Methods On Eliminating Severe Slug In Riser Systems By Combine Choking And Gas Lift

Multi-phase flow is commonplace in oil and gas production industry.Harmful flow pattern-severe slug in pipeline-riser systems happen when the rates of liquid and gas hit low number.The existence of severe slug threatens the optimal operation causing a plethora of problems,such as vibration of pipes,pipeline corrosion,high pressure,ect.Most of the current calculation models of the severe slug are based on laboratory pipelines which are in low pressure and cannot be translated to large riser systems.Most studies on eliminating this problem focus on experiments and software simulation,however,there is no established model for method combining chocking and gas lift.Therefore,this thesis will focus on these aspects of research.First,I will analyze physical processes and establish the gas-liquid continuity equations for the pipeline-riser system.The gas state equation and drift flow relationship are inteoduced as the closed equation.This model emphasizes the gas compressibility and the angle of the riser tilt.These partial differential equations are solved by method of characteristic,obtaining a one-dimensional quasi-steady-state model that can simulate large vertical risers and large inclined risers.Once the model is established,the observation data from various scholars under different experimental conditions along with the calculation data of OLGA software are used as a verification method.This will prove the efficacy to simulate different flow patterns,such as 1.cycle with fall back,2.cycle without fall back,3.steady flow and 4.unstable oscillations.This model accurately calculates the important parameters of the severe slug flow such as the length of slug,flow cycle,etc.,which shows that the model calculation results are sufficient.On the basis of the severe slug flow model,a model of eliminating severe slug by combining chocking and gas lift is established,and it performed well in comparison with the experimental values.The current problems and challenges of this method will also be discussed.