| In the development of gas reservoir,with the reduction of gas reservoir pressure and the increase of water content,the natural gas is no longer capable of lifting liquid to surface which triggers gradual accumulation of liquid in the bottom of the wellbore.Liquid loading will seriously reduce the productivity of the gas wells,even completely kill gas wells and off production.The liquid-carrying capacity of the natural gas can be effectively improved by using the vortex tools.Recognizing the mechanism of vortex tools,grasping the decay law of swirling flow and predicting the effective length of vortex tools for liquid discharge in gas wells is very important for guiding the field application and promoting the application and popularization of the technology of gas recovery by liquid unloading using vortex tools.The critical liquid carrying droplet model and liquid film model in the swirling flow field are established.From two aspects of mathematical modeling and numerical simulation,the effective length of vortex tools for liquid discharge in gas wells is studied in this paper.The effective length of vortex tools is composed of two parts: the maintenance length of swirling flow and the length of the liquid film existence.First,based on the equal relationship between total surface free energy of droplets and total turbulent kinetic energy of gas,a prediction model of critical liquid-carrying velocity in gas wells considering droplet size,droplet deformation and the effect of droplet deformation on surface free energy is proposed.Based on the force analysis of liquid film and gas-liquid two phase,force balance equations in a vertical tube is established in this paper.The criterion of liquid entrainment based on the critical gas velocity and the critical liquid film flow rate is proposed.The influence of liquid film atomization process and the droplet deposition process at the gas-liquid interface were considered in the calculation model of liquid entrainment under dynamic equilibrium state and a new prediction model for continuous liquid film carrying is established for vertical gas wells which take into account the influence of liquid entrainment on liquid holdup.a new model for predicting the critical liquid-carrying velocity in swirling flow field and droplet model and film model are contained.The existing critical liquid-carrying velocity model are compared,and further to elucidate the mechanism of liquid-carrying and technical principle of vortex tools for liquid discharge in gas wells.Secondly,the decay law of tangential velocity for free swirl flow and swirl number is analyzed from theory,and the maintenance length of free swirl is predicted,and the existence length prediction model of liquid film is established considering the effects of droplet entrainment.Lastly,based on the ANSYS software,the flow field characteristics of the vortex tools for liquid discharge in gas wells are simulated.The liquid distribution nephogram,the axial velocity distribution nephogram,the tangential velocity distribution nephogram and the change law of swirl number are obtained,and the maintenance length of swirl flow in gas wells is predicted based on the swirling number.The research results of the paper clarify the mechanism of the vortex tools for discharge,and reveal the decay change law of the swirl flow.The theoretical basis and technical support are provided for the application of the technology to promote the gas extraction technology of the eddy current drainage in the field of gas field.It provides theoretical basis and technical support for promoting the application of the vortex tools for discharge in gas wells. |
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