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 tonnes. 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 by 2050.