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Enhanced Oil Recovery (EOR) is a generic term for techniques for increasing the amount of oil that can be extracted from an oil field. Using EOR, 30-60 %, or more, of the reservoir's original oil can be extracted compared with 20-40 % using primary and secondary recovery.

Enhanced oil recovery is also called improved oil recovery or tertiary recovery (as opposed to primary and secondary recovery).

Contents 1 How it works 2 Economic costs and benefits 3 Examples of current EOR projects 4 Potential for EOR in United States 5 References 6 See also 7 External link

This improved extraction is achieved by either gas injection, thermal recovery, or chemical injection.

Gas injection is the most commonly used EOR technique. Here, gas such as carbon dioxide (CO₂), natural gas, or nitrogen is injected into the reservoir whereupon it expands and thereby pushes additional oil to a production wellbore, and moreover dissolves in the oil to lower its viscosity and improves the flow rate of the oil. The prospects of using CO₂ has gathered much interest, as this would allow storing it away from the atmosphere and hence a tool to combat global warming. However, the extra oil extracted would, when combusted, add additional CO₂ to the atmosphere, partially or completely offsetting the benefits of the removed CO₂. Oil displacement by CO₂ injection relies on the phase behaviour of CO₂ and crude oil mixtures that are strongly dependent on reservoir temperature, pressure and crude oil composition. These mechanisms range from oil swelling and viscosity reduction for injection of immiscible fluids (at low pressures) to completely miscible displacement in high-pressure applications. In these applications, more than half and up to two-thirds of the injected CO₂ returns with the produced oil and is usually re-injected into the reservoir to minimize operating costs. The remainder is trapped in the oil reservoir by various means.

Other techniques include thermal recovery (which uses heat to improve flow rates), and, more rarely, chemical injection, where polymers are injected to increase the effectiveness of waterfloods, or the use of detergent-like surfactants to help lower the surface tension that often prevents oil droplets from moving through a reservoir.

The injection of gas costs money — in the case of CO₂ typically between 0.5-8.0 US$ per tonne of CO₂. The increased extraction of oil on the other hand, is an economic benefit with the revenue depending on prevailing oil prices. Onshore EOR have paid in the range of a net 10-16 US$ per tonne of CO₂ injected for oil prices of 15-20 US$/barrel. With oil prices at a currently more realistic level of 50 US$/barrel, the economic benefit rises to about 30 US$ per tonne CO₂.

In Canada, a CO₂-EOR project has been established by EnCana at the Weyburn Oil Field in southern Saskatchewan. The project is expected to inject a net 18 million ton CO₂ and recover an additional 130 million barrels of oil, extending the life of the oil field by 25 years [1]. When combusted, this extra volume of oil will produce nearly 60 million ton CO₂, so in this case carbon capture and storage in combination with EOR leads to more CO₂ emissions than without injection of CO₂. Since CO₂ injection began in late 2000, the EOR project has performed largely as predicted. Currently, some 1600 m3 (10,063 barrels) per day of incremental oil is being produced from the field.

In United States, the Department of Energy (DOE) has estimated that full use of 'next generation' CO₂-EOR in United States could generate an additional 240 billion barrels of recoverable oil resources. Developing this potential would depend on the availability of commercial CO₂ in large volumes, which could be made possible by widespread use of carbon capture and storage. For comparison, the total undeveloped US domestic oil resources still in the ground total more than 1000 billion barrels, most of it remaining unrecoverable. The DOE estimates that if the EOR potential were to be fully realised, State and local treasuries would gain $280 billion in revenues from future royalties, severance taxes, and state income taxes on oil production, aside from other economic benefits. For the climate, the CO₂ released from the combustion of 240 billion barrels of oil would be on the order of 100 billion tonnes of CO₂, equivalent to four times the annual global CO₂ emissions.

• IPCC Special Report on Carbon dioxide Capture and Storage. Chapter 5, Underground geological storage. Intergovernmental Panel on Climate Change (IPCC), 2005.

• US Department of Energy analysis of EOR potential Game Changer Improvements Could Dramatically Increase Domestic Oil Resource Recovery. An analysis by Advanced Resources International, Arlington, VA, for the U.S. Department of Energy’s Office of Fossil Energy. Advanced Resources International, February 2006. See also press release

• Carbon capture and storage

• US Department of Energy Information page on Enhanced Oil Recovery/CO₂ Injection.

• UMass Lowell invention for enhanced oil recovery Commercialization Planned for Enhanced Oil Recovery Method

• Massachusetts Technology Portal Licensable Technology

• Mississippi Oil Journal Map Oil Well Map of EOR CO2 field in Brookhaven Mississippi