Study On Liquid Accumulation And Pigging Of The Wet Gas Gathering Pipeline Network In A Gas Field

With the development and production of natural gas fields,wet gas gathering and transportation process have been increasingly employed which is capable of cutting down equipment investment and operating costs.Induced situations as reduction of pipeline transmission efficiency and increasement of pipeline inner-wall corrosion definitely present challenges to the safety and efficiency of pipeline network operation.It is therefore imperative to conduct research on liquid accumulation and pigging of the wet gas gathering pipeline network.The liquid accumulation model was developed based on the wet gas gathering system in a gas field.Parameter studies in terms of liquid accumulation and liquid holdup distribution were carried out with consideration of influencing factors involving gas flow rate of pipeline network,liquid mass fraction of gas,outlet temperature of gas gathering station,and inlet pressure of terminal gas gathering station.Results show that the decrease of gas flow rate,the increase of liquid mass fraction of gas,the decrease of outlet temperature of gas gathering station and the increase of inlet pressure of terminal gas gathering station all can cause the amount of liquid accumulation and the number of pipeline sections increase.The degree of affection to liquid accumulation from each operational parameter was implemented based on orthogonal experimental design.Results show that gas flow rate of the pipeline network has the most profound effect on liquid accumulation whereas outlet temperature of gas gathering station influences the least.Adjusting the gas flow rate can be preferred for controlling the liquid