NACE Corrosion Expro 2004
New Orleons, USA
Corrosion by Suphate-Reducing Bacteria that Utilize Nitrate
16S rRNA gene sequencing was used to identify a sulfate-reducing bacterium (SRB) from a Danish North Sea oilfield water injection system. This species was cultivated, purified and subsequently identified as being >97% similar to Desulfovibrio gracilis.
Like some other Desulfovibrio species this SRB, strain OP102, could reduce nitrate as an electron acceptor and produce ammonia in the absence of sulfate. In addition, in the presence of sulfate, when nitrate was dosed at 100mg/l it was again reduced by the bacterium, with some ammoniun production. Therefore, this mechanism could be important in oilfield systems where nitrate is applied to prevent sulfide generation by SRB which leads to reservoir souring.
In static tests the influence of this Desulfovibrio on corrosion was assessed using carbon steel coupons, in the presence of sulfate and in the presence of sulfate with 100mg/l nitrate. Corrosion rates were less than 1.5 mpy when coupons were incubated in the same water, with sulfate and with nitrate. Furthermore, the occurence of pitting corrosion was fairly low under all circumstances.