Hybrid hypothesis of the formation of natural gas and oil in the bowels of the Earth
The combination of biogenic and abiogenic mechanisms allows us to explain the wide range of oil and gas deposits on Earth. Synthesis gas formed in deep processes can serve as an intermediate link between mantle reactions and the formation of organic hydrocarbons.
Discussions about the origin of oil have been going on for over 150 years. In the 19th century, the famous scientist Professor of Kyiv Polytechnic Dmytro Mendeleev put forward the hypothesis of the abiogenic origin of oil, suggesting that it is formed as a result of chemical reactions in the deep layers of the Earth. At the same time, most geologists supported the biogenic theory, according to which oil deposits are formed from the remains of organic matter under the influence of temperature, pressure and anaerobic processes.
Modern research shows that both hypotheses may be partially correct, which is supported by geochemical and experimental data.
Geological confirmation is:
• Deep oil and gas fields: Identification of hydrocarbon deposits in igneous and metamorphic rocks where biogenic origin is unlikely (e.g., oil fields in Precambrian rocks of Canada, Sweden, and Ukraine).
• Isotopic anomalies: Some deposits have carbon isotopic ratios (¹³C/¹²C) that are more consistent with inorganic origins than with the remains of ancient biomass.
• Mantle methane: Large emissions of methane have been detected in ocean floor hydrothermal systems, which are formed without the participation of organic matter.
Key mechanisms of hydrocarbon formation in the Earth’s interior
1. Biogenic pathway (sedimentary basins, organic origin)
The deposition of plankton, algae, bacteria, and organic matter in the bottom layers of oceans and seas.
Conditions: high pressure, temperature, anaerobic environment.
Catalytic processes involving clay minerals and microorganisms lead to the formation of oil and natural gas.
Long-term thermocatalytic decomposition of organic matter forms hydrocarbon molecules (CH₄, C₂H₆, C₃H₈, petroleum compounds).
Magnesium salts are one of the main components of seawater. Where millions of years ago there were sea basins that later dried up, an increased concentration of these salts was formed. Further deposition of layers with carbon sources (plant residues, wood that turned into coal, etc.) at this place can most likely become a source of gas and oil.
2. Abiogenic pathway (deep processes, igneous rocks)
In the bowels of the Earth (mantle, magmatic regions), there is high temperature and pressure, which contributes to the formation of synthesis gas (CO + H₂).
Studies confirm that magnesium oxide (MgO) and magnesium chloride (MgCl₂) can catalyze reactions between hydrogen and carbon:
MgO+2HCl+C→MgCl2+CO+H2
Synthesis gas (CO + H₂) is a key raw material for the formation of methane, gasoline, and gas condensate by the Sabatier Fischer-Tropsch reactions:
CO+3H2→CH4+H2O
nCO+(2n+1)H2→CnH2n+2+H2O
This explains the presence of gas and oil in deep igneous rocks where organic residues are absent.
3. Mechanism of interaction between biogenic and abiogenic processes
Synthesis gas, formed in deep processes, migrates through faults into sedimentary basin zones, interacting with organic residues.
Natural gas is formed both by the decomposition of organic matter and by chemical reactions between mantle gases and sedimentary rocks. The interaction of mantle hydrogen (H₂) and carbon monoxide (CO) with organic material in sedimentary deposits produces methane (CH₄) and long-chain hydrocarbons.
The influence of mantle fluids in the form of gases and liquids containing hydrogen (H₂), methane (CH₄), carbon dioxide (CO₂), carbon monoxide (CO), heavy hydrocarbons (C₂H₆, C₃H₈, C₄H₁₀ and longer chains) on oil deposits explains the formation of heavy hydrocarbons and their isotopic anomalies.
Evidence and natural analogues
Analysis of the isotopic composition of deep gases (with a high content of ³He) indicates the mantle origin of some of the deposits. Well-known examples of deep gas deposits located in igneous rocks are the Ukrainian Shield and the Oceanic Ridges.
Volcanic and hydrothermal sources rich in methane and hydrocarbons that cannot be explained by biogenic means. However, high-temperature experiments have shown that methane can be formed from carbon and hydrogen at pressures typical of the deep crust.
Laboratory Fischer-Tropsch studies have confirmed the possibility of the formation of long-chain hydrocarbons, including those involving MgO, MgCl₂, and CO + H₂, under conditions similar to the Earth’s mantle.
As we can see, this hybrid model opens up new prospects for oil and gas exploration not only in traditional sedimentary basins, but also in magmatic regions and deep faults of the Earth.
