Abstract
Nitrate treatment is increasingly used for selective control of sulfate-reducing bacteria (SRB) and associated biogenic generation of hydrogen sulfide. Nitrate is now widely added to seawater injection systems to mitigate reservoir souring. The use of nitrate in seawater injection has not been observed to increase corrosion rates of carbon steel and there is some evidence that it may actually reduce corrosion. However, in produced water re-injection (PWRI) systems the situation with respect to corrosion is more unpredictable and nitrate treatment has sometimes been associated with increased general and localised corrosion.
A laboratory-testing programme has been conducted to investigate the possibility of using corrosion inhibitors to prevent this potential problem. A total of six corrosion inhibitors were evaluated. Both the general corrosion and pitting corrosion rates were measured in the presence of biofilm, containing a high nitrate-reducing bacteria (NRB) population.
Determinations were made by electrochemical measurements supported by microscopic examination of electrode surfaces after test completion.
The increased general corrosion rate and pitting penetration rates that were observed during nitrate treatment were substantially reduced by the best performing inhibitors.
