What is petroleum?

Nearly everyone has heard or read about petroleum, the fuel that produces gasoline that people in the modern world still use every day. But not everyone has the rudimentary knowledge about this material known as “black gold”.

What is petroleum?
Raw petroleum.

Structure of the oil

Petroleum is a useful mineral that exists as a viscous, greasy liquid and is usually black (but can also be transparent or other colors). Chemically, oil is a mixture of hydrocarbons with sulfur, nitrogen, and other compounds. The smell of the oil can also vary, depending on the content of aromatic hydrocarbons and sulfur compounds in its composition.

The hydrocarbons present in oil are chemical compounds consisting of carbon (C) and hydrogen (H) atoms. Generally, the hydrocarbon formula is CxHy. The simplest hydrocarbon is methane, which has one carbon atom and four hydrogen atoms, its formula is CH4. Methane is a light hydrocarbon that is always present in oil.

Depending on the quantitative ratios of the different hydrocarbons that make up the oil, the properties of the oil also vary. Oil can be transparent and flow as easily as water, but it can also be black, thick and tar-like (tar).

From a chemical point of view, ordinary (traditional) petroleum has the following basic elements: Carbon – 84%; Hydrogen – 14%; Sulfur – 1-3% (as sulfides, disulphides, hydrogen sulphide or pure sulfur); Nitrogen – less than 1%; Oxygen – less than 1%; Metals – less than 1% (including iron, nickel, vanadium, copper, chromium, cobalt, molybdenum…); Salt – less than 1% (calcium chloride, magnesium chloride, sodium chloride…).

Oil and associated gas are located at a depth of a few tens of meters to 5-6 km, and at a depth of 6 km or less, there is only gas, and at a depth of 1 km or more – only oil. Most hydrocarbon-rich strata are located at depths of 1 to 6 km, where oil and gas exist in different combinations.

Oil usually accumulates in rock layers called reservoirs that have the function of collecting and storing mobile materials (such as oil, gas, water). Simply, the seam can be thought of as a very strong and dense sponge that is absorbent and holds oil.

Origin of oil

Oil formation is a very long process, going through many stages and taking up a period of time by some estimates of 50-350 million years.

The most commonly proven and recognized to date is the theory of the organic origin of the oil, otherwise known as the biological theory. According to this theory, oil is formed from the remains of microorganisms that existed tens or even hundreds of millions of years ago in large water bodies (especially in shallow water). When dead, these microorganisms create layers of material with high organic matter content at the bottom. Layer after layer, gradually sinking deeper and deeper (this process takes millions of years); the layers below are subjected to the increasing pressure of the layers above, accompanied by an increase in temperature. Since these biochemical-chemical processes occur in an anaerobic environment (without exposure to oxygen), organic matter is converted to hydrocarbons.

Some hydrocarbons are formed in the gaseous state (lightest), others in the liquid state (heavier), and some in the solid state (heaviest, like coal). Thus, the mobile mixture of hydrocarbons in the gas and liquid state, under the influence of high pressure, gradually moves by percolating through the rock layers towards places of lower pressure (usually upstream). above). The motion continues until the gaseous or liquid hydrocarbon encounters a thick layer of impervious rock in its path and is forced to stop. This is the trap, which is formed as a reservoir layer that is covered with an impenetrable layer of soil and rock. In this trap, a mixture of hydrocarbons gradually accumulates, forming what we commonly call an oil field.

Since the material density of oil is often much less than that of water (water is always present with the oil as evidence of its marine origin), the oil always moves upwards and accumulates at the top. water surface. If there is gas, the gas will be at the top, above the oil.

In some areas, hydrocarbons in the form of oil and gas do not encounter a trap on their way to the earth’s surface. When escaping to the ground, under the influence of many physicochemical factors, their structure is destroyed and they change to exist in the form of other matter.