Oil as an elixir of life

Microbes worsen the quality of fossil fuels

Soils may differ greatly in their properties, such as color, density or toughness. Particularly tough petroleum oils are even used as a material in the arts and crafts, as the small figure made from Chinese crude oil shows. Above all, biological degradation processes in the deposits lead to the mentioned changes in the properties of the oil. © Heinz Wilkes
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Most of today's extracted oil is characterized by low density and viscosity. Accordingly easy and inexpensive it can be promoted. But due to the scarcity of resources increasingly tough and therefore difficult to be promoted crude oil economically becoming more interesting. However, scientists have now been able to prove that microbes live in these deposits and even feed on the petroleum. Their metabolic activities reduce the quality of the oil and lead to problems in the promotion.

The production of large quantities of viscous petroleum is mainly due to the activity of microorganisms in the deposits. For example, sulfate-reducing bacteria are able to utilize certain hydrocarbons from oil deposits as an energy source for their metabolic processes. But even in the "deep biosphere" the microbes are dependent on liquid water as their habitat. Accordingly, they prefer to settle at the border of oil and water resources. If there is sulfate or carbon dioxide for respiration and other vital nutrients such as nitrogen and phosphorus in the water, the conditions for biodegradation are particularly good.

Oil-eaters on the trail

To better understand the mechanisms and effects of biodegradation, Heinz Wilkes of the GeoForschungsZentrum (GFZ) Potsdam and his team are investigating the mechanisms that lead to the formation of viscous petroleum. The researchers were able to prove that microbial metabolic processes can take place in oil reservoirs under anaerobic conditions. This explains the enormous amounts of biodegradable petroleum in many reservoirs, although there is not enough oxygen available there. The results of the research also suggest that biodegradation, depending on the geological conditions in different deposits, can lead to very different changes in petroleum composition.

Schematic representation of the mechanisms during biodegradation in a crude oil deposit © GFZ Potsdam

Because the microorganisms preferentially "eat" certain constituents of the soil, the composition and thus also the chemical and physical properties of the residues change. Thus, the microbial activity in the storage facility leads to a significant reduction in the quality of the soil. In particular, the high levels of sulfur, organic acids and metals cause significant problems in the promotion and processing. For example, the microbes can produce hydrogen sulphide, which is extremely toxic to humans. When this gas combines with iron or other metals, solid black crusts form, clogging the conveyors. In addition, the toxic gas promotes corrosion of the pipelines.

Assess cost-effectiveness

As the extent of biodegradation increases, so-called "API density" decreases. This physical parameter is based on the specific gravity of the soil. It is the most important indicator of the oil industry for the quality and thus also the economic value of oil. In this context, the geologist Rouven Elias from the GFZ Potsdam succeeded in deriving the API density from the chemical nature of the oil using special analytical methods and thus a better prediction of the quality of the deposits before the To facilitate promotion. The peculiarity: the quality of the oil can be determined from just a small sample from a test well, which considerably simplifies the search for suitable storage facilities. display

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Leaflet fat 200 million years ago - Erd l heute (pdf, 0.4 MB)

Deep Biosphere Research at the GFZ Potsdam

(Heinz Wilkes & Rouven Elias, GFZ Potsdam, 13.04.2007 - AHE)