Seawater Injection is an essential procedure in many offshore facilities in the North Sea. This water passes through a variety of different treatments and environments. It is chlorinated, filtered, deoxygenated and treated with biocide and other chemicals. The water is then injected into reservoirs under high pressure and sometimes high temperatures, to eventually (after months or years) break through into the production system, where it is subject to various different temperature environments.

Microorganisms react rapidly to changes in their environment, particularly temperature and salinity; given their short generation times, the effects on the microbial population can be pronounced. The objective of this study was to characterise the microbial communities entering and leaving the reservoir with particular emphasis on sulfate-reducing bacteria (SRB) and Archaea, which are believed to be the major cause of microbiologically-influenced corrosion (MIC).

Denaturing gradient gel electrophoresis (DGGE) and fluorescence in situ hybridisation (FISH) were applied to sessile and planktonic samples collected from a number of North Sea seawater injection and production systems to compile a database of the microbial communities found in these systems. The FISH data were compared, to determine common traits and gross differences between topside seawater and production equipment locations. Additionally, the counts of SRB/ Archaea types were assessed and consideration was given to how these may influence the risk of MIC. DGGE data was used to track certain organisms through the systems to find commonalities; primarily, if there were any relationship exists between biofilm communities at different locations in the two systems.

The results indicate that there are similarities as well as subtle differences between the two systems and these are discussed in detail in this paper.

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