Tertiary Recovery

Tertiary recovery is also known as enhanced oil recovery (EOR) and is the third phase of oil extraction from an oil reserve. This phase of removal allows petroleum companies to remove a significant amount of oil from a reserve which they would not be able to access without these enhanced methods.

Oil extraction from a site begins with primary recovery, during which a combination of pressure and pumps generally will bring about 10 percent of the available oil to the surface. The second phase of recovery involves injecting water or gas into the reserve to displace more of the oil reserve, usually 20 to 40 percent. Finally, companies employ tertiary recovery to recover any remaining oil which may be accessible.

There are three primary methods of tertiary recovery.

1. With thermal recovery, the reservoir is heated, often with the introduction of steam. This warms the oil, thinning it so that it loses some of its viscosity and is more apt to flow.
2. In gas injection, the pumping of gases, such as carbon dioxide, nitrogen, or natural gas, into the reservoir is used. The gases expand, and the pressure pushes the remaining oil through the reservoir.
3. Using chemical injection involves injecting polymers, which are long-chained molecules, into the reservoir to lower surface tension and allow the oil to flow more freely. This method is used significantly less frequently than thermal recovery or gas injection. Less than one percent of tertiary recovery in the U.S. is through chemical injection.

According to the U.S. Department of Energy, the use of carbon dioxide in EOR, often written CO₂-EOR has significant potential. In the past, the carbon dioxide used for this type of recovery came from naturally occurring carbon dioxide reserves. However, today, it is possible to harvest carbon dioxide from natural gas processors, and from fertilizer and ethanol production plants. Pipelines can then transport carbon dioxide to an injection site. One site in Canada hopes to extend a field’s life by up to 25 years through the use of CO₂-EOR.

The decision of whether to use CO₂-EOR  on a site largely depends on the site’s geography and geology. It can be a very costly process, and though it may extend the life of the oil field, it can sometimes be too costly for a producer to consider it a worthy investment. Global demand and production drive the cost of oil. When deciding whether or not to undertake this type of tertiary recovery, a producer will look at current and projected oil prices to determine the action’s worth.