Pre-screening of induced seismicity risks for CO2 injection at Trüllikon, Switzerland

Successful carbon injection operations depend critically on the management of risks, like induced seismicity. Here, we consider the bowtie risk management framework to organize pre-screening efforts around a prospective CO₂ injection operation near Trüllikon, Switzerland. First, potential barriers/threats are appraised via a literature review of the regional seismotectonics, hydrogeology, and nearby induced seismicity cases – which suggests a natural propensity for earthquakes because of the proximity to the Neuhausen Fault and a lack of effective underlying hydrogeological barriers. Next, we engineer barriers to fault reactivation by quantifying the fault slip potential. The closest (∼700 m) and most susceptible (∼3.0 km) portions of the Neuhausen Fault would require ∼1.7 MPa and ∼0.47 MPa for reactivation, respectively. The most susceptible (unknown) faults are normal slip (168° strike) that require ∼0.23 MPa for reactivation. Injection simulations indicate pressure changes on Neuhausen Fault segments of 0.01–0.05 MPa – values that are 1–2 orders-of-magnitude smaller than those needed for fault reactivation. These engineered barriers limit the potential for fault reactivation. However, if these barriers prove totally ineffective, we have also designed a traffic light protocol as a reactive mitigation measure. Forecast estimates of nuisance, damage, and fatalities are used to infer the last-possible stopping-point based on a comparison with operation-ending risks encountered at Basel and St. Gallen. This indicates a red- and yellow-lights of M_W ∼2.0 and M_W ∼0.0, respectively. We synthesize these disparate pre-screening analyses to recommend performance targets for real-time seismic monitoring. Future CO₂ operations will likely find our approach helpful for designing effective risk management.