Challenges and Practices in Tubingless Well Abandonment for Enhanced Carbon Capture and Storage (CCS) Efficiency

Abstract This paper addresses challenges and best practices for abandoning tubingless legacy wells for Carbon Capture and Storage (CCS) projects, particularly in the Gulf of Thailand (GoT). Tubingless completions, prevalent in the GoT due to cost-effectiveness, pose unique abandonment challenges due to limited borehole access and potential crossflow between reservoir zones. The paper emphasizes importance of a thorough risk assessment for all legacy wells within the area of review in case of leakage, categorizing them based on risk and prioritizing remediation efforts. It highlights stringent requirements for CCS well abandonment, including caprock restoration, crossflow prevention between zones with different pressure regimes, and use of multiple barriers to ensure long-term CO2 containment. The paper also discusses suitability of Class G cement as a long-term barrier material based on recent carbonation tests. Finally, it advocates for developing innovative solutions and technologies for slimhole accessibility to enhance abandonment procedures in tubingless wells, ensuring safe and effective long-term storage of CO2.