The Study On Numerical Simulation Method Of Severe Slug With Dispersed Bubbles

With the growing demands toward energy,there is a need to exploit more and more oil and gas.After extensive development of the inland oilfields,the industry now gradually shifts its attention towards offshore.An important method of offshore oil and gas development is subsea production system,which can expand the scope of central platform and increase production efficiency.However,since the deep sea environment is rough and severe,especially when there are long tie-backs during production,the way how to insure that oil and gas can flow through pipeline system fluently becomes one of the critical issues in subsea production system.Severe slug is a common issue in subsea flow assurance.It happens at the interconnection of horizontal pipe and riser and is a kind of periodic phenomena which may accompany high pressure fluctuations.So it may not only damage the pipeline system,but also will influence the facilities downstream.As a result,it is necessary to conduct in-depth research into this flow pattern.After a deep literature review,the author found that traditional severe slug models only regarded severe slug as continuous gas flowing together with continuous liquid,while more and more experiments revealed that there might be dispersed bubbles inside liquid.From the numerical models of separate flow and bubbly flow,one can know that there are distinct differences between the model of dispersed bubbles and continuous gas.So using the traditional two-phase model seems not that reasonable.To cover the shortages of traditional two-phase models,this thesis did a lot of work as shown below:1)Based on two-fluid model and referred to the calculating method of drag force in the AIAD model,it built up a new numerical model which could be applied to 2D simulation and 3D simulation.For validation of the numerical model,it ran several cases that were same as what Fabre had done in his experiment.The results showed that the newly built model was effective.2)Then it discussed the way to model dispersed bubbles.By choosing proper interfacial models from those excellent research,it made up an accurate bubbly flow model.That model was also validated according to some experiments.3)After that,this thesis combined the 2D(or 3D)severe slug model and the bubbly flow model by bubble breakup and coalescence mechanism and formed a new numerical model that could simulate severe slug with dispersed bubbles.Due to the reason that this model had taken dispersed bubbles into account,it showed good performance on modelling those newly found phenomenon4)Finally,this thesis analyzed the influence of dispersed bubbles towards severe slug by a simplified model and the B(?)e criterion.The model built in this thesis can be used in more situations than traditional models.And it also acts more accurate,especially in those non-traditional severe slug.The analysis in chapter 4 has also revealed the influence of dispersed bubbles.In all,this thesis has done a lot of meaningful and valuable work,and it will help push the study of severe slug modelling a little forward.