Fluid Injection-Rate Controls on Seismic Moment

Fluid-induced shear reactivation of pre-stressed faults poses a project terminating risk during reservoir stimulation in geothermal, CO₂ sequestration, wastewater disposal injection and hydraulic fracturing operations. Micro-earthquakes (MEQs) can be tolerated but fluid injection is capable of triggering large earthquakes that can cause major damage to surface infrastructure. Understanding the linkage between fluid-injection volume or injection rate and seismic moment is essential in safeguarding such infrastructure. We report shear experiments that specifically explore the link between fluid-injection rate and seismic moment resulting from shear reactivation of laboratory faults. Experiments are performed on granitoid cores from the UtahFORGE EGS demonstration site containing a single inclined fracture and with small-scale roughness added to the fracture surface. We inject fluids into the fracture and measure the resulting slip and drop in frictional shear stress. We record reactivation and pressure distributions over a range of fluid injection rates. Along-fault pressure distributions are progressively less-uniform as injection rates increase representing a switch from steady-state to transient conditions. Triggered shear displacement is used as a proxy for seismic moment and is indexed against cumulative injection volume and rate. Preliminary results suggest that seismic moment and injection volume increase with increased fluid-injection rates.