Materials Performance

JUN 2019

Materials Performance is the world's most widely circulated magazine dedicated to corrosion prevention and control. MP provides information about the latest corrosion control technologies and practical applications for every industry and environment.

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12 JUNE 2019 W W W.MATERIALSPERFORMANCE.COM New Bacteria Monitoring Technique Provides Rapid Measurement in the Field I n oil and gas production, accurately monitoring the bacteria population is an important tool to mitigate microbiologically inf luenced corro- sion (MIC), prevent reservoir souring, and optimize biocide treatment strategies. Bacteria are pervasive and can be present in the entire system—from the reservoir to the ref inery. In addition, it is common for bacteria to be living in seawater injec- tion systems. A lthough the precise num- ber of the corrosion failures in oil and gas production due to bacteria is not avail- able, it is estimated that failures due to MIC are between 10 and 50%. 1 A new method to detect bacteria in oil and gas f ields has been developed and used to test, apply, and optimize f it-for- purpose bacteria control chemicals. The technique provides rapid bacteria mea- surement that can be performed com- pletely at the well site to provide real- time, post-treatment testing to ensure biocide applications are effective. According to NACE International member A lyn Jenkins with Schlumberger in Aberdeen, Scotland, U.K., and James Fajt and Anna Murphy with Schlum- berger in Houston, Texas, USA, 2 a variety of bacteria can be present in the oilf ield, including sulfate-reducing bacteria (SRB), acid-producing bacteria (A PB), and iron-oxidizing bacteria (IOB). These bac- teria can metabolize nutrients found in oilf ield waters to create several corrosive substances. Hydrogen sulf ide (H 2 S) is gen- erated by SRB; and carbon dioxide (CO 2 ), volatile fatty acids (V FA) (formic, lactic, propionic, and acetic acids), and inor- ganic acids (e.g., sulfuric acid [H 2 SO 4 ]) are produced by A PB. The presence of SRB in a reservoir will ultimately cause reservoir souring. Addi- tionally, the presence of H 2 S in produced waters can reduce the effectiveness of corrosion inhibitors injected further downstream and necessitate the use of sulf ide scavengers or nitrate treatments, as well as affect the performance of tub- ing, f lowlines, and riser metallurg y with the possibility of causing environmen- tally assisted cracking. H 2 S, CO 2 , and V FA also can reduce the pH of produced water, which increases its corrosivity. IOB form layers of oxides and hydroxides on the metal surface, which result in oxygen- reduced areas that, in turn, allow SRB to thrive. IOB have also been reported to promote underdeposit corrosion. In addition to being present in the planktonic form as f loating organisms, A PB and SRB can be present in the sessile state, where they adhere to the metal sur- face and form a biof ilm that excretes a sticky exopolymer that attracts other bacteria. Biof ilms are diff icult to treat with biocides and require a pigging pro- gram to remove them. Overall, the pres- ence of bacteria in oil production can result in MIC pits on the metal surface that ultimately may lead to failures. Jenkins, Fajt, and Murphy note that Localized corrosion and pits caused by SRB. Photos courtesy of Schlumberger. MATERIAL MATTERS

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