Abiogenic petroleum origin

The theory of abiogenic petroleum origin states that petroleum (or crude oil) is primarily created from non-biological sources of hydrocarbons located deep in the crust of the Earth. The theory stands in contrast to the more widely held conventional view that petroleum is created from the remains of ancient living matter. The constituent precursors of petroleum (mainly methane) are commonplace and it is possible that appropriate conditions exist for hydrocarbons to be formed deep within the Earth. Although this theory is supported by a large minority of geologists in Russia, where it was intensively developed in the 1950s and 1960s, it has only recently begun to receive attention in the West, where the biogenic theory is still believed by the vast majority of petroleum geologists. Planetary scientist Thomas Gold was one of the abiogenic theory's greatest proponents in recent years. Although it was originally denied that abiogenic hydrocarbons exist at all on earth, this is now accepted by Western geologists. The orthodox position now is that while abiogenic hydrocarbons exist, they are not produced in commercially significant quantities, so that essentially all hydrocarbons that are extracted for use as fuel or raw materials are biogenic. A variation of the abiogenic theory includes alteration by microbes similar to those which form the basis of the ecology around deep hydrothermal vents. One prediction of this theory is that other planets of the solar system or their moons have large petroleum oceans, either from hydrocarbons present at the formation of the solar system, or subsequent chemical reactions. That this theory is receiving increasing attention from Western geologists is indicated by the fact that the American Association of Petroleum Geologists scheduled a conference to meet in Vienna in July 2004 entitled "Origin of Petroleum—Biogenic and/or Abiogenic and Its Significance in Hydrocarbon Exploration and Production". The conference had to be canceled, however, due to financial considerations. Instead, AAPG will be holding a one-day session on the topic at the June 2005 annual meeting in Calgary, Alberta. If the theory is correct, then it could greatly change future energy development.

Comparison of theories

There are two theories on the origin of carbon fuels: the biogenic theory and the abiogenic theory. The two theories have been intensely debated since the 1860s, shortly after the discovery of widespread petroleum deposits. There are several differences between the biogenic and abiogenic theories.

Raw material

Events before conversion

Conversion to petroleum and methane

Formation of coal

Evidence supporting abiogenic theory

Supergiant oil fields

Nikolai Alexandrovitch Kudryavtsev, a great Russian geologist, was the first to enunciate the modern abiotic theory of petroleum. He studied the Athabasca Tar Sands in Alberta, Canada and concluded that no "source rocks" could form the enormous volume of hydrocarbons. Therefore abiotic deep petroleum is the only plausible explanation.

Cold planetary formation

In the late 19th century it was believed that the Earth was extremely hot, possibly completely molten, during its formation. One reason for this was that a cooling, shrinking, planet was necessary in order to explain geologic changes such as mountain formation. A hot planet would have caused methane and other hydrocarbons to be outgassed and oxidized into carbon dioxide and water, thus there would be no carbon remaining under the surface. Planetary science now recognizes that formation was a relatively cool process until radioactive materials accumulate together deep in the planet.

Known hydrocarbon sources

Carbonaceous chondrite meteorites contain kerogen-like carbon and hydrocarbons. Heated under pressure, this material would release hydrocarbon fluids in addition to creating solid carbon deposits. Further, at least ten bodies in our solar system are known to contain at least traces of hydrocarbons. Meteorite ALH84001, believed to be from Mars, contains carbonate minerals which were formed about 3.9 billion years ago. The deposits are in igneous rock. On Earth, microorganisms often create carbonates. However, the material could also have been formed by water carrying carbon dioxide, or by hot carbon-dioxide-bearing fluids. Kerogen-like material has also been detected in interstellar clouds and dust particles around stars.

Methane On Earth

Methane is typically found on Earth, when not in gas deposits, in methane hydrate deposits under high pressure under deep abyssal plains of oceans, ostensibly forming from the decay of sinking biotic materials. These methane hydrates do subduct in many areas toward the mantle and may thus provide the methane needed to supply a constant supply of petroleum seeping upwards into traps where it collects.

Methane not on Earth

Methane has been detected or is believed to exist in several locations of the solar system. It is believed to have been created by abiotic processes, except possibly on Mars. In 2004, the Cassini spacecraft confirmed methane clouds and hydrocarbons on Titan, a moon of Saturn. Traces of methane gas also are in the thin atmosphere of the Earth's Moon. Methane has also been detected in interstellar clouds.

