The growing severity of global climate change has highlighted the importance of CO₂ sequestration as a key strategy for reducing CO₂ emissions and mitigating global warming. To this end, sedimentary basins worldwide contain extensive yet underexplored saline aquifers with substantial sequestration potential for long-term CO₂ sequestration. In this study, the suitability and mechanical responses of CO₂ sequestration in a representative half-graben saline aquifer were systematically unraveled through integrated theoretical analysis and multi-physics-coupled numerical simulations. Key factors, such as temperature, pressure, reservoir properties, and caprock distribution, were evaluated based on well logging and mud logging data. Taking the evaluation results as a basis, optimal reservoir-caprock combinations were identified and classified into three types according to their spatial distribution: Single caprock-reservoir, lower interlayer-caprock-reservoir, and upper interlayer-caprock-reservoir. To simulate the mechanical responses during CO₂ injection and sequestration, corresponding conceptual models were developed. The results indicate that Type Ⅲ reservoir-caprock combinations, featuring upper mudstone interlayers, exhibit the lowest caprock stress, reduced leakage risk and enhanced sequestration security, which should be prioritized in sequestration site selection. Our findings provide valuable insights for selecting safe and effective CO₂ sequestration sites in saline aquifers across regional sedimentary basins.

Carbon dioxide capture, utilization and storage technology is considered to be one of the most effective strategies to mitigate CO₂ emissions. In this process, CO₂ that is injected into seabed sediments under specific temperature and pressure conditions is sealed in the form of CO₂ hydrate, known for its high gas storage density and exceptional security features. This method has significant advantages compared with onshore geological storage schemes. Thus far, however, there has been no industrial demonstration of CO₂ hydrate storage, and the CO₂ hydrate storage potential in the South China Sea remains underexplored without targeted evaluations. In this study, the phase equilibrium mechanism is combined with the volumetric method to describe and evaluate the CO₂ hydrate storage distribution range, effective thickness, and potential volume available for CO₂ hydrate storage. Based on the latest exploration and development data from the Qiongdongnan Basin, along with geological structure data, multibeam bathymetry, local high-resolution three-dimension multichannel seismic reflection data, logging data, and submarine heat flow data, the distribution of the CO₂ hydrate storage stability zone is determined. The results show that the effective thickness and regional scope of CO₂ hydrate storage in the concerned area can be determined by virtue of the local water depths and the submarine temperature and pressure of 18 virtual wells. The minimum water depth in the Qiongdongnan Basin that satisfies the temperature and pressure conditions needed for CO₂ sediment storage is established as 415 m. The theoretical geological storage capacity of CO₂ hydrate in the Qiongdongnan Basin is determined as 5.75×10¹¹ to 8.73×10¹¹ t, where the value range of E is between 0.56 and 0.85. These findings offer a solid foundation for China to create, advance and execute a viable strategy for CO₂ hydrate storage.