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Thermal recovery is a technique which is used in the extraction of heavy oils. These oils are normally trapped in an oil field because they are too viscous to flow into a well. With thermal recovery, they can be accessed, increasing the yield of an oil field and extending its lifetime. These techniques are used in oil fields all over the world, and new approaches are often being developed in response to the rising demand for crude oil for a variety of uses, from manufacture of plastics to production of fuels and lubricants.
Thermal recovery relies on a very simple principle: when oil is heated, it undergoes physical and chemical changes. People may have noticed this while cooking, when they swirl cold oil into a pan and the oil thins and spreads as the pan heats. In the case of thermal recovery, rather than bringing the oil to the heat, the heat is brought to the oil, and the oil becomes less viscous, thinning enough that it will flow into the wells so that it can be extracted.
Heat is often introduced in the form of steam which is injected into the well. Gases and chemicals can also be injected for thermal recovery. These processes add to the cost of oil extraction, sometimes considerably, although they are balanced out by the price which the oil can fetch on the open market. The benefits of extending the life of an oil field and extracting as much oil as possible from a site are also weighed when considering whether or not to use thermal recovery.
An alternative to thermal recovery is mining. Mining only works for shallow deposits which can be easily accessed. In mining, the oil is uncovered by digging for it, and then extracted and treated. This is not an option when oil deposits are buried deep below the surface, requiring in situ recovery of the oil. Mining and thermal recovery can both be polluting and destructive processes.
Some governments have actively promoted thermal recovery practices. These governments want to make sure that their oil fields are utilized to the maximum, reducing dependence on oil from foreign deposits. They may also be concerned about the environmental impact of oil extraction, reasoning that it may be better to fully exploit one oil field than to open additional oil fields as the oil becomes more difficult to extract. Thermal recovery can also be used in oil fields which have been closed due to lack of production, to ramp up production again.