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Friday, February 01, 2008


Oil Not a Fossil Fuel? [Ken Green]

Although you would not know it from reading articles about energy in the popular press, there are actually two competing theories about the nature of oil and natural gas. The dominant paradigm is that oil and natural gas are biogenic: that is, they are formed from compression of the remains of photosynthetic organism over centuries and millennia. The rival paradigm, which was developed in the 1800s by Russian scientists and popularized in the west by polymath Thomas Gold, is that oil and natural gas are abiogenic: that is, they are formed from non-biological chemical processes that convert carbon from one of the Earth's inner layers (the mantle) into longer carbon-chains as these lighter carbon compounds rise toward the surface of the Earth.

The different implications of the theories are relatively profound. In the biogenic theory, oil can only form in certain places over historical periods, and can only be formed and exist in a certain range of temperatures and pressures called the oil window, which generally corresponds to a layer of the earth from about 4-6 km under the surface, and then rise upward from there. In a biogenic framework, oil and natural gas are temporally finite, that is, they're non-renewable, and they are geographically constrained. That is, the place to look for oil and natural gas is in areas where oil-windows are possible, with geological formations that would retain the hydrocarbons (porous reservoirs and capstones). In the abiogenic theory, by contrast, hydrocarbons form perpetually at greater depths from carbon that was present from Earth's formation, and are then utilized by micro-organisms that convert the short-chain hydrocarbons into longer chains as they move through what Gold called the "deep hot biosphere." Depending on formation rates, the abiogenic theory might allow for self-renewing petroleum reservoirs, all over the globe, taking petroleum out of the category of "fossil fuel."

An article in Science today seems to suggest that the abiotic theory is correct. In a fairly dense article entitled "Abiogenic Hydrocarbon Production at Lost City Hydrothermal Field," researchers Proskurowski et al., find evidence of the abiogenic formation of short-hydrocarbon chains in an area where hydrocarbons would not otherwise be able to form by the biogenic theory. What Proskurowski et al. identified was the formation of carbon chains 1 to 4 carbon atoms in length, with shorter chains forming deeper, and with isotopic signatures ruling out biogenic origins. The conclusion of the article is as follows: "Our findings illustrate that the abiotic synthesis of hydrocarbons in nature may occur in the presence of ultramafic rocks, water, and moderate amounts of heat."

Even if oil and natural gas are abiogenic, there is no guarantee that the rates of formation are relevant in terms of changing our thinking about whether oil reservoirs are likely to deplete or not: It could still take millenia and huge areas to generate enough petroleum to be meaningful as an energy source. But an abiogenic view of petroleum formation could well change where we look for oil, and where we expect to find it. Conventional wisdom is that there are no more huge undiscovered petroleum reservoirs, but that wisdom has constrained where people look. With recent deep water finds like Chevron's Jack field, and now increased evidence for abiogenic petroleum synthesis, new exploration efforts could well turn the frown of the "peak oil hypothesis" upside down.
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Anyway, interesting article. Especially since it will infuriate the gloom and doom crowd.

BTW, you have to have a subscription to Science Magazine to read the whole article - I don't...

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