CCUS Well Integrity and Wellbore Leakage Estimation Case Study

Well integrity is the most significant risk for containment in CO2 storage sites. To effectively prevent and mitigate the risk, it is important to properly assess it in a structured, consistent, and repeatable manner. This paper will present a well integrity assessment workflow and describe its components. The workflow will then be applied on a case study where a selected well will be analyzed for a demonstration of the methodology. The assessment workflow is focused on the analysis of legacy wells in prospective storage sites. It covers all activities from the point of data collection, review and analysis, assessment of well barriers and their risk of failure, the identification of leak paths, and the probabilistic estimation of wellbore leakage volumes. Risk level for each well can be determined based on well barrier assessment or leakage volume, which will then allow the project owner to prioritize proactive monitoring or subsequent remedial action. The application of the workflow is demonstrated on the analysis of a real well, selected based on common characteristics found in legacy wells in storage sites. The assessment of a study well shows the practical implementation of the workflow. It demonstrates the need and the value of the required inputs, the calculations and qualitative analysis done, the assumptions made, and the type of results that are obtained. The case study shows the complexities of the workflow implementation, and the solution to obstacles often found during the assessment. The results, and the adequate interpretation of them, are valuable components of the storage site’s risk assessment and useful for communication with stakeholders. Several well integrity studies have been conducted throughout the years with varying methodologies. The work presented here aims to provide a process that is repeatable, that minimizes human biases and perception, and that is necessary to equitably compare results between wells or sites; and that produces consistent risk assessments based on available information.