Underground salt cavern CO₂ storage (SCCS) offers the dual benefits of enabling extensive CO₂ storage and facilitating the utilization of CO₂ resources while contributing the regulation of the carbon market. Its economic and operational advantages over traditional carbon capture, utilization, and storage (CCUS) projects make SCCS a more cost-effective and flexible option. Despite the widespread use of salt caverns for storing various substances, differences exist between SCCS and traditional salt cavern energy storage in terms of gas-tightness, carbon injection, brine extraction control, long-term carbon storage stability, and site selection criteria. These distinctions stem from the unique phase change characteristics of CO₂ and the application scenarios of SCCS. Therefore, targeted and forward-looking scientific research on SCCS is imperative. This paper introduces the implementation principles and application scenarios of SCCS, emphasizing its connections with carbon emissions, carbon utilization, and renewable energy peak shaving. It delves into the operational characteristics and economic advantages of SCCS compared with other CCUS methods, and addresses associated scientific challenges. In this paper, we establish a pressure equation for carbon injection and brine extraction, that considers the phase change characteristics of CO₂, and we analyze the pressure during carbon injection. By comparing the viscosities of CO₂ and other gases, SCCS’s excellent sealing performance is demonstrated. Building on this, we develop a long-term stability evaluation model and associated indices, which analyze the impact of the injection speed and minimum operating pressure on stability. Field countermeasures to ensure stability are proposed. Site selection criteria for SCCS are established, preliminary salt mine sites suitable for SCCS are identified in China, and an initial estimate of achievable carbon storage scale in China is made at over 51.8-77.7 million tons, utilizing only 20%-30% volume of abandoned salt caverns. This paper addresses key scientific and engineering challenges facing SCCS and determines crucial technical parameters, such as the operating pressure, burial depth, and storage scale, and it offers essential guidance for implementing SCCS projects in China.

Subsurface geothermal energy storage has greater potential than other energy storage strategies in terms of capacity scale and time duration. Carbon dioxide (CO₂) is regarded as a potential medium for energy storage due to its superior thermal properties. Moreover, the use of CO₂ plumes for geothermal energy storage mitigates the greenhouse effect by storing CO₂ in geological bodies. In this work, an integrated framework is proposed for synergistic geothermal energy storage and CO₂ sequestration and utilization. Within this framework, CO₂ is first injected into geothermal layers for energy accumulation. The resultant high-energy CO₂ is then introduced into a target oil reservoir for CO₂ utilization and geothermal energy storage. As a result, CO₂ is sequestrated in the geological oil reservoir body. The results show that, as high-energy CO₂ is injected, the average temperature of the whole target reservoir is greatly increased. With the assistance of geothermal energy, the geological utilization efficiency of CO₂ is higher, resulting in a 10.1% increase in oil displacement efficiency. According to a storage-potential assessment of the simulated CO₂ site, 110 years after the CO₂ injection, the utilization efficiency of the geological body will be as high as 91.2%, and the final injection quantity of the CO₂ in the site will be as high as 9.529 × 10⁸ t. After 1000 years sequestration, the supercritical phase dominates in CO₂ sequestration, followed by the liquid phase and then the mineralized phase. In addition, CO₂ sequestration accounting for dissolution trapping increases significantly due to the presence of residual oil. More importantly, CO₂ exhibits excellent performance in storing geothermal energy on a large scale; for example, the total energy stored in the studied geological body can provide the yearly energy supply for over 3.5 × 10⁷ normal households. Application of this integrated approach holds great significance for large-scale geothermal energy storage and the achievement of carbon neutrality.