24 - Is Oil Really Organic?...Why Some Believe It Is Not
Updated: Oct 2, 2018
Crude Oil is a fossil fuel that generated from the decomposition of organic material. Despite this widely accepted explanation of oil origin, some hold that petroleum is formed by non-biological processes, deep in the Earth’s mantle, and has migrated to the Earth's crust. This last contradicts the traditional view that oil is a finite source of energy, and promotes the notion that primordial hydrocarbons exist somewhere at great depths on earth (~700 km).
What Are The Theories That Explain Oil Origins?
Oil origin theories can be categorized in two groups:
Biotic, also known as biogenic, or organic
Abiotic, also knows as abiogenic, or inorganic
We are using the terms Organic and Inorganic Theory for simplification
Organic Theory
Organic theory is the most popular theory that explains oil origin. it holds that hydrocarbons generated mostly from microscopic marine organisms, that died and rested on the seafloor before sedimentary rocks came off the land and buried them beneath. Over millions of years, the sedimentation process buried the organic material deep enough where temperature and pressure rose to a point where it broke down the organic matter, which in turn released its hydrocarbon content.
The released hydrocarbon migrated upward. Where most quantities are believed to have seeped to surface and evaporated, while the rest had encountered a geological trap which prevented seepage, and allowed them to accumulate in what we call today an oil reservoir.
Inorganic Theory (or Hypothesis)
Although inorganic theory has been promoted by several scientists, it remains unpopular and surrounded by skepticism. This theory holds that hydrocarbons, mostly in the form of methane, were formed during the creation of the planet and do exist in the Earth's mantle.
These hydrocarbons migrated to the Earth's crust through deep faults. As they moved upward, they were exposed to chemical reactions that made them more complex in composition, complex enough to create oil.
Inorganic Theory Evidences
The inorganic theory has been promoted mainly by two scientists:
Nikolai Kudryavtsev in 1951 with his theory of Deep Abiotic Petroleum, and
Thomas Gold from 1979 to 1998 with his Deep Gas Theory
The following are the main claimed evidences that were presented by Inorganic Theory proponents in support of their theory:
Bituminous Sands Can’t be formed from Organic Matter
As per the Inorganic theory proponent, there is no source rock that can form such an enormous amount of oil. The only logical explanation (according to them) is the migration of hydrocarbons to surface through deep faults.
Sedimentary Reservoirs lie on top of fractured basement
Significant oil reservoirs are mainly found around deformation belts where tectonic forces could have created deep faults, allowing methane migration to Earth's crust resulting in the formation of giant oilfields.
Biomarkers are just contamination
As hydrocarbon migrates, it gets contaminated with bacteria that feed on hydrocarbons. This explains the organic footprint in oil.
Hydrocarbons exist in the Solar System
Hydrocarbons (mostly methane) are a major component of planetary bodies in our solar system. For instance, Jupiter, Saturn, Uranus and Neptune all have significant amount of methane in their atmosphere.
Mid-Oceanic ridges vent methane
Methane, coming from Earth's mantle, vents from mid-oceanic ridges as a result of hydrothermal activities
"Hydrocarbons are not biology reworked by geology (as the traditional view would hold), but rather geology reworked by biology" Thomas Gold
Inorganic Theory opponents view
Opponents of the inorganic theory have analyzed the theory and came up with several counter arguments, below are some of them:
Insufficient CO2
it is believed that there is insufficient carbon dioxide (CO2) in the Earth's crust to achieve the necessary reaction to form complex hydrocarbons.
Upper Mantle is too oxidizing
It is also believed that the Earth's upper mantle is too oxidizing for methane to exist is such abundance and to become the main form of carbon.
Source Rocks exist in bitumen
The argument about the source rocks and bitumen took place before the development of gas chromatography and mass spectrometry in the 1980's.
Thermodynamic refute inorganic theory
While the chemistry behind the inorganic theory might be proven correct in the laboratories, there is enough evidences that such chemical reaction is thermodynamically unlikely to take place in environments such as the Earth's mantle.
Magma not faults
It is believed that the only way to transport volatile gases from the mantle to surface is through the magma, and not through deep faults.
Temperature not faults
High geothermal gradients near deformation belts is what enhanced hydrocarbon formation, and not the migration of oil through faults.
Spacial hydrocarbon is organic
As recently uncovered, the methane found on Saturn's largest moon, Titan, contains organic compounds.
Final Words
Encountering oil in fractured basement is not common, but not unheard of as there might be several ways for it to exist other than the Inorganic theory.
On the other hand, some researchers proved that some of the inorganic theory chemistry can take place within earth, yet probably not in commercial quantities.
Therefore, the Inorganic theory might not be the correct explanation of oil origins. However; it cannot be dismissed yet.
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