Utah FORGE Modeling & Simulation Forum #13

“Impact of injection rate ramp-up on nucleation and arrest of dynamic fault slip”

Presented by: Federico Ciardo (ETH-Zurich)

December 15, 2021 at 11 am MST

Injection of fluid into the subsurface is a common operation in many industrial applications, such as wastewater disposal, hydraulic fracturing and deep geothermal energy exploitation. One of the drawbacks of these engineering applications is the generation of seismicity that in some severe cases might lead to a complete shutdown of operations.

The injection scenario, either in terms of pressure or volumetric rate, is one of the key controlling parameters for fluid induced seismicity. Numerous studies on the effects of injection parameters on earthquakes nucleation and occurrence along faults have been carried out. Most of them, however, assume idealized injection scenarios such as constant fluid over-pressure or constant injection volumetric rate.

In this contribution, we investigate extensively the effect of a finite ramp-up of injection rate, commonly present in many realistic injection protocols, on slip stability along a planar frictional weakening fault under plane-strain conditions (see Figure). We solve the coupled hydro-mechanical problem and investigate all the slip development regimes in the problem parametric space, including stable a-seismic slip, nucleation of a finite size dynamic event and nucleation of a run-way dynamic rupture.

Our results suggest that injection-induced seismicity can be mitigated by controlling the fault pressurization rate, in the limit when fluid diffusion time scale is lower than injection ramp-up time scale. Analytical derivations support our numerical results. The findings of this work can be useful for practical designing of injection operations in hydro-shearing type of stimulations.