Microbial analysis of backflowed injection water from a nitrate-treated North Sea oil reservoir |
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Authors: | Gunhild Bødtker Kristine Lysnes Terje Torsvik Eva Ø Bjørnestad Egil Sunde |
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Institution: | (1) Unifob Petroleum, Allégaten 41, 5007 Bergen, Norway;(2) Centre for Integrated Petroleum Research (CIPR), Allégaten 41, 5007 Bergen, Norway;(3) StatoilHydro, Forusbeen 50, 4035 Stavanger, Norway;(4) Unifob Petroleum, Jahnebakken 5, 5020 Bergen, Norway |
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Abstract: | Reservoir souring in offshore oil fields is caused by hydrogen sulphide (H2S) produced by sulphate-reducing bacteria (SRB), most often as a consequence of sea water injection. Biocide treatment is
commonly used to inhibit SRB, but has now been replaced by nitrate treatment on several North Sea oil fields. At the Statfjord
field, injection wells from one nitrate-treated reservoir and one biocide-treated reservoir were reversed (backflowed) and
sampled for microbial analysis. The two reservoirs have similar properties and share the same pre-nitrate treatment history.
A 16S rRNA gene-based community analysis (PCR-DGGE) combined with enrichment culture studies showed that, after 6 months of
nitrate injection (0.25 mM NO3
−), heterotrophic and chemolithotrophic nitrate-reducing bacteria (NRB) formed major populations in the nitrate-treated reservoir.
The NRB community was able to utilize the same substrates as the SRB community. Compared to the biocide-treated reservoir,
the microbial community in the nitrate-treated reservoir was more phylogenetically diverse and able to grow on a wider range
of substrates. Enrichment culture studies showed that SRB were present in both reservoirs, but the nitrate-treated reservoir
had the least diverse SRB community. Isolation and characterisation of one of the dominant populations observed during nitrate
treatment (strain STF-07) showed that heterotrophic denitrifying bacteria affiliated to Terasakiella probably contributed significantly to the inhibition of SRB.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. |
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Keywords: | Microbial community Nitrate treatment Nitrate-reducing bacteria Sulphate-reducing bacteria Reservoir souring |
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