Crude-oil biodegradation via methanogenesis in subsurface petroleum reservoirs

More than half of the world's oil inventory consists of biodegraded heavy oil and tar sand deposits. Recovery of oil from these sources is complicated and expensive. Recent findings suggest that anaerobic bacteria may cause this hydrocarbon degradation, but the actual degradation pathway occurring in oil reservoirs remains obscure. Using a combination of laboratory oil degradation experiments and analysis of oilfield samples, it is now shown that the dominant process of subsurface biodegradation is methanogenesis, involving anaerobic degradation of oil hydrocarbons to produce methane. This suggests an alternative way of exploiting these 'difficult' oilfields: by accelerating the natural hydrocarbon degradation process, it may be possible to recover energy as methane, rather than conventionally as oil.