Analysis of Crude Oil Effect for Co2 Corrosion of Carbon Steel - a Rotating Cylinder Electrode Approach

Crude oils, especially heavy crude oils, are rarely used in multiphase-flow loop experiments because of the experimental difficulties. Variations in the tested fluid viscosity, emulsification processes, water cut (WC), flow velocity and flow patterns, interactions between the crude oil and brine, the difficulty in obtaining metal/environment electrical continuity by covering the metal surface with crude oil, and the difficulty of selecting appropriate instrumentation to monitor the experiment are some of these problems. Studies indicate that crude oil can change the brine chemistry and influence the preferential oil/water metal-surface wettability, which impacts the corrosion process. Based on the assumption that corrosion would only occur when free water is separated from an emulsion, the risks could be reduced by transporting emulsified crude oils. However, as the solubility of water in crude oil is low, free water can be formed at the bottom of horizontal pipelines when the emulsion destabilizes, causing an increase in corrosion processes. In previous author’s studies, carbon-steel flow-induced corrosion (FIC) tests were carried out in a multiphase-flow corrosion loop containing a liquid phase of brine plus light or heavy crude oils (WC 80) with a gaseous phase of CO2. Higher corrosion rates for heavy crude oil were observed, which were not expected. No experimental studies in multiphase-flow corrosion loops using heavy crude oils in CO2-brine solution were found in the literature. In attempting to understand the reason for the higher aggressiveness of the heavy crude oil, rotating cylinder electrode (RCE) tests were performed under the same conditions used in the multiphase-flow loop.