Petroleum: characteristics, structure, types, obtaining, uses

It is therefore a dark, oily mixture, composed of several groups of organic molecules, among which hydrocarbons stand out, the lightest being the most highly valued by the chemical and fuel industry.

Oil pump

Oil was already used for approximately 6,000 years in Assyria and Babylon, whose inhabitants collected it in oil outcrops, in the form of bitumen near the Euphrates, using bitumen to glue bricks. It therefore consisted of one of its many indirect uses.

The first distillation of oil is attributed to the Persian sage Al-razi in the 9th century, who invented an alembic that he used to obtain kerosene. More than a thousand years later, it would be discovered that this substance could be broken down into many more distillates, each with its own properties, compositions, and applications.

Oil has served as a raw material for the production of many derivatives, including most plastics, used in the manufacture of refrigerators, airplanes, automobiles, etc. However, the terrible impact of plastic on marine ecosystems has driven the search for renewable and ecologically friendly sources for the synthesis of biodegradable plastics.

Oil characteristics


Different types of oil (from the lightest on the left, to the heaviest on the right), where it is appreciated that it is not always a dark and super viscous liquid. Source: Glasbruch2007 / CC BY-SA (

Oil is a liquid of variable color, and can be black or dark brown. It can also have a tan, yellowish or greenish hue, its coloration being related to its chemical composition.

It is found under the surface of the earth or the bottom of lakes or seas, so to be extracted, a drilling procedure must be carried out to obtain it.

Oil contains hundreds of components (hydrocarbons), which are obtained through the fractional distillation technique. This produces the separation of hydrocarbons as well as other components according to the difference between their boiling points .


Oil is a fossil fuel that originated from dead organisms, such as phytoplankton, zooplankton, and algae that were deposited to the bottom of ancient seas. Later, they were covered by sediments that formed sedimentary rocks.

These rocks structured a geological basin. There, the organic material, subjected to high temperatures and pressures for millions of years, in addition to suffering bacterial degradation, originated hydrocarbons and other millions of related compounds.

Oil has the following chemical composition: carbon 83 to 85%, hydrogen 10 to 14%, nitrogen 0.1 to 2%, oxygen 0.05 to 1.5%, and sulfur 0.05 to 6%. This composition is highly dependent on the geographic locations of the oil, as well as its type and amounts of dissolved heavy metals.

Chemical structure of petroleum

Oil is a mixture of many organic compounds , the majority of which are hydrocarbons. Therefore, they are molecules with carbon skeletons and linked to hydrogen atoms. However, we also find oxygen, nitrogen and sulfur heteroatoms, integrating other types of compounds that enrich oil.

Thus, the chemical structure of these molecules can be very varied. For example: paraffins and isoparaffins consist of saturated hydrocarbons, while olefins have one double bond. We also have naphthenes, which are cyclic but saturated molecules, such as cyclohexane and decalin.

Among the compounds with cyclic structures are also those of aromatic types: naphthalene, anthracene, benzene, toluene, phenanthrene, etc.

In petroleum there are families of polar macromolecules called resins and asphaltenes, the latter being responsible for dark colorations and high viscosities. Likewise, we have petroporphyrins, within which many heavy metals are trapped.

Thus, oil has molecules with small structures, linear, branched, unsaturated chains, aromatic rings, conjugated systems, and even a conglomerate of rings that resemble carbonaceous archipelagos.

How do you get oil?

Oil drilling rig

Oil fields or geological basins of oil are found in the subsoil, so obtaining oil is a difficult and expensive process. Obtaining oil can be subdivided into two phases: exploration and drilling-extraction.


The exploration is the realization of the pertinent investigation that allows the location of the oil deposits. This research is based on geological, geophysical, geochemical, seismographic and exploratory drilling studies that indicate the profitability of the exploitation of the deposits.

The exploration is carried out in three stages:

  • Preparation of geological maps, based on geological studies and with the support of satellite photographs.
  • Identification of areas of interest that present suitable conditions for oil exploitation.
  • Carrying out exploratory drilling that confirms the existence of exploitable oil fields.


Oil and gas drilling tower

The drilling rig consists of a steel tower approximately 50 m high, whose function is to lower and raise the drilling instrument.

The drilling instrument is a metal body that ends in a drill bit or trepan. Depending on the terrain the bit will have teeth to break through the rocks, knives to separate the chipped rocks, and diamonds to pierce through the terrain.

The bit can drill between 35 and 600 cm per hour, as it rotates driven by a motor. During drilling, drilling mud is injected, consisting of water, clay and chemicals that seek to give consistency to the well wall and refresh the bit.

As drilling progresses, 12 m tubes are placed, each one constituting the well casing, the purpose of which is to prevent the walls of the well from collapsing.

Drilling tool

When the geological basin or oil field is reached, the oil rises driven by its outward pressure. But when the pressure drops, it is necessary to place a deep extraction pump: these pumps are the rocker arms that identify the oil fields.

Types of oil

Industrial oil storage facility

The types of oil have been established based on criteria such as its density , sulfur content, and composition. Likewise, they can be classified according to their origin.

