Monitoring oil pipeline microbiologically influenced corrosion (MIC) and its mitigation using a biofilm/MIC test kit

Microbiologically influenced corrosion (MIC) is caused by microbial biofilms. In this work, an oilfield produced water sample was analyzed using a newly developed disposable electrochemical biofilm/MIC test kit consisting of two solid-state electrodes in a 10 mL standard serum vial for assessing biofilm growth, biocorrosivity and biocide treatment efficacy. The produced water sample was found to be low in microbial cell counts and nutrients. To simulate a possible worst-case scenario, the produced water sample was subcultured at 37 °C using enriched artificial seawater (EASW) for 3 rounds before being used as the seed culture for further MIC and biocide tests. The electrochemical test results from the 10 mL biofilm/MIC test kit including polarization resistance ( R p ) from linear polarization resistance scans and corrosion current density ( i corr ) from Tafel scans indicated a corrosion rate sequence of no biocide treatment >20 ppm ( w / w ) tetrakis hydroxymethyl phosphonium sulfate (THPS) > 50 ppm THPS. R p was able to predict biofilm maturity time using the incubation time when R p leveled off (i.e., time to reach maximum corrosivity). Two common electron transfer promotors were found to accelerate MIC in the test kit vial injection tests, pointing to extracellular electron transfer-MIC as the main mechanism. This observation was consistent with the 30% corrosive sulfate reducers among all microbes in the mixed culture sample found by metagenomics. In the coupon incubation tests in 125 mL anaerobic vials, the 7-d X60 carbon steel weight loss was 1.1 ± 0.2 mg/cm 2 (2.9 mpy uniform corrosion rate) without biocide treatment. With 20 ppm THPS biocide in EASW, it dropped to 0.5 ± 0.2 mg/cm 2 (1.3 mpy), and with 50 ppm THPS, it became negligible. The corresponding MIC pit depths were 10.5, 8.9 μm, and no well-defined pits, respectively for the three biocide treatment conditions. The weight loss data confirmed the corrosion rate sequence from the biofilm/MIC test kit. This work presents a new MIC monitoring and biocide treatment assessment system for oilfield applications using the new biofilm/MIC test kit.