PETROLEUM
chemical elements vary over fairly narrow limits as follows:
Composition by weight
Element Percent range
Carbon 83 to 87%
Hydrogen 10 to 14%
Nitrogen 0.1 to 2%
Oxygen 0.05 to 1.5%
Sulfur 0.05 to 6.0%
Metals < 0.1%
Four different types of hydrocarbon molecules appear in crude oil. The relative
percentage of each varies from oil to oil, determining the properties of each oil.
Composition by weight
Hydrocarbon Average Range
Paraffins 30% 15 to 60%
Naphthenes 49% 30 to 60%
Aromatics 15% 3 to 30%
Asphaltics 6% remainder
Most of the world's oils are non-conventional.
Crude oil varies greatly in appearance depending on its composition. It is usually black
or dark brown (although it may be yellowish, reddish, or even greenish). In the reservoir
it is usually found in association with natural gas, which being lighter forms a gas cap
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