A recent critical review published in Engineering titled “Corrosion and Material Degradation in Geological CO₂ Storage: A Critical Review” by Xin Fan, Qing Hu, and Y. Frank Cheng from the University of Calgary and the Ningbo Institute of Materials Technology and Engineering, Chinese Academy of Sciences, provides an in-depth analysis of the challenges associated with corrosion and material degradation in geological CO₂ storage systems. The study underscores the significance of carbon capture and storage (CCS) as a mature and commercialized technology aimed at reducing greenhouse gas emissions effectively and economically.

The review highlights that long-term geological storage of captured CO₂ is a primary method due to its minimal impact on surface ecological environments and high safety levels. However, the integrity of CO₂ storage wellbores can be compromised by the corrosion of steel casings and degradation of cement in supercritical CO₂ storage environments, potentially leading to CO₂ leakage. The authors examine the physical and chemical properties of CO₂ in its supercritical phase, the principle of geological CO₂ storage, and the unique geo–bio-chemical environment involving aqueous media and microbial communities in CO₂ storage.

The study reveals that the corrosion of steel casings in supercritical CO₂ environments is primarily influenced by the presence of water, which forms an acidic electrolyte when CO₂ dissolves in it. The dominant cathodic reaction during steel corrosion involves the electrochemical reduction of H⁺ ions to produce H₂ molecules, especially at low pH levels. The authors also discuss the formation of iron carbonate (FeCO₃) scale on the steel surface, which can act as a diffusion barrier to electrochemically active species, thereby reducing corrosion kinetics.

The review identifies several factors that affect corrosion rates, including the presence of impurity gases such as SO₂, NO_x, O₂, and N₂, which can alter the phase state and physiochemical properties of supercritical CO₂. The concentration and variety of these impurities can vary significantly depending on the CO₂ capture source. The study emphasizes the need for a quantitative assessment of the impact of these impurity gases on corrosion, as well as the development of standardized methods for replicating the corrosive environments encountered in supercritical CO₂ storage.

The authors also highlight the degradation of cement in geological CO₂ storage environments, which is closely tied to its carbonation process. CO₂ reacts with calcium compounds in the cement, leading to a reduction in pH and subsequent weakening of the cement structure. This degradation can result in the formation of micro-annuluses or crevices in the cement, causing localized pitting corrosion on the casings.

The review concludes by discussing potential avenues for further research in steel corrosion within geological CO₂ storage systems. These include the development of standardized methods for replicating corrosive environments, quantitative assessment of the impact of impurity gases, modeling for long-term corrosion prediction, and the development of high-performance corrosion control solutions, particularly corrosion inhibitors.

This critical review provides crucial guidance for understanding and managing corrosion risks in geological CO₂ storage systems, emphasizing the importance of maintaining wellbore integrity to ensure the long-term safety and effectiveness of CO₂ storage.

The paper “Corrosion and Material Degradation in Geological CO₂ Storage: A Critical Review,” is authored by Xin Fan, Qing Hu, Y. Frank Cheng. Full text of the open access paper: https://doi.org/10.1016/j.eng.2025.02.021. For more information about Engineering, visit the website at https://www.sciencedirect.com/journal/engineering.