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In the past, chemical, thermal, and miscible techniques have been used by the industry on a commercial scale. EOR techniques require the injection of chemical compounds dissolved in water, the injection of steam, or the injection of a gas that is miscible with the oil in place. As a result, all current EOR techniques are much more expensive to implement than normal secondary water injection projects. Therefore, the amount of oil that can ultimately be recovered by existing EOR techniques is directly related to the price of [[crude oil]].
In the past, chemical, thermal, and miscible techniques have been used by the industry on a commercial scale. EOR techniques require the injection of chemical compounds dissolved in water, the injection of steam, or the injection of a gas that is miscible with the oil in place. As a result, all current EOR techniques are much more expensive to implement than normal secondary water injection projects. Therefore, the amount of oil that can ultimately be recovered by existing EOR techniques is directly related to the price of [[crude oil]].
All EOR projects begin with an analysis of the nature, location, and causes of residual oil saturations (''S''<sub>or</sub>) that remain after primary and/or secondary recovery operations. The main factors that control the value of ''S''<sub>or</sub> are pore geometry, rock [[wettability]], and the properties of the displaced (oil) and displacing (injected) fluids. Fluid properties of particular interest are interfacial tension, viscosity, and density. In combination with the heterogeneity of the reservoir, these properties result in the overall recovery (''E''<sub>R</sub>) for any recovery scheme.
All EOR projects begin with an analysis of the nature, location, and causes of residual oil saturations (''S''<sub>or</sub>) that remain after primary and/or secondary recovery operations. The main factors that control the value of ''S''<sub>or</sub> are pore geometry, rock [[wettability]], and the properties of the displaced (oil) and displacing (injected) fluids. Fluid properties of particular interest are interfacial tension, [[viscosity]], and density. In combination with the heterogeneity of the reservoir, these properties result in the overall recovery (''E''<sub>R</sub>) for any recovery scheme.
The overall recovery is the product of displacement efficiency (''E''<sub>D</sub>), and sweep efficiency (''E''<sub>S</sub>). The displacement efficiency is inversely proportional to the residual oil saturation, while the sweep efficiency is inversely proportional to the mobility ratio (''M'') between the injected fluids and the oil in place (see “[[Waterflooding]]”). ''M'' is usually stated in terms of the [[Relative permeability]] of a fluid phase (''k''<sub>r</sub>) divided by the phase's viscosity (''μ'') relative to the same ratio for the other phase, such as for a waterflood:
The overall recovery is the product of displacement efficiency (''E''<sub>D</sub>), and sweep efficiency (''E''<sub>S</sub>). The displacement efficiency is inversely proportional to the residual oil saturation, while the sweep efficiency is inversely proportional to the mobility ratio (''M'') between the injected fluids and the oil in place (see “[[Waterflooding]]”). ''M'' is usually stated in terms of the [[Relative permeability]] of a fluid phase (''k''<sub>r</sub>) divided by the phase's viscosity (''μ'') relative to the same ratio for the other phase, such as for a waterflood: