Study of H2S Exposure on Biocides: Impacts on Efficacy

Abstract Souring of a well can occur abiotically or primarily biotically, wherein sulfate-reducing bacteria (and other microbes) convert sulfate-bearing minerals into H2S. Biocides are used as treatment for a system to control microbial population and mitigate their associated risks including microbiologically induced corrosion, biofouling and/or souring of production fluids. However, H2S is a reactive molecule and can react with certain biocides, leaving producers with uncertainty about the biocide treatment programs. A full understanding of the extent of reaction is of interest to align treatment programs with actual effective dose rate. In this study, two biocides, tris(hydroxymethyl) nitromethane (THNM) and 3,3'-methylene-bis(5-methyloxazolidine) (MBO), that are reactive with H2S were investigated for their relationship with H2S exposure and efficacy. Biocides were exposed to low-end and high-end theoretical H2S consumption on a molar basis, using H2S gas exposure. A long-term planktonic kill study was conducted using the two biocides neat and consumed at various dosages to determine effect on the biocidal activity. ATP values were analyzed for microbial quantification at various time points. The results showed exposure to H2S did not significantly impact biocidal efficacy. Additionally, long-term microbial control varies in dosages between THNM and MBO.