Enhanced oil recovery (EOR)

Glossary / Oil and gas / Enhanced oil recovery (EOR)

Enhanced oil recovery (EOR), also known as tertiary recovery, is a set of techniques and processes employed in the oil and gas industry to extract additional oil from reservoirs after primary and secondary recovery methods have been utilized. EOR methods aim to improve extraction efficiency and increase the overall recovery factor of oil reservoirs.

The primary and secondary recovery methods typically recover only a portion of the oil in place, leaving a significant amount behind. EOR techniques are employed to target and mobilize the remaining oil by altering the reservoir conditions and fluid behavior. These methods are typically applied in mature or challenging reservoirs where conventional recovery methods prove insufficient.

Various EOR techniques exist, but they generally fall into three main categories:

1. Thermal EOR. This method involves the application of heat to the reservoir to reduce oil viscosity and enhance fluid mobility. Steam injection is the most common thermal EOR technique, where steam is injected into the reservoir to heat the oil and improve its flow characteristics. Other thermal methods include in-situ combustion and electric heating.

2. Chemical EOR. Chemicals, such as polymers, surfactants, and alkalis, are injected into the reservoir to alter the properties of oil and improve its displacement from the rock pores. Chemical EOR techniques include polymer flooding, surfactant flooding, and alkaline flooding. These methods help reduce interfacial tension, improve sweep efficiency, and enhance oil recovery.

3. Miscible EOR. In this method, fluids that mix uniformly with oil, such as carbon dioxide (CO2) or hydrocarbon gases, are injected into the reservoir to dissolve in the oil and improve its displacement. Miscible EOR techniques include CO2 flooding and hydrocarbon gas injection.

EOR techniques are complex and require careful reservoir characterization, simulation, and monitoring to optimize their effectiveness. Factors such as reservoir properties, fluid behavior, economics, and environmental considerations influence the selection and implementation of EOR methods.

Enhanced oil recovery plays a crucial role in
maximizing oil production and extending the economic life of reservoirs. It enables the recovery of a higher percentage of the original oil in place and contributes to meeting global energy demands while utilizing existing resources more efficiently.

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Frequently Asked Questions

Enhanced oil recovery (EOR) is a process of increasing the amount of oil that can be extracted from an oil reservoir by using various techniques that go beyond the primary and secondary recovery methods. EOR methods include injecting gases such as CO2, steam, or chemicals into the reservoir to decrease oil viscosity or increase pressure, thus allowing for increased oil production.

The recovery rate for Enhanced Oil Recovery (EOR) varies depending on the type of method used. Generally, EOR can increase recovery rates by 10-20% compared to primary and secondary recovery methods. However, the recovery rate can be as high as 60-80% in some cases. Factors such as reservoir properties, fluid type, and method efficiency can impact the ultimate recovery rate.

Examples of enhanced oil recovery include thermal methods such as steam injection and in-situ combustion, chemical methods like polymer flooding and surfactant flooding, and physical methods such as water flooding and gas injection. These methods are employed to increase the amount of oil that can be extracted from reservoirs by altering the properties of the oil and rock.

The most common type of enhanced oil recovery (EOR) used for heavy oil is thermal recovery. This method involves injecting steam into the reservoir to heat the oil, reduce its viscosity, and enhance its flow. Steam injection techniques such as cyclic steam stimulation (CSS), steam flooding, and steam-assisted gravity drainage (SAGD) are commonly employed to extract heavy oil reserves by making the oil easier to produce and recover.