Fundamental investigations of sour oilfield corrosion

摘要

Dissolved H_2S is a primary reagent for internal (sour) corrosion of oilfield equipment fabricated from carbon steel. The resulting aqueous phase species stimulate corrosion primarily through supplying reactant for the cathodic process; iron dissolution occurs at anodic sites. Solid corrosion products may also appear as a consequence of H_2S induced corrosion. If adherent to the carbon steel substrate, such solids can significantly reduce the rate of corrosion, and so are integral to material sustainability. Given the importance of sour corrosion scales, there is significant on-going effort to understand them. Substantial progress has been made, in particular as regards established scales. Lacking, however, are nanoscale details about the nucleation and growth of these scales, including the surface structure/chemistry prior to scale initiation. On this basis, we have adopted a surface science type approach in attempt to address these topics. Using UHV-STM, we have examined the adsorption of H_2O/H_2S onto Fe(UO). finding significant variation as a function of both exposure and substrate temperature. Both long range and short range ordered phases are observed, apparently arising from mass transport of substrate material. Such results demonstrate the dynamic nature of the iron substrate, even when exposed to technologically insignificant quantities of pertinent species, suggesting that our mechanistic understanding of sour oilfield corrosion is currently highly limited.