Pre-screening of induced seismicity risks for CO<inf>2</inf> 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 MW ∼2.0 and MW ∼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.