Development of physical techniques for hydrate monitoring and early warning systems
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One of the challenges that the petroleum industry faces is to ensure unimpeded flow of hydrocarbons. During production, transportation and processing, there can be free water in the produced fluid, and/or changes in temperature and pressure can lead to water condensation causing ice and/or hydrates formation. Gas hydrates pose serious flow assurance, economic and safety concerns. Chemical inhibitors are widely used to reduce the risks associated with hydrates. However, the upstream injection of hydrate inhibitors is generally based on thermodynamic model predictions and estimations of the worst conditions without much downstream measurements. This thesis presents a research work in which a number of techniques were investigated with the ultimate aim to mitigate hydrate risks during hydrocarbon recovery. Hydrate Monitoring Techniques are where the hydrate stability zone (HSZ) could be determined by testing downstream samples. Spectroscopy, dielectric permittivity, and freezing point depression methods were experimentally examined. A novel pseudo concentration approach was created as a result of this research work. This approach is more reliable and robust than the historically developed correlation, since it takes into account the pressure, hydrate structure and inhibitor type effects. Spectroscopy, dialectic permittivity set-ups and a freezing point prototype device based on Peltier heat pumps have been designed, built and tested. Hydrate Early Warning Techniques are where the hydrate formation could be detected based on water memory phenomenon. This phenomenon suggests that sampled fluid under specific conditions can carry remnant molecular structure related to hydrate formation if it had taken place. Spectroscopy, onset of ice formation and onset of hydrate formation were investigated. During this work, a multiple probe freezing apparatus and hydrate mini-rig prototypes have been designed, built, and tested. These techniques can provide technical measures for hydrate monitoring and early warning, helping to lessen the risk of pipeline blockages as well as to minimise the amount of chemicals required to inhibit any hydrate formation, hence improve the production economics and reduce the impact on the environment. Moreover, the investigated techniques show a potential to be deployed in Supervisory Control And Data Acquisition (SCADA) systems widely used in the petroleum industry for reservoir/production monitoring and management.