Enhanced Oil Recovery
Enhanced oil recovery defines methods of recovering stranded oil that remains in reservoirs after primary depletion.
Oil is first produced from reservoirs under primary recovery (due to in-situ reservoir pressure aided by pumps) and followed by secondary recovery. Secondary recovery generally occurs by a waterflood, where 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.
Waterfloods can be followed by tertiary recovery techniques, referred to as enhanced oil recovery, or EOR. Primarily used in declining oil fields, EOR can occur as thermal recovery where heat injection reduces oil viscosity, chemical recovery to lower the surface tension and enhance reservoir flow, or gas injection that displaces and mixes with oil. Gas injection of carbon dioxide (CO2) has become the most significant technique, commonly referred to as CO2-EOR, and is often used interchangeably with EOR.
CO2-EOR has been successful in a handful of fields around Wyoming, including 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, please see the University of Wyoming’s Enhanced Oil Recovery Institute website.
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