Microbial Corrosion in the Oil Industry: A Corrosionist's View

Abstract

In view of the scientific and technical challenges as well as the considerable economic stakes (amounting to millions of U.S. dollars), this chapter focuses on the recent developments on the corrosion of steel by sulfidogenic anaerobes. The corrosion layer is an active membrane where a looped interaction between the corrosion electrochemistry and the chemistry and transport of reactants and reaction products may significantly alter the composition of the local electrolyte at the corroding metal surface. A conductive layer is thus a corrosion layer containing a continuous network of an inert electronic conductor galvanically coupled to the metallic substratum. In the case of FeS and microbial corrosion, this merely electric effect is not thought to be decisive, since (i) all iron sulfides are more or less conductive and (ii) the most conductive one, pyrite, is also commonly associated with the best level of protectiveness, whereas corrosive layers usually contain mackinawite (formerly kansite), which is one of the less conductive sulfides. The mechanism of pitting corrosion has been widely documented for stainless steels in chloride media or other passive metals like Al or Ti alloys. However, since the protectiveness of corrosion layers is sensitive to an applied polarization, an equivalent process also exists for carbon and low-alloyed steels. A widespread ecological niche also includes all the low-temperature oil reservoirs where indigenous bacteria have survived, possibly since the original deposition of the biomass. Sulfate-reducing bacteria (SRB) thrive in many deaerated and sulfate-bearing environments, and in a latent state under aerated conditions.