• Xiao, Xiong
• Pradhan, Vijay
• Boxall, John A.
• Rowland, Darren
• May, Eric F.
• Jiao, Fuyu
• Ghafri, Saif Z. S. Al

Abstract

<p>Accurate predictions and precise control of the allowable water content in CO₂-rich fluids are required in large-scale pipeline operations. Especially during transient shut-in and re-start operations, the pressure decrease associated with cooling may cause the CO₂-rich mixture to pass through its dew point, producing an aqueous liquid phase. The pH of this liquid aqueous phase will rapidly decrease as carbonic acid is formed, greatly accelerating the corrosion rate of the carbon steel pipeline. The phase behaviour of CO₂-rich fluid mixtures is qualitatively different to that of hydrocarbons, and standard oil and gas property packages in process simulation software may be inadequate for predicting dew points and other key properties. An extensive literature survey reveals 34 data sets where water contents of CO₂-rich fluids have been measured near conditions relevant to CO₂ pipelines. Following consistency tests, 23 data sets were found to be of good quality and 11 data sets were found to be of poor quality. The good-quality data were compared with predictions from 6 equations of state. Overall, Multiflash's RKS (Advanced) model was found to provide the best agreement with the aqueous dew point data of CO₂-rich fluid phases. A case study is presented wherein it is demonstrated that the formation of a corrosive aqueous phase can be avoided during shut-in via introduction of a relatively small volume of ethanol.</p>

Topics

• impedance spectroscopy
• Carbon
• corrosion
• simulation
• steel
• positron annihilation lifetime spectroscopy
• Photoacoustic spectroscopy
• liquid phase