Impact of depth-dependent geological controls for assessing energy capacity of subsurface Compressed Air Energy Storage in Porous Media

Acknowledging the intrinsic geological and thermodynamic complexities of the subsurface (e.g., storage volume, reservoir pressure and temperature), is critical to understand and comprehensively model Compressed Air Energy Storage in porous rocks. For the first time, the maximum energy density and energy capacity of a conceptual porous reservoir (e.g., sandstones, limestones) working on adiabatic and isothermal compression/decompression processes is evaluated under distinct depth-dependent thermodynamic conditions (isochoric vs isobaric), to assess which system can provide optimal subsurface storage. Analysis for different subsurface volumetric scenarios indicate that a single adiabatic-isobaric system is the most favourable, able to provide up to 156 kWh/m 3 of energy density and achieve up to 1 TWh of storage capacity at a maximum operating depth of 3000 m. These results unveil the full potential of long-duration CAES in porous media to support the future non-carbon emitting energy grids, both by accommodating the excess production and variability from renewables, and by providing black start capability.