Microbial Nitrogen and Sulfur Metabolism and its Relation to Corrosion Risk on Offshore Oil Production Platforms

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The potential for microbiologically-influenced corrosion (MIC) of oilfield produced waters collected from the topsides of two offshore FPSO (floating, production, storage, and offloading) vessels exposed to various sulfur (S) and nitrogen (N) chemistries was investigated. Produced water was incubated at high temperature (54 °C) for 154 days with exposure to various nitrate and nitrite injection chemistries under sour and non-sour conditions, and microbial community analysis, N and S transformation monitoring, and corrosion coupon weight loss were used to assess MIC risk. Low concentrations of nitrate or nitrite (0.5 mM) did not effectively inhibit detrimental sulfate reduction by sulfate-reducing microorganisms (SRM), while 5 mM nitrate and nitrite treatments displayed successful sulfate reduction inhibition. Microbial community compositions did not differ dramatically between topside sampling locations from a single FPSO in response to various nitrate, nitrite, and sulfide treatments determined by microbial community analysis, however the microbial community structures between the two FPSO platforms revealed differences. The highest corrosion rates which may be MIC-attributed based on comparisons with sterile controls were measured in microcosms wherein no nitrate, nitrite or sulfide was added (0.48 mm/year). Despite its successful sulfate reduction inhibition, the addition of 5 mM nitrite into produced water microcosms conferred corrosion rates of up to 0.17 mm/year in sterile controls, indicating a chemical corrosion effect. In related work, the purification of the sulfide utilizing enzyme sulfide:quinone oxidoreductase (SQR) from Thiobacillus denitrificans was also performed successfully using a reproducible and scalable method for future use on a previously developed biosensor for sulfide detection. The knowledge gained from this thesis work can be used to inform the MIC risks associated with nitrate and nitrite injection within the topside machinery of offshore oil recovery operations, a previously poorly characterized environment. The efficient enzyme purification method offered in this thesis provides an avenue for continued development of a sulfide biosensor for future use in monitoring sulfidogenesis in produced water samples such as those on offshore oil production facilities.
microbiologically-influenced corrosion, offshore oil recovery, produced water, FPSO, topside, nitrate injection, nitrite injection, souring, sulfide, biosensor
Nicoletti, D. S. (2020). Microbial Nitrogen and Sulfur Metabolism and its Relation to Corrosion Risk on Offshore Oil Production Platforms (Master's thesis, University of Calgary, Calgary, Canada). Retrieved from https://prism.ucalgary.ca.