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    Rheology of waxy crude oils in relation to restart of gelled pipelines

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    Publication date
    2020-01-16
    Author
    Fakroun, A.
    Benkreira, Hadj
    Keyword
    Waxy crude oil
    Rheology
    Re-start pressure yield stress
    Crystallisation
    Rights
    © 2020 Elsevier. Reproduced in accordance with the publisher's self-archiving policy. This manuscript version is made available under the CC-BY-NC-ND 4.0 license.
    Peer-Reviewed
    Yes
    
    Metadata
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    Abstract
    Waxy crude oils are pumped hot but upon power cut, pumping stops, the oil cools leading below the wax appearance temperature to precipitation of the wax and the formation of a gel throughout the pipe. In such a situation, what is the minimum pressure required to restart flow, not to merely deform the gel or break it? This paper provides a solution to this problem using microscopic observations under controlled cooling conditions and rheological data conducted in constant stress mode under controlled temperature and cooling conditions and restart experiments in laboratory pipelines replicating the rheometric conditions and deviations from them to inform large diameter operation in the field. Three important findings derive from the experimental data collected: (i) A fragmentation stress , rather than the static stress that precedes it, is found to be the more accurate predictor of flow re-start pressures; (ii) Waxy crude oils gels exhibit true yield stress and yielding process but also show flow on application of the slightest stress below yielding; (iii) This flow, in the elastic region, is jagged rather than continuous suggesting a consolidation process of the crystals and their agglomerates forming the gel. In the broader context of the existence of a yield stress, the data presented here show that there is such a thing as a yield stress and the concepts of a yield stress and that everything flows are not mutually exclusive.
    URI
    http://hdl.handle.net/10454/17283
    Version
    Accepted manuscript
    Citation
    Fakroun A and Benkreira H (2020) Rheology of waxy crude oils in relation to restart of gelled pipelines. Chemical Engineering Science. 211: 115212.
    Link to publisher’s version
    https://doi.org/10.1016/j.ces.2019.115212
    Type
    Article
    Collections
    Engineering and Informatics Publications

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