Effect of the Stress Regime on Injection-Induced Seismicity

ABSTRACT: The distribution of local stress regime has a significant influence on natural earthquakes, while its role in controlling injection-induced fault reactivation and associated seismicity remains poorly understood. This paper investigates the relationship between fault aseismic slip, seismic slip and seismicity magnitude under different stress regime. Results show that the seismic slip zone will exceed the pressurized area with the increase of initial slip tendency under the strike-slip-faulting stress regime. Compared with fluid pressure, the seismic slip is mainly determined by a sudden increase of the shear stress at the aseismic slip zone boundary. In addition, the location of the microseismic events moves towards the fluid pressure propagation front. The larger slip area and seismicity magnitude are easier to be induced under strike-slip-faulting stress regime than thrust-faulting stress regime. The tensile failure and higher permeability of the fault induced at injection phase for normal-faulting stress regime leads to a greater seismogenic hazard at the shut-in stage. 1 INTRODUCTION In recent years, induced seismicity events have been increased rapidly due to the injection of large volume fluid into reservoir formations (Rutqvist et al., 2015; Ellsworth, 2013). These earthquakes are triggered by reactivating critically stressed faults. The fault reactivation process is highly dependent on the stress regime, the pore pressure, the hydrological properties of the fault and surrounding rock. The range of geological reservoirs may reached up to several kilometers and the in-situ stress and fault geometry experience obvious variation. A large number of geophysical observations have shown that the regional reservoir stress is a key control factor for fault slip behaviour (Sheikholeslami et al., 2021). The magnitude and frequency of the natural earthquakes have a strong relationship with stress regime (Scholz, 2015). It is postulated by Amini and Eberhardt (2019) that a critical fault in strike-slip fault stress regime respond differently than that in a normal or thrust fault stress regime. However, the effect of stress regime on spatiotemporal evolution of injection-induced fault reactivation and seismicity is still not clear.