Assessing the feasibility of retrofitting legacy wells for CO2 geological sequestration

In the United States (U.S.), the Environmental Protection Agency (EPA) oversees geologic sequestration (GS) wells, designating them as “Class VI wells”. However, the few operational Class VI wells and those in the permitting process are insufficient for the scale of sequestration needed. An effective solution to boost storage capacity is retrofitting legacy oil and gas wells into sequestration wells. Our analysis applies the Reusing EXisting wells for CO₂ Storage Operations (REX-CO₂) qualitative screening tool to evaluate the feasibility of retrofitting legacy Class II wells into Class VI wells for geological CO₂ sequestration. We examine regulatory requirements, well integrity factors, and publicly available data from a pilot study on 15 wells in New Mexico. In addition to the REX-CO₂ assessment, we propose primary and secondary barriers based on individual well documentation to address key integrity challenges. We find that wellbore retrofits for long-term carbon dioxide sequestration are only suitable for wells that possess the correct combination of well factors. For these wells, retrofitting could offer significant time and cost savings over drilling new wells. The study highlights the importance of improving publicly available wellbore data and regulatory coordination to enhance future well retrofit evaluations.