Numerical Simulation Study Of Gas-water Two-phase Flow In Low-production Gas Wells

As the gas well productivity decreases,liquid produced of the reservoir gradually accumulates at the bottom of the well to form an unloading liquid.Due to the influence of gas well liquid loading,there are a specific phenomenon that the gas-loaded water shows upper and lower circulation disturbance flow in the process of gas well production.It changes the distribution of wellbore fluid medium and velocity,the curves of production profile logging appear obviously abnormity,and the conventional gas-liquid two-phase interpretation model such as slip model?drift-flux model and so on can not reasonably explain and evaluate production dynamics of each production layer in low-yield gas wells.To study on the law of gas-liquid two-phase flow and master the production flow state of low-yielding gas well,it is particularly important to establish an interpretation model for low production gas wells.This paper deals with the gas-liquid two-phase flow in the liquid-loading section of low-yield gas well,characteristics of low-yield gas-liquid two-phase flow are studied by using CFD numerical simulation technique,which lays a foundation for the establishment of gas-liquid two-phase interpretation model.The main work of this paper is as follows:The second chapter introduces calculation flow and models of the CFD numerical simulation,analyzes the advantages and disadvantages of the CFD numerical methods and the scope of application,providing a reference for the selection of the physical model required for the numerical simulation of gas-liquid two-phase flow with low production.In the third chapter,based on the actual well structure characteristic parameters and actual production range of low production gas wells,the geometry model of 125mm pipeline matching with the actual production string is established by using ICEM modeling software,and the reasonable simulation scheme is made.Then the VOF multiphase flow model and the k-? turbulence model in FLUENT software are used to simulate the incompressible air-water gas-liquid two-phase flow at low flow rate.It studies the flow patterns of the gas-liquid two-phase flow under different gas-liquid flow rates,determines distribution of gas-liquid two-phase flow pattern at low flow rate,and analyzes the influence of different gas-liquid phase flow rate on the flow pattern.In the fourth chapter,based on the three gas-liquid two-phase flow patterns(dispersed bubble,cap flow and slug flow)determined in the third chapter,the cross-section data of flow regions are obtained by using CFD-post-processing software with equal spacing.The velocity profiles of gas-liquid two-phase flow under different flow patterns are established,the velocity distribution of gas-liquid two-phase flow at low flow rate is analyzed,and the gas-liquid two-phase velocity under different flow patterns is determined.In addition,the simulation results is compared with the experimental data to verify the reliability of the simulation.The results show that the distribution of gas-liquid two-phase flow regimes at low flow rate are mainly dispersed bubble flow,cap flow and slug flow,but there is obvious circulation disturbance flow in the pipe during the rising process of slug bubbles.The small and dispersed bubbles flow slowly upward in the liquid accumulation column.The velocity profile of a single bubble is obviously flat and single peak distribution.The velocity distribution of gas-liquid two-phase flow is not uniform,the range of gas-phase velocity is 0.4-0.8m/s.The velocity of liquid phase around the small bubble is relatively low,it is only 0.1?0.3m/s.Cap flow and slug flow steadily in the center of the pipeline,they have regular gas-liquid two phase interface and symmetrical velocity distribution of gas-liquid two-phase flow.The slug bubble flows upward at the uniform velocity of 0.8?0.9m/s,and the velocity of cap-like flow is relatively low,which is 0.3?0.5 m/s.For cap flow,there is some difference between the left and right sides of the liquid flow rate.With the increase of flow rate of gas phase and liquid phase,the flow pattern transformation of dispersed bubble-cap-slug flow is accelerated.As the liquid level raises,intensifying the liquid column oscillation,the gas-liquid two phase flow happens irregular flow at the bottom of the tube,the phenomenon of the bubble fall off from both sides of the cap flow and the slug flow becomes remarkable,and the rising slug bubble and the falling small bubble flow up and down.