A breakthrough in the understanding of how microbes break down underground deposits of oil could revolutionise the extraction of fossil fuels to make the process cleaner for the environment and more energy efficient, scientists have announced.
Instead of using energy-intensive methods of extraction, it may soon be possible to use the natural microorganisms that feed on underground hydrocarbons to convert heavy oil to natural gas, which is easier to extract and a 'greener' source of fuel.
Scientists believe that if the technique can be demonstrated to work on a large scale on underground deposits, it could lead to a massive increase in the availability of fossil fuel without a corresponding increase in greenhouse-gas emissions.
They estimate, for instance, that by 'fertilising' the populations of subterranean microbes that already exist in oil fields it may be possible to speed up the conversion of heavy oil to natural gas by many thousands of times, and possibly double the exploitable reserves of fossil fuel.
The oil industry expends a lot of energy extracting heavy oil deposits such as tar-like bitumen, which has to be melted with superheated steam injected down boreholes. If such deposits could be broken down by microbes into methane, or natural gas, the extraction would be cleaner and more efficient, said Professor Steve Larter, of the University of Calgary in Canada.
"The main thing is you'd be recovering a much cleaner fuel. Methane is, per energy unit, a much lower carbon dioxide emitter than bitumen. Also, you wouldn't need all the upgrading facilities and piping on the surface," he said.
Ultimately, it may even be possible to use microbes to convert heavy oil directly into hydrogen rather than methane. This would effectively mean that oil reserves could be exploited without the release of any carbon dioxide, the professor added.
His team of scientists carried out a series of experiments showing how oil-eating microbes can convert heavy oil into methane by a process of anaerobic fermentation in the absence of oxygen. It is this natural biodegradation of hydrocarbon deposits that produces natural gas fields.
"This is the main process that?s occurring all over the Earth, in any oil reservoirs where you've got biodegradation. Instead of 10 million years, we want to do it in 10 years. We think it?s possible. We can do it in the laboratory. The question is whether we can do it in a reservoir," Professor Larter said.
The results of experiments, which are published in the journal Nature, show that it may be possible to fertilise underground microbes with trace minerals, such as phosphorus, or vitamins which will boost their numbers and so vastly increase the rate of biodegradation. One way to do this would be simply to pump waste water down boreholes. "It raises the exciting prospect of accelerating this process so that it is possible to recover the energy as methane or even possibly as hydrogen," he added.
At present, the oil industry manages to recover only about 17 per cent of the energy that exists as subsurface deposits of heavy oil. Using microbes in the extraction process could double this recovery by retrieving clean-burning natural gas, leaving the hard-to-handle bitumen and toxic contaminants deep underground, he said.
Ultimately, it may even be possible to block microbes that convert hydrocarbons to methane and stimulate the production of others that convert them to hydrogen and carbon dioxide. The carbon dioxide could be left underground and the hydrogen extracted as the perfect clean fuel.
"If we could recover molecular hydrogen we could have a carbon-free energy source from a fossil fuel reservoir. It is a more difficult trick, but it is the Holy Grail we are seeking," Professor Larter said.
Working with geologists from the UK's University of Newcastle, the scientists have shown that the degradation of heavy oil into methane it a practical possibility. The Norwegian oil company Norsk Oil and Energy is also involved in the work.
Professor Larter said that it is too early to give reliable estimates of the amount of oil that could be exploited with the technique but he said that if it works underground then the prospects are potentially huge. "You're talking about a colossal increase in recovery. It's difficult to say how much, but certainly a doubling of recovery would not be a major issue if the process can be demonstrated in the subsurface deposits of oil," he said.