Numerical Simulation For Gas-liquid Two-phase Severe Slugging In A Pipeline-vertical Riser System

In the development of offshore oil and gas resources,the submarine pipeline comprised of the downward inclined pipeline and a riser pipe connected to offshore platform is needed to transport oil and gas.The gas-liquid two-phase flow is not stable in this type of pipelines.One important problem appeared in such a pipeline-riser system is a severe slugging phenomenon.When this happens,the liquid slugs built up in the system sometimes are longer than one or several riser heights.Severe slugging will lead to drastic fluctuation of pressure and flow rate in riser that will damage pipeline system and production equipment.As a result,a deep research on severe slugging becomes more and more important and has practical engineering value.On the basis of mathematical modeling and CFD simulation,gas-liquid flow pattern and the flow parameter characteristics of gas-liquid severe slugging in classical pipeline-vertical riser system were researched.The main work is as follows.(1)A transient mathematical model for severe slugging was developed on the basis of continuity equation and the momentum equation.The liquid slug velocity,liquid slug lengths,pressure fluctuation,period,void fractions were obtained by solving mathematical model.This mathematical model provides an accurate and efficient evaluation method for severe slugging.(2)Numerical simulations were conducted for the gas-liquid flow patterns of the severe slugging in a declination pipeline-vertical riser system by using Fluent software.Flow processes of several types of severe slugging were presented and the pressure fluctuation,liquid slug velocity,period,void fractions were obtained,and numerical results are in good agreement with the experimental ones.(3)The flow processes of SS??SS??SS? and stable flow and the characteristics of flow parameters are analyzed.The results indicate that the variation of pressure and velocity is periodic,these parameters have certain trend in each flow stage and the change of parameters is related to the gas superficial velocity.(4)The gas-liquid two-phase severe slugging in a horizontal-vertical riser system is simulated by using Fluent software.It is verified that severe slugging does not occur in this kind of pipeline system.(5)The proposed 2D CFD method was also applied to analyze the influence of gas-liquid physical parameters on the severe slugging in a pipeline-riser system.The liquid are chosen as water and kerosene,the gases are chosen as air and methane,results show that the physical parameters of the liquid have remarkable influence on the characteristics of the severe slugging,but the influence of the gas physical parameters is not significant.