Numerical Study Of Severe Slug Flow In Marine S-Shaped Riser System

In the exploitation of marine oil and gas resources,multi-phase transportation pipelines are often used to transport oil and gas,and multi-phase transportation pipelines are composed of pipes laid on the seabed and risers connected to offshore platforms.The gas-liquid two-phase flow in this form of pipeline is easy to form a liquid plug of several times the height of the riser to block the pipeline,and severe slug flow will occur,which will cause significant fluctuations in the pressure,flow rates and other parameters in the pipeline,resulting in pipeline and the downstream equipment produces violent vibration,which may even cause damage to the pipeline or equipment,forcing the shutdown of production.Therefore,the in-depth study of severe slug flow has become more and more important and has academic significance and practical engineering application value.Aiming at the S-shaped riser system,which is one of the main forms of deep-sea oil and gas gathering and transportation,the two-dimensional CFD method is used to numerically simulate the gas-liquid two-phase severe slug flow in the pipe.Using Fluent software to simulate the flow process of severe slug flow type I,type II and type III,and analyze the change characteristics of the characteristic parameters of severe slug flow.The results show that the changes of pressure,flow and other parameters are all periodic,and correspond to the changing trends in each flow stage.On the probability density distribution chart of liquid holdup,it is found that the severe slug flow type I presents a bimodal structure,the severe slug flow type III presents a unimodal structure,and the severe slug flow type II presents two structures of unimodal and bimodal.The simulation of severe slug flow in the S-shaped riser under different gas-liquid fluid shows that the density and viscosity of the liquid phase have a greater impact on the pressure,period,and liquid holdup of the downdip pipe section of the severe slug flow,while the influence of the physical parameters of the gas phase is very small.The simulation of the gas-liquid two-phase flow in the S-shaped riser when the inclination angle of the down-dip tube is 0 degrees found that a small liquid plug will be formed at the bottom of the S-shaped riser,but because the down-dip tube is horizontal,the liquid is spread flat in the horizontal tube.As a result,the gas space in the pipe section is smaller than when it is inclined,and the gas quickly passes through the small liquid plug and enters the riser.There will be gas-liquid mixed flow in the riser,and severe slug flow will not be formed.The research results of this paper are helpful to better understand the flow process of severe slug flow in S-shaped riser and the variation law of characteristic parameters,which has certain guiding significance.