Does crude oil have a fixed chemical composition?

Answer 1

• No, it is not not. Crude oil differs from one type to another depending the type and amount of impurities.

• An oil well produces predominantly crude oil, with some natural gas dissolved in it. Because the pressure is lower at the surface than underground, some of the gas will come out of solution and be recovered (or burned) as associated gas or solution gas. A gas well produces predominantly natural gas. However, because the underground temperature and pressure are higher than at the surface, the gas may contain heavier hydrocarbons such as pentane, hexane, and heptane in the gaseous state. At surface conditions these will condense out of the gas to form natural gas condensate, often shortened to condensate. Condensate resembles petrol in appearance and is similar in composition to some volatile light crude oils.

• The proportion of light hydrocarbons in the petroleum mixture (or crude oil) varies greatly among different oil fields, ranging from as much as 97 percent by weight in the lighter oils to as little as 50 percent in the heavier oils and bitumens.

• There are four main types of hydrocarbons found in crude oil.

1. paraffins (15-60%)
2. naphthenes (30-60%)
3. aromatics (3-30%)
4. asphaltics (remainder)

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