Introduction



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Oil Recovery in the beginning of the hydrocarbon energy history was much simpler than today. Many of the first drilled wells spewed "light" oil from nothing but the hydrostatic pressure gradient. That is not typically the case in the modern oil industry because there are not nearly as many new fields being discovered (especially of light oil). In order to extract liquid hydrocarbons in nearly depleted wells or wells containing high viscosity fluids, enhanced (tertiary) oil recovery is necessary.

So what is Enhanced Oil Recovery (EOR)?

When wells have already been subjected to Primary and Secondary recovery methods, engineers must decide what technique is most effective to continue producing a well. There are many methods of EOR, commonly seperated into 3 categories:

Although techniques outside of these categories are developing, these are the most commonly successful methods.

Before diving into some specific EOR processes, lets discuss Primary and Secondary recovery.

Primary recovery, or natural production, is essentially caused by the reservoir pressure being greater than the pressure at the bottom of a well. The higher pressure below exerts an upward force on the fluids allowing them to flow through the well to the surface. When there is no longer a pressure difference between the reservoir and the bottom of the well, Secondary recovery occurs. Primary recovery typically accounts for 10% of reservoir production (BP).

Secondary recovery is generally the injection of fluids to maintain reservoir pressure. Gas and/or water are injected to both maintain pressure to allow the fluids to flow to the surface, and to create a front to move oil towards the well. Gas and water injection essentially function on the different densities between oil, gas, and water. Because of many reasons, even Secondary techniques cannot produce all of the oil in a reservoir, but they increase production from 10% to 35% (BP).

Now lets explore some types of EOR and the physics behind them.

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