The impacts of geothermal gradients on compressed carbon dioxide energy storage in aquifers

Abstract

Compressed CO2 energy storage in aquifers (CCESA) is new low-cost large scale energy storage technology. To further improve the energy efficiency of CCESA, we propose to combine the geothermal system with CCESA. In order to study the influence of geothermal energy on CCESA, aquifers with large vertical interval and different geothermal gradients from 0.026–0.07 °C/m are designed. The 3d wellbore-reservoir grid of underground part of CCESA was established. The simulation covering 100 days of intermittent initial gas fill and 50 days of cyclic injection and production was conducted. The hydrodynamic and thermodynamic behaviors and energy efficiency of the system were analyzed, comparatively. In the gas fill period, the higher the geothermal gradient, the farther the front of CO2 plume diffuses in the target aquifer, and thus the smaller the pressure accumulation. The temperature, pressure and energy efficiency of produced CO2 increases with the increase of geothermal gradient, while the density of released fluid decreases. The energy efficiency is greater than 1.0 under 6 geothermal gradients. The average energy efficiency of high- and low-pressure reservoirs can reach 1.282 and 1.061 under the geothermal gradient of 0.07 °C/m, which is 21.79 % and 5.5 % higher than that of 0.026 °C/m. The total energy efficiency of the joint system finally can reach 95.1 %. This research well confirms that the geothermal energy can dramatically improve the efficiency of CCESA and can enhance its application.