Dynamics of corrosion rates associated with nitrite or nitrate mediated control of souring under biological conditions simulating an oil reservoir.

Representative microbial cultures from an oil reservoir and electrochemical techniques including potentiodynamic scan and linear polarization were used to investigate the time dependent corrosion rate associated with control of biogenic sulphide production through addition of nitrite, nitrate and a combination of nitrate-reducing, sulphide-oxidizing bacteria (NR-SOB) and nitrate. The addition of nitrate alone did not prevent the biogenic production of sulphide but the produced sulphide was eventually oxidized and removed from the system. The addition of nitrate and NR-SOB had a similar effect on oxidation and removal of sulphide present in the system. However, as the addition of nitrate and NR-SOB was performed towards the end of sulphide production phase, the assessment of immediate impact was not possible. The addition of nitrite inhibited the biogenic production of sulphide immediately and led to removal of sulphide through nitrite mediated chemical oxidation of sulphide. The real time corrosion rate measurement revealed that in all three cases an acceleration in the corrosion rate occurred during the oxidation and removal of sulphide. Amendments of nitrate and NR-SOB or nitrate alone both gave rise to localized corrosion in the form of pits, with the maximum observed corrosion rates of 0.72 and 1.4 mm year(-1), respectively. The addition of nitrite also accelerated the corrosion rate but the maximum corrosion rate observed following nitrite addition was 0.3 mm year(-1). Furthermore, in the presence of nitrite the extent of pitting was not as high as those observed with other control methods.