There are several different methods of Enhanced Oil Recovery including:
- Thermal recovery - which involves the introduction of heat such as the injection of steam to lower the viscosity, or thin, the heavy viscous oil, and improve its ability to flow through the reservoir.
- Gas injection: which uses gases such as natural gas, nitrogen, or carbon dioxide (CO2) that expand in a reservoir to push additional oil to a production wellbore, or other gases that dissolve in the oil to lower its viscosity and improves its flow rate.
- Chemical injection: which can involve the use of long-chained molecules called polymers to increase the effectiveness of waterfloods, or the use of detergent-like surfactants to help lower the surface tension that often prevents oil droplets from moving through a reservoir.
- CO2 injection - which uses CO2 to act as a solvent, a pressurizing agent, and reduces the oil’s viscosity.
Therefore, each field must be heavily evaluated to determine which type of EOR will work best on the reservoir.
This is done through reservoir characterization, screening, scoping, and reservoir modeling and simulation.
Enhanced oil recovery processes are well known for their efficiency in incrementing oil production; however, the selection of the most suitable method to adopt for specific field applications is challenging.
Petroleum companies and scientists look to EOR for its potential to prolong the life of wells in proven or probable oil fields.
Proven reserves are those with a greater than 90% chance that oil will be recovered, and probable reserves have a more than 50% chance of recovering petroleum.