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Enhanced oil recovery (EOR) is used to recover stranded oil that remains in reservoirs after primary production.
Oil is first produced due to the high pressures of buried reservoirs pushing the hydrocarbons to the surface. This pressure difference can be aided by pumps. Secondary recovery generally occurs by a waterflood, in which water is injected into the reservoir to physically displace the residual oil, which is subsequently recovered by adjacent production wells. The success of waterfloods depends on the permeability of the reservoir and the properties of the oil.
Tertiary recovery techniques are also referred to as enhanced oil recovery, or EOR. The three most common EOR techniques are heat injection, chemical injection, and gas injection. Heat injection enhances reservoir productivity by reducing the viscosity of crude oil. Chemical injection decreases surface tension and capillary pressure within the reservoir through the interaction of various chemicals with oil. Gas injection is currently the most common EOR technique. The gas—usually carbon dioxide (CO₂)—displaces and mixes with oil to enhance production. CO₂ injection is commonly referred to as CO₂-EOR, and the term is often used interchangeably with EOR.
CO₂-EOR has been successful in several fields around Wyoming, including the Lost Soldier and Wertz fields and the Monell unit in the Patrick Draw field of the Greater Green River Basin; Salt Creek field in the Powder River Basin; and Beaver Creek field in the Wind River Basin. Grieve field, in the Wind River Basin, began CO₂-EOR operations in early 2013. Most of these fields underwent secondary waterflooding prior to CO₂-EOR.
For more information on enhanced oil recovery in Wyoming, see the University of Wyoming’s Enhanced Oil Recovery Institute website.
CO₂ can also be injected into deep rock formations for long-term underground storage, called geologic storage or sequestration (GS). For more information on this process, see the page on CO₂ storage.
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