Investigation On Severe Slugging Phenomenon And Elimination Methods In Multiphase Riser Pipe System

Severe slugging phenomenon is commonly encountered in multiphase pipeline of offshore petroleum exploitation system. In this study, the severe slugging phenomena in decline-riser test pipe, decline-riser test pipe with addition gas volume, plummet-decline-riser test pipe, and decline-flexible riser test pipe were studied systematically. The inner diameter of test pipe is 0.051m. The mechanism and flow characteristics of severe slugging phenomenon were analyzed. A bypass-pipe method for eliminating severe slugging was developed and verified with the experiments. The main contents and conclusions are as follows:The flow pattern maps of severe slugging in 4 sets of test pipe were studied and compared. It was found that the occurring range of severe slugging depends on the layout of test pipe. The decline angle and the gas volume of pipe before riser pipe influence the occurring range of severe slugging. The occurring range of severe slugging in 0°decline pipe is smaller than that of -1°～-4°. When decline angle is between -1°and -4°, the influence of decline angle on the occurring range of severe slugging is very weak. With the gas volume of pipe before riser pipe increasing, the occurring range of severe slugging expands. the occurring range of severe slugging predicted by B?e equation is smaller than experimental results. A modified equation was developed.The flow characteristics of severe slugging in 4 sets of test pipe were studied and compared. It was found that the influences of gas superficial velocity, liquid superficial velocity and the gas volume of pipe before riser pipe on flow characteristics of severe slugging are obvious, but the influence of decline angle is weak. Severe slugging phenomenon have strict period characteristic. The length of period decreases with gas superficial velocity, liquid superficial velocity and decline angle (-4°~-1°) increasing. The pressure fluctuation of severe slugging depends on gas superficial velocity, liquid superficial velocity and the gas volume of pipe before riser pipe. The maximum value of pressure fluctuation occurs at the boundary of SS I and SS II. The experimental studies of severe slugging in decline-riser pipe with additional gas volume were carried out extensively. At higher liquid superficial velocity, the abduction slug of gas velocity was found. The abduction slug impacts on bottom of riser pipe heavily and influences the period characteristic of severe slugging. By analyzing the flow characteristic of severe slugging in decline-flexible riser pipe, two steps of blowout stage and slug formation stage were described.Based on the mass conservation of gas and the momentum conservation of the liquid in the pipeline, a mathematics model of severe slugging in decline-riser pipe and decline-flexible riser pipe with additional gas volume was developed. The mathematics model was verified by comparing the results of experimental and model. It was found that the model fit well to experimental result. The model can precisely predict the characteristic of severe slugging such as period, slug velocity etc.A bypass-pipe method for eliminating severe slugging was developed and verified with the experiments. The bypass-pipe method was modified to eliminate the severe slugging in decline-riser pipe with additional gas volume. It was found that the occurring range of severe slugging, especially the SS I, become smaller when bypass-pipe opened. Liquid superficial velocity has little influence on effect of bypass-pipe method. A mathematic model was educed using the pressure balance of bypass-pipe and riser pipe. The model can carry out the design of bypass-pipe and the control of adjust valve.