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Science

Making crude oil useful

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Crude oil is a mixture of hydrocarbons. These are separated into useful products, such as fuels, using a process called fractional distillation.

The demand for short hydrocarbon molecules is greater than their supply in crude oil, so a reaction called cracking is used. Cracking converts long alkane molecules into shorter alkanes and alkenes, which are more useful. The exploitation of oil can damage the environment - for example, through oil spills.

Crude oil

Fossil fuels

Crude oil, coal and gas are fossil fuels. They were formed over millions of years, from the remains of dead organisms:

  • crude oil and gas were formed from dead sea creatures
  • coal was formed from dead plants

The fossil fuels are finite resources - there is only a limited supply of them in the Earth’s crust. They took so long to form that they cannot be replaced once they have been used up. They are non-renewable fuels.

How crude oil was formed

Crude oil is found trapped in some of the sedimentarysedimentary: Sedimentary rocks are formed when rock fragments are deposited and pressed together. rocks of the Earth's crust.

Millions of years ago, huge numbers of microscopic animals and plants - plankton - died and fell to the bottom of the sea. Their remains were covered by mud.

As the mud sediment was buried by more sediment, it started to change into rock, as the temperature and pressure increased. The plant and animal remains were ‘cooked’ by this process, and slowly changed into crude oil.

Oil is less dense than the water in the rocks and will rise as a result of pressure from below, often escaping altogether if the rocks are permeable.

If some of the rocks above the oil are impermeable, the oil cannot rise through them, so it gets trapped underneath.

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