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    The Development of a Knowledge-Based Wax Deposition, Three Yield Stresses Model and Failure Mechanisms for Re-starting Petroleum Field Pipelines. Building on Chang and Boger’s Yield Stresses Model, Bidmus and Mehrotra’s Wax Deposition and Lee et al.’s Adhesive-Cohesive Failure Concepts to better Underpin Restart Operation of Waxy Crude Oil Pipelines

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    PhD Thesis (13.30Mb)
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    Publication date
    2017
    Author
    Fakroun, Abubaker A.
    Supervisor
    Benkreira, Hadj
    Keyword
    Elasticity
    Yield stresses model
    Wax deposition
    Effective yield stress
    Waxy crude oil
    Failure acceleration
    Pipeline restart
    Adhesive-cohesive failure
    Crystallisation
    Morphology
    Rights
    Creative Commons License
    The University of Bradford theses are licenced under a Creative Commons Licence.
    Institution
    University of Bradford
    Department
    Faculty of Engineering and Informatics
    Awarded
    2017
    
    Metadata
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    Abstract
    Twenty years ago, Chang et al. (1998) introduced the three-yield stresses concept (dynamic, static and elastic limits) to describe yielding of waxy crude oils cooled below the wax appearance temperature (WAT). At the time, the limits in rheological instruments were such that they never actually measured the elastic-limit, a key fundamental property. Using modern instruments, this research succeeds in recording for the first time the entire yielding process down to stresses of 10-7 Pa and shear rate of 10-6 min-1 as a function of temperature, cooling rate and stress loading rate using two waxy oils of different origins and wax content. A four-yield stress model is established using derivative data (dynamic fluidity and failure acceleration). In addition, calorimetry (DSC) and microscopy (CPM) helped extract WAT, the gel and pour points and link gel crystal structure and its yielding and breakage to rheological properties. The yielding stresses measured rheologically were tested in laboratory pipelines at two diameter scales, 6.5mm and 13.5mm to compare stresses in uniform and non-uniform cooling. It is demonstrated that rheological instruments can only predict gel breaking pressure when the cooling rate is low, i.e. yielding at the pipe wall. A complementary heat transfer study was performed on a section of pipe statically cooled, both experimentally and theoretically to predict the gel front-liquid oil interface that develops in industrial pipeline where gel breaking occurs. This key information together with rheological data provide the means to predict accurately restart pressures of shut gelled pipelines that have eluded previous research.
    URI
    http://hdl.handle.net/10454/16792
    Type
    Thesis
    Qualification name
    PhD
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