Oilfields usually represent extreme environments, where physicochemical conditions appear at first sight to be generally unsuitable for living organisms to develop. However, these environments, usually poor in nitrates and oxygen, harbour a rich diverse community of microorganisms. The most widely represented and best-known types are sulfate-reducing, methanogenic and fermentative bacteria.
Nitrate-reducing bacteria, on the other hand, have received little research attention regarding their biology and role. Nevertheless some of their bacteria are known also to have the ability to oxidize sulfates. These components, which can result from metabolic activity of sulfate-reducing bacteria, prove dangerous for the environment and corrosive for drilling equipment. Nitrate injection is practised in some regions of the world in order to restrict the emission of sulfites produced during processes of exploitation of oil deposits. This input of nitrates stimulates nitrate-reducing bacteria, initially present in low quantities in the waters associated with oil reservoirs, to proliferate (2). They thus induce at once inhibition of the development of sulfate-reducing bacteria and oxidation of sulfides that such microorganisms produce.
The question remains of determining whether or not these nitrate inputs into the petroleum reservoir environment can favour the growth of populations of nitrate-reducing microorganisms different from those which oxidize the sulfides, in this way modifying the microbial ecology of oil wells. IRD scientists are therefore investigating in the laboratory the metabolism of novel nitrate-reducing bacteria, especially those able to oxidize organic acids. These acids are often present in the waters of oil reservoirs.
Marie Guillaume | alfa
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