Enhanced oil recovery (EOR) refers to a set of techniques and processes used to extract additional oil from reservoirs after primary and secondary recovery methods have been exhausted. EOR systems employ various mechanisms to enhance oil production, including thermal methods, chemical methods, and miscible displacement methods. These techniques are implemented depending on the characteristics of the reservoir and the type of oil present.

Thermal methods, such as steam injection and in-situ combustion, involve the injection of heat into the reservoir to reduce oil viscosity, improve mobility, and enhance oil flow. Chemical methods utilize various chemicals, such as polymers, surfactants, and alkalis, to alter the properties of the reservoir fluids,facilitating the displacement of oil from the reservoir.

Miscible displacement methods, such as carbon dioxide (CO2) flooding and nitrogen injection, involve injecting a miscible fluid into the reservoir to mix with the oil and reduce its viscosity. CO2 flooding is particularly effective in reservoirs with light or intermediate crude oil, where CO2 can dissolve in the oil and significantly increase its volume, thereby improving oil recovery.

The selection of the appropriate EOR system depends on various factors, including the reservoir characteristics, fluid properties, economic considerations, and environmental impact. EOR techniques can significantly increase oil recovery from a reservoir, leading to extended production life, enhanced production rates, and improved overall oil field economics. However, implementing EOR systems requires careful planning, extensive reservoir characterization, and ongoing monitoring to optimize performance and ensure long-term viability.