Describe the methods of oil recovery.

There are several methods of oil recovery that are used to extract oil from underground reservoirs. Some of the most common methods include:

1. Primary recovery: This method involves using the natural pressure of the reservoir to push the oil to the surface. This is typically the initial method used to extract oil from a reservoir and involves drilling a well and allowing the oil to flow to the surface.

2. Secondary recovery: This method involves injecting water or gas into the reservoir to help push the oil to the surface. Water flooding is a common secondary recovery method, where water is injected into the reservoir to displace the oil and push it towards the production well.

3. Enhanced oil recovery (EOR): This method involves using advanced techniques to extract oil that is not easily recoverable using primary or secondary methods. EOR techniques include injecting chemicals, steam, or other substances into the reservoir to help loosen the oil and push it to the surface.

4. Hydraulic fracturing (fracking): This method involves injecting a mixture of water, sand, and chemicals into the reservoir at high pressure to create fractures in the rock and release the trapped oil. Fracking is commonly used in shale oil and gas extraction.

5. Thermal recovery: This method involves heating the reservoir to reduce the viscosity of the oil and make it easier to extract. Steam injection is a common thermal recovery method, where steam is injected into the reservoir to heat the oil and push it to the surface.

Overall, the method of oil recovery used depends on the characteristics of the reservoir and the type of oil being extracted. Each method has its own advantages and disadvantages, and the most appropriate method is chosen based on factors such as cost, efficiency, and environmental impact.

Primary Oil Recovery

- Natural Drive: Pressure from the reservoir rock and fluids drives oil to the surface through existing channels.
- Gas Expansion: Natural gas dissolved in oil expands and pushes oil towards the wellbore.
- Water Drive: Water encroaches into the reservoir and pushes oil towards the wellbore.

Secondary Oil Recovery

- Waterflooding: Water is injected into the reservoir to displace oil towards production wells.
- Gas Injection: Natural gas or carbon dioxide is injected into the reservoir to reduce oil viscosity and increase its flow rate.
- Enhanced Oil Recovery (EOR)

Tertiary Oil Recovery

- Thermal Recovery:
- Steam Injection: Hot steam is injected into the reservoir to reduce oil viscosity and mobilize it.
- In-Situ Combustion: A fuel is injected into the reservoir and ignited to release heat and reduce oil viscosity.
- Chemical Recovery:
- Polymer Flooding: Polymers are injected into the reservoir to increase the viscosity of water and improve its displacement of oil.
- Surfactant Flooding: Surfactants are injected to reduce the surface tension between oil and water, enabling easier displacement.
- Miscible Gas Injection: Carbon dioxide or other hydrocarbons are injected into the reservoir to mix with oil and reduce its viscosity.
- Microbial Enhanced Oil Recovery (MEOR): Bacteria or other microorganisms are introduced into the reservoir to produce gases or solvents that increase oil recovery.