilization of the subsurface. Understanding the fault behavior is the key to successful management and mitigation of injection-induced seismic risks. As a fundamental approach, laboratory experiments have been extensively conducted to assist constraining the processes that lead to and sustain various injection-induced fault slip modes. Here, we present a state-of-the-art review on the emerging topic of injection-induced seismicity from the laboratory perspective. The basics of fault behavior, including fault strength and instability, are first briefly summarized, followed by the paradoxical stability analysis arising from the current theoretical framework. After the description of common laboratory methods and auxiliary techniques, we then comprehensively review the effects of fault properties, stress state, temperature, fluid physics, fluid chemistry and injection protocol on fault behavior with particular focus on the implications for injection-induced seismicity. We find that most of the shear tests are conducted under displacement-driven conditions, while the number of injection-driven shear tests is comparatively limited. The review shows that the previous work on displacement-driven rock friction and fault slip modes partially unravel the mystery of injection-induced fault behavior, and recent experimental studies on the injection-driven response of critically stressed faults provide complementary insights. Overall, laboratory experiments have substantially advanced especially our understanding of the roles of fault roughness, fault mineralogy, stress state, fluid viscosity, fluid induced mineral dissolution, and injection rate in injection-induced seismicity, which has been successfully used to interpret many field observations. However, there are still outstanding questions in this area, which could be addressed by future experimental studies, such as the feasibility of seismic-informed adaptive injection strategy for mitigating seismic risks, cold fluid injection into critically stressed faults under hydrothermal conditions, and fault friction evolution during cyclic injection spanning from undrained to drained conditions.
