Development and application of spectroscopy techniques for monitoring hydrate and corrosion risks
Haghi, Reza Khodaparast
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Pipelines are used to transport hydrocarbons from production wells to different locations for various purposes (e.g. processing, refinery, power generation, etc.) and CO2-rich fluids from the emission sources for disposal in suitable geological storage sites. The presence of water in such hydrocarbon and/or CO2 transport pipelines may result in corrosion, ice and/or gas hydrate formation and even pipeline blockage, so the fluid system should meet certain dehydration and/or inhibition requirements. This work describes the development and application of different spectroscopic (UV-VIS and NIR) methods for identifying and controlling flow assurance issues relating to gas hydrate and corrosion. For hydrates, a Fourier Transform Near-Infrared (FTNIR) spectroscopy method using chemometric models was developed to measure the concentration of main hydrocarbon gases (Methane through butanes) under in-situ pressure (up to 13.8 MPa). This approach was then used for detecting initial signs of hydrate formation based on reduction in the concentration of some preferential components in the gas phase. Furthermore, injection of hydrate inhibitors based on the calculated/measured hydrate phase boundary, water cut, pressure and temperature conditions, and the amount of inhibitor lost to non-aqueous phases is a commonly used method for avoiding gas hydrates problems. Thus, it is crucial to monitor salt and inhibitor concentration in the fluids along the pipeline and/or downstream in order to optimise the injection rate. To address this requirement, a novel method was developed by combining UV and NIR spectra to predict the concentration of salt and hydrate inhibitors (THIs and KHIs) simultaneously in aqueous solutions. In the case of corrosion, the potential of visible spectroscopic technique was investigated for determining the pH in CO2/ CO2-rich mixtures saturated water, and CO2/ CO2-rich mixtures saturated NaCl solutions at pressures up to 15 MPa and temperature ranges from 293.15 to 323.15 K. Furthermore, we described and evaluated a model that uses a robust thermodynamic basis for describing the solubility of gases in the aqueous phase and Pitzer’s theory for determining the activity coefficients of the ionic species involved. The model was tested in concentrated NaCl solutions under CO2 pressure at realistic industrial operating temperatures. The developed spectroscopic techniques were experimentally evaluated at lab conditions. Results show that these techniques can be applied to detect initial signs of hydrate formation, to optimise hydrate inhibitor injection rate, and to measure the pH of CO2 saturated H2O/brine systems in the downhole/wellbore/pipeline region.