Assessment of Geochemical Limitations to Utilizing CO2 in Compressed Energy Storage Systems in Porous Saline Aquifers

Abstract:

Intermittent energy production limits increased reliance on renewable energy. Compressed Energy Storage (CES) of air, CO2, or H2 in porous formations is a promising technology for energy storage. CES operation involves using excess energy to inject gas in the storage medium and extract it during periods of excess demand to drive turbines. Using saline aquifers as storage mediums with CO2 as a working gas has advantages over typical air storage in caverns. However, the geochemical interaction of CO2 and saline brine during CES operation has not been considered. This work utilizes reactive transport simulations to evaluate the CO2-brine-mineral geochemical reactions that occur during energy storage in a porous aquifer and compares them to reactions that would occur if the same system were used for CO2 sequestration. A CES plant with continuous and periodic operational schedules are considered. The continuous schedule consists of a 12-hour injection and extraction cycle while the periodic schedule consists of a 6 hour shut-in period between 7 hours of injection and 11 hours of extraction. As expected, CO2 creates conditions favorable for dissolution of carbonate and aluminosilicate minerals. However, the cyclic flow regime during compressed energy storage limits the dissolution extent significantly after the initial stages of injection and extraction such that CO2 is a viable choice of working gas. In the injection-only flow regime, synonymous with CO2 sequestration, 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 non-uniformly to 31.1% and 25.8% closest and furthest from the injection well, respectively.