Carbon geological storage (CGS) projects are designed to securely store carbon dioxide (CO 2 ) for thousands of years. Because of this, there are several studies to evaluate the potential risks of long-term storage of CO 2 in geological formations. This paper presents a new method for the qualitative risk assessment of CGS: the risk assessment of stored CO 2 (RA-CO 2 ) method. It consists of the systematic and structured identification of CO 2 release risk scenarios arising from: seal, well, and fault and fracture zones. The uncertainties associated to each mapped risk scenario and the risks are qualitatively evaluated using the RA-CO 2 method. The characteristics of the RA-CO 2 method enable a comprehensive understanding of the underground evolution and future behaviour of the CO 2 in various time scales and their influence on safety. For future studies, the validation of the proposed RA-CO 2 method using a real case study is recommended.Keywords: risk assessment of stored CO 2 ; RA-CO 2 method; qualitative risk assessment; CO 2 leakage; CO 2 geological storage; CGS.Reference to this paper should be made as follows: Paraguassú, M.M., Câmara, G., Rocha, P.S. and Andrade, J.C.S. (2015) 'An approach to assess risks of carbon geological storage technology', Int.

Carbon geological storage (CGS) projects are designed to securely store carbon dioxide (CO 2 ) for thousands of years. Because of this, there are several studies to evaluate the potential risks of long-term storage of CO 2 in geological formations. This paper presents a new method for the qualitative risk assessment of CGS: the risk assessment of stored CO 2 (RA-CO 2 ) method. It consists of the systematic and structured identification of CO 2 release risk scenarios arising from: seal, well, and fault and fracture zones. The uncertainties associated to each mapped risk scenario and the risks are qualitatively evaluated using the RA-CO 2 method. The characteristics of the RA-CO 2 method enable a comprehensive understanding of the underground evolution and future behaviour of the CO 2 in various time scales and their influence on safety. For future studies, the validation of the proposed RA-CO 2 method using a real case study is recommended.Keywords: risk assessment of stored CO 2 ; RA-CO 2 method; qualitative risk assessment; CO 2 leakage; CO 2 geological storage; CGS.Reference to this paper should be made as follows: Paraguassú, M.M., Câmara, G., Rocha, P.S. and Andrade, J.C.S. (2015) 'An approach to assess risks of carbon geological storage technology', Int.