Background and Method Carbon capture and storage (CCS) technology represents the primary technical direction for large-scale carbon emission reduction. Among various CCS techniques, geologic CO₂ sequestration in saline aquifers holds great potential, establishing it as a major technique for future carbon storage. Based on a review of the current status of research on global geologic CO₂ sequestration in saline aquifers, this study comprehensively analyzed the technical difficulties, challenges, and prospects of this technology, focusing on the dilemma of the application of this technology under complex geological conditions in China.

Results and Conclusions A huge gap in both the technical R &D and engineering practices of geologic CO₂ sequestration in saline aquifers remains between China and developed Western countries, especially in evaluation technologies for the storage capacity and safety of long-term, megaton-scale geologic CO₂ sequestration. The actual storage capacity of a site is identified as a primary factor affecting the storage costs, including the amount of storage, single-well-controlled amount of storage, and injectability. Technical difficulties with the calculation of the amount of storage include establishing high-precision 3D geological models of saline aquifers, determining the storage efficiency factor, obtaining the limit pressure of cap rock rupture and fault opening, and correctly understanding the logical relationships between the amounts of storage of various storage mechanisms. A higher single-well-controlled amount of storage is associated with a smaller drilling engineering quantity, with primary influential factors including the heterogeneity, scale, and physical properties of sand bodies. Injectability represents the capacity to achieve the amount of storage. For the siting of injection wells, it is necessary to conduct fine-scale geological evaluation of the lateral connectivity and wettability of the target sand bodies. Areas with overlapping sand bodies with high porosity, high permeability, and low formation pressure, also known as sweet spots for CO₂ injection, should be selected to ensure that supercritical CO₂ injected into saline aquifers can migrate outward from wellbores. Safety is a key concern in technical research on techniques for geologic CO₂ sequestration in saline aquifers, including the sealing performance, stability, and monitorability of target geobodies. Specifically, for the siting of geologic CO₂ sequestration, it is essential to gain a correct understanding of the importance of traps and ultimate sealing pressure for the sealing performance. Primary challenges in research on the stability of geobodies for CO₂ sequestration include the difficulty in conducting stability evaluation under complex geological conditions, accurately determining engineering parameters of sites, and developing rational mathematical models for numerical simulations. Research on the monitorability primarily faces challenges of determining the locations for monitoring deployment and selecting appropriate monitoring technologies. Additionally, the wide application of geologic CO₂ sequestration in saline aquifers also encounters challenges of reaching an international consensus, protectionism for sequestration technologies, high costs of sequestration technologies, long-term storage safety, disputes over mineral rights, and relevant policies and subsidies. Geologic CO₂ sequestration in saline aquifers holds great application prospects. The combination of this technology with the decarbonization of high-carbon industries and emerging energy technologies will contribute to prolonged utilization duration of fossil fuels and enhanced stability of new energy supply.