Microbiologists Derek Lovley and Robert Anderson of the University of Massachusetts at Amherst have found that bacteria living just below the earth's surface can be coaxed to rapidly convert oil to methane gas in oil-rich soil. Their findings, which are spelled out in a paper in the April 13 issue of the journal Nature, could change the way the oil exploration industry operates. The research is funded by the National Science Foundation (NSF).
Petroleum engineers often hit pockets of methane when exploring for oil. According to Lovley, specialized microorganisms that live deep in the earth break down oil to its simplest form, and the result of that process is what we call "natural gas," or methane. Underground pockets of explosive gas are oil-exploration hazards because they generally are contiguous to valuable oil reserves.
In the summer of 1999, Lovley and Anderson examined the site of a contaminated aquifer where crude oil had spilled, 30 feet below the surface of the earth near Bemidji, Minnesota. With the help of a grant from NSF's Life in Extreme Environments Program, they studied anaerobic metabolic processes of microbes living in and around the oil spill. The contamination had changed the composition of the microbial community from what was normally found in the Minnesota soil to something similar to what would be found near oil reservoirs. Unlike soil found much deeper in the earth, however, there was no sulfate in this soil. Until Lovley and Anderson's study, sulfate was thought to be a necessary ingredient in the process microbes use to break down oil.
"We know that microbial processes found in shallow environments are also common to deeper environments," explains Lovley, "We study microbes at shallow levels because it's hard to sample them down as deep as the oil reserves."
The researchers incubated the sediments in the laboratory under conditions that mimicked those found in the subsurface of the earth. Surprisingly, as soon as Lovley and Anderson added the oil component hexadecane with a carbon-14 tracer to the sediment, methane gas carrying the tracer was produced "without a lag." The two concluded that the microbes in the soil were converting the hexadecane and other oil components in the soil to methane gas, in the same way deep-dwelling microbes might complete the methane process in a natural environment.
"We found that, contrary to what was previously believed, it's not necessary to have sulfate present in order for microbes to produce methane from oil," says Lovley. "This is important because significant amounts of sulfate are not usually found in oil reservoirs. This finding is very useful, with a potential for widespread application to the petroleum industry." In some cases, he said, it might be beneficial to use microorganisms to convert the oil in reservoirs to methane because methane is easier to extract than oil.
Adds Lovley, "When we better understand the conditions under which microorganisms convert oil to methane, we should be able to better predict where explosive deposits of methane will be located. This should make oil exploration a bit safer."
NSF is an independent federal agency which supports fundamental research and education across all fields of science and engineering, with an annual budget of about $4 billion. NSF funds reach all 50 states, through grants to about 1,600 universities and institutions nationwide. Each year, NSF receives about 30,000 competitive requests for funding, and makes about 10,000 new funding awards.