some microbes have been breaking down petroleum into methane deep within the earth for ages. But we do not know the bacteria or how they do it. A recent study has revealed the answers, with scientists producing methane from petroleum in the laboratory by feeding these microbes.
Over millions of years, some bacteria have adapted to conditions deep below the soil, deriving their energy by consuming the oil. In turn, they lace the petroleum with impurities like sulphur, thereby making it unusable without refining. "This biodegradation of crude oil ... has affected the majority of the world's oil, making recovery of the purified oil costly," said a paper published in the online edition of the journal Nature on December 12, 2007. The end result of the breakdown is methane.
"In a typical petroleum reservoir, you can extract 35 per cent of the oil, with 65 per cent remaining unextracted," said microbial ecologist I M Head of the University of Newcastle in the uk, one of the authors. "The equivalent figure for gas is 70 per cent and 30 per cent. If we can convert oil into methane, then the recovery of energy goes up."
Accelerating the biodegradation also offers a route to obtaining an energy source that is otherwise difficult to recover from oil fields, said the team led by D M Jones of the University of Newcastle; researchers from the University of Calgary's School of Civil Engineering and Geosciences in Canada and the R&D Centre of Norsk Hydro Oil & Energy in Norway. The researchers took non-degraded oil from the North Sea fields and tracked its reaction path under anaerobic conditions. In the presence of methanogenic bacteria, methane production was incubated and studied for 686 days.
Previous studies had suggested that bacteria responsible for this biodegradation were aerobic. It is now apparent that the methanogenic microbes, like archaebacteria, work in the absence of oxygen. This is significant because the reservoirs of petroleum do not have enough oxygen, if any at all.
If the conversion of crude into gas in the laboratory can be replicated at the commercial level, the heavy oil industry might be in for a revolution. Oil companies would then focus on recovering only the clean-burning natural gas, leaving the hard-to-handle bitumen and contaminants deep underground. The researchers said oil companies are eager to try the method in field conditions.
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