Simulation of Injection-Induced Slip on a Rate-and-State Fault Considering Poroelastic Effects: A Comparison with Coulomb Failure Stress Criterion

Abstract

ABSTRACT The Coulomb failure stress (CFS) criterion based on the Mohr-Coulomb friction theory is commonly used to explain physical mechanisms governing injection-induced seismicity. While the CFS criterion can evaluate the onset of fault reactivation caused by fluid perturbations, it cannot tell the kinematic process of fault failure (seismic or aseismic slip). An alternative model for simulating time-dependent earthquake cycles is the rate-and-state friction model, which provides evolving friction depending on slip rate and slip history. To explore the dynamics and stability of fault slip associated with fluid injection, we extend a spring-slider system with a rate-and-state dependent friction law by incorporating the evolving fluid pressure and poroelastic stress. Simulations of continuous constant fluid mass injection rate scenarios using the developed model suggest that injection-induced fault slip behavior is controlled by fault orientation, diffusivity and poroelasticity, and injection rate. Compared to the CFS criterion, our model can offer a temporal component to fault friction and provide new insights on slip, slip rate and trajectory in phase space. We also investigate the relation between cumulative slip displacement versus cumulative injection volume, as well as the event recurrence interval. Our proposed approach has the potential application for evaluating the reactivation of pre-existing faults embedded in the reservoir associated with fluid pressure operations in the field practice. INTRODUCTION It has been well established that fluid injection into subsurface reservoirs can induce earthquakes (Healy et al., 1968; Raleigh et al., 1976). One of the most frequently discussed scientific issues is the physical mechanism that causes earthquakes to nucleate in response to fluid injection. The Coulomb failure stress criterion based on the Mohr-Coulomb friction theory is commonly used to explain the mechanism of induced seismicity (Ge & Saar, 2022). The Coulomb failure stress (CFS) and the change in Coulomb failure stress (ΔCFS) can be expressed as (Equation) (Equation) where μ is the friction coefficient that is assumed to be constant above, τ, σn and P refer to shear stress, normal stress (positive for compression), and pore pressure acting on the fault, respectively. Δτ, Δσn and ΔP denote the changes of shear stress, normal stress and pore pressure, respectively.