Abiogenic petroleum origin

The abiogenic petroleum origin hypothesis proposes that most of Earth's petroleum and natural gas deposits were formed inorganically, commonly known as abiotic oil. Scientific evidence overwhelmingly supports a biogenic origin for most of the world's petroleum deposits.

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. 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.

| Gold, Kenney

| Proposed mechanisms of abiotically chemically synthesizing hydrocarbons within the mantle

| Gold

| The existence of methane hydrate deposits

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| Gold

| Surface carbon budget and oxygen levels stable over geologic time scales

| Gold

| The association of hydrocarbons with helium, a noble gas 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.
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.

One reaction not involving silicates, but only iron(II) oxide, which can produce hydrogen is:

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.

However, several geologists analysed the results and said that no hydrocarbon was found. is via natural analogs of the Fischer–Tropsch process known as the serpentinite mechanism or the serpentinite process.

:(2n+1)

Serpentinites are ideal rocks to host this process as they are formed from peridotites and dunites, rocks which contain greater than 80% olivine and usually a percentage of Fe-Ti spinel minerals. Most olivines also contain high nickel concentrations (up to several percent) and may also contain chromite or chromium as a contaminant in olivine, providing the needed transition metals.

However, serpentinite synthesis and spinel cracking reactions require hydrothermal alteration of pristine peridotite-dunite, which is a finite process intrinsically related to metamorphism, and further, requires significant addition of water. Serpentinite is unstable at mantle temperatures and is readily dehydrated to granulite, amphibolite, talc–schist and even eclogite. This suggests that methanogenesis in the presence of serpentinites is restricted in space and time to mid-ocean ridges and upper levels of subduction zones. However, water has been found as deep as , so water-based reactions are dependent upon the local conditions. Oil being created by this process in intracratonic regions is limited by the materials and temperature.

Serpentinite synthesis

A chemical basis for the abiotic petroleum process is the serpentinization of peridotite, beginning with methanogenesis via hydrolysis of olivine into serpentine in the presence of carbon dioxide.

Biotic (microbial) hydrocarbons

The "deep biotic petroleum hypothesis", similar to the abiogenic petroleum origin hypothesis, holds that not all petroleum deposits within the Earth's rocks can be explained purely according to the orthodox view of petroleum geology. Thomas Gold used the term "the deep hot biosphere" to describe the microbes which live underground. Research continues to attempt to characterise crustal sources of methane as biogenic or abiogenic using carbon isotope fractionation of observed gases (Lollar & Sherwood 2006). There are few clear examples of abiogenic methane-ethane-butane, as the same processes favor enrichment of light isotopes in all chemical reactions, whether organic or inorganic. δ13C of methane overlaps that of inorganic carbonate and graphite in the crust, which are heavily depleted in 12C, and attain this by isotopic fractionation during metamorphic reactions.

One argument for abiogenic oil cites the high carbon depletion of methane as stemming from the observed carbon isotope depletion with depth in the crust. However, diamonds, which are definitively of mantle origin, are not as depleted as methane, which implies that methane carbon isotope fractionation is not controlled by mantle values.

Commercially extractable concentrations of helium (greater than 0.3%) are present in natural gas from the Panhandle-Hugoton fields in the US, as well as from some Algerian and Russian gas fields.

Helium trapped within most petroleum occurrences, such as the occurrence in Texas, is of a distinctly crustal character with an Ra ratio of less than 0.0001 that of the atmosphere.

Biomarker chemicals

Certain chemicals found in naturally occurring petroleum contain chemical and structural similarities to compounds found within many living organisms. These include terpenoids, terpenes, pristane, phytane, cholestane, chlorins and porphyrins, which are large, chelating molecules in the same family as heme and chlorophyll. Materials which suggest certain biological processes include

The presence of these chemicals in crude oil is a result of the inclusion of biological material in the oil; these chemicals are released by kerogen during the production of hydrocarbon oils, as these are chemicals highly resistant to degradation and plausible chemical paths have been studied. Abiotic defenders state that biomarkers get into oil during its way up as it gets in touch with ancient fossils. However a more plausible explanation is that biomarkers are traces of biological molecules from bacteria (archaea) that feed on primordial hydrocarbons and die in that environment. For example, hopanoids are just parts of the bacterial cell wall present in oil as a contaminant. Olefins, the unsaturated hydrocarbons, would have been expected to predominate by far in any material that was derived in that way. He also wrote: "Petroleum ... [seems to be] a primordial hydrocarbon mixture into which bio-products have been added."

