Synergistic Effect of Sulphate-Reducing Bacteria and CO₂ on the Corrosion of Carbon Steel in Synthetic Produced Water Available to Purchase

The effect of sulphate-reducing bacteria (SRB) and carbon dioxide (CO₂) on the general and localized corrosion of carbon steel in synthetic produced water (SPW) was investigated. The synthetic produced water was saturated with various concentrations of CO₂. Experiments were carried out in a rotating cage apparatus using a mixed culture of sulphate-reducing bacteria obtained from an oil field in Venezuela. During the experiments the pH, planktonic bacterial count, and concentrations of sulphide, sulphate, iron, calcium and magnesium ions in the solution were measured. After the experiment, the sessile bacteria count and mass loss of the carbon steel test coupons were determined, the corrosion products on the metal surface were identified using X-ray diffraction, and the corrosion morphology was determined using optical microscopy, scanning electron microscopy and laser profilometry. Both general and localized pitting corrosion rates of carbon steel were found to nearly double in solutions containing 10% CO₂ and 10% SRB compared to solutions containing either CO₂ or SRB alone (synergistic effect). Higher CO₂ concentrations killed both sessile and planktonic SRB; under these conditions the general and localized corrosion rates were determined by CO₂ concentration (sweet corrosion).