The properties of crude oil include physical properties and chemical properties. Physical properties include color, density, viscosity, freezing point, solubility, calorific value, fluorescence, optical rotation and so on. Chemical properties include chemical composition, composition and impurity content. Wax content refers to the percentage of paraffin and ceresin in crude oil at normal temperature and pressure. Paraffin wax is a white or yellowish solid, composed of higher alkanes, and its melting point is 37℃-76℃. Paraffin is dissolved in oil in the form of colloid underground, and can be separated from oil when the pressure and temperature decrease. The temperature at which paraffin in formation crude oil begins to crystallize and precipitate is called wax precipitation temperature. The higher the wax content, the higher the wax precipitation temperature.

Wax deposition temperature is high, and oil wells are prone to wax deposition, which is not conducive to oil well management. The asphaltene content in crude oil is less, generally less than 65438 0%. Asphaltene is a black solid substance with high molecular weight (greater than 1000) and polycyclic structure. Insoluble in ethanol and petroleum ether, soluble in benzene, chloroform and carbon disulfide. When the asphaltene content increases, the quality of crude oil deteriorates.

Hydrocarbons in crude oil are mainly divided into alkanes, cycloalkanes and aromatics. According to the different composition of hydrocarbons, it can be divided into three types: paraffin-based oil, naphthenic base oil and intermediate base oil. Paraffin-based petroleum contains more alkanes; Cycloalkyl petroleum contains more naphthenes and aromatics; Intermediate base oil is between the two. The crude oil that has been exploited in China is mainly based on low sulfur paraffin. Crude oil in Daqing and other places belongs to this category. Among them, the most representative Daqing crude oil has low sulfur content, high wax content and high freezing point, which can produce high-quality kerosene, diesel oil, solvent oil, lubricating oil and industrial paraffin. Shengli crude oil has high gum content (29%), high specific gravity (about 0.9 1) and high wax content (about 15-2 1%), which belongs to the sulfur-bearing intermediate group. Gasoline fraction has good lead sensitivity and is rich in naphthenes and aromatics, so it is a good reforming raw material. On average, crude oil consists of the following elements or compounds:

Carbon -84%

Hydrogen-14%

Sulfur-1 to 3% (hydrogen sulfide, sulfide, disulfide and elemental sulfur)

Nitrogen-less than 1% (basic compound containing amino group)

Oxygen-less than 1% (existing in organic compounds such as carbon dioxide, phenol, ketone and carboxylic acid)

Metal-less than 1% (nickel, iron, vanadium, copper, arsenic)