A Risk-Based Approach for Well-Integrity Management for a CO2 Geological Storage Project

Abstract

This article, written by Assistant Technology Editor Karen Bybee, contains highlights of paper SPE 122510, ’A Risk- Based Approach for Well Integrity Management Over Long Term in a CO2 Geological Storage Project,’ by Y. Le Guen, SPE, V. Meyer, O. Poupard, E. Houdu, and R. Chammas, SPE, Oxand S.A., originally prepared for the 2009 SPE Asia Pacific Oil and Gas Conference and Exhibition, Jakarta, 4-6 August. The paper has not been peer reviewed. A risk-based methodology associated with well integrity is proposed within CO2 geological storage. The main objectives of this approach are to identify and quantify risks associated with CO2 leakages along wells over time (from tens to thousands of years), to evaluate risks, and to propose relevant actions to reduce unacceptable risks. Introduction Concerns about greenhouse-gas emissions are growing. Both authorities and industries are thinking about solutions to reduce their emissions to adhere to the convention signed in Kyoto. The carbon capture and storage (CCS) technology constitutes one of the most suitable technologies to reduce greenhouse-gas emissions in the atmosphere. Pilots already exist worldwide. However, a large-scale deployment can be questioned for some of them. Among various issues, public fear, environmental impacts, economical aspects with respect to CO2 geosequestration, and possible gas leakages still constitute major issues. Wellbores constitute the only intrusive and manmade element of the storage system in the geologic systems. Moreover, the wellbore-integrity assessment implies a number of specificities, because of the time scales involved, the properties of the stored fluid and to the uncertainties characterizing the physical parameters and mechanisms. Demonstrating that the wellbore constitutes a safe barrier for CO2 confinement over the long term is of paramount importance for large CCS acceptance and deployment. The full-length paper presents a quantitative risk-based methodology to evaluate the performance and the risks associated with well integrity in the long term, taking into account the degradations and aging of the components of the well coupled to porous-media flow occurring in a well. A statistical approach is integrated into the methodology to deal with the uncertainties associated with both the well characteristics and the input to the model. To illustrate the methodology and demonstrate its relevance to provide operators with operational recommendations, a synthetic case study is proposed. Performance and Risks Methodology The present methodology has been developed in accordance with a risk-based process. Here, risk is not just a concept but also a metric that can be quantified. Risk can be defined as the combination of the likelihood of a failure event (i.e., its probability) and the magnitude of its impact. The uncertainties of the system are converted into the notion of probability, and the quantitative CO2-leakage mass assessed into the notion of severity.