The abiogenic petroleum origin hypothesis proposes that most of Earth's petroleum and natural gas deposits were formed inorganically, commonly known as abiotic oil.Abiotic Oil a Theory Worth Exploring: Oil may not be formed the way we think it is. U.S. News & World Report, Sept. 14, 2011 Scientific evidence overwhelmingly supports a biogenic origin for most of the world's petroleum deposits. Mainstream theories about the formation of hydrocarbons on Earth point to an origin from the decomposition of long-dead organisms, though the existence of hydrocarbons on extraterrestrial bodies like Saturn's moon Titan indicates that hydrocarbons are sometimes naturally produced by inorganic means. A historical overview of theories of the abiogenic origins of hydrocarbons has been published.
Thomas Gold's "deep gas hypothesis" proposes that some natural gas deposits were formed out of hydrocarbons deep in the Earth's mantle. Earlier studies of mantle-derived rocks from many places have shown that hydrocarbons from the mantle region can be found widely around the globe. However, the concentration of such hydrocarbons is low. While there may be large deposits of abiotic hydrocarbons, globally significant amounts of abiotic hydrocarbons are deemed unlikely.
Overview hypotheses Some abiogenic hypotheses have proposed that oil and gas did not originate from fossil deposits, but have instead originated from deep carbon deposits, present since the formation of the Earth.
The abiogenic hypothesis regained some support in 2009 when researchers at the KTH Royal Institute of Technology in Stockholm reported they believed they had proven that fossils from animals and plants are not necessary for crude oil and natural gas to be generated.
History An abiogenic hypothesis was first proposed by Georgius Agricola in the 16th century and various additional abiogenic hypotheses were proposed in the 19th century, most notably by Prussian geographer Alexander von Humboldt (1804), the Russian chemist Dmitri Mendeleev (1877) and the French chemist Marcellin Berthelot. Abiogenic hypotheses were revived in the last half of the 20th century by Soviet scientists who had little influence outside the Soviet Union because most of their research was published in Russian. The hypothesis was re-defined and made popular in the West by astronomer Thomas Gold, a prominent proponent of the abiogenic hypothesis, who developed his theories from 1979 to 1998 and published his research in English.
Abraham Gottlob Werner and the proponents of neptunism in the 18th century regarded basaltic sills as solidified oils or bitumen. While these notions proved unfounded, the basic idea of an association between petroleum and magmatism persisted. Von Humboldt proposed an inorganic abiogenic hypothesis for petroleum formation after he observed petroleum springs in the Bay of Cumaux (Cumaná) on the northeast coast of Venezuela. He is quoted as saying, "the petroleum is the product of a distillation from great depth and issues from the primitive rocks beneath which the forces of all volcanic action lie". Other early prominent proponents of what would become the generalized abiogenic hypothesis included Dmitri Mendeleev and Berthelot.
In 1951, the Soviet geologist Nikolai Alexandrovitch Kudryavtsev proposed the modern abiotic hypothesis of petroleum. On the basis of his analysis of the Athabasca Oil Sands in Alberta, Canada, he concluded that no "source rocks" could form the enormous volume of hydrocarbons, and therefore offered abiotic deep petroleum as the most plausible explanation. (Humic coals have since been proposed for the source rocks.) Others who continued Kudryavtsev's work included Petr N. Kropotkin, Vladimir B. Porfir'ev, Emmanuil B. Chekaliuk, Vladilen A. Krayushkin, Georgi E. Boyko, Georgi I. Voitov, Grygori N. Dolenko, Iona V. Greenberg, Nikolai S. Beskrovny, and Victor F. Linetsky.
Following Thomas Gold's death in 2004, Jack Kenney of Gas Resources Corporation has recently come into prominence as a proponent of the theories, supported by studies by researchers at the Royal Institute of Technology (KTH) in Stockholm, Sweden.
Foundations of abiogenic hypotheses
Within the mantle, carbon may exist as hydrocarbons—chiefly methane—and as elemental carbon, carbon dioxide, and carbonates. The abiotic hypothesis posits that the full suite of hydrocarbons found in petroleum can be generated either in the mantle by abiogenic processes, or by biological processing of those abiogenic hydrocarbons, and that the source-hydrocarbons of abiogenic origin can migrate out of the mantle into the crust until they escape to the surface or are trapped by impermeable strata, forming petroleum reservoirs.
Abiogenic hypotheses generally reject the supposition that certain molecules found within petroleum, known as biomarkers, are indicative of the biological origin of petroleum. They contend that these molecules mostly come from microbes feeding on petroleum in its upward migration through the crust, that some of them are found in meteorites, which have presumably never contacted living material, and that some can be generated abiogenically by plausible reactions in petroleum.
