ABSTRACT

Sampling of pigging debris was performed from three multiphase pipelines that previously were exposed to microbiologically influenced corrosion (MIC) due to high abundances of sulfate-reducing prokaryotes (SRP) and methanogens. Sampling was also performed from a water injection pipeline to investigate differences in the microbial community. Quantification of microorganisms using qPCR analysis revealed that numbers of SRP and methanogens were in the range of 103 to 105 cells/g in the multiphase pipelines and 103 to 105 cells/ml in the water injection pipeline. The metabolic activity determined by RT-qPCR was relative low. NGS sequencing analysis detected Methanothermococcus to be most active in multiphase pipelines and Desulfohalobiaceae in the water injection pipeline as potentially hydrogen-scavenging and MIC-causing microorganisms. Further, Methanocalculus and Desulfovibrio were found in significant proportions showing that methanogens were the major MIC-causing microorganisms in multiphase pipelines and sulfate-reducing bacteria in injection water pipelines. The MIC risk was determined to be low when quantified using the pre-established company model, due to low bacterial numbers present in the samples. By combining qPCR, RT-qPCR, and NGS we were able to provide a more accurate MIC analysis, though, the application of molecular microbiological methods needs further development to improve and validate sampling procedures, methodology, and data interpretation for determining MIC factors.

INTRODUCTION

Microbiologically influenced corrosion come in to play in many oil field production systems as a risk of integrity loss. The consequences of corrosion in wells, pipelines, and topsides production facilities are substantial due to downtime during replacement of production facilities and impact on safety and environment. In multiphase production systems with relative high water activity and relative low temperatures, microorganisms play a significant role causing MIC. Hence, understanding the factors that facilitate growth of microorganisms and their impact on corrosion of oil field systems are important to take the right measures for prolonging the lifetime of production facilities. For more than a decade, molecular microbiological methods have been applied in the oil industry. This has given important knowledge about abundances of key microorganisms that potentially can scavenge hydrogen from carbon steel.1,2,3 Hence, this is believed to be the major mechanism of MIC, although, less investigated mechanisms may contribute to the MIC mechanism such as direct electron uptake and local souring by decreasing pH.2

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