<p>To enhance the economic viability and safety of geological CO₂ storage, the co-injection of dissolved CO₂ during geothermal operations has been proposed. However, existing research on such dual-injection strategies primarily focuses on evaluating heat extraction efficiency, with limited attention given to comprehensively understanding the migration and transformation of CO₂. This study investigates these aspects in the Guantao Formation sandstone geothermal reservoir in Dezhou, Shandong Province, China, as a case study. Numerical simulations were conducted to investigate the impact of CO₂ injection on heat recovery efficiency, while quantitatively evaluating the capacity and evolution of CO₂ storage. The simulation results indicate that dissolved CO₂ injection leads to calcite dissolution and increased porosity near the injection well, particularly at shallower depths. Consequently, a larger volume of injected fluid enters the formation from upper regions of the injection well and flows towards the production well, resulting in a slight decrease in production fluid temperature (up to 0.2 ℃). Furthermore, chlorite within the formation also dissolves and releases ferrous ions into solution, which react with carbonic acid to form siderite, a mineral capable of fixing CO₂. In the base case model scenario, after 1000&#xa0;years, the proportion of CO₂ stored through mineralization in the formation reached 24.2%, surpassing previous predictions for mineralization storage ratios achieved by injecting CO₂ in gaseous or supercritical states. Furthermore, it is found that increasing injection and production rates can further enhance the extent of CO₂ mineralization and storage.</p>