Fault reactivation in response to fluid injection into the subsurface is controlled by a number of site-specific and operational parameters. We investigate the effects of variable fluid injection rate on the stability of a nearby fault using three-dimensional fully coupled poroelastic finite element simulations for injection into a multi-layer sequence containing a favorably orientated normal fault that extends from the injection reservoir into underlying crystalline basement. We consider three injection scenarios with constant, increasing, and decreasing injection rates but same overall injection duration and same total injection volume. Our simulations demonstrate that maximum excess pore pressure and Coulomb failure stress are highly dependent on the injection strategy. Increasing and constant injection rates always result in increasing excess pore pressure and Coulomb failure stress along the fault. An initially high injection rate followed by a decrease in injection rate results in lower maximum excess pore pressure and Coulomb failure stress compared to constant or increasing injection rate cases. These results suggest that fault reactivation potential associated with wastewater injection can be reduced with a site-specific assessment of geologic, reservoir geomechanical, and operational conditions including injection duration, rate, and overall injection volume prior to the start of injection.

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