Comparison of sulphide corrosivity of sulphate‐ and non‐sulphate‐reducing prokaryotes isolated from oilfield injection water

The microbiologically influenced corrosion (MIC) of water injection systems by sulphate‐reducing prokaryotes (SRP) has caused many problems in the oil industry. These prokaryotes produce H₂S, which reacts aggressively with steel and is thus widely considered to be the main cause of bacterial corrosion of industrial oil equipment. However, current microbiological treatments and controls have not taken into account other groups of sulphidogenic prokaryotes, which also produce H₂S or its derivatives and with the same adverse effects of MIC. In the present work, sulphidogenic prokaryotes were isolated from water injection systems and identified by DNA sequencing. The identified species included sulphate‐reducing Desulfovibrio termitidis and non‐sulphate‐reducing Escherichia coli. Biocorrosion tests were carried out on API 5L grade X65 carbon steel. Electrochemical impedance spectroscopy, polarisation resistance, open circuit potential and weight loss were carried out. Steel corrosion resulting from the production of the metabolite H₂S by SRP and non‐SRP was observed, with sulphide generation by SRP much greater than that by non‐SRP. These results confirm the need to investigate and consider the role of not only SRP but also non‐SRP in order to improve the control over bacterial corrosion of oil‐industry equipment.