Comparing water-disposal and CO2-storage induced earthquakes

To date, only several small-scale CO₂ storage projects, injecting about 1 Mt of CO₂ per year, exist worldwide. Induced seismicity has been recorded during operation. Overall, magnitudes of the seismic events are small (below M=3). Nevertheless, there is the concern that future large-scale projects will induce significantly larger magnitudes, like it is observed for basin-scale waste-water disposal. For instance, large-scale water disposal in Oklahoma and Kansas (USA) induced thousands of widely felt M3+ earthquakes with a maximum magnitude of M=5.8. We analyze seismicity and injection data from CO₂-storage projects including Quest (CA), Decataur (USA), In-Sahla (Algeria), Otway (AUS) and Gorgon (AUS). We compute the normalized seismic response of the subsurface to injection of a unit volume of CO₂ using the Seismogenic Index (SI) and compare it to water-disposal case studies. We find that the SI at CO₂-storage sites is smaller compared to water-disposal cases. It indicates a lower seismic hazard per injected volume of CO₂. We discuss physical processes that could explain our observations and show how earthquake magnitude probabilities can potentially be upscaled, considering CO₂ storage volumes needed in the future.