Quantitative Evaluation and Prevention Technology of Microbiologically Influenced Corrosion Under Deposit in a Middle East Carbonate Oilfield

Water flood development mode was adopted to enhance oil recovery in a Middle East carbonate oilfield. The injected water is a mixture from the produced water and clear water. The water quality of the injected water basically meets the requirement standards except that total sulfide content is about 100mg/L. However, the water injection system has still encountered severe microbiologically influenced corrosion perforation and scaling blockage after less than 2 years, which affects the crude oil production in the oilfield. This paper aims to find out the mechanism of microbiologically influenced corrosion under deposit, and propose the prevention strategy. The maximum likelihood estimation (MPN) and fluorescent staining methods are applied to study the enrichment change of sulfate-reducing bacteria (SRB) under deposit. And then the synergistic effect of scale and SRB on uniform and localized corrosion was quantitatively evaluated using methods such as weight loss test, potentiodynamic polarization curve, white light interferometer, and scanning electron microscopy. On this basis, the electrochemical test and surface analysis methods are used to optimize the integrated inhibitor system for corrosion, scale inhibition, and sterilization. The results show that the number of SRB under deposit reached the peak value of about 2×108 cells/mL after 7 days, which is nearly one order of magnitude more than the number of SRB floating in the solution. It was clear that SRB is significantly enriched in the deposit. The synergistic effect between deposit and SRB can significantly accelerate the corrosion of carbon steel. The contribution of synergistic effect to uniform corrosion and localized corrosion of carbon steel is as high as 70% and 50% respectively. The synergistic effect of deposit and SRB on corrosion is mainly the promotion of under-deposit corrosion and the acceleration of microbiologically influenced corrosion. The S type small molecular weight corrosion inhibitor and its composite system have excellent anti-corrosion effects under scale, with a corrosion inhibition efficiency of 90%. After on-site application, the corrosion perforation rate is reduced more than 80%. This study provides useful practical experience to mitigate under-deposit SRB corrosion of high salinity and high acidity water injection systems.