The Reservoir

Recovery Techniques
(Extraction of petroleum)

1.) Primary recovery
The majority of energy comes from reservoir, the natural mechanisms. These include expansion of the natural gas at the top of the reservoir, expansion of gas initially dissolved in the crude oil, natural water displacing oil downward into the well, and gravity drainage resulting from the movement of oil within the reservoir from the upper to the lower parts where the wells are located.

Recovery factor for oil reservoirs

Recovery factor for each processes

2.) Secondary recovery
After the pressure falls and at some point, underground pressure is insufficient to force the oil to the surface. After natural reservoir energy decrease, secondary recovery methods are applied. They rely on the supply of external energy into the reservoir. Hence, secondary recovery techniques increase the reservoir’s pressure by water injection, natural gas reinjection and gas lift, which injects air, carbon dioxide or some other gas into the bottom of the well, reducing the overall density of fluid in the wellbore. on average, the recovery factor after primary and secondary oil recovery operations is between 35 and 45%, depending on the properties of the oil and the characteristics of the reservoir rock.

Displacement of oil by water

Theoretical example to show the effect on displacement efficiency of viscosity and density differences between oil and water

Gas injection

3.) Enhanced oil recovery (EOR) or Tertiary recovery
Increasing the mobility of the oil in order to increase extraction. According to the US department of Energy, there are three techniques for EOR which is thermal processes, gas injection(miscible processes) and chemical processes.

3.1) Thermal processes : using heat to reduce oil viscosity (for heavy oil)
3.1.1 Surface heat generation

Hot water flooding : hot water is injected into the reservoir through specially distributed injection wells to reduce the viscosity of the crude oil, allowing it to move more easily toward production wells. Hot water flooding, also known as hot water injection, is typically less effective than a steam-injection process because water has lower heat content than steam. Nevertheless, it is preferable under certain conditions such as formation sensitive to fresh water.
Steam flooding : steam generated at surface is injected into the reservoir through specially distributed injection wells to heat up the crude oil and reduce its viscosity as same as hot water flooding but stream is more effective than hot water flooding because steam contains massive latent heat which is far more than specific heat of water.
Cyclic steam injection : steam is injected and then subsequently put back on production. A cyclic steam-injection process includes three stages. The first stage is injection, during which a slug of steam is introduced into the reservoir. The second stage, or soak phase, requires that the well be shut in for several days to allow uniform heat distribution to thin the oil. Finally, during the third stage, the thinned oil is produced through the same well. The cycle is repeated as long as oil production is profitable. Cyclic steam injection is also called steam soak or the huff `n puff (slang) method.

Hot water flooding

Steam flooding

Cyclic steam injection (steam soak, or more colloquially, "huff and puff")

3.1.2 Underground heat generation

In situ combustion or fire flooding : a flame is generated in the reservoir by igniting a fire at the sand face of an injection well. Continuous injection of air or other gas mixture with high oxygen content will maintain the flame front. As the fire burns, it moves through the reservoir toward production wells. Heat from the fire reduces oil viscosity and helps vaporize reservoir water to steam. The steam, hot water, combustion gas and a bank of distilled solvent all act to drive oil in front of the fire toward production wells.

Temperature profile and fluid distribution in a reservoir during laboratory test of in situ combustion recovery process

3.2) Miscible processes : to create miscible zone to eliminate/reduce capillary force (for medium and light oil)

Hydrocarbon solvent injection : e.g. LPG, kerosene, gasoline.
Enriched hydrocarbon gas injection : A slug of methane enriched with propane, butane, or pentane and tailed by gas and/or water is injected into the reservoir.
High-pressure hydrocarbon gas injection : Miscible at high pressure. Continuous injection of high pressure methane, ethane, or flue gas into reservoir.
Carbon dioxide injection : Miscible at high pressure, dissolved in oil and reduction in viscosity.
Nitrogen injection : Miscible at high pressure, usually cheaper than carbon dioxide or a hydrocarbon derived gas.

Mobilisation of immobile oil

Solvent & Enriched gas & Carbon dioxide injection

3.3) Chemical processes : to increase viscosity of displacing fluid (polymer flooding) and reduce capillary force (surfactant and caustic flooding)

Polymer flooding : Polymer dissolved in injected water in order to increase the water viscosity, to prevent bypassing and improve recovery.
Surfactant flooding : Soaps or soap-like chemical, attracted to water and oil forming micro-emulsion in order to reduce capillary force and also alter the wettability or the reservoir rock to improve oil recovery.
Caustic flooding : Also known as alkaline flooding in which an alkaline chemical such as sodium hydroxide or sodium carbonate is injected during polymer flooding or water flooding operations in order to reduce capillary force and interfacial tension between oil and water. Alkaline flooding is not recommended for carbonate reservoirs because of the abundance of calcium: the mixture between the alkaline chemical and the calcium ions can produce hydroxide precipitation that may damage the formation.

Surfactant flooding

Polymer flooding

Reference

Go For the Food

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Recovery Techniques (Extraction of petroleum)

Go For the Food

Recovery Techniques
(Extraction of petroleum)