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SYDNEY: New research reveals that the hydrocarbon elements of oil and gas may be able to form deep in the Earth's crust without the need for fossilised organic matter.
A team led by researchers at the Carnegie Institution's Geophysical Laboratory, in Washington DC, have studied the chemical reactions of methane at high temperatures and pressures and under oxidising conditions. They say that this shows that – theoretically at least – oil can form deep in the Earth's crust without the need for decomposing plants or animal material.
Most of the crude oil and gas we use was formed hundreds of millions of years ago when vast forests decomposed under great heat and pressure below sediment in the Earth's crust.
20,000 times atmospheric pressure
But experts have also wondered if some of these hydrocarbons might form chemically in the upper mantle and are then transported through faults and fissures to shallower regions, contributing to petroleum reserves.
Methane is the simplest hydrocarbon and is abundant in the atmosphere. The new study, detailed in the journal Nature Geoscience used a diamond anvil cell (a device which puts samples under immense pressures) and a laser heat source, to subject methane to conditions which mimic those found deep inside the Earth.
Pressures there can exceed 20 thousand times that at sea level, while temperatures can exceed 1,200°C.
"We demonstrated the chemical transformation of methane to heavier saturated hydrocarbons such as ethane, butane and propane and its reversibility under the conditions of the upper Earth's mantle," said the Carnegie Institution's Alexander Goncharov.
Improved techniques
The results suggest that heavier hydrocarbons than methane could exist deep down within the crust, he said, and this process may even have contributed to our oil and gas reserves today.
Although previous experiments have reported formation of heavier hydrocarbons from methane under high pressures and temperatures, according to Goncharov, the molecules could not be identified and the process was not proven. "We overcame this problem with our improved laser-heating technique where we could cook larger volumes more uniformly," he said.
Study co-author, Vladimir Kutcherov said this theory backs up research which suggests that hydrocarbons formed in this was seep up through deep faults in the Earth's crust, where they form larger deposits. "So, our planet may have enormous, inexhaustible resources of hydrocarbons," he said.
An old idea
This idea is many decades old; e.g., see the late Thomas Gold at Cornell. That doesn't mean it's wrong. However, it is advancing very slowly.