Types of Crude Oils

Crude oils vary widely in appearance and viscosity from field to field. They range in

colour, odour, and in the properties they contain. While all crude oils are essentially

hydrocarbons, the differences in properties, especially the variations in molecular

structure, mean that a crude is more or less easy to produce, pipeline, and refine. The

variations may even influence its suitability for certain products and the quality of those

products.

Crudes are roughly classified into three groups, according to the nature of the

hydrocarbons they contain.

Paraffin-based Crude Oils

These contain higher molecular weight paraffins which are solid at room temperature, but

little or no asphaltic (bituminous) matter. They can produce high-grade lubricating oils.

Asphaltic Based Crude Oils

Contain large proportions of asphaltic matter, and little or no paraffin. Some are

predominantly naphthenes so yield a lubricating oil that is more sensitive to temperature

changes than the paraffin-base crudes.

Mixed Base Crude Oils
The "gray area" between the two types above. Both paraffins and naphthenes are present,
as well as aromatic hydrocarbons. Most crudes fit this category.
Crude oils usually contain small amounts of combined oxygen, nitrogen and sulphur.
Crude oils obtained from various localities have widely different characteristics
indicating that the hydrocarbons have different properties. Nearly all crude oils will give
ultimate analyses within the limits shown below:

Classification of crude oils based on Gas Oil Ratio:

Black Oil ; solution GOR, (Rs) less than 2,000 scf/bbl

Volatile oil : solution GOR, (Rs) greater than 2,000 scf/bbl