Numerical verification on the feasibility of compressed carbon dioxide energy storage in two aquifers

Compressed carbon dioxide energy storage in aquifers (CCESA) is a new large-scale energy storage technology derived from geological carbon dioxide sequestration, compressed air energy storage in aquifers, and compressed carbon dioxide energy storage. However, there have been no practical applications so far. In this study, we present a numerical model that simulates the whole process of gas filling period and daily cyclic period of the subsurface system of CCESA with two wellbores and two aquifers, and reveal the hydrodynamic and thermo-dynamic properties, energy efficiency, and the influences of wellbore and aquifer locations, injection tempera-ture and injection rate on system performance. The results show that the fluctuation ranges of pressure and temperature in the wellbores and aquifers increase with time, especially in the high-pressure aquifer where the maximum and minimum pressures are 15.96 and 9.78 MPa after 200 days of cycles. The maximum energy ef-ficiency of the system can reach 1.022. Within 100 days of cushion gas filling and 200 days of cycles, the maximum horizontal CO2 transportation distance in aquifers is 198.1 m, indicating a strong sealing effect of the system. The system energy efficiencies of the two target aquifers are very similar for different vertical intervals, while the variations in wellbore pressure and temperature differ significantly, which affects the energy efficiency and stability of the surface plant. Low-temperature CO2 injection is beneficial to improving the energy efficiency of the system. Increasing injection-production rate can directly improve power generation rate, and energy ef-ficiency is also higher for higher flow rates.