Poroelastic stress change and fault slip modeling of fluid injection induced seismicity

Solid matrix stress and pore pressure changes due to fluid injection are key factors for inducing earthquakes on pre-existing faults. In this study, we examine their relative roles in triggering seismicity and fault slip under both wastewater disposal and hydraulic fracturing scenarios. We first present modeling results of poroelastic stress changes on a previously unmapped fault near Cushing, Oklahoma, due to injection at multiple wastewater disposal wells within 10 km of distance, where over 100 small to moderate earthquakes were reported between 2015/09 to 2016/11 including a Mw5.0 event at the end of the sequence. Despite the dominating amplitude of pore pressure change, we find that earthquake hypocenters are well correlated with positive shear stress change, which determines the regimes of Coulomb stress change. Depending on the relative location of the disposal well to the recipient fault and its sense of motion, fluid injection can introduce either positive or negative Coulomb stress changes, therefore promoting or inhibiting seismicity. Our results suggest that interaction between multiple injection wells need to be considered in induced seismicity hazard assessment, particularly for areas of dense well distributions. Next, we plan to apply the model to simulate poroelastic stress changes due to multi-stage hydraulic fracturing wells near Dawson Creek, British Columbia, where a dense local broadband seismic array has been in operation since 2016. We will investigate the relative amplitudes, time scales and spatial ranges of pore pressure versus solid matrix stress changes in influencing local seismicity, and potential fault slip. Finally, we have developed a rate-state friction framework for calculating slip (aseismic and seismic) on a pre-existing fault under perturbations from the poroelastic stress model results for both the disposal and hydraulic fracturing cases. Preliminary fault slip simulation results suggest the design of hydraulic stimulation stages and flow-back strategy, either allowing perturbations to passively dissipate or actively reducing to the pre-stimulation level, is critical for inducing seismic versus aseismic slip on a pre-existing fault.