Enhanced Oil Recovery (EOR)

Enhanced oil recovery (EOR) is the process of recovering oil not already extracted from an oil reservoir through primary or secondary recovery techniques. Those techniques rely on natural or enhanced pressures to force oil out of the ground. EOR methods alter the chemical composition of the oil itself, to make it easier to extract.

Enhanced oil recovery is also known as tertiary recovery.

Enhanced oil recovery techniques are expensive and not always useful. This phase of oil extraction allows petroleum companies to remove a significant amount of oil from a reserve that they would not be able to access without these enhanced methods. EOR is employed after primary and secondary processes have been exhausted or are unable to be utilized on a particular reserve.

Primary recovery is the first stage of production and extraction relies on the natural rise of the oil due to pressure differences between the oil field and the bottom-hole of the well. Secondary recovery techniques inject water or gases into the ground, which attempts to force the hydrocarbons to the surface through applied pressure.

Petroleum companies and scientists look to enhanced oil recovery (EOR) for its potential to prolong the life of wells proven or probable oil fields. Proven reserves are those with a higher than 90-percent chance that the oil will be recovered and likely fields have an over 50-percent chance of petroleum recovery. The U.S. Department of Energy or DOE identifies three main processes of EOR extraction.

1. Gas injection uses various gases to both force oil to the surface and to lower its viscosity. The less viscous the oil, the easier it flows. Gases used include nitrogen and natural gas. However, the most common gas is carbon dioxide. Initially CO₂ extraction was limited to oil fields near naturally occurring CO₂ reservoirs, or within pipeline range. Now, new techniques are making it possible to recycle CO₂ from industrial applications such as natural gas processing, fertilizer, ethanol, and hydrogen plants in locations where naturally occurring reservoirs are not available. Highly advanced initiatives are exploring the possibility of portable CO₂ through nanoparticle-stabilized foams and gels. As a result of this research and development, the Energy Department considers CO₂ recovery to be the most promising EOR technique.
   
2. Thermal injection uses heat to thin the oil for smoother extraction. A standard method is steam flooding, in which steam is pumped into the well. When the steam condenses into hot water, the oil is heated and made less viscous. Another type of thermal injection is fire flooding, which combusts oil on the periphery of a reservoir through oxygen injection, which creates enough heat to drive out the oil closer to the well.
   

The newest technology, developed in Russia, is plasma pulse. The method involves bombarding oil fields with low-energy emissions, which lowers viscosity much like the conventional EOR techniques. One promising feature of plasma pulse it that it is less potentially harmful to the environment since it does not involve injecting gases, chemicals or heat into the earth.