Crude oil, also known as “black gold“, is a liquid or semi-solid combustible material. Like coal and natural gas, it is a non-renewable fossil fuel and one of the important primary energy sources in the world.It is composed of a very complex mixture of different hydrocarbons, mainly consisting of oily (hydrocarbon), asphaltene (dark brown or black brittle solid), colloid, and carbonaceous (a non-hydrocarbon).
The physical properties of crude oil vary from place to place and from reservoir to reservoir. There is no fixed chemical composition and therefore no fixed physical constants.Generally speaking, the density of crude oil is 0.8~1.0g/cm3, viscosity range is very wide, freezing point difference is also very big (-60℃~32℃), boiling point range is above 500℃ at room temperature, soluble in a variety of organic solvents, insoluble in water, but can form emulsion with water.
The chemical elements that make up crude oil, chiefly the hydrocarbons of carbon and hydrogen.The proportion of carbon in crude oil is 83%~87%, hydrogen 11%~14%, sulfur (0.06%~0.8%), nitrogen (0.02%~1.7%), oxygen (0.08%~1.82%), trace non-metallic elements (phosphorus, chlorine, iodine, etc.) and trace metal elements (nickel, vanadium, iron, antimony) and other impurities.
Although the basic elements of crude oil are similar, a large variety of crude oils are produced from different regions and formations.In the crude oil of different origin, the structure and proportion of various hydrocarbons vary greatly, among which straight-chain alkanes, cycloalkanes and aromatic hydrocarbons are the main components, and the proportion usually reaches more than 90%.However, the content of different hydrocarbons often varies greatly, and the composition of non-hydrocarbon compounds, that is, those containing sulfur, nitrogen and oxygen, is very small.When crude oil is extracted, it also contains metal salts, mainly a mixture of sodium, calcium, magnesium and other chlorides. The salt content is usually 0.02% to 0.055%. Therefore, after crude oil is extracted from the ground, it can be processed by dehydration and desalting.
Crude oil is a heterogeneous commodity, and the quality of crude oil from different origins often varies greatly, so it is difficult to be standardized like metals and other industrial products. The characteristics of diversified quality of crude oil are also reflected in the production, trade, processing and pricing of crude oil.