Enhanced Oil Recovery
Enhanced oil recovery (EOR), also known as “tertiary recovery,” is a process for extracting oil that has not already been retrieved through the primary 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.
Definition: Enhanced Oil Recovery (EOR) is a set of techniques used to extract oil that cannot be retrieved through primary or secondary recovery methods by altering the chemical composition or physical properties of the oil to make it easier to extract.
Origin: The origins of EOR can be traced back to the early 20th century when the oil industry began exploring ways to extract more oil from already exploited reservoirs. With technological advancements, EOR techniques saw significant development in the mid to late 20th century, particularly in chemical, thermal, and gas injection methods.
Categories and Characteristics: EOR techniques are mainly divided into three categories: chemical flooding, thermal recovery, and gas injection.
- Chemical Flooding: Involves injecting chemicals (such as polymers and surfactants) to reduce oil viscosity or alter the oil-water interfacial tension, thereby enhancing recovery. The advantage is a significant increase in recovery rates, but the cost is relatively high.
- Thermal Recovery: Involves injecting steam or hot water to reduce oil viscosity, making it easier to flow. This method is suitable for reservoirs with high-viscosity oil. The advantage is mature technology, but it has high energy consumption.
- Gas Injection: Involves injecting gases (such as carbon dioxide or nitrogen) to increase reservoir pressure or alter the physical properties of the oil. The advantage is improved recovery rates and reduced greenhouse gas emissions, but it requires complex injection equipment.
Specific Cases:
- Case 1: In the Permian Basin of Texas, USA, the use of carbon dioxide injection (gas injection) significantly improved the recovery rate of the oil field. By injecting carbon dioxide, not only was the oil's flowability increased, but the reservoir pressure was also enhanced, allowing more oil to be extracted.
- Case 2: In the Athabasca oil sands region of Canada, the Steam-Assisted Gravity Drainage (SAGD) technique (thermal recovery) successfully extracted large amounts of high-viscosity oil. By injecting steam, the viscosity of the oil was reduced, making it easier to flow and collect.
Common Questions:
- Question 1: Is the cost of EOR techniques high?
Answer: Yes, EOR techniques are generally more expensive than primary and secondary recovery methods, but they can significantly increase recovery rates, thereby enhancing the economic benefits of the oil field. - Question 2: Are all oil fields suitable for EOR techniques?
Answer: Not all oil fields are suitable for EOR techniques. The choice of EOR method depends on specific reservoir conditions, such as oil viscosity, reservoir temperature, and pressure.
