| The natural gas condensate pipeline will face serious liquid accumulation in the pipe,increased friction,and pressure drop in the later stage,which will seriously affect the safety of oilfield production.Therefore,it is necessary to take pigging operations regularly to ensure the safe and efficient operation of production.However,for traditional pigging operations,there are problems such as too fast pigging velocity,low pigging efficiency and large pigging slug volume.In order to solve these problems,the middle opening bypass pig scheme has been studied,which can not only reduce the pig velocity,but also greatly reduce the pigging slug volume.In this paper,through theoretical analysis,numerical simulation,laboratory experiments and other methods were used to conduct extensive and in-depth research on the movement characteristics of the bypass pig and the pigging liquid migration characteristics in the horizontal-riser system,and further promote the application of the bypass pig in engineering.Firstly,CFD software was used to establish the motion physical model of the bypass pig in the riser system.By changing the difference between the pig and the driving gas velocity and the size of the bypass hole,analyze the liquid accumulation in front of the pig during the movement of the riser.The research shows that as the difference between pig velocity and driving speed increases,the shape of the liquid plug in the riser gradually evolves from bubble flow to annular flow.The evolution of the shape is related to the amount of gas passing through the bypass hole and pig-generated slug can be eliminated by controlling the amount of gas.The high-speed photography of the liquid accumulation in the riser can verify the accuracy of the CFD software simulation.Secondly,through the establishment of a visualized horizontal-riser pipe system,extensive indoor experiments are carried out to study the motion law of the bypass pig in the pipeline under single gas phase and gas-liquid two-phase conditions.The interaction between the bypass rate,driving gas velocity,and apparent liquid velocity on the pig movement velocity,pipeline pressure fluctuation and terminal liquid level are analyzed.The research shows that in the horizontal-rise pipe system,there is a linear relationship between the pigging velocity and the driving gas velocity under single gas phase and gas-liquid two-phase conditions.The presence of effusion makes the pressure fluctuations in the complicated system,and the bypass pig can better smooth the pressure fluctuations through the bypass hole and ensure the smooth operation of the pigging process.The bypass hole can better smooth the pressure fluctuations and ensure the smooth operation of the pigging process.The bypass pig can reduce the amount of pigging slugs,extend the slug outflow time,and reduce the load of terminal equipment.Finally,the engineering application criterion for bypass pigs are proposed.Combined with CNOOC’s bypass pigging project,the pig preliminary investigation and bypass optimization were carried out,and the friction value was designed and measured.The accuracy of the multiphase flow software was judged based on the field test results.The research shows that that the friction value is sensitive to changes in pipeline parameters and accurate frictional force value can improve the accuracy of pigging prediction.The Leda Flow software is more accurate for bypass pigging motion and terminal effusion. |
