On the sustainability of CO₂ storage through CO₂ – Enhanced oil recovery

This work uses pilot examples of CO₂ enhanced oil recovery to analyze whether and under which circumstances it is exergetically favorable to sequester CO₂ through enhanced oil recovery. We find that the net storage efficiency (ratio between the stored and captured CO₂) of the carbon capture and storage (CCS)-only projects is maximally 6–56% depending on the fuel used in the power plants. With the current state of technology, the CCS process will re-emit a minimum of 0.43–0.94 kg of CO₂ per kg of CO₂ stored. From thermodynamics point of view, CO₂ enhanced oil recovery (EOR) with CCS option is not sustainable, i.e., during the life cycle of the process more energy is consumed than the energy produced from oil. For the CCS to be efficient in reducing CO₂ levels (1) the exergetic cost of CO₂ separation from flue gas should be reduced, and/or (2) the capture process should not lead to additional carbon emission. Furthermore, we find that the exergy recovery factor of CO₂-EOR depends on the CO₂ utilization factor, which is currently in the low range of 2–4 bbl/tCO₂ based on the field data. Exergetically, CO₂ EOR with storage option produces 30–40% less exergy compared to conventional CO₂ enhanced oil recovery projects with CO₂ supplied from natural sources; however, this leads to storage of >400 kg of extra CO₂ per barrel of oil produced.