Numerical study on the hydrodynamic and thermodynamic properties of compressed carbon dioxide energy storage in aquifers

Solving the undesirable intermittence and fluctuation problems of renewable energy production needs complementary energy storage on a large scale. Compressed air energy storage in caverns (CAES-C) has been verified as an effective technique. To further improve the energy storage efficiency and save costs, compressed air energy storage in aquifers (CAES-A) and compressed carbon dioxide energy storage in aquifers (CCES-A) were proposed successively. However, the operation performances of CCES-A, especially the hydrodynamic and thermodynamic properties of its underground components (the wellbore-reservoir system), are not clear. Here we introduce a coupled wellbore and reservoir model, T2WELL-ECO2N, initially used for geologic carbon sequestration simulation, for simulating the dynamics of CO2 injection and production through wellbore in both the construction and operation stages of CCES-A. The temperature, pressure, CO2 saturation and transfer, energy efficiency, maximum system cycle times, total stress change induced by CO2 injection in aquifer, and sensitivity analysis of permeability in the wellbore-reservoir system of the designed CCES-A are comprehensively studied. The simulation results show that during the operation stage the CO2 is supercritical and fluctuates in both wellbore and aquifer where the CO2 saturation decreases and CO2 bubble generally moves to the central and lower parts of the target aquifer rather than the outside direction. The system itself effectively alleviates the loss of CO2 mass from the side walls of the aquifer. The fact that the cold CO2 zone in the aquifer can continuously receive energy by heat transfer from the surroundings helps the energy efficiency of the CCES-A system gradually increase, and even reach 1.1. The system cycle times exceed 1000 days when the aquifer permeability is larger than 5.0 x 10(-13) m(2), indicating that CCES-A needs less time to reconstruct the cushion gas compared with CAES-A and can lower the operating cost accordingly. (C) 2019 Elsevier Ltd. All rights reserved.