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Effect of Porosity and Permeability Evolution in Injection-Induced Aseismic Slip

Yuyun Yang, & Eric Dunham

Published October 19, 2020, SCEC Contribution #10846

It is widely recognized that fluid injection can trigger fault slip. However, the processes by which the fluid-rock interactions facilitate or inhibit slip are poorly understood and are generally neglected or oversimplified in most models of injection-induced slip. In this study, we perform a 2D antiplane shear investigation of the propagation of aseismic slip that occurs in response to fluid injection into a permeable fault governed by rate-and-state friction. We account for pore dilatancy and permeability evolution that accompany slip, and quantify how these two processes affect pore pressure diffusion, which impacts the propagation of aseismic slip. The fault response to injection has two phases. In the first phase, slip is negligible and pore pressure closely follows the standard linear diffusion model. Pressurization of the fault triggers aseismic slip in the immediate vicinity of the injection site. In the second phase, the aseismic slip front expands outward and dilatancy causes pore pressure to depart from the linear diffusion model. The aseismic slip front overtakes the pore pressure contours, with both fronts subsequently advancing at constant migration rate along fault. We quantify how prestress, initial state variable, injection rate, and frictional properties affect the migration rate of the aseismic slip and pore pressure contours, finding values ranging from less than 50 to 1000 m/day for typical parameters. Additionally, we make a comparison to the case when porosity and permeability evolution are neglected, which results in a purely linear pore pressure diffusion. In this case, the aseismic slip front migration rate and total slip are much higher. Our modeling shows that the stress state of the fault and injection rate are the primary controlling factors for aseismic slip propagation, and that porosity and permeability evolution, especially dilatancy, fundamentally alter the behavior of the system.

Yang, Y., & Dunham, E. (2020). Effect of Porosity and Permeability Evolution in Injection-Induced Aseismic Slip. Journal of Geophysical Research, Solid Earth,. doi: 10.1002/essoar.10504578.1.