Critical Knowledge Gaps for Understanding Water-Rock-Working Phase Interactions for Compressed Energy Storage in Porous Formations

Storage of air or compressed gas in porous formations is a promising means of large-scale, long-term energy storage, but salt caverns have predominantly been used for storage to date. Porous formations are ubiquitous and have high capacities but introduce new, complex water-rock-working phase interactions due to their greater depths, variable pressure, and saturation with saline brines. Extensive work in the context of geologic sequestration in porous formations has advanced understanding of these interactions and can be leveraged to assess energy storage systems. However, key differences in these systems need to be considered, notably the range of possible working phases (hydrogen, CO2, air, methane, and gas mixtures) and cyclic injection-extraction flow patterns. Recent advancements in understanding of water-rock-working phase interactions in the context of geologic CO2 sequestration have illuminated the need to understand the properties of the working gas under storage conditions to accurately assess storage capacity and the relative permeability and capillary pressure to assess injectivity and operational efficiency. Following injection, geochemical interactions between the working gas and formation brine and minerals can change formation and caprock properties that impact operational and storage security but have largely not been considered in energy storage systems.