The density of carbon dioxide (CO2) increases drastically as it transitions from gaseous to supercritical form upon pressurization in subsurface reservoirs. This behavior is advantageous for CO2 utilization as a cushion gas because more working gas could be injected and produced for a given reservoir size if the reservoir could be cycled between subcritical and supercritical pressures. Simulations of porous media compressed air energy storage (PM-CAES) with CO2 as the cushion gas have been carried out using TOUGH2 and T2Well to investigate pressurization and gas-gas mixing effects. Simulations of coupled wellbore-reservoir PM-CAES reveal that strong pressure gradients in the vicinity of the injection/production well dominate the pressure field. These results show that unlike the existing cavern CAES systems, PM-CAES is dominated by pressure gradients and spatially variable energy storage within the reservoir. What this means for PM-CAES with CO2 as cushion gas is that the largest pressure changes are near the well, making it desirable to position the air-CO2 interface close to the well where the CO2 cushion will undergo the sub- to supercritical transition. However, cushion gas at such locations is subject to strong and undesirable air-CO2 mixing and subsequent production of CO2 up the well. These simulations suggest that CO2 cushion gas should be located at the far outer margins of storage reservoirs where mixing will be very slow and thereby prevent CO2 production up the well. In this configuration, the super-compressibility of CO2 will not occur, but CO2 can be geologically sequestered potentially earning value for the PM-CAES project depending on the price of carbon.

Simulations of porous media compressed air energy storage (PM-CAES) with CO<sub>2</sub> as cushion gas

248th National Meeting (2014)

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Simulations of porous media compressed air energy storage (PM-CAES) with CO2 as cushion gas

Simulations of porous media compressed air energy storage (PM-CAES) with CO₂ as cushion gas