Discovery of Mechanism of Biodegradation of Crude Oil to Methane Could Lead to Cleaner Oil-Sands Production and Enhanced Energy Recovery from Oilfields
An international team of researchers has shown how anaerobic microbes in oil deposits around the world—including in unconventional sources such as the oil sands—naturally break down crude oil into methane in the reservoir.
Their discovery—published in the journal Nature—could lead to more energy-efficient, economic ways to extract difficult-to-recover energy from oilfields or heavy oil and oil-sands deposits.
Biodegradation of crude oil into heavy oil in petroleum reservoirs is a problem worldwide for the petroleum industry. The natural process, caused by bacteria that consume the oil, makes the oil viscous and contaminates it with pollutants such as sulfur. This makes recovering and refining heavy oil difficult and costly.
Some studies have attributed the biodegradation to aerobic bacteria, stimulated by the surface recharge of oxygen-bearing waters. This hypothesis has been supported empirically by the likelihood of finding biodegrade oils at higher levels of degradation near the surface.
More recent findings, however, suggested that anaerobic processes dominate in the subsurface environment, despite slow reaction kinetics and uncertainty as to the actual degradation pathways.
The team of researchers, including scientists from the University of Calgary (Canada), the University of Newcastle (UK) and Norsk Hydro Oil & Energy in Norway, report in Nature that the dominant process is, in fact, fermentation by anaerobic methanogenic bacteria that live in oil reservoirs.
Their data suggests a common methanogenic biodegradation mechanism in subsurface degraded oil reservoirs which results in consistent patterns of hydrocarbon alteration and the common association of dry gas with severely degraded oils observed worldwide.
This is the main process that’s occurring all over the Earth, in any oil reservoir where you’ve got biodegradation.—Steve Larter, University of Calgary
Using a combination of microbiological studies, laboratory experiments and oilfield case studies, the team demonstrated the anaerobic degradation of hydrocarbons to produce methane. The findings offer the potential of feeding the microbes and rapidly accelerating the breaking down of the oil into methane.
Instead of 10 million years, we want to do it 10 years. We think it’s possible. We can do it in the laboratory. The question is: can we do it in a reservoir?—Steve Larter
Doing so would transform the heavy oil/oil sands industry, which now manages to recover only about 17% of a resource that consists of six trillion barrels worldwide. Oil sands companies would be able to recover only the clean-burning natural gas, leaving the hard-to-handle bitumen and contaminants deep underground.
Understanding biodegradation also provides an immediate tool for predicting where the less-biodegraded oil is located in reservoirs, enabling companies to increase recovery by targeting higher-quality oil.
It gives us a better understanding of why the fluid properties are varying within the reservoir. That will help us with thermal recovery processes such as SAGD (steam-assisted gravity drainage).—Steve Larter
The research team also discovered an intermediate step in the biodegradation process involving a separate family of microbes that produce carbon dioxide and hydrogen from partly degraded oil, prior to it being turned into methane. This paves the way for using the microbes to capture this CO2 as methane, which could then be recycled as fuel in a closed-loop energy system. This would keep the CO2 out of the atmosphere.
The petroleum industry already has expressed interest in trying to accelerate biodegradation in a reservoir, according to the researchers. Field tests may begin by 2009.
D. M. Jones, I. M. Head, N. D. Gray, J. J. Adams, A. K. Rowan, C. M. Aitken, B. Bennett, H. Huang, A. Brown, B. F. J. Bowler, T. Oldenburg, M. Erdmann & S. R. Larter; “Crude-oil biodegradation via methanogenesis in subsurface petroleum reservoirs”; Nature, Published online 12 December 2007 doi: 10.1038/nature06484