The word “oil” is usually used for a description of a fossil mineral. There are several equivalent terms that are also used to describe this material. They include: “crude oil,” “petroleum,” and more rare, “naphtha.” The word oil has Latin origin coming from oleum. When talking about the usage of this word, it should be noted, that petroleum is used as often as oil.
What is oil from geological view?
Oil is a fossil mineral which is spread through the Earth’s crust in different parts of the world. This is a fossil that has formed millions of years ago due to different geological and other processes. Its masses are usually collected in oil fields. The amount of resources of the mineral can be different for different oil fields, as well as it can vary in its composition.
There are several theories which explain the origin of oil. Among them, biogenic (organic) and abiogenic (inorganic) theories are most widely accepted by scientific words. Both of the explanations give the answer to the question “what is oil?” in their own way, radically different from one another.
From biogenic point of view, oil contains substances that were formed by means of anaerobic decomposition of animal and plant matter that was collected on the bottoms of huge water reservoirs, such as lakes, seas and oceans. Over the millions of years the bottoms of ancient seas were covered with the dead organic matter. This matter was then covered with the sand brought by the water flows. This sand and other solid particles caused the isolation of the animal and plant remains from water and any oxygen dissolved in it. They also created elevated pressure underneath. At the same time, the geological structure of the planet’s surface was changing, and these traps of organic remains were put lower beneath the Earth’s surfaces. That only caused greater increase in pressure and temperature. In addition, the organic matter was a media for living and development of microorganisms. These bacteria were gradually decomposing organic residua. Finally, over the millions of years due to all these physical and biological processes, the substances that make up oil today have been formed.
Supporters of inorganic (abiogenic) theory argue that oil has been formed due to geological processes that involved chemical reactions between inorganic substances, such as carbides and water. Water was reaching carbide minerals through the crack in the Earth’s crust. When a carbide reacts with water, different hydrocarbons (the main constituents of petroleum) are formed. These hydrocarbons could be transformed from one class to another, therefore, this could explain the variety of them which exists in the crude. Organic markers are explained by bacteria living in extreme conditions deep in under the ground.
Today, more and more scientists support a theory of mixed origin, which combines organic and inorganic ones.
What is oil? Chemical explanation
Oil is a complex mixture of millions of gaseous, solid and liquid substances of different molecular size and functionality. They include mainly hydrocarbons (substances that are composed of carbon and hydrogen atoms only) of paraffin, naphthene and aromatic structure. The amount of hydrocarbons present in oil can range from 50% to 97%. Also, oil contains nonhydrocarbon constituents, such as nitrogen-, oxygen- and sulfur-containing substances. The amount of these compounds is rather small, however the have a great influence on physical and chemical properties of products derived from petroleum. There also some trace amounts of metals, usually, nickel and vanadium, as parts of organic substances.