Abstract
Souring, the production of sulfide by sulfate-reducing bacteria in oil fields, can be remediated by nitrate injection. However, continuous amendment of sulfate-containing injection water with nitrate leads to microbial zonation. The combination of nitrate and biocide that may break this zonation and control souring more effectively was investigated here using bioreactors injected with excess volatile fatty acids and 2 mM sulfate or 2 mM sulfate and 2 mM nitrate. Biocide was pulsed with long duration (5 days) at low concentrations or short duration (1 h) at high concentrations. The success of these strategies was determined by the time needed for sulfide recovery. The results indicated that pulsed biocide can be synergistic with continuous nitrate. However, it depends on the type of biocide, its concentration, and the length of the pulse. Hence, pulsed biocide can improve souring control with continuous nitrate injections, if the appropriate product and injection strategy are chosen.
