Enhanced oil recovery

Enhanced oil recovery

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Enhanced oil recovery

Enhanced Oil Recovery (abbreviated 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 ^[1] compared with 20-40% ^[2] using primary and secondary recovery.

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

How it works
Economic costs and benefits
Examples of current EOR projects
Potential for EOR in United States
References
See also
External links

How it works

This improved extraction is achieved by gas injection, chemical injection, or thermal recovery (which includes cyclic steam, steamflooding, and fireflooding).

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. 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 such as Rhamnolipids to help lower the capillary pressure that often prevents oil droplets from moving through a reservoir.

Economic costs and benefits

Adding oil recovery methods adds to the cost of oil — 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.^[3] Onshore EOR has paid in the range of a net 10-16 US$ per tonne of CO₂ injected for oil prices of 15-20 US$/barrel. Prevailing prices depend on many factors but can determine the economic suitability of any procedure, with more procedures and more expensive procedures being economically viable at higher prices. Example: With oil prices at around 130 US$/barrel, the economic benefit is about 100 US$ per tonne CO₂.

Examples of current EOR projects

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 of oil, extending the life of the oil field by 25 years http://www.netl.doe.gov/publications/proceedings/01/carbon_seq/2a1.pdf. 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.

Potential for EOR in United States

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 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 , 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 of oil would be on the order of 100 billion tonnes of CO₂, equivalent to four times the annual global CO₂ emissions.

References

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