Possibilities and Challenges for Mitigating Seismic Hazard from Earthquakes Induced by Disposal of Wastewater by Deep Injection

English Abstract:

Within North America east of the Rocky Mountains, earthquakes induced by fluid-injection activities associated with oil and gas production account for much of the contemporary seismic hazard (e.g., Ellsworth, 2013). This component of hazard is mostly due to disposal by deep injection of co-produced wastewater. Only a small fraction of wastewater disposal operations induce earthquakes large enough to be felt because the injection target is most often a deep aquifer that can readily accept large volumes of injected liquid with little or no seismic response. The exceptions, as reported in various case histories (e.g., Horton, 2012), evidently occur if elevated pore pressure due to injection is transferred into the zone of a fault that is prone to slip seismically in the ambient stress field. This pore pressure transfer may occur where the fault intersects the aquifer or it may involve an intermediate high-permeability channel between the aquifer and the earthquake-prone fault, which is often located in the crystalline basement. Accordingly, one way to reduce the likelihood of inducing earthquakes large enough to be felt or damaging is to avoid fluid injection in the vicinity of faults that are prone to reactivation. Because these faults are rarely mapped beforehand, it is necessary to have seismic networks in place capable of detecting and locating earthquakes at low magnitude thresholds. Timely evidence of fault reactivation could be used to avoid inducing earthquakes of greater consequence. Traffic Light systems, which use seismic data to decide when injection operations need to be adjusted, have proven to be effective for short-term injection activities such as development of Enhanced Geothermal Systems. More research is needed, however, to find out if earthquake control based on early identification of fault reactivation is feasible for longer-term wastewater injection projects.