Modelling of Corrosion Electrochemistry in Sweet Environments Relevant to Oil and Gas Operations

• Main Author: Sanadhya, Sanskar
• Format: Doctoral or Postdoctoral Thesis
• Language: English
• Published: 2017
• Subjects: Localised Corrosion; Pitting Corrosion; Carbon Dioxide; FEM; Physiochemical Model; Electrochemistry; Carbon Steel; Oil and Gas Industry; Carbonic acid
• Online Access: https://research.manchester.ac.uk/en/studentTheses/f3771ec2-1a7b-4315-9a91-9ed8af5de1fa; https://pure.manchester.ac.uk/ws/files/75066545/FULL_TEXT.PDF

The research reported in this doctoral thesis involves constructing physiochemical models that reproduce the transport behaviour of aqueous chemical species present in environments relevant to the oil and gas industry to gain an improved insight into the local electrochemistry near the electroactive surface (uniform corrosion) or inside the pit (pitting corrosion). The first part of the project involved constructing physiochemical models with one dimensional geometry with aqueous chemical species and chemical and electrochemical processes observed in oxygen (O2) containing brine environments to determine the changes in the local electrolyte composition and the potential within an initiated pit for a variety of external physical and chemical conditions. It was determined that the bottom of the pit suffers greatly from the effects of iR drop (Ohmic drop) if the pit geometry is taken to be macroscopic. The model was extended to include additional aqueous chemical species in conjunction with the chemical and electrochemical processes observed in carbon dioxide (CO2) rich environment to investigate the effects of CO2 on the local electrolyte chemistry at the bottom of the pit. It was found that the proton reduction electrochemical process on its own was incapable of supplying the high currents experimentally measured in CO2 environments via the buffering effect. The second part of the project was to investigate the influence of different experimental conditions on the polarisation behaviour of near static carbon steels in CO2 saturated brine electrolyte via multiple electrochemical measurement techniques. The key observation from this study was the presence of two distinct mass transport limited regions on the cathodic polarisation curve at natural pH (3.775). From the physiochemical model fitted to the experimental cathodic curve, the first mass transport limited region, occurring at lower cathodic potentials, was identified to be the direct reduction of carbonic acid while the second wave, occurring at slightly ...