A review of carbon storage in saline aquifers: Mechanisms, prerequisites, and key considerations

The emission of carbon dioxide (CO2) is globally recognized as a significant contributing factor to climate change. The natural sequestration of CO2 in reservoirs is widely recognized as a robust strategy for mitigating carbon emissions. Based on comprehensive analysis of geographic data pertaining to sedimentary thickness and other relevant characteristics, it has been determined that the total global storage capacity ranges between 8000 Gt. and 55,000 Gt. (giga tonne − Gt. = 1012 kg). The current understanding of deep saline formations suggests having the greatest potential for CO2 storage due to their high storage capacity. This work reviews the studies addressing the active trapping mechanisms, requirements and key aspects related to CO2 storage in saline aquifers. The active CO2 geo-storage mechanisms during CO2 injection include structural, capillary, dissolution, and mineralization. To improve CO2 trapping, methods such as foam co-injection, application of nano particles and microbial methods are comprehensively addressed in this work. Based on the findings, to enhance injectivity and storage in narrow, low-permeability saline aquifers, hydraulic fracturing is advised, while acknowledging the potential storage efficiency improvement offered by heterogeneity in rock formations. This study emphasizes prioritizing water-wet conditions for enhanced storage and containment security, highlighting the advantages of employing horizontal wells in such formations. Additionally, for increased safety and cost-effectiveness in CCS systems, this study recommends co-injecting substances like SO2 and CH4 to address pollutants in CO2 streams, stressing the importance of a holistic approach for maximizing efficiency and safety in saline formations.