Abstract
AbstractUnderstanding the physical mechanisms governing fluid‐induced fault slip is important for improved mitigation of seismic risks associated with large‐scale fluid injection. We conducted fluid‐induced fault slip experiments in the laboratory on critically stressed saw‐cut sandstone samples with high permeability using different fluid pressurization rates. Our experimental results demonstrate that fault slip behavior is governed by fluid pressurization rate rather than injection pressure. Slow stick‐slip episodes (peak slip velocity < 4 μm/s) are induced by fast fluid injection rate, whereas fault creep with slip velocity < 0.4 μm/s mainly occurs in response to slow fluid injection rate. Fluid‐induced fault slip may remain mechanically stable for loading stiffness larger than fault stiffness. Independent of fault slip mode, we observed dynamic frictional weakening of the artificial fault at elevated pore pressure. Our observations highlight that varying fluid injection rates may assist in reducing potential seismic hazards of field‐scale fluid injection projects.
Highlights
Induced seismicity associated with fluid injection has been reported worldwide
Both critically stressed saw‐cut samples started to slide towards the end of the first fluid injection stage, suggesting that the magnitude of fluid pressure controls fault slip initiation, as predicted by equation 1
Slow stick‐slip episodes occur at the fast fluid pressurization rate applied in test SC1
Summary
Induced seismicity associated with fluid injection has been reported worldwide. Waste‐water injection in Oklahoma resulted in induced seismicity with event magnitudes as large as M5 (Keranen et al, 2014). Pore fluid pressure plays an important role in triggering fault reactivation. Induced seismicity is understood as a manifestation of the effective stress principle in Coulomb failure. Onset of fault instability may occur once the shear stress τ resolved along a fault plane exceeds the shear strength τp.
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