Analysis On The Characteristics Of Severe Slugging In Pipeline-catenary Riser System Of POT Deep-sea Oilfield

With the development of ocean petroleum industry expanding to the deep sea areas,the pipeline-catenary riser system has been used as an effective gathering and transferring system in the development of deep sea oilfield.Severe slugging is an unstable phenomenon with slug length equal to or longer than the height of riser in catenary riser.A series of large adverse effect caused by fluctuations of pressure and flow rates on operation of piping system and production equipments.In order to study on the characteristics of severe slugging in pipelinecatenary riser system,the following woks have been carried out in this paper.The criterion conditions where the severe slugging flow can be produced in the catenary riser were obtained based on the formation mechanisms of severe slugging,considering the quality of liquid fallback.It has been contrast with the flow pattern which is obtained by the experient.The results show that criterion conditions can determine the producing of severe slugging effectively.The transform boundaries of various flow patterns are analyzed.The ranging of production parameters which may produce severe slugging in POT deep-sea oilfield pipeline-catenary riser system has also been given.In view of different characteristics for four stages of slug formation,slug production,blowout and liquid fallback,based on momentum conservation equation,mass conservation equation and gas status equation,considering fluid physical property and transient effects,combined with drift flux model,an one-dimensional transient mathematical model is presented to simulate severe slugging in catenary/vertical-riser systems.Runge-Kutta method is used to solve the model accurately and quickly.The results show that,for pipelinecatenary riser system,the calculation results about pressure amplitudes and periods are in good agreement with the experimental results and the simulation results of POT deep-sea oilfield by OLGA.It can calculate the characteristics parameters of severe slugging accurately.According to the calculation results of one-dimensional transient mathematical model,the cycle characteristics of severe slugging I,II,III and the changing laws of characteristics such as pressure,cycle,eruption time,slug length as well as liquid velocity at the riser outlet of severe slugging with different gas and liquid superficial velocity are analyzed.Choking method with a choke valve at the top of riser is applied on eliminate severe pipeline slugging in POT deep-sea oilfield,for the problem of valve opening,OLGA software is used to simulate the characteristics parameters changing of severe slugging under different valve opening.At last,the best valve opening for POT deep-sea oilfield is presented in this paper.