Induced seismicity and its implications for CO2 storage risk

Seismicity induced by fl uid injection and extraction is a widely observed phenomenon. These earthquakes can exceed magnitudes of M 6 and have the potential to impact on the containment, infrastructure and public perceptions of safety at CO2 storage sites. We examine induced seismicity globally using published data from 75 sites dominated by water injection and hydrocarbon extraction to estimate the timing (relative to injection/extraction), locations, size range and numbers of induced earthquakes. Most induced earthquakes occur during injection/extraction (~70%) and are clustered at shallow depths in the region of the reservoir. The rates and maximum magnitudes of induced earthquakes generally increase with rising reservoir pressures, total fluid volumes and injection/extraction rates. The likelihood of an earthquake greater than or equal to a given magnitude being induced during injection is approximately proportional to the total volume of fluid injected/extracted, which appears to provide a proxy fo r changes in rock dynamics. If this observation holds for C O2 storage sites, then we can expect the rates and maximum magnitudes of induced earthquakes to be significantly higher fo r commercial-scale operations (e.g., 50 Mt) than for pilot projects (e.g., 50 kt). In accord with these results the risks associated with induced seismicity may also rise with project size. Mitigation and monitoring measures at commercial-size sequestration sites, including installation of microseismic networks, public education on the expected seismicity and pressure relief wells, will be key for risk reduction.