# Enhanced Oil Recovery (EOR): What it Means, Examples

## What Is Enhanced Oil Recovery (EOR)?

Enhanced oil recovery (EOR), also known as “tertiary recovery,” is a process for [extracting oil](https://www.investopedia.com/articles/active-trading/102214/economics-oil-extraction.asp) that has not already been retrieved through the [primary](https://www.investopedia.com/terms/p/primary-recovery.asp) or secondary oil recovery techniques.

Although the primary and secondary recovery techniques rely on the pressure differential between the surface and the underground well, enhanced oil recovery functions by altering the chemical composition of the oil itself in order to make it easier to extract.

### Key Takeaways

*   Enhanced oil recovery (EOR) is the practice of extracting oil from a well that has already gone through the primary and secondary stages of oil recovery.
*   Depending on the price of oil, EOR techniques may not be [economically viable](https://www.investopedia.com/terms/e/economic_efficiency.asp).
*   EOR techniques can affect the environment negatively, though new innovations in the sector may help reduce this impact in the future.

## How Enhanced Oil Recovery Works

Enhanced oil recovery techniques are complex and expensive and therefore are employed only when the primary and secondary recovery techniques have exhausted their usefulness. Indeed, depending on factors such as the [cost of oil](https://www.investopedia.com/articles/economics/08/determining-oil-prices.asp), it may not be economical to employ EOR at all. In those cases, oil and gas might be left in the reservoir because it is simply not profitable to extract the remaining amounts.

![Image](https://www.investopedia.com/thmb/FCT6i7D9uah-SLuamIExFx_6WQU=/1500x0/filters:no_upscale():max_bytes(150000):strip_icc()/dotdash_Final_Enhanced_Oil_Recovery_EOR_Definition_Apr_2020-01-bb06d16f90004c1f9e7f75356404f368.jpg)

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## Three Main Types of EOR Techniques

In the first type of technique, gases are forcefully injected into the well in a way that both forces the oil to the surface and reduces its viscosity. The less viscous the oil, the easier it flows and the more cheaply it can be extracted. Although various gases can be used in this process, [carbon dioxide](https://www.investopedia.com/articles/investing/092915/5-countries-produce-most-carbon-dioxide-co2.asp) (CO2) is used most often. 

This specific use of carbon dioxide likely could continue or even increase in the future, as recent advances make it possible to transport CO2 in the form of foams and gels. To some, this could be a significant improvement as it would allow CO2 injections to be utilized in areas far removed from naturally occurring carbon dioxide reservoirs.

> **Important**
>
> On the other hand, there are grave concerns about the continued use of carbon dioxide because of its harmful effects on the environment. Currently, most countries are seeking alternative modes of energy that are more sustainable than CO2.

Other common EOR techniques include pumping steam into the well in order to heat the oil and make it less viscous. Similar outcomes can be achieved through so-called “fire flooding,” which involves lighting a fire around the periphery of the oil reservoir in order to drive the remaining oil close to the well. 

Finally, various polymers and other chemical structures can be injected into the reservoir to reduce viscosity and increase pressure, although these techniques are often prohibitively expensive.

## Using Enhanced Oil Recovery Methods

[Petroleum companies](https://www.investopedia.com/top-oil-and-gas-stocks-q2-2023-7377009) and scientists look to EOR for its potential to prolong the life of wells in proven or probable [oil fields](https://www.investopedia.com/terms/o/oil-field.asp). [Proven reserves](https://www.investopedia.com/terms/p/proven-reserves.asp) are those with a greater than 90% chance that oil will be recovered, and [probable reserves](https://www.investopedia.com/terms/p/probable-reserves.asp) have a more than 50% chance of recovering petroleum.

Unfortunately, EOR techniques can produce negative environmental side effects, such as causing harmful chemicals to leak into the groundwater. One recent technique that might help reduce these environmental risks is called plasma pulsing. Developed in Russia, plasma pulse technology involves radiating oil fields with low-energy emissions, thereby lowering their viscosity much like conventional EOR techniques.

Because plasma pulsing does not require injecting gases, chemicals, or heat into the ground, it may prove to be less environmentally harmful than the other current methods of oil recovery.