Enhanced Oil Recovery (EOR) is usually known as producing oil in tertiary phase.
EOR applies steam or gas to change the properties of the hydrocarbons in the reservoir. EOR can also restores pressure and oil displacement in the reservoir.
There are three main types of EOR, including thermal recovery, gas injection , and chemical injection.
Thermal Recovery involves the introduction of heat to the reservoir to reduce the viscosity of the oil such as injection of steam to thin the heavy viscous oil, and enhancing its ability to flow through the reservoir. Thermal techniques now accounts for over 50% of EOR in the US.
Gas Injection involves injecting natural gas, nitrogen, or carbon dioxide into the reservoir that expand to push additional oil to a production wellbore, or other gases that mix with or dissolve in the oil to decrease its viscosity and improves its flow rate. Gas injection technique accounts for nearly 60% of EOR in the US. This technique is widely considered by producers due to the win-win situation for injecting carbon dioxide underground for long-term storage that could become an important way to remove excess amounts from the atmosphere.
Chemical Injection helps to free trapped oil within the reservoir. This technique involves the use of long-chained molecules called polymers into the reservoir to increase the effectiveness of water-flooding or to boost the use of detergent-like surfactants to help decrease the surface tension that inhibits the flow of oil moving through a reservoir. This technique has been utilized the least for about 1% of EOR in the US.
Even though it is very expensive to produce oil by tertiary phase, EOR can increase production from a well up to 75% recovery.