Modelling of fluid pressure migration in a pressure sensitive fault zone subject to cyclic injection and implications for injection-induced seismicity

Abstract

Summary Fault zones often serve as the major fluid pathways in a variety of geo-energy systems, such as deep geothermal systems. However, injection-induced instability of faults can sometimes lead to large-magnitude earthquakes. Cyclic injection has thus been proposed as an alternative injection protocol to better manage and mitigate the associated seismic risks. The risks of injection-induced seismicity depend primarily on the extent and magnitude of the fluid pressure perturbation. When fluid is injected into a fault zone, the local fault permeability will be enhanced, which in turn promotes the migration of fluid along the fault. This nonlinear process is further complicated during cyclic injection via alternating the injection pressure. In this study, both numerical and analytical modeling are conducted to investigate cyclic fluid injection into a fault zone with pressure sensitive permeability, in which the local fault permeability changes as a function of the local effective stress. The match with laboratory-scale experimental and field-scale analytical results of cyclic fluid injection verifies the accuracy of the numerical model. The parametric study reveals that the injection pressure attenuation, quantified by the amplitude ratio and phase shift, is enhanced by a lower initial fault permeability, a smaller stress sensitivity coefficient, and a shorter period of pressure cycle (i.e. a higher frequency). Besides, the amplitude of the pressure cycle has a negligible effect on the injection pressure attenuation. We also discuss the implications of our results for the less amenable far-field seismic hazard and post shut-in seismicity.

Fluid-induced aseismic slip may explain the non-self-similar source scaling of the induced earthquake sequence near the Dallas-Fort Worth Airport, Texas

“…The transition can occur when reduced shear strength or slip resistance leads to slip in a part of the asperity while the rest of the asperity remains strong. When faults are not fully locked during the interseismic period, stress perturbations associated with a fluid injection can cause the fault to release a portion of its energy (Ji et al, 2023). Numerical modeling by Marguin & Simpson (2023) suggest that fluidpressure perturbations result in slow-slip events that have relatively lower stress drops, slip, and slip velocity.…”

The role of temperature‐enhanced fault closure in promoting postinjection pressure diffusion and seismicity in enhanced geothermal systems

“…We compared the four shut‐in scenarios to quantify the relative contribution of each mechanism to postinjection pressure diffusion and seismic hazard. Fault properties in our numerical model were set according to Ji et al (2023). The values of rock properties were consistent with typical granitic rock (Chen et al, 2021; Ji, 2020).…”

“…Note that the normal stress and the shear stress acting on the fault are assumed to be constant at the depth of 4000 m (cf. Ji et al, 2023;De Simone, 2017).…”

“…The changes of fluid properties with temperature were set according to the functions listed in Liu et al (2021). Properties of the laboratory fault including porosity, compressibility, and stress sensitivity coefficient were taken from Ji et al (2023). The input parameters in the numerical model for thermal processes' validation are listed in Table 1.…”

Pressure dependence of permeability in cracked rocks: experimental evidence of non-linear pore-pressure gradients from local measurements

“…They also adopted such an exponential pressure dependence for the permeability of a natural Grimsel granodiorite (David et al, 2018), and finally concluded that this relationship was suitable for relatively high effective stress ranges. The exponential law model was also widely used in describing the pressure dependence of permeability in faults (Evans et al, 1997;Ji et al, 2023).…”