A minority of geologists--mostly Russians--have long argued (since at least the 1890s) that petroleum (oil, natural gas and bitumens) was formed through inorganic processes operating on carbon sourced from the earth's mantle
. That is, organic matter was not buried and slowly turned into petroleum.
Instead, theories for an inorganic origin ranged from hydrocarbons raining from the sky early in the Earth's formation and later expelled into the surface rocks where it's now found, to vulcanism, to the degassing of large volumes of methane from the mantle and later transformed into petroleum. In all cases the presence of organic markers was attributed to the petroleum picking them up as it moved through crustal rocks containing organic material. I recall hearing during my undergraduate days of petroleum being found in granitic rocks, but the petroleum was felt to have somehow migrated there.
Unforunately for the inorganic theory, all major petroleum discoveries have come from methods that assume an organic formation process, leaving only minor petroleum finds unexplained.
This may change. A recent article in the highly regarded journal Science
reports that short chain hydrocarbons (presumably methanes or its homologs, the abstract doesn't say--P
) found in a hydrothermal field are likely to have formed inorganically (the term of art is abiogenically). The article is sure to invigorate the debate over the origin of petroleum. From the abstract
Low-molecular-weight hydrocarbons in natural hydrothermal fluids have been attributed to abiogenic production by Fischer-Tropsch type (FTT) reactions, although clear evidence for such a process has been elusive. Here, we present concentration, and stable and radiocarbon isotope, data from hydrocarbons dissolved in hydrogen-rich fluids venting at the ultramafic-hosted Lost City Hydrothermal Field. [...]
Radiocarbon evidence rules out seawater bicarbonate as the carbon source for FTT reactions, suggesting that a mantle-derived inorganic carbon source is leached from the host rocks. 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.
Does this suggest that new methods will be developed to locate petroleum, hopefully is huge quantities? Well, yes and no. Although the abstract understandably hedges, petroleum companies will doubtless support follow-up research to determine whether marketable quantities of abiogenic oil can exsist. It's also likely that a few test wells will be drilled in promising areas. On the other hand, as noted, theories of inorganic petroleum formation are as old as pertroleum wells, and previous searches (mostly in the USSR) based on these principles never produced petroleum in significant quantities.
Even if this research leads to new discoveries, it is unlikely that it will replace the organic formation model of searching for petroleum.
Labels: Chemistry, Petroleum