Severe slugging with multiphase fluid transport and phase separation in subsea pipelines

Igbokwe, Loveday Chidozie (2020) Severe slugging with multiphase fluid transport and phase separation in subsea pipelines. Doctoral (PhD) thesis, Memorial University of Newfoundland.

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Abstract

Flow assurance and separation of multiphase oil and gas flows are becoming more challenging as offshore development advances into more difficult environments. Petroleum fluids are required to be transported to processing facilities over long distances and through difficult terrain, as well as under varying temperatures and pressures. Severe slugging is a well-known flow assurance problem that limits effective offshore petroleum production. Gas-lifting and topside choking have been used for decades to mitigate this flow problem in fluid transport and processing. However, the application of these techniques has been challenged by design, cost, and footprint constraints. The introduced complexities require detailed understanding of the detailed dynamics of fluid flow in highly compact designs. Systematic experimental and modeling investigations of severe slugging in pipeline-riser systems can provide useful information on these slugging mechanisms and characteristics. Experimental studies are conducted in this thesis to determine the mechanisms and key parameters involved in the slugging performance in fluid processing installations. Through well designed experimental tests, the impacts of actuators on slugging are examined. This thesis also focuses on control systems to suppress slugging in the pipeline-riser system using experimental analysis and control models. The research also presents new models that predict phenomena of slugging behaviour, and more importantly, fitting for control designs in offshore flow separation. Furthermore, this thesis identifies and quantifies the process variables and conditions associated with both slugging and non-slugging regions, leading to the development of more effective solution methods and correlations. Relevant correlations (including slugging frequency, production rates, gas injection rate, compression requirements, and operating pressures) are developed by dimensional analysis techniques. The study develops new models, data and useful information for better understanding of slugging in pipeline systems. Sensitivity analyses to assist in the selection and design of more accurate control methods are also presented. The research outcomes provide improved and more robust models and guidelines for implementing slugging mitigation measures.

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