THPS in oil field system: How rare taxa can increase MIC risk

Abstract

Microorganisms implicated in Microbially influenced corrosion (MIC) in oil field system are part of the autochthonous microbial community. The development of those microorganisms is controlled by the addition of biocides. The effect of THPS on an autochthonous oil-degrading community was evaluated in an anaerobic oil field simulating reactor with forced circulation, containing water from a crude oil storage tank, sludge and crude oil. Two doses of THPS of 400 and 600 ppm were applied at interval of 15 days.The concentration of bacteria, archaea, sulfate-reducing microorganisms (SRM), methanogens, sulfur-oxidizing bacteria and hydrocarbon-degrading bacteria was estimated using qPCR. The first dose of THPS significantly increased the concentration of all microbial populations, suggesting a hormetic dose-response. Immediately before the second dose, only SRM decreased significantly compared to the initial concentration. All populations increased their concentration above the initial values after two-dose applications.The microbial community composition was assessed using Illumina sequencing of 16S rRNA gene. Biocide treatment impacted the abundances of rare species, affecting the syntrophic relationships with the accumulation of acetate and inhibition of crude oil degradation. Especially, the abundance of acetogens, hydrogenotrophic methanogens and SRM populations increased, contributing to MIC risk.The proper selection of the biocide to control MIC in oil fields should consider its effect on the autochthonous microbial community, taking into account also the rare taxa. The use of molecular tools and models simulating the field condition could result in a closer approximation to the real situation in oil fields.