Making a meal of oil reserves

A study of the organisms that “eat” about half the world’s reserves of oil provides another intriguing contribution to understanding of the extent of global resources.

There are many known examples of reserves that have been degraded by bacteria, a microbial diet with huge economic implications because the oil is made less valuable, though methane is sometimes produced as a side effect.

The degraded oils are denser “heavy oils” often found in the form of tar sands. Well known examples include those in Athabasca, Canada, and the Orinoco tar sands in Venezuela. In British waters, examples include the North Sea Alba field and the Clair field, west of Shetland.

Biodegraded oils are less valuable than non-degraded oils – and often not counted as reserves – because they contain fewer hydrocarbons and more nitrogen, oxygen and sulphur containing compounds, making them more expensive to process.

Oil-eating organisms were once thought to infest relatively shallow wells, or wells where there is a supply of oxygen dissolved in waters from the surface, because the bugs responsible are aerobes – creatures that require oxygen to respire. And the extent of anaerobic degradation in deeper reservoirs has been a matter of debate, especially as no organism has been isolated that has been shown to degrade hydrocarbons under the conditions found in deep petroleum reservoirs.

Now evidence that other reserves, notably deeper reserves, can be attacked by anaerobes – creatures which, in total, weigh as much as the world’s plants and can survive and thrive in the absence of oxygen – has been uncovered by Drs Martin Jones and Carolyn Aitken of the University of Newcastle upon Tyne. With Prof Steve Larter of the University of Calgary, they recently reported in the journal Nature how they found the chemical by-products typical of anaerobic hydrocarbon degradation from a large fraction of 77 degraded oil samples from around the world. The results suggest that anaerobic hydrocarbon degradation – by organisms that have not yet been isolated – is common in sub-surface oil reservoirs.

The finding, said Dr Jones, will help to provide a better understanding of sub-surface oil degradation. “Eventually a better understanding of the degradation mechanisms may be useful in helping to better predict the occurrence of biodegraded oils.”