Unusual deposits

Hydrocarbon deposits have been found in places that are said to be poorly explained by biogenic theory. Some oil fields are being refilled from deep sources, although this does not rule out a deep biogenic source rock. In the White Tiger field in Vietnam and many wells in Russia, oil and natural gas are being produced from reservoirs in granite basement rock. In the Vietnamese case, this rock is believed to have no oil-producing sediments under it, so the biogenic theory requires the oil to have migrated laterally dozens of kilometers along faults from source rock.

Deep microbes

Microbial life has been discovered 4.2 kilometers deep in Alaska and 5.2 kilometers deep in Sweden. Methanophile organisms have been known for some time, and recently it was found that microbial life in Yellowstone National Park is based on hydrogen metabolism. Other deep and hot extremophile organisms continue to be discovered. U.S. Geological Survey (USGS) scientist Frank Chapelle and his colleagues from the USGS and the University of Massachusetts have discovered a potential analog for life on other planets. A community of Archaea is thriving deep in the subsurface source of a hot spring in Idaho. Geothermal hydrogen, not organic carbon, is the primary energy source for this methanogen-dominated microbial community. This is the first documented case of a microbial community completely dominated by Archaea.

Diamondoids

Tiny diamondoids occur in oils and condensates. They have similar diamond structure and probably the same origin, i.e. from earth´s mantle.

Helium

Helium gas has close association with petroleum. Although ³He is primordial, much He gas is from radioactive decay of uranium. Helium gas is associated with light oils, sometimes accompanied by nitrogen that allow petroleum to reach shallow levels in crust.

Trace metals

Nickel (Ni),vanadium (V),lead (Pb),arsenic (As),cadmium (Cd),mercury (Hg) and others metals frequently occur in oils. Some heavy crude oils, such as Venezuelan heavy crude have up to 45% in vanadium pentoxide in their ash, high enough that it is a commercial souce for vanadium. These metals are common in earth´s mantle.

Thermodynamics

The Second Law of Thermodynamics prohibits spontaneous generation of hydrocarbons heavier than methane at low pressures. Thermodynamic calculations and experimental studies confirm that n-alkanes (common petroleum components) do not spontaneously evolve from methane at pressures typically found in sedimentary basins, and so the theory of an abiotic origin of hydrocarbons suggests deep generation (below 200 km . )

Biology

Life as we know is mainly based on carbon. First living organisms (archaeobacteria) of course needed to food and this food at least was primordial methane or petroleum. They live at deep levels in crust and they are oil contaminants too became into parts of biomarkers found in natural petroleum. Photossynthesys is a very complicated process that primitive organisms got to achieve the surface of our planet, probably this situation occurred with its evolution seeking for food when petroleum or methane upwelling locally ceased, then making your own food, i.e. autotrophs.

Fischer-Tropsch Synthesis of oil

Another possible formation of inorganic oil is via Fischer-Tropsch Synthesis. The Fischer-Tropsch process converts carbon dioxide, carbon monoxide, and methane into liquid hydrocarbons of various forms. The carbon dioxide and carbon monoxide is generated by partial oxidation of coal and wood-based fuels. This process was developed and used extensively in World War II by Germany, which had limited access to crude oil supplies. It is today used in South Africa to produce most of that country's diesel from coal. Since there are large but finite coal reserves in the world, this technology could be used as an interim transportation fuel if conventional oil were to disappear. There are several companies developing the process to enable practical exploitation of so-called stranded gas reserves, those reserves which are impractical to exploit with conventional gas pipelines and LNG technology. A similar process is thought to occur deep within the crust of the earth when mantle peridotite is hydrolysed becoming serpentinite while releasing hydrogen. In the presence of catalyst transition metals (e.g. Fe, Ni) hydrogen reacts with carbon dioxide from carbonate rocks and results n-alkanes (hydrocarbons).

Deep structures and petroleum association

Petroleum is found in close correlation to deep structures in the earth, mainly over crustal plate limits (convergent as subduction or continental collision and divergent boundaries). Also over meteorite impact structures since faults can reach earth's mantle. When observe distribuition of oil fields along the arcs for instance Indonesia, Persian Gulf, Apennines in Italy (gas and oil fields), Alaska, Barbados Arc continuing towards Trinidad & Tobago and Venezuela, Atlantic rift and riftogenic basins, this can be confirmed.

Why oil is frequently found in sedimentary basins?

