Effect of sulfate-reducing bacteria from salt scale of water flooding pipeline on corrosion behavior of X80 steel

Abstract

As a means to enhance the recovery of oil reservoirs, waterflooding is widely employed in field development. However, because injected water contains solid impurities and incompatible characteristics, water injection pipelines often suffer from scaling and blocking. In addition, because these pipelines are typically buried in underground soil, microbial bacteria are derived from humid and oxygen-deficient environments, causing serious microbial corrosion on the basis of scaling corrosion. The objective of this study was to analyze the corrosion behavior under the combined effect of sulfate-reducing bacteria (SRB) and the scale layer (CaCO3) induced inside a water injection pipeline. With an X80 steel pipeline as the experimental material and an oilfield injected water simulation solution as the experimental medium, this study conducted weight-loss tests and electrochemical experiments. Combined with the experimental results, scanning electron microscopy, electrochemical impedance spectroscopy, element and phase analyses, and 3D corrosion morphology reconstruction technology were used to explore the changes and mechanism of corrosion behavior under the combined effect of CaCO3 scale layer and SRB in water injection pipelines used in oilfields. The study results showed that a nonuniformly distributed CaCO3 scale layer can provide sites for SRB metabolic activity and also serve as a channel for the exchange of corrosion ions. The corrosion rate of the water injection pipeline increased significantly under the combined effect of the CaCO3 scale layer and SRB, and pitting corrosion under the biofilm/scale layer was serious. In the presence of iron oxides, SRB could interact with CaCO3, causing microbial dissimilation and reduction of iron oxides, forming a loose FeS product film, and accelerating the corrosion process of steel pipelines.