Study on impacts of seasonal heat storage on CO2 geological sequestration and parameter optimization

Aquifer thermal energy storage (ATES) using CO2 is an effective technology to facilitate the on-site consumption of renewable energy, reuse of the surface waste heat and the carbon reduction. However, the inadequate coupling effect between heat storage and CO2 sequestration, as well as the limited parameter characterization, restrict the commercial deployment of CO2-ATES technology. Therefore, this study further explored the interaction mechanism between CO2 heat storage and sequestration through numerical simulations, in which impacts of heat storage on CO2 migration and sequestration characteristics were compared and summarized. Thermal performances and storage performances of the five-spot well network were explored. Then, effects of the injection temperature, injection flow rate, well spacing and drilling depth on the heat breakthrough time, heat recovery, CO2 aquifer sequestration and cap rock breakthrough were quantitatively analyzed. Finally, optimization suggestions and the sensitivity analysis were provided considering multiple aspects. Results show that injecting the isothermal CO2 with the initial reservoir still results in temperature variations. In heat storage areas, although heat storage enhances flow performance, it reduces CO2 solubility. Meanwhile, while gas capture at the well bottom increases, the sequestration efficiency experiences a slight reduction. Appropriate storage schemes achieve a heat recovery ratio of 90 %, a CO2 aquifer sequestration ratio of 51 % and a cap rock breakthrough ratio of less than 3.5 %. Higher injection flow rates and a shallow drilling depth are suitable to the heat storage, while lower injection temperatures and a deep drilling depth are prioritized for the CO2 sequestration. The closer the well spacing, the better the system performance. The most sensitive indicator is thermal breakthrough time, and the most sensitive parameters are well spacing and injection flow rate. This study is expected to provide the heat storage guidance for the optimization direction, decision-making and optimization results prediction, promoting the technology commercialization.