ABSTRACT

The combined effect of sulphate-reducing bacteria (SRB) and CO2 on the corrosion of carbon steel in produced water were investigated using a rotating cage. During the experiment, pH, planktonic SRB, and concentrations of sulphide, sulphate, iron, calcium and magnesium ions were monitored. After the experiment, the sessile SRB were enumerated by serial dilution and optical microscopy, scanning electron microscopy, mass loss and laser profilometry were used to identify corrosion products, bacterial cell and corrosion rate. Both mass loss and localized pitting corrosion were two and three times higher in solutions containing 10 % SRB and 10 % CO2 respectively compared to solutions containing either 10% CO2 or 10% SRB alone. Higher CO2 concentrations killed SRB which indicates that production water with CO2 concentrations higher than 10%, where the pH drops below 5.5 and can down until 4.3, the potential risk of MIC by SRB decreases. A commercial package of treatment based on quaternary ammonium salts as filmic corrosion inhibitors, glutaraldehyde with quaternary ammonium salts as biocide and polyepoxysuccinic acid as scale inhibitor decreased corrosion rate by 96%, controlled the SRB lower than 102 cells/cm2 and reduce the risk of scales.

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