Enhanced oil recovery is the tertiary oil production. It is a method to increase production of a well up to 75%. It does not rely on natural rise of hydrocarbons, nor the use of water injection. EOR is mainly divided into three:
1.Thermal Recovery :
Heat is added via steam (or possibly other media) enabling a better flow of the hydrocarbons. This happens because the higher temperature causes a lower viscosity of the hydrocarbons.
2. Chemical Injection :
The use of chemicals to render the properties of the hydrocarbons (and injected water), to ease its movement in the reservoir. The properties may be surface tension (capillary pressure) or viscosity (for injected water).
3. Gas Injection :
This method 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 improve its flow rate .