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Abstract
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.
Highlights
IntroductionIt is currently perceived that the elevated concentration of carbon dioxide (CO2) in the atmosphere (caused by anthropogenic or human activities) is a major contributor to global temperature rise or climate change
It is currently perceived that the elevated concentration of carbon dioxide (CO2) in the atmosphere is a major contributor to global temperature rise or climate change
We assume that the captured CO2 is compressed to a sufficiently high pressure at the capture site so that no recompression is required in the storage site
Summary
It is currently perceived that the elevated concentration of carbon dioxide (CO2) in the atmosphere (caused by anthropogenic or human activities) is a major contributor to global temperature rise or climate change. CO2 has excellent dissolution properties and above a relatively small pressure (called the minimum-miscibility pressure, MMP) becomes miscible with the in-situ oil and drags the oil out of pores through several mechanisms such as interfacial-tension reduction, viscosity reduction and oil swelling. This combined with the availability of the infra-structure and facilities in place, and the structural integrity of the oil reservoirs in containing fluids over very long times provides an opportunity to use CO2 and store it permanently underground, because the produced hydrocarbons can compensate for part of the CCS cost and reduce the net emission of CO2 [7,8].
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