Investigation On A Severe Slugging Control Method Based On The Flow Conditioning Mechanism Of ?-shaped Pipe

Severe slug flow is often generated in the gathering pipeline-riser system of the offshore oil and gas field development system.Severe slug flow may lead to many disadvantages such as overflow of downstream separator and lack of gas supply of compressor,so the study on the control method of severe slug flow is of great importance.The flow conditioning method can restrain severe slug flow in the riser by converting the gas-liquid stratified flow into other flow patterns in the upstream gathering pipeline of the riser using flow conditioning device such as venturi-shaped device,hilly-terrain device and wave pipes.In this paper,the experimental method and numerical simulation are used to study the gas-liquid two-phase flow characteristics of a new type of flow conditioning device?-shaped pipe and the method of controlling the severe slug flow.A number of?-type pipe sections for experimental testing were designed and tested.Each?-shaped pipe section was installed in the horizontal test section of the multiphase flow experimental system.The electroconducting sensor was used to measure the upstream and downstream liquid;And the three-dimensional CFD numerical model was established for the horizontal tube with?-shaped pipe section.The liquid phase fraction ratio and the gas-liquid phase distribution along the pipeline were obtained.The effects of geometrical and flow conditions on the flow conditioning effects of the?-shaped pipe were discussed by analyzed the experimental and numerical simulation results,It has been demonstrated that:?1?the?-shaped pipe is capable of realizing two physical processes,namely liquid blocking to gas and gas carrying-over to liquid,through which the stratified flow is converted into an intermittent flow;?2?an increase of the count of the basic units?N?and the ratio?r/D?of the bend radius to pipe diameter can increase the cycle time of the above processes;the increase of N allows more gas to pass the main bend prior to the liquid and the increase of r/D is beneficial for the liquid buildup upstream of the main bend allowing more gas to be carried over through the main bend,resultantly,the fluctuation intensity increases and both the intermittency of the gas-liquid flow and the flow conditioning effects of the?-shaped pipe are enhanced;?3?an increase of the superficial liquid velocity(U_SL)at a constant superficial gas velocity(U_SG)is favorable to the liquid buildup upstream of the main bend allowing more gas to be carried over through the main bend;an increase of the system pressure?P?results in a drop of U_SG weakening the gas carrying-over capability;an increase of U_SG while decreasing U_SL can strengthen the gas carrying-over ability but induce an decrease of the liquid quantity carried-over through the main bend due to a reduced liquid supply and buildup quantity,weakening the flow conditioning effects of the?-shaped pipe.The two-dimensional CFD numerical model is established for the Pipeline-riser system,Pipeline-?-shaped pipe-riser system and Pipeline-?-shaped pipe-riser-‘valve'-system.The change law of flow parameter including differential pressure of riser,pressure drop of?-shaped pipe,outlet velocity,outlet mass flowrate,outlet liquid holdup and phase distribution with geometry parameter?r/D,N?and installation position?Lw/D?is studied by simulation.Study shows:?1?The?-type pipe can control severe slugging;?2?The increasement of r/D enhances the intermittent of liquid phase and gas phase.The alternative entry of large section of gas and liquid phase generate more short liquid slugs than long slugs and the long liquid slug is separated into short ones,which enhances the control effect;?3?The increasement of N enhances the intermittent of liquid phase and gas phase,more gas phase enter the riser,separates the long slugs into short ones and collapses the short slugs with N increasing.Meanwhile,the entry of more gas generates flow section simply consisting of gas in riser and the control effect is enhanced;?4?When the?-shaped pipe is installed closer to the bottom of the riser,the trend of the intermittent flow recovery after flow adjustment is the weaker trend of the stratified flow,control effect is more enhanced;?5?Under the condition of this study,it is not obvious to increase the effect of the throttle valve to improve the control effect of severe slug flow when installed the?-shaped pipe and the throttle valve at the same time.