OIL doesn’t come from dead plants and animals, but from plain old rock, a controversial new study claims.
The heat and pressure a hundred kilometres underground produces hydrocarbons from inorganic carbon and water, says J. F. Kenney, who runs the Gas Resources Corporation, an oil exploration firm in Houston. He and three Russian colleagues believe all our oil is made this way, and untapped supplies are there for the taking.
Petroleum geologists already accept that some oil forms like this. “Nobody ever argued that there are no inorganic sources,” says Mike Lewan of the US Geological Survey. But they take strong issue with Kenney’s claim that petroleum can’t form from organic matter in shallow rocks.
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To suggest that all petroleum comes from rocks under high pressure is to “recklessly disregard” the disciplines of organic chemistry and decades of research in petroleum geochemistry, says Brian Brister of the New Mexico Bureau of Mines and Mineral Resources.
The textbook view is that most oil forms over millions of years from organic matter trapped in buried sediments and heated to between 75 and 200°C. Microbes convert some organic material buried just below the surface into hydrocarbons. At greater depths, the heat and pressure cause chemical reactions which produce hydrocarbons from the remaining organic material. Typical commercial oilfields are between 500 and 700 metres deep, with the deepest wells about 6 kilometres down. Almost no oil or gas is expected below 10 kilometres.
Kenney and his team are among a small group of dissenters who believe oil has other, deeper origins. In the Proceedings of the National Academy of Sciences (vol 99, p 10,976), they write that methane would be preferentially formed at low pressures, instead of the heavier hydrocarbons of petroleum.
It takes pressures of about 30,000 atmospheres – corresponding to a depth of 100 kilometres – to make the heavier compounds more stable. They say that this implies “the genesis of natural petroleum must occur at depths not less than 100 kilometres”.
In their lab, they showed that heavy hydrocarbons can be produced under those conditions by heating a mixture of iron oxide, marble and water to 900°C at high pressure. Chemists don’t quibble with those results, but what orthodox petroleum geologists can’t believe is Kenney’s assertion that petroleum cannot form at the shallow depths where organic matter is found because the heavier hydrocarbons are unstable.
Trace compounds present in oils match organic deposits in the apparent source rocks, says Lewan, and experiments confirm the link. “We can simulate natural oil generation in the laboratory from organic-rich source rock.”
Even if Kenney’s conclusions about deep oil formation are only partly true, they might open the door for whole new areas of exploration. Advocates hope their findings mean undiscovered oil reserves are waiting for us deep underground, although Brister says boreholes to these depths have so far yielded only traces of hydrocarbons.