Quantitative Risk Assessment of Leakage through Legacy Wells in Support of Permit Application for a Large-scale CO2 Injection Project in Southwestern US

Abstract

The US DOE funded San Juan Basin CarbonSAFE project is focused on developing an integrated CCS project located in the San Juan Basin, NM, USA. One of the primary requirements of the Class VI permit application that will have to submitted for the project is demonstrating that the proposed CO2 injection operations will not lead to endangerment of underground sources of drinking waters (USDW) due to leakage through legacy (or existing) wells that may lie within a pressure dependent area of review (AoR). Using a CO2 injection scenario, we demonstrate various steps associated with evaluation of endangerment of USDW. An area of review associated with the injection scenario was delineated using the results of numerical reservoir simulations and existing wells penetrating the target zone within the AoR were identified. The identified wells included plugged and abandoned wells as well as salt-water disposal wells. Not all the wells fell within the predicted boundary of CO2 plume. A quantitative assessment was performed to evaluate the risks associated with CO2 and brine leakage through the existing wells within the area of review. The leakage risk assessment was performed using the NRAP-open-IAM tool developed by US DOE’s National Risk Assessment Partnership. The tool utilized predictions of pressures and saturations in the storage reservoir, characterization data on existing wells within the area of review, and information on regional groundwater aquifer. The NRAP-open-IAM calculations indicated no significant threat to regional groundwater due to leakage through the existing wells within the predicted area of review. Information on well status, well completions as well as plugging and abandonment was utilized in conjunction with the results of leakage risk assessment and reservoir simulations to evaluate the need for corrective actions. Our evaluation indicated that a phased approach for corrective actions could be utilized based on multiple factors including, status of the existing wells, their locations within the predicted pressure and saturation plume and no predicted endangerment of groundwater through leakage risk assessment. Results of this project will be a good reference for other projects that will need to address corrective actions for the legacy wells while developing CO2 injection permit applications.

Keywords: UIC Class VI permit application, leakage risks, legacy wells, quantitative risk assessment, NRAP-open-IAM, corrective action plan