A theory long on the fringes of petroleum science gained some support from new research this week, but it is probably not enough to launch the concept into the mainstream.
The idea: What if fossil fuels were not fossil after all? What if hydrocarbons could form from chemical reactions deep inside the earth, rather than from the "pressure cooking" of organic matter?
"[Abiogenic] origin of oil has been proposed by many before, but there are arguments pro and contra," said Alexander Goncharov, a geophysicist at the Carnegie Institution.
Goncharov and his colleagues in Russia and Sweden have experimentally shown for the first time that ethane and heavier hydrocarbons can be produced under the pressure and temperature conditions of the upper mantle, the slightly viscous layer of the earth directly below the crust. Their research was published this week in Nature Geoscience.
"Our results provide a link which was previously missing or was doubtful because of a lack of in situ measurements ... for the upper mantle conditions," Goncharov said. "Thus, our work suggests there is a possibility for the [abiogenic] oil formation in the deep earth and that there is a potential to find more oil fields than expected if one assumes that oil could be formed only biogenically."
The researchers used a diamond anvil cell and a laser heat source to subject methane -- a primary component of natural gas -- to conditions that mimic the earth at 40 to 95 miles deep.
Under those conditions, the methane reacted and formed petrochemical feedstock ethane and propane and butane, which are used as fuels, as well as molecular hydrogen and graphite. When the ethane was subjected to the same conditions, it formed methane, suggesting heavier hydrocarbons could exist deep under the earth's surface. And the reversibility -- methane forming ethane, and vice versa -- implies the production of saturated hydrocarbons is thermodynamically controlled and does not necessarily require organic matter.
The idea of abiogenic hydrocarbon genesis is not new.
Dmitri Mendeleev, developer of the first periodic table, suggested in the late 19th century that hydrocarbons were generated inside the earth from the mixing of water and iron carbide.
Later, during the height of the Cold War, an entire Russian-Ukrainian school of thought emerged proposing that the fuels used to power homes, cars and power plants were not derived from ancient organic matter, but from chemical reactions deep inside the earth. The traces of plant and animal remains found alongside hydrocarbon reservoirs in sedimentary rocks are just contamination, the Russian-Ukrainian scientists said.
Oil and natural gas could be found in any type of rock, they added, flagrantly going against one of the principle tenets of traditional petroleum science.
But their theories have never been accepted by the mainstream industry.
"I don't think anybody in the research field doubts that methane could be formed this way," said Wayne Ahr, a petroleum geologist at Texas A&M University. "The problem is if it existed in commercial quantities, it seems someone would have found it by now."
Barry Katz, a geochemist at Chevron Corp., agreed.
"I don't disagree with the idea," Katz said. "I disagree with the idea of commercial quantities. There's no question that it's coming out of the system. However, it's not coming out in commercial quantities."
And while the oil and gas industry is not necessarily looking for hydrocarbons in the same rocks that mantle-derived methane and ethane would have formed in, the resource has not been encountered on a commercial scale during any petroleum exploration or scientific drilling in other rock types, Katz said.
Still, the researchers remain optimistic.
"The contribution of this abiogenic mechanism to hydrocarbon accumulation in major petroleum deposits found in active subcontinental settings of craton margins and rift zones could be actively searched in the future," they wrote in the paper.
But more work needs to be done.
"The synthesis and stability of the compounds studied here as well as heavier hydrocarbons over the full range of conditions within the earth's mantle now need to be explored," said Vladimir Kutcherov, a co-author on the paper and a professor at the Royal Institute of Technology in Sweden. "In addition, the extent to which this 'reduced' carbon survives migration into the crust needs to be established. These and other related questions demonstrate the need for a new experimental and theoretical program to study the fate of carbon in the deep earth."