An approach to assess risks of carbon geological storage technology

Abstract

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.

Sealing of fractures in a representative CO2 reservoir caprock by migration of fines

“…However, the probability of leakage from well designed and properly regulated carbon storage reservoirs is expected to be quite low 2,31–34 . Although the overall risk of failure through these scenarios is considered to be low, quantitative assessment of these risks is generally not available because historic data for these failure scenarios is not available 13 . Instead, expert judgement based on experience in the oil and gas industry, natural analogue studies, and modeling is used to estimate the potential of leakage from carbon storage reservoirs 24,35–38 …”

“…In order for geologic CO 2 storage to be acceptable from a scientific, regulatory, and public perception standpoint, risks associated with the technology must be carefully evaluated 9 . Wells and pre‐existing non‐transmissive faults and fractures in caprock have been identified as potential risks for the safe and secure storage of CO 2 injected in reservoirs, as they could serve as conduits for CO 2 and/or brine to migrate from the storage reservoir into overlying aquifers 9–14 . Specific mechanisms that could result in CO 2 leakage from a reservoir include reactivation of faults in the caprock, reactivation of faults hydraulically connected to the reservoir, induced shear failure of the caprock, hydraulic fracturing of the caprock, leakage from the injection well, and exceedance of the capillary membrane seal pressure 15–17 …”