Wellbore leakage risk assessment and management for a nearshore carbon storage candidate site

Risk assessment of geological storage sites is necessary to ensure the feasibility and safety of the project, and wellbore leakage is usually considered the primary concern of geological risk. In this study, we used a system approach to evaluate the potential wellbore leakage risks at a nearshore candidate site, examined the possible impact areas, and proposed risk management strategies according to the evaluation results. First, we developed numerical simulations based on recent studies for a candidate site in Taishi Basin, Taiwan. Large-scale single-well injection simulations with an injection rate of one million tons of carbon dioxide per year for a period of fifty years were performed to evaluate the possible pressure build-up around the injection well, as well as hypothetical monitoring wells. Next, these simulations were used to conduct subsequent wellbore leakage risk assessments for various risk scenarios using the latest National Risk Assessment Partnership's Open-Source Integrated Assessment Model (NRAP-Open-IAM) tool. The resulting storage performance and leakage risk profiles of different risk scenarios given a range of possible reservoir responses from NARP-Open-IAM were analyzed to evaluate the site-specific leakage risk acceptability for commercial-scale operation. The optimistic scenario (high permeability/high porosity) could result in only small brine leakage (no CO2 leakage), and the worst scenario (low permeability/low porosity) could lead to CO2 leakage since the pressure build-up around the wellbore is so high and exceeds the conventional 10% pressure increase threshold. Considering the geologic uncertainties, these results indicate that injection well pressure management is crucial for the site. Since there are no existing deep wells in the nearshore area and the nearest shallow groundwater wells are located far away, the risk of leakage from existing wells is extremely low. Therefore, the potential leakage pathways would be the future monitoring and injection wells within the impact area, particularly in the reach of the migrated CO2 plume. For this nearshore candidate site, the proposed risk management strategies focus on two key aspects: carefully monitored injection well operations and auxiliary reservoir layers as buffers above the injection zone.