Induced seismicity, observations, risks and mitigation measures at CO2 storage sites

Abstract Seismicity produced by human activities (i.e. induced seismicity) has been widely reported over the last 40 years. To date few induced earthquakes have been recorded at CO 2 storage sites, however, the volumes of injected CO 2 and the number of operational sites are small. A review of induced seismicity from different types of fluid injection and extraction sites confirms that these events are typically ≤4.5 in magnitude (M) and in many cases have no reported earthquakes. Although the size (and associated risks) of induced earthquakes at CO 2 storage sites is most likely to be small, these events could decrease seal integrity or raise public concerns, while rare larger events (>M5) could also have ramifications for CCS beyond a single site. These risks can be reduced by careful site selection and development of site-specific risk reduction and mitigation programmes. Forecasts of induced seismicity using physical and statistical models and real-time monitoring will be key planning and decision making tools. The utility of monitoring and mitigation programmes will be maximized by establishing prior to injection, site performance and management guidelines for acceptable levels of induced seismicity, and agreed control measures. Further improvements to risk management practices, understanding induced seismicity processes and stakeholder confidence may be achieved by; a) increasing the number of publically available induced earthquake catalogues for development and testing of physical and statistical models, b) undertaking more systematic studies of individual sites populated by well constrained sub-surface geomechanical information and seismicity data complete down to small magnitudes (e.g., M-3), c) enhancing the physical reality of numerical dynamic models, d) studying the scaling effects of seismicity associated with moving from pilot projects to full commercial implementation of CO 2 storage, e) developing standard risk management procedures and guidelines for induced seismicity at CCS sites and,f) filling induced seismicity knowledge gaps in the CCS community by collaborating with seismologists and modellers working in other industries.