Hydrogen sulfide production by sulfate-reducing bacteria (SRB) in oil fields (souring) can be eliminated through the activity of nitrate-reducing bacteria (NRB). Two distinct classes of NRB have been described. The heterotrophic NRB (hNRB) reduce nitrate using similar oil organics as used by SRB for the reduction of sulfate. These inhibit SRB by competitive exclusion. The nitrate-reducing, sulfide-oxidizing bacteria (NR-SOB) directly oxidize sulfide with nitrate. Many of these use only CO2 as the carbon source and do not compete with SRB for oil organics. Both hNRB and NR-SOB produce nitrite as an intermediate in nitrate reduction, which strongly inhibits SRB. The NR-SOB Thiomicrospira sp. strain CVO has previously been shown to be an effective agent for sulfide removal in situ and in laboratory studies. A continuous up-flow packed-bed bioreactor was inoculated with a microbial consortium obtained from the same oil field. Although SRB-generated sulfide was removed by nitrate addition, community analysis indicated that strain CVO did not become a major component under these conditions. Also, strain CVO could not be established in the bioreactor by bioaugmentation. Two related microorganisms Sulfurospirillum sp. strains NO2B and KW became major community members during nitrate treatment. These were found to have both hNRB and NR-SOB activity and be capable of producing large amounts of nitrite, make them ideal agents for souring control.

Subject
Hydrogen sulfide, Nitrites, Sulfates, Ammonia, Acetates, Souring, Nitrates, Nitrogen, Oilfields, Ports and harbors, Sulfides, Risk reduction, Oil
Keywords:
Sulfate-reducing bacteria, souring control, nitrate, upflow bioreactor
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2006
Association for Materials Protection and Performance (AMPP)
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