This hypothesis was later demonstrated to have been a misunderstanding by Robinson, related to the fact that only short duration experiments were available to him. Olefins are thermally very unstable (which is why natural petroleum normally does not contain such compounds) and in laboratory experiments that last more than a few hours, the olefins are no longer present.

The presence of low-oxygen and hydroxyl-poor hydrocarbons in natural living media is supported by the presence of natural waxes (n=30+), oils (n=20+) and lipids in both plant matter and animal matter, for instance fats in phytoplankton, zooplankton and so on. These oils and waxes, however, occur in quantities too small to significantly affect the overall hydrogen/carbon ratio of biological materials. However, after the discovery of highly aliphatic biopolymers in algae, and that oil generating kerogen essentially represents concentrates of such materials, no theoretical problem exists anymore. Also, the millions of source rock samples that have been analyzed for petroleum yield by the petroleum industry have confirmed the large quantities of petroleum found in sedimentary basins.

Empirical evidence

Occurrences of abiotic petroleum in commercial amounts in the oil wells in offshore Vietnam are sometimes cited, as well as in the Eugene Island block 330 oil field, and the Dnieper-Donets Basin. However, the origins of all these wells can also be explained with the biotic theory.

Siljan Ring crater

The Siljan Ring meteorite crater, Sweden, was proposed by Thomas Gold as the most likely place to test the hypothesis because it was one of the few places in the world where the granite basement was cracked sufficiently (by meteorite impact) to allow oil to seep up from the mantle; furthermore it is infilled with a relatively thin veneer of sediment, which was sufficient to trap any abiogenic oil, but was modelled as not having been subjected to the heat and pressure conditions (known as the "oil window") normally required to create biogenic oil. However, some geochemists concluded by geochemical analysis that the oil in the seeps came from the organic-rich Ordovician Tretaspis shale, where it was heated by the meteorite impact.

In 1986–1990, the Gravberg-1 borehole was drilled through the deepest rock in the Siljan Ring in which proponents had hoped to find hydrocarbon reservoirs. It stopped at the depth of due to drilling problems, after private investors spent $40 million. This well also sampled over of methane-bearing inclusions.

In 1991–1992, a second borehole, Stenberg-1, was drilled a few miles away to a depth of , finding similar results.

Bacterial mats

Direct observation of bacterial mats and fracture-fill carbonate and humin of bacterial origin in deep boreholes in Australia are also taken as evidence for the abiogenic origin of petroleum.

Examples of proposed abiogenic methane deposits

Panhandle-Hugoton field (Anadarko Basin) in the south-central United States is the most important gas field with commercial helium content. Some abiogenic proponents interpret this as evidence that both the helium and the natural gas came from the mantle.

The Bạch Hổ oil field in Vietnam has been proposed as an example of abiogenic oil because it is 4,000 m of fractured basement granite, at a depth of 5,000 m. However, others argue that it contains biogenic oil which leaked into the basement horst from conventional source rocks within the Cửu Long basin.

A major component of mantle-derived carbon is indicated in commercial gas reservoirs in the Pannonian and Vienna basins of Hungary and Austria.

Natural gas pools interpreted as being mantle-derived are the Shengli Field and Songliao Basin, northeastern China.

The Chimaera gas seep, near Çıralı, Antalya (southwest Turkey), has been continuously active for millennia and it is known to be the source of the first Olympic fire in the Hellenistic period. On the basis of chemical composition and isotopic analysis, the Chimaera gas is said to be about half biogenic and half abiogenic gas, the largest emission of biogenic methane discovered; deep and pressurized gas accumulations necessary to sustain the gas flow for millennia, posited to be from an inorganic source, may be present. Local geology of Chimaera flames, at exact position of flames, reveals contact between serpentinized ophiolite and carbonate rocks.

Fischer–Tropsch process can be suitable reaction to form hydrocarbon gases.

Geological arguments

Incidental arguments for abiogenic oil

Given the known occurrence of methane and the probable catalysis of methane into higher atomic weight hydrocarbon molecules, various abiogenic theories consider the following to be key observations in support of abiogenic hypotheses:

the serpentinite synthesis, graphite synthesis and spinel catalysation models prove the process is viable

The proponents of abiogenic oil also use several arguments which draw on a variety of natural phenomena in order to support the hypothesis:

the modeling of some researchers shows the Earth was accreted at relatively low temperature, thereby perhaps preserving primordial carbon deposits within the mantle, to drive abiogenic hydrocarbon production
the presence of methane within the gases and fluids of mid-ocean ridge spreading centre hydrothermal fields.
the lack of any hydrocarbon within the crystalline shield areas of the major cratons, especially around key deep-seated structures which are predicted to host oil by the abiogenic hypothesis.
The Gravberg-1 well only produced of oil, which later was shown to derive from organic additives, lubricants and mud used in the drilling process.
Kudryavtsev's Rule has been explained for oil and gas (not coal)—gas deposits which are below oil deposits can be created from that oil or its source rocks. Because natural gas is less dense than oil, as kerogen and hydrocarbons are generating gas the gas fills the top of the available space. Oil is forced down, and can reach the spill point where oil leaks around the edge(s) of the formation and flows upward. If the original formation becomes completely filled with gas then all the oil will have leaked above the original location.
ubiquitous diamondoids in natural hydrocarbons such as oil, gas and condensates are composed of carbon from biological sources, unlike the carbon found in normal diamonds.

In 1986, the team published a prognostic map for discovering giant oil and gas fields at the Andes in South America based on abiogenic petroleum origin theory. The model proposed by Prof. Yury Pikovsky (Moscow State University) assumes that petroleum moves from the mantle to the surface through permeable channels created at the intersection of deep faults.

The technology uses 1) maps of morphostructural zoning, which outlines the morphostructural nodes (intersections of faults), and 2) pattern recognition program that identify nodes containing giant oil/gas fields. It was forecast that eleven nodes, which had not been developed at that time, contain giant oil or gas fields. These 11 sites covered only 8% of the total area of all the Andes basins. 30 years later (in 2018) was published the result of comparing the prognosis and the reality. Colombia, and Volcanera (Llanos basin, Colombia), Camisea (Ukayali basin, Peru), and Incahuasi (Chaco basin, Bolivia). All discoveries were made in places shown on the 1986 prognostic map as promising areas. for instance, corresponding hydrocarbons were detected during a probe flyby through the tail of Halley's Comet in 1986.

Drill samples from the surface of Mars taken in 2015 by the Curiosity Rover's Mars Science Laboratory revealed the presence of benzene and propane in 3 billion-year-old rock samples taken from Gale Crater.

References

Bibliography

Kudryavtsev N.A., 1959. Geological proof of the deep origin of Petroleum. Trudy Vsesoyuz. Neftyan. Nauch. Issledovatel Geologoraz Vedoch. Inst. No.132, pp. 242–262

External links

Deep Carbon Observatory
"Geochemist Says Oil FieldsMay Be Refilled Naturally", New York Times article by Malcolm W. Browne, September 26, 1995
"No Free Lunch, Part 1: A Critique of Thomas Gold's Claims for Abiotic Oil", by Jean Laherrere, in From The Wilderness
"No Free Lunch, Part 2: If Abiotic Oil Exists, Where Is It?", by Dale Allen Pfeiffer, in From The Wilderness
"No Free Lunch, Part 3: The Proof", by Ugo Bardi and Dale Allen Pfeiffer, in From The Wilderness
The Origin of Methane (and Oil) in the Crust of the Earth, Thomas Gold
abstracts from AAPG Origin of Petroleum Conference 06/18/05 Calgary Alberta, Canada
Gas Origin Theories to be Studied, Abiogenic Gas Debate 11:2002 (AAPG Explorer)
Gas Resources Corporation - J. F. Kenney's collection of documents