Assessment of Geochemical Limitations to Utilizing CO₂ as a Cushion Gas in Compressed Energy Storage Systems

Compressed energy storage (CES) of air, CO₂, or H₂ in porous formations is a promising means of energy storage to abate the intermittency of renewable energy production. During operation, gas is injected during times of excess energy production and extracted during excess demands to drive turbines. Storage in saline aquifers using CO₂ as a cushion or working gas has numerous advantages over typical air storage in caverns. However, interactions between CO₂ and saline aquifers may result in potential operational limitations and have not been considered. This work utilizes reactive transport simulations to evaluate the geochemical reactions that occur during injection and extraction operational cycles for CES in a porous formation using CO₂ as a cushion gas. Simulation results are compared with similar simulations considering an injection-only flow regime of geologic CO₂ storage. Once injected, CO₂ creates conditions favorable for dissolution of carbonate and aluminosilicate minerals. However, the dissolution extent is limited in the cyclic flow regime where significantly smaller dissolution occurs after the first cycle such that CO₂ is a viable choice of cushion gas. In the injection-only flow regime, larger extents of dissolution occur as the fluid continues to be undersaturated with respect to formation minerals throughout the study period and porosity increased uniformly from 24.84% to 33.6% throughout the simulation domain. For the cyclic flow conditions, porosity increases nonuniformly to 31.1% and 25.8% closest and furthest from the injection well, respectively.