Repurposing Existing Depleted Wells for CO2 Storage – A Comprehensive and Complex Evaluation Framework for Well Integrity and Workover Feasibility

Abstract Highly depleted reservoirs offer significant potential for carbon capture and storage (CCS) due to their proven capacity for fluid containment and established infrastructure. However, converting existing wells in these reservoirs for carbon dioxide (CO2) storage presents distinct challenges. Over time, pressure depletion, thermal changes, and structural stress impact integrity, risking potential CO2 leakage and compromising long-term containment. Aging, highly depleted wells often experience integrity issues due to corrosion, cement degradation, and the suitability of tubing and casing materials for CO2 injection. These challenges underscore the need for rigorous assessment to ensure effective CO2 storage in old wells. The lack of standardized evaluation frameworks further complicates the assessment of well fitness for CO2 storage. As part of the Storage Development Plan (SDP) for CO2 storage site in Malaysia, PETRONAS CCS Solutions Sdn. Bhd. identified several highly depleted fields as potential injection sites for CO2. A structured and systematic Well Repurposing Screening criteria was established, emphasizing the suitability of conversion factors such as cement and tubular compatibility with CO2 parameters, well integrity issues, access to target reservoirs, and corrosion of existing tubing. To complete the evaluation, workover feasibility factors such as the complexity of retrieving existing completion, tubing accessibility, cement remedial complexity, and milling complexity are assessed to ensure informed decision-making on repurposing existing wells before concept selection. This model has been applied to evaluate nine development wells, with the assessment results further discussed in this paper. Additionally, this comprehensive framework provides criteria for legacy well integrity and Plug and Abandonment (P&A) assessment. Repurposing existing wells for CO2 storage offers significant cost savings and environmental benefits compared to drilling new wells. It reduces financial burdens by utilizing already established infrastructure, minimizing the need for additional drilling expenses. Repurposing existing wells provides a more sustainable and economically viable solution for advancing CO2 storage initiatives, making it a preferable alternative to new well drilling. This approach is not only conducive to PETRONAS’s CCS efforts but also provides a comprehensive reference for the industry. It focuses on early-stage screening, risk management and cost minimization, leading to safer and more robust CCS projects.