According to its density

The API (American Petroleum Institute) is used as a reference term to name the density of oil, establishing this based on the density of the water taken as a reference (1000 kg / m 3 ).

So we have for oil or crude:

  • Light: API> 31.1º (less than 870 kg / m 3 ).
  • Medium: API between 31.1º and 23.3º (870 to 920 kg / m 3 ).
  • Heavy: API between 23.3º and 10º (920 to 1000 kg / m 3 ).
  • Extra heavy: API <10º (> 1000 kg / m 3 ).

The scale has been created in such a way that light crudes have high API values, while heavy crudes have low API values.

According to its sulfur content

One of the most important impurities in oil is sulfur, which is why crude oils are classified based on their sulfur content in:

  • Sweet crude: 0.5% sulfur.
  • Acidic crude: more than 2% sulfur.

According to its composition

Oil can be classified according to its composition in:

Paraffin-based oils

There is a predominance of saturated or paraffinic hydrocarbons.

Asphalt or naphthenic base oils

Ethylene and diethylene, cyclic (naphthenic) and benzene or aromatic hydrocarbons predominate.

Mixed base oils

Any type of hydrocarbons are included in its composition.  

According to its origin (crude reference)

Among other reference crude oils, we have the following:


It comes from deposits in the North Sea, between Norway and the English region of Scotland.

West Texas Intermediate (WTI)

It is the lightest oil produced in the United States.

OPEC basket

It is a mixture of crude oil produced by the organization of oil exporting countries. This crude is heavier than the previous ones.

Tapis (Malaysia)

It is a very light oil.

Petroleum derivatives

Offshore oil platform

Most of the fractional distillation is made up of fuels, which represent 86% of the total petroleum derivatives.

Petroleum fuels are present in diesel and other related chemicals, such as jet fuels and heavy oil fuels.

In addition to fuels, oil has other important derivatives, including: asphalt, roofing tar, paraffin wax, lubricants, microcrystalline wax, refined bitumen, petroleum coke and sulfur, a petroleum pollutant.

Oil refineries provide sulfur, which is used in industry. In addition, they produce detergents, paraffins, solvents and other petrochemical products.

The latter are chemical compounds present in oil that are transferred to the petrochemical industry for processing. Petrochemicals include olefins.

Olefins include ethylene, propylene, and butadiene. Ethylene glycol is produced from ethylene, which serves as the basis for obtaining polyester fibers and resins, as well as for the synthesis of ethyl alcohol. In addition to olefins, there are aromatic petrochemicals.

Oil uses


Car refueling gasoline

Gasoline, some variants of kerosene, and diesel are used as fuels in passenger vehicles, food, industrial products and equipment, drinking water, etc. In addition, gases such as propane are used in homes and industries in combustion processes.

Gasoline is the petroleum derivative that is produced in the highest proportion, being a mixture of hydrocarbons with a carbon number between 4 and 12. It is produced by fractional distillation in a temperature range between 40 and 200 ºC. It is the favorite product of petroleum, along with diesel, kerosene, plastics, and many others.


Plastics are made from petroleum derivatives, for example, olefins. Several chemical compounds belong to them, among them: ethylene, propylene and butadiene, which make up three essential monomers for the synthesis of polymers such as polyethylene, polypropylene and polybutadiene, among others.

Ethylene is the raw material for obtaining polyester fibers and resins. Polyester is used in the manufacture of fabrics, in the manufacture of corrosion resistant equipment and ducts.

Meanwhile, ethylene dichloride is used for the synthesis of vinyl chloride. Vinyl chloride serves as the basis for the manufacture of polyvinyl chloride (PVC), plastic used in coating, pipes for drinking water and plumbing, etc.

Propylene is used in the manufacture of polypropylene plastic, widely used in the packaging of food and medical products.

Butadiene, on the other hand, is used in the manufacture of carpet fibers, paper coating and plastic pipes.

The aromatic chemicals benzene, toluene and xylene (BTX) are transformed into polymers and plastics. Nylon, a thermoplastic, is also made from petroleum derivatives.


Oil serves as a source of oils for machinery and engines of transport vehicles that act by reducing friction between metallic mechanical components, thus increasing their life. Meanwhile, petroleum jelly is a lubricant used in personal care.

Heavy oil derivatives

The asphalt forms an agglomerate used in the paving of avenues and roads. Pitch and tar form a complex that is used in roof waterproofing. Petroleum coke is used to obtain solid fuels. Paraffin wax, on the other hand, is used in making candles and wax colors.


Oil has been used to obtain or manufacture paint thinners, such as thinner, solvents, ethyl alcohol, aspirin, lipstick, paints, chewing gum, nylon pantyhose and leggings, solar panels, eyeliners, varnishes, bottles plastics, detergents, insecticides and fungicides.

It has also allowed the production of acrylics, isopropyl alcohol, synthetic rubber, soaps, fertilizers, medicines, flooring materials, recording discs and tapes, refined bitumen, etc.

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