Abstract Microbiologically influenced corrosion (MIC) is a major problem in the oil and gas industry. Although the exact mechanism by which this occurs is not well understood, it is recognized that byproducts produced by sessile bacteria located on the metal surface are responsible for the corrosion. However, many of the biocide treatment programs that have been developed thus far have focused only on planktonic organisms, ignoring the root cause of the problem. The goal of this research was to develop and implement sessile monitoring and analysis capabilities to assist in biocide selection.
Initial laboratory testing was performed using a representative selection of bacteria inoculated into a closed flow loop system containing removable biostuds. Sessile bacteria populations were analyzed before and after biocide treatment using serial dilutions and denaturing gradient gel electrophoresis (DGGE). A biocide/surfactant combination shown to be effective in the lab was tested in a field trial to demonstrate a correlation between laboratory testing and field use. Data collected in the field was analyzed by quantitative PCR (qPCR) as well as DGGE.
The biocide/surfactant tested in the laboratory led to a 3-log reduction in sessile bacteria without regrowth 24 hours after treatment. Bacterial enumeration determined by serial dilution was confirmed by DGGE analysis. This biocide/surfactant combination was also tested in a field trial where a 3- to 5-log reduction in bacterial numbers was determined by qPCR, a dramatic reduction in bacterial species observed by DGGE, and reduced pitting of the corrosion coupons identified.
In conclusion, we have implemented new testing capabilities that allow us to identify biocides effective at removing sessile organisms in the laboratory. Importantly, we have also shown that these laboratory results are recapitulated in field trials. These methods can now be utilized to ensure that the most efficacious biocide is chosen to mitigate bacterial populations that could potentially cause MIC in an asset-specific manner.
Introduction It has been estimated that up to 20% of all corrosion may be influenced by the presence of microorganisms (Flemming, 1996). In fact, the role of sulfate-reducing bacteria (SRBs) in anaerobic corrosion of metals was implicated as early as 1934 (Von Wolzogenkuhr, 1934), although it was not until more recently that SRBs, such as Desulfovibrio sp., have been identified and described as part of a process referred to as microbiologically influenced corrosion (MIC). SRBs are not the only type of bacteria that are associated with corrosion of metal surfaces. Numerous other bacteria including Acidothiobacillus thiooxidans, Leptothrix sp., and Pseudomonas sp. are also believed to play an important role in MIC through other mechanisms such as sulfate oxidation to sulfuric acid, iron oxidation, iron reduction, and acid production (Reviewed by Little, 2007). The results of microbiologically influenced corrosion (MIC) can be severe and include accelerated corrosion of a pipe surface, the high cost of premature line replacement due to corrosion, line shut-in resulting in production downtime, and environmental contamination due to leaks.