Some of the evidence used to support abiogenic theories includes: ProponentsItem Gold The presence of methane on other planets, meteors, moons and comets Gold, Kenney Proposed mechanisms of abiotically chemically synthesizing hydrocarbons within the mantle Kudryavtsev, Gold Hydrocarbon-rich areas tend to be hydrocarbon-rich at many different levels Kudryavtsev, Gold Petroleum and methane deposits are found in large patterns related to deep-seated large-scale structural features of the crust rather than to the patchwork of sedimentary deposits Gold Interpretations of the chemical and isotopic composition of natural petroleum Kudryavtsev, Gold The presence of oil and methane within non-sedimentary rocks upon the Earth Gold The existence of methane hydrate deposits Gold Perceived ambiguity in some assumptions and key evidence used in the conventional understanding of petroleum origin. Gold Bituminous coal creation is based upon deep hydrocarbon seeps Gold Surface carbon budget and oxygen levels stable over geologic time scales Kudryavtsev, Gold The biogenic explanation does not explain some hydrocarbon deposit characteristics Szatmari The distribution of metals in crude oils fits better with upper serpentinized mantle, primitive mantle and chondrite patterns than oceanic and continental crust, and show no correlation with sea water Gold The association of hydrocarbons with helium, a noble gas
Recent investigation of abiogenic hypotheses
, little research is directed towards establishing abiogenic petroleum or methane, although the Carnegie Institution for Science has reported that ethane and heavier hydrocarbons can be synthesized under conditions of the upper mantle. Research mostly related to astrobiology and the deep microbial biosphere and serpentinite reactions, however, continues to provide insight into the contribution of abiogenic hydrocarbons into petroleum accumulations. Rock porosity and migration pathways for abiogenic petroleum.Kitchka, A., 2005. Juvenile Petroleum Pathway: From Fluid Inclusions via Tectonic Pathways to Oil Fields. AAPG Research Conference, Calgary, Canada, 2005.Abstract Mantle peridotite serpentinization reactions and other natural Fischer–Tropsch analogs. Primordial hydrocarbons in meteorites, comets, asteroids and the solid bodies of the Solar System. Primordial or ancient sources of hydrocarbons or carbon in Earth. Primordial hydrocarbons formed from hydrolysis of metal carbides of the iron peak of cosmic elemental abundance (chromium, iron, nickel, vanadium, manganese, cobalt). Isotopic studies of groundwater reservoirs, sedimentary cements, formation gases and the composition of the noble gases and nitrogen in many oil fields.
Common criticisms include:
If oil was created in the mantle, it would be expected that oil would be most commonly found in fault zones, as that would provide the greatest opportunity for oil to migrate into the crust from the mantle. Additionally, the mantle near subduction zones tends to be more oxidizing than the rest. However, the locations of oil deposits have not been found to be correlated with fault zones, with some exceptions.
Proposed mechanisms of abiogenic petroleum Primordial deposits Thomas Gold's work was focused on hydrocarbon deposits of primordial origin. Meteorites are believed to represent the major composition of material from which the Earth was formed. Some meteorites, such as carbonaceous chondrites, contain carbonaceous material. If a large amount of this material is still within the Earth, it could have been leaking upward for billions of years. The thermodynamic conditions within the mantle would allow many hydrocarbon molecules to be at equilibrium under high pressure and high temperature. Although molecules in these conditions may disassociate, resulting fragments would be reformed due to the pressure. An average equilibrium of various molecules would exist depending upon conditions and the carbon-hydrogen ratio of the material.
Creation within the mantle Russian researchers concluded that hydrocarbon mixes would be created within the mantle. Experiments under high temperatures and pressures produced many hydrocarbons—including n-alkanes through C10H22—from iron oxide, calcium carbonate, and water. Because such materials are in the mantle and in subducted crust, there is no requirement that all hydrocarbons be produced from primordial deposits.
Hydrogen generation Hydrogen gas and water have been found more than deep in the upper crust in the Siljan Ring boreholes and the Kola Superdeep Borehole. Data from the western United States suggests that aquifers from near the surface may extend to depths of to . Hydrogen gas can be created by water reacting with silicates, quartz, and feldspar at temperatures in the range of to . These minerals are common in crustal rocks such as granite. Hydrogen may react with dissolved carbon compounds in water to form methane and higher carbon compounds. Proceedings of the Third International Symposium on Observation of the Continental Crust through Drilling held in Mora and Orsa, Sweden, September 7–10, 1987
One reaction not involving silicates, but only iron(II) oxide, which can produce hydrogen is: Ferrous oxide + water → magnetite + hydrogen
This redox reaction closely resembles the Schikorr reaction involving the partial oxidation and conversion of iron(II) hydroxide (green rust) in magnetite, hydrogen and water: Ferrous hydroxide → magnetite + hydrogen + water
The above reaction operates best at low pressures. At pressures greater than , almost no hydrogen is formed.
Thomas Gold reported that hydrocarbons were found in the Siljan Ring borehole and in general increased with depth, although the venture was not a commercial success.Gold, Thomas. 2001. The Deep Hot Biosphere: They Myth of Fossil Fuels. Copernicus Books. New York. pp. 111-123. (softcover edition).
However, several geologists analysed the results and said that no hydrocarbon was found.
Serpentinite mechanism
In 1967, the Soviet scientist Emmanuil B. Chekaliuk proposed that petroleum could be formed at high temperatures and pressures from inorganic carbon in the form of carbon dioxide, hydrogen or methane.