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Abstract:
Oil reservoir souring and associated material integrity challenges are
of great concern to the petroleum industry. The bioengineering strategy
of nitrate injection has proven successful for controlling souring in
some cases, but recent reports indicate increased corrosion in
nitrate-treated produced water reinjection facilities.
Sulfide-oxidizing, nitrate-reducing bacteria (soNRB) have been suggested
to be the cause of such corrosion. Using the model soNRB Sulfurimonas
sp. strain CVO obtained from an oil field, we conducted a detailed
analysis of soNRB-induced corrosion at initial nitrate-to-sulfide (N/S)
ratios relevant to oil field operations. The activity of strain CVO
caused severe corrosion rates of up to 0.27 millimeters per year (mm
y(-1)) and up to 60-mu m-deep pitting within only 9 days. The highest
corrosion during the growth of strain CVO was associated with the
production of zero-valent sulfur during sulfide oxidation and the
accumulation of nitrite, when initial N/S ratios were high. Abiotic
corrosion tests with individual metabolites confirmed biogenic
zero-valent sulfur and nitrite as the main causes of corrosion under the
experimental conditions. Mackinawite (FeS) deposited on carbon steel
surfaces accelerated abiotic reduction of both sulfur and nitrite,
exacerbating corrosion. Based on these results, a conceptual model for
nitrate-mediated corrosion by soNRB is proposed.
IMPORTANCE Ambiguous reports of corrosion problems associated with the
injection of nitrate for souring control necessitate a deeper
understanding of this frequently applied bioengineering strategy.
Sulfide-oxidizing, nitrate-reducing bacteria have been proposed as key
culprits, despite the underlying microbial corrosion Citation mechanisms
remaining insufficiently understood. This study provides a comprehensive
characterization of how individual metabolic intermediates of the
microbial nitrogen and sulfur cycles can impact the integrity of carbon
steel infrastructure. The results help explain the dramatic increases
seen at times in corrosion rates observed during nitrate injection in
field and laboratory trials and point to strategies for re- Editor
ducing adverse integrity-related side effects of nitrate-based souring
mitigation.
