Cement additives to mitigate wellbore cement degradation in CO2 corrosive environment: A review

To mitigate climate change concerns and fulfil the net-zero emission targets, CO2 geological utilization and storage (CGUS) is currently the most promising strategy for reducing anthropogenic CO2 emission levels. CGUS involves injecting captured CO2 into deep geological formations. Wellbore cement, as an integral part of the CGUS system, is chemically unstable in CO2-rich conditions because exposure of its hydrated products to CO2 causes physicochemical changes that are harmful to the cement matrix. Exposure to CO2 results in cement degradation and integrity loss, which is a major cause of CO2 leakage via wellbores. Therefore, to minimize cement integrity loss, cement slurry must be properly prepared. Researchers have made notable advancements formulating cement by incorporating diverse additives into cement to boost its resistance to CO2 corrosion. This review intends to summarize the findings from recent advances of CO2 corrosion remediation using various cement additives, as well as to highlight their potential to be incorporated into wellbore cement to mitigate CO2 corrosion. Furthermore, the key mechanisms by which different additives enhance the effectiveness of CO2 corrosion mitigation have been demonstrated. In light of current research advances and existing problems, gaps in the research have been identified and considerations for future development of formulations of CO2-resisting wellbore cement slurry have been provided.