Fluid injection-induced fault slip during unconventional energy development:A review

An unusual increase in seismicity rate near the development and production sites of unconventional energy(e.g.,natural gas and geothermal fluids)has been attributed to subsurface fluid injection.Damaging and hazardous earthquakes in many countries(e.g.,China,South Korea,and the United States)have motivated tremendous effort to understand the complexity of fault slip behaviors in response to fluid pressurization.This study reviews key characteristics of injection-induced fault slip and highlights prediction and mitigation strategies relevant to unconventional energy projects.This capability relies on adequate understanding and characterization of first-and second-order friction and stability behaviors of faults as well as impacts of fluid pressurization and its role in triggering aseismic,seismic,and transitional slip behaviors.Suitable methods of investigation and characterization are noted together with typical examples together with scientific advances in our understanding towards forewarning and mitigation.Present challenges are addressed relating to the understanding of complex secondorder friction behaviors and the location and characterization of blind faults.These needs are aided in the integration of multi-scale and multi-physical data obtained from laboratory,numerical,and field studies to offer crucial information for induced hazard preparedness and rapid run-up assessment.Finally,emerging technologies contributing to an improved understanding,such as data analytics and machine learning,are discussed in heralding the next frontier for injection-induced seismicity research.