This is because sedimentary basins fill and cover depression areas where occurred deep faults associated to plate limits (rifts, convergent subduction or collision between two plates) and sedimentary strata form good reservoirs (pore spaces) and seals that trap hydrocarbons and these reservoirs are connected to deep sources, through deep faults. Petroleum also occur in crystalline basement but most petroleum companies prefer to drill sedimentary basins, maybe looking for large reservoirs and/or by erroneous idea that petroleum would be formed from organic debris (cooking of kerogen).

Ambiguous results

Ongoing research has changed the status of some information. For example, some biomarkers which were interpreted as evidence supporting the biogenic theory have been undermined by finding similar materials in thermophilic situations which are part of abiogenic theories.

Biomarkers

Chemicals of biological origin have been found in many geologic hydrocarbon deposits. These biomarkers were believed to be from known surface sources. Due to the difficulty in culturing and sampling deep heat-loving bacteria, thermophiles, little was known of their chemistry. As more is learned of bacterial chemistry, more biomarkers seem likely to be due to bacterial action. Hopanoids, called the most abundant natural products on Earth, were believed to be indicators of oil derived from ferns and lichens but are now known to be created by many bacteria, including archaea. Sterane was thought to have come from processes involving surface deposits but is now known to be produced by several prokaryotes including methanotrophic proteobacteria.

Deep hot carbon sources

Carbonate lava

Carbonatites are intrusive carbonate-mineral-rich igneous rocks. Although they are deposits of carbon from an igneous source, the geology behind their creation is not understood.

Hydrothermal vents

Hydrothermal vents expel mineral-rich geothermally heated water.

Evidence supporting biogenic theory

Unusual deposits

While it is true that some oil fields do not conform to the standard model of a fixed amount of oil trapped in a sedimentary basin, these examples are accommodated by the biogenic model. For example, the White Tiger field (Cuu Long Basin) cited above is located in an area where significant normal faulting brings relatively young sedimentary rocks into contact with older, fractured horst blocks of igneous rocks. The produced oil is described as typically lacustrine (derived from lake deposits), consistent with the migration of hydrocarbons from the organic-rich sediments into the fractured basement. In Eugene Island 330, a large production area of that is currently being recharged, a deep source rock is indicated, and the chemical composition of the recharging oil strongly indicates that it is leaking from a deep, intermediate reservoir. US continuous hydrocarbon reservoirs. One type of unusual deposit that one might to expect to find if the abiogenic hypothesis is true would be hydrocarbons trapped in sedimentary basins that do not contain conventional source rocks. Evidence for such deposits is lacking. Many economically disappointing wells have been drilled into geologic structures that would be expected to trap hydrocarbons, but there are no hydrocarbons present. Oil companies have learned that an appropriate source rock is necessary before they will commit to drilling a well in a potential new field.

Biomarkers

It has been argued that the abiogenic theory does not explain the detection of various biomarkers in petroleum. Microbial consumption does not yet explain some trace chemicals found in deposits. Materials which suggest certain biological processes include tetracyclic diterpane and oleanane. Although extremophile microorganisms exist deep underground and some metabolize carbon, some of these biomarkers are only known so far to be created in surface plants. This evidence is consistent with the biogenic hypothesis, although it might be true that these hydrocarbons have merely been in contact with ancient plant residues. There also is evidence that low-temperature relatives of hyperthermophiles are widespread, so it is also possible for biological deposits to have been altered by low-temperature bacteria which are similar to deeper heat-loving relatives.

Petroleum origin, peak oil, and politics

The topic of the origin of petroleum is linked to discussions of projected declines in petroleum production, variously referred to with such terms as "peak oil" or "Hubbert's peak". Also, as many aspects of the abiogenic theory were developed in the former Soviet Union by Russian and Ukrainian scientists during the Cold War, some proponents see a pro-Western bias in the promotion of the biogenic theory. Thus, in addition to the scientific merits of competing hypothoses, political and economic considerations often influence discussions of petroleum origins. For example, some opponents of the 2003 invasion of Iraq believe that the prospect of declining oil production, supported by the biogenic theory, lead the United States to secure Iraqi oil supplies through military action. Some environmentalists accuse abiogenic theory supporters of a "cornucopian" worldview that incorrectly sees no limits to human exploitation of petroleum supplies. Conversely, some supporters of the abiogenic theory accuse their opponents of an unwarranted Malthusian viewpoint that needlessly limits the use of hydrocarbons as an energy source. These aspects of the controversy may be seen in many of the online articles in the External links section below.

See also

References

# # # # # # Article link Category:Extremophiles Category:Geology Category:Peak oil Category:Petroleum

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