Get to know the types of crude oil

Author: Asadullah Gholampour
Light crude oil with low specific gravity is much more important than heavy oil. Typically, light crude oil is richer in saturated hydrocarbons, especially straight-chain alkanes, compared to heavy crude oil.
Very heavy crude oil and bitumen have a high viscosity and are semi-solid containing a large amount of heteroatom compounds (nitrogen, oxygen, and sulfur) and a small amount of hydrocarbon, which even reaches 30-40%. Metal compounds such as nickel, vanadium (mostly in the form of vanadyl and iron ions) are also present in crude oil. Heavy crude oil is crude oil that has a high concentration and does not flow easily in the oil extraction well. This type of oil is called heavy because its relative density is higher than light crude oil. In the strict definition, any type of liquid crude oil whose API density is lower than 20 degrees is called heavy crude oil. This type of oil is more viscous than light crude oil. In geology, oil from oil sands is classified as extra heavy oil. Heavy and extra-heavy crude oil are similar to the residue left over from refining light crude oil. Their difference with light oil is high density, stickiness at tank temperature, high percentage of sulfur, nitrogen, oxygen and heavy metals.
The amount of heavy and extra-heavy crude oil reserves in the world is more than twice that of conventional crude oil, and the largest reserves of heavy and extra-heavy crude oil in the world are in Canada and Venezuela. The cost of extracting and refining heavy crude oil is more complicated and higher, and for this reason, their price is lower than light crude oil and they have fewer customers.
There are different types of crude oil. Perhaps no two crude oils can be found whose characteristics are exactly the same, but it is possible to obtain characteristics through which, and by comparing them with the characteristics of leading crude oils such as Brent, WT, and Dubai, a reasonable price for them in the market. Gained. Among these features are lightness and heaviness, sourness and sweetness. The amount of sulfur in oil is one of the most important factors affecting its price.

Hydrogen sulfide (H2S), which is also known as sulfhydric acid or hydrosulfuric acid, increases the corrosiveness of distillation devices due to its acidic properties and causes irreparable damage to the environment due to its toxicity. Therefore, its removal from crude oil is necessary and expensive. Hydrocarbon molecules are lighter than water. These molecules move from the place where they are formed and are called reservoir rocks, through the empty spaces (pores) filled with water, and of course, always towards the top of the surface.
Hydrocarbons flow to the surface as tar pits, oil seeps, or natural gas seeps unless their flow is cut off or trapped. Paraffinic and naphthenic oils are generally light, although they are often waxy and viscous, and their sulfur content is usually low and are considered mature oils. Most of the world’s crude oils are paraffinic, naphthenic, and aromatic (intermediate). Petroleum oils are very few. According to the available crude oil reserves, the aromatic (intermediate) type is the most important, which includes the huge Cretaceous and Jurassic deposits of the Middle East. In each homogeneous series, the stability increases as the number of carbon atoms decreases.
Methane (CH4) is the most stable hydrocarbon. The stability of paraffins and naphthenes is not much different. There is an inverse correlation between the presence of oil and the rank of coal, as a result, whenever the rank of coal rises, the percentage of carbon rises and there is no more oil, because oil is relatively sensitive to metamorphosis. Various products are obtained by refining crude oil by distillation or absorption into various components of hydrocarbon groups. Most of these products are transformed into important consumables by changing their physical and molecular structure through cracking, reforming and other processes.
In the next step, these materials lead to intermediate or final products during separation processes, such as extraction, hydrogenation and sweetening.