Definition of 'Tertiary Recovery'
A technique used to extract the remaining oil from previously drilled and now less desirable reservoirs where primary and secondary extraction methods are no longer cost effective. Tertiary recovery has proven worthwhile in several parts of the United States, including Utah, Texas and Mississippi, where these reservoirs are less desirable because their oil is more difficult to extract or requires more processing. Either problem means that recovering this oil is more expensive and probably less profitable, but tertiary recovery can still be profitable if market prices for oil are high enough.
Investopedia explains 'Tertiary Recovery'
One way to stimulate tertiary recovery is to inject carbon dioxide (CO2) into a reservoir. This method can yield as much as 17% of a field's original oil in place. Occidental Petroleum, Denbury Resources and Anadarko Petroleum have used this technique in North America. One difficulty with CO2 injection is that petroleum companies must secure an adequate supply of CO2 before they can implement tertiary recovery.
Tertiary recovery is also called "enhanced oil recovery" or "EOR."