Earthquakes induced by fluid injection - Implications for secure CO2 storage

It is well understood that the injection of fluids into the subsurface can trigger seismic activity. Recently, the US unconventional gas boom has lead to an increase in the volumes of produced water being disposed in geological formations and a concomitant increase in triggered seismic events. This issue is especially pertinent for CCS, because in addition to the seismic hazard, induced events at CCS sites, should they occur in caprocks, will pose a risk to storage integrity. We re-examine case examples of seismic activity induced by waste water injection. Specifically, we consider the magnitudes and spatial distributions of induced events. The rates and volumes of CO2 injection likely to be needed for CCS exceed rates/volumes that are known to have triggered moderate-sized events, highlighting the importance of considering induced seismicity when selecting and operating CCS sites. The majority of events are observed to occur below the injection intervals, which must be considered favourable for CCS, although it cannot be guaranteed that this would be repeated at CCS sites. Induced seismicity typically occurs within 15km of injection sites, which suggests a minimum radius for geomechanical appraisal prior to CO2 injection.