ABSTRACT
The oil and gas industry faces high annual costs due to corrosion of metal infrastructure. To some extent, these corrosion issues are caused by growth of microorganisms and referred to as microbiologically influenced corrosion (MIC). Microbial activity influences the overall chemistry of a given system, which, in turn, influences the electrochemical processes at the metal–environment interface. Various microbial processes (e.g., sulfidogenesis, fermentation, 88acetogenesis, methanogenesis) can contribute to MIC in oil and gas industrial systems and infrastructure. Sulfate-reducing microorganisms have garnered significant attention due to their frequent association with corrosive biofilms in anoxic settings. Additional problems can arise due to SRM-mediated production of toxic and corrosive hydrogen sulfide (H2S), which contributes to reservoir souring during seawater flooding. Bioengineering strategies, such as nitrate injection, have often proven successful for controlling souring and subsequent corrosion during in vitro and in situ trials by stimulating the activity of nitrate-reducing microorganisms. Despite reported successes, nitrate-based bioengineering has come under scrutiny in light of recent studies showing that nitrate can lead to severe corrosion under some conditions. Nitrate treatment or unintentional ingress of oxygen can lead to redox potential shifts and subsequent formation of highly corrosive inorganic compounds (e.g., elemental sulfur, S0), which can severely damage metal infrastructure. In recent years, our understanding of MIC in oil systems has gradually increased, and bioengineering strategies, such as injection of nitrate, have been successful in some cases but not in others. This chapter provides an overview of potential corrosion mechanisms related to nitrate injection and ingress of oxygen in sour systems. Microbial and chemical transformations during oil production are discussed to explain and help predict corrosion hazards in sour oil systems.
