Comprehensive Review of Sealant Materials for Leakage Remediation Technology in Geological CO₂ Capture and Storage Process

Carbon capture and storage (CCS) technology has been widely investigated to decrease the greenhouse effect. Geological CO2 storage sites are targeted mainly on depleted petroleum reservoirs or deep saline aquifers. However, CO2 leakage might take place through wellbores, cap rocks, reservoir fractures, or faults during or after the process of CO2 storage leading to environmental problems. To minimize these hazards, different kinds of sealants have been developed and applied. This review aims to summarize those materials applicable to CO2 leakage remediation. On the basis of the sealing mechanisms and compositions of different sealant materials, they were divided into seven major types: Portland cement, geopolymer cement, resins, biofilms barriers, gel systems, foams, and nanoparticles. For different types of sealants, their application background, chemical and physical properties, CO2 leakage remediation mechanism, impact factors of sealing performance, advantages, and limitations were summarized. Future development directions for these sealant materials are also recommended. To solve the problem caused by the weak acid-resistant performance of Portland cement, anti-CO2 materials should be developed and added to the formulation. Environmentally friendly materials need to be designed to replace some current user-hostile compositions in the geopolymer cement. Moreover, chemicals that can control the geopolymerization process are also required because of the high curing temperature requirement for the recent geopolymer productions. The injectivity of Portland cement and resin limits its application for in-depth CO2 leakage control; however, gels with relatively low viscosity during the injection can be a good alternative, although their thermal stability and strength need to be further enhanced. Biotechnology and nanotechnology are perspectives to be applied in the CO2 leakage control process. Foams with good stability might be used for CO2 leakage remediation in the porous medium without fractures, but their life cycle should be prolonged