Corrosion management is essential to secure integrity and reduce downtime. In 2010, extensive
corrosion was observed in a carbon steel separator at the South Arne facility. Biocide dosing and
microbial monitoring have been ongoing since. To provide the necessary knowledge for selection of the
optimal biocide treatment at South Arne, culprit microorganisms were identified and enumerated.
Methanogens were identified to be dominant in the system, with as major representative the genus
Methanothermococcus, thus this was enriched and grown as biofilm in a specially designed Multiwell
Plate Assay. This method allows for numerous chemical dosages and combinations tests to verify
biocide efficiency and potential synergies with other production chemicals. The effect and compatibility
of glutaraldehyde, THPS and H2S scavenger on system-derived biofilm in produced water (PW) was
studied.
The triazine-based H2S scavenger, up to 1000 ppm, promotes activity and supports growth of
methanogens. When biofilms were exposed to combinations of triazine-based H2S scavenger and
biocide, the biocide effects were reduced. Thus, increased biocide dosages were needed to reduce
microbial growth and obtain a similar effect to treatments consisting solely of biocide. The combination
of regular system monitoring, identification of culprit microorganisms, and specified biocide efficiency
evaluation provides valuable knowledge and in-depth understanding of which corrosive microorganisms
survive the given biocide treatment, prompting further improvements and increasingly specific and
efficient corrective actions.