Study On The Control Method Of Slug Flow In The Process Of Pigging And Stopping The Restart Of M Gas Field

The gathering and transportation pipeline Line 1 of M gas field is composed of 7 sections,featuring wet gathering and transportation containing high content of sulfur,great drops and effusion in low-lying areas.Segmented pigging operation in sequence and restart of emergency shutdown would lead to a great amount of pigging and start slug flow,which would easily produce hydrate inside the pipeline and cause overflow of separator in the master gas collection station.Drawing experience from enterprises and gas fields at home and abroad,in their successful operations to control the slug flow of gas-liquid transportation pipeline,the author,in this article,optimized the pigging operation proposal,put forward the method to control the separator,formulated the general method and procedures concerning the restart of shutdown for the gas field with high sulfur content as well as designed and improved related slug flow suppression devices.Major research contents are as follows:(1)A series of research results at home and abroad have been studied,including pigging models for the multi-phase flow pipeline,dynamical models to produce the natural gas hydrate,typical pigging techniques and proposals,restart techniques of shutdown for the gas-liquid transportation pipeline,and research status for devices to control the slug flow.Meanwhile,some deficiencies existing in current researches,such as lack of studies on the gathering and transportation system of highly sulfur-containing gas field,monotonous method to control the slug flow and low practicability of the slug flow suppression device,were discussed to analyze the great differences between the highly sulfur-containing gas field and the general gas field in terms of pigging operation and the restart of shutdown process.(2)Firstly,several pigging proposals were preset to analyze the operation parameter changes for the gathering and transportation pipeline Line 1 and determine a reasonable pigging sequence for sections.Then,the movement trails of slug flow during the pigging process were tracked to analyze the volume and length of the slug flow as well as the sequence and time it needs to get inside the separator.In line with the principle that in the event where the separator could deal with the largest load of slug flow and provides the maximum utilization of surge volume,the minimum duration for one pigging operation can be achieved,the "critical pigging proposal" was designed.Guided by the "critical pigging proposal",the locations along which hydrate were possibly formed were identified and verified.The ground eddy devices designed for the high sulfur-containing gas field was designed and improved,including eddy blade,blade lifting device,H2S filter cover,which would help to drainage the effusion in low-lying areas and control the slug flow.Moreover,the application effects of the device were analyzed.(3)The "Extreme pigging proposal" was designed to ensure the shortest duration for operations of "pigging + filming" and reduce the influences of these two operations on the adaptability of acid gas removal device in the purification plant.Furthermore,the processing ability of the separator in this proposal was checked and the formation process of hydrate caused by the slug flow in some low-lying areas was analyzed.Firstly,under the guidance of the "extreme pigging proposal",the device used to drain the effusion in low-lying areas was recommended to prevent ice blockage.Then,the applicability of such device for the gathering and transportation pipeline of M gas field was demonstrated and studied.Thirdly,effusion drainage effects of different device models were predicted.(4)Firstly,some parameters concerning the pigging operations of end pipelines with huge drops were optimized,including volume of blowing air,time of blowing and air volume of pigging ball-pushing to control the pigging slug flow.Secondly,based on the liquid level and pressure of the separator in the gas gathering master station as the control variables and reduction of emergency drainage time of the separator as the control target,the control method of the separator was optimized to relieve the impact of pigging slug flow on the separator.Thirdly,the structure of the bypass pigging device was improved to prevent the backflow of the pigging slug flow.Fourthly,related operation parameters of the bypass pigging device were analyzed to figure out the optimal bypass rate applicable to the bypass pigging device of the end pipeline with large drops.(5)Firstly,the method to calculate the safe shutdown time was put forward to prevent the formation of hydrate inside the pipeline after the emergency shutdown.Secondly,parameter changes during the process of shutdown were analyzed to determine the safe shutdown time of the pipeline.Meanwhile,the change rules of the safe shutdown time under different working conditions were studied.Thirdly,the research method for the restart proposal was raised and multiple start proposals were preset to analyze the parameter changes under different start proposals.Fourthly,by adopting the phased change method of transportation volume,the increase rate of air volume was controlled and the best proposal to prevent the formation of the start slug flow was determined.What’s more,the general method and procedures for the restart of emergency shutdown for the high sulfur-containing gas field were concluded.