Risk-based monitoring designs for detecting CO2 leakage through abandoned wellbores: An application of NRAP's WLAT and DREAM tools

As geologic CO2 storage (GCS) moves towards industrial-scale deployment, strategies must be developed to ensure long-term environmental risks related to potential leakage are managed. One approach to is to perform risk-based subsurface monitoring targeting early leak detection. Early detection is particularly important to address the risk associated with leakage along legacy wells. The challenge in risk-based monitoring is that leakage impacts are expected to be small in comparison with the footprint of the stored CO2 plume and could occur over considerable depths, ranging from the storage formation up to surficial aquifers. Here we demonstrate the application workflow of two of the National Risk Assessment Partnership's (NRAP) computational tools, WLAT (Wellbore Leakage Analysis Tool) and DREAM (Designs for Risk Evaluation and Management), to a hypothetical CO2 storage site based on a study area in the Midwestern United States. By incorporating site specific wellbore integrity analyses, results show how fluid leakage may be estimated, evaluated, and monitored in terms of risk. For the selected site, three monitoring wells were ultimately needed to detect all possible CO2 leaks and six monitoring wells were needed to minimize time to leak detection. Such analyses inform stakeholders about long-term liability and monitoring costs of GCS projects.