A study of using cosmic-ray muon radiography to detect CO₂ leakage from a primary storage into geological formations

In CO₂ geological sequestration, a combination of monitoring techniques needs to be in place to timely detect possible CO₂ leakage from a primary storage along unanticipated pathways to shallower formations. This research aims to methodologically investigate the feasibility of a novel radiographic technique, i.e. cosmic-ray muon radiography, as a complementary continuous monitoring method. As an example, this method was tested on a geological model to monitor CO₂ leakage into upper freshwater aquifers. The effectiveness of the method was preliminarily established by high-fidelity simulations, including the sensitivity for responding to CO₂ leakage and the spatial resolution that can be achieved by the method. The simulation results indicate an increase of penetrating flux of the cosmic-ray muons with the increase of CO₂ leakage in the monitored aquifers. The sensitivity tends to be higher in monitoring leakage taking place in shallower depths. At depths of about 200 m, the detectable CO₂ can be as low as 3 % measured in volume fraction with a relatively high confidence level. The spatial resolution can be achieved within a range from 10 to 20 m for measurements at depths of no more than 520 m, demonstrating the effectiveness of the method.