Hydrocarbons, origin and availability

Oil and gas consist of hydrocarbons of varying composition from light gases such as methane and ethane, to complex mixtures of liquid substances more or less viscous at the surface temperature, such as naphtha (hydrocarbons of low viscosity) and bitumen (high viscosity hydrocarbons).

Both oil and gas may be combusted in oxygen at different temperatures according to the composition of the mixtures.

For that reason both are used as fuels for multiple purposes: for cooking (kerosene, natural gas), for car and truck engines (fuel oil and gasoline), aircraft engines (special gasoline), etc.

The exploitation of sources of oil and natural gas

Since ancient times human societies exploited the major hydrocarbons.

upwelling sites.

Where there were gas emissions and emissions of hydrocarbons and natural bitumen tar, local populations used them for lighting, heating and other purposes. This is the case of the tar lakes in Mesopotamia (Iraq) and the coastal regions of Venezuela.

From those beginnings, the role of oil as an energy source has been growing.

This trend has particularly accelerated since the invention of the combustion engine in the late nineteenth century.

Throughout the twentieth century, the consumption of oil increased exponentially up to the contemporary situation in which it represents the major source of energyworldwide.

While they are consumed everywhere, the production areas are restricted to certain geological areas, such as the foothills of some mountain ranges, continental shelves and surroundings of volcanic arcs.

Less frequently fields are located in continental shields and granite massifs.

Because of the economic role and its relative scarcity, it is of  of particular interest to know the origin, dynamics and location of sources of hydrocarbon deposits that can be exploited.

Theories about the origin of hydrocarbons

 Since  late 19th Century two theories about the origin of terrestrial hydrocarbons coexisted:

1) The biogenic theory, which held that hydrocarbons were of biological origin, resulting from the accumulation and “maturation” of fossil plants and animals, and

2)      The mineral or abiogenic theory, which argued that hydrocarbons were of mineral origin coming from inside the Earth, accumulating in areas with suitable geological conditions or sprouting in liquid or gas seeps on the surface.

The biogenic theory

Since the early 20th Century the biogenic hypothesis was imposed worldwide, particularly in Western countries.

Today, most geologists, both oil and structural geologists, sedimentologists and geophysicists, are inclined to think that hydrocarbons, oil and natural gas, have an old biological origin, and for that reason they are often called “fossil fuels”.

Being defined as fuels of biological origin, dependent on the accumulation of organic matter through geological time, their volumes would necessarily be restricted to the sedimentary basins and its vicinity. Sedimentary mantles are relatively thin (in geophysical terms). They are usually a few hundred or thousands of meters thick, and rarely exceed 10 kilometers, slightly more than one thousandth of the terrestrial radio (which is 6,500 km).

The conclusion of this prevailing scientific paradigm is that the exploitation of this resource gradually will fade and inevitably will end in the near future.

The mineral theory or abiogenic

The biogenic theory, which is accepted by most geologists, has been and is being challenged by some scientists, particularly Russians and Ukrainians, who argue that both oil and natural gas are of mineral origin, coming from inside the Earth, that their volumes are very large, and therefore it is unlikely that they will be exhausted in the foreseeable future.

The mineral theory was originally driven in the nineteenth century by famous Russian chemist Dmitri Mendeleev, French chemist Marcellin Berthelot and others.

In 1877 Mendeleev said:

“A capital fact is that oil is born in the depths of the earth, and that it is there where we must seek its origin” 1 

Another scientist who developed the theory of mineral oil was the Russian geologist Nikolai Alexandrovich Kudryavtsev.

This researcher proposed the abiotic hypothesis in 1951 based on the huge volumes of hydrocarbons accumulated in bitumimous sands of Alberta, Canada, which he thought inexplicable in the absence of a plausible mother rock.

In 1967, Ukrainian geologist Emmanuil Chekaliuk developed a thermodynamic theory of the origin of oil. He sustained that it formed at high pressure and temperature deep in the Earth’s mantle. At the time it was noted that the theory had been confirmed by experimental studies by J.F. Kenney and his Russian colleagues.  

In the decades from 1970 to 2000, based on the above work, the Austrian astrophysicist Thomas Gold formulated a theory about the origin and evolution of hydrocarbons which he considered were generated from depth. This hypothesis included several innovative elements introducing a real paradigmatic review of many terrestrial geological processesl.

Gold’s vision goes beyond the oil issue to address multiple aspects in the field of earth sciences, proposing, with very solid criteria, new ways to interpret many geological phenomena, including the origin of metallic minerals and ores.
From "Unexhaustible? Petroleum and natural gas", D.Anton, Piriguazú Ediciones.