How CO2-EOR Works

How does CO2-EOR work? CO2-EOR works most commonly by injecting CO2 into already developed oil fields where it mixes with and “releases” the oil from the formation, thereby freeing it to move to production wells. CO2 that emerges with the oil is separated in above-ground facilities and re-injected into the formation. CO2-EOR projects resemble a closed-loop system where the CO2 is injected, produces oil, is stored in the formation, or is recycled back into the injection well.

Today, most of the CO2 used in EOR operations is from natural underground ‘domes’ of CO2. With the natural supply of CO2 limited, man-made CO2 from the captured CO2 emissions of power plants and industrial facilities (e.g., fertilizer production,ethanol production, cement and steel plants) can be used to boost oil production through EOR. Once CO2 is captured from these facilities, it is compressed and transported by pipeline to oil fields.

Primary Production refers to a new oil field discovery where production wells are drilled into a geological formation and oil or gas is produced using the pent-up energy of the fluids in the reservoir.

At the end of primary production a considerable amount of the oil remains in place, with sometimes as much as 80-90 percent still “trapped” in the pore spaces of the reservoir. (Melzer, 2012)

If an oil field is not abandoned after primary production, it moves into a secondary production phase wherein a substance (usually water) is injected to repressurize the formation. New injection wells are drilled or converted from producing wells, and the injected fluid sweeps oil to the remaining producing wells. Secondary production could yield up to an equal or greater amount of oil from primary production. But this has the potential to ultimately leave 50-70 percent of the original oil remaining in the reservoir since much of the oil is bypassed by the water that does not mix with the oil. (Melzer, 2012)

Primary and secondary production are sometimes referred to as “conventional” oil production practices.

During tertiary production, oil field operators use an injectant (usually CO2) to react with the oil to change its properties and allow it to flow more freely within the reservoir. Almost pure CO2 (>95 percent of the overall composition) has the property of mixing with oil to swell it, make it lighter, detach it from the rock surfaces, and cause the oil to flow more freely within the reservoir to producer wells. In a closed loop system, CO2 mixed with recovered oil is separated in above-ground equipment for reinjection. CO2-EOR typically produces between 4-15 percent of the original oil in place. (ARI, 2010)


  • Advanced Resources International (ARI), Improving Domestic Energy Security and Lowering CO2 Emissions with “Next Generation” CO2-Enhanced Oil Recovery (CO2-EOR), June 20, 2011, DOE/NETL-2011/1504.
  • Melzer, L. S. (2012). Carbon Dioxide Enhanced Oil Recovery (CO2-EOR): Factors Involved in Adding Carbon Capture, Utilization and Storage (CCUS) to Enhanced Oil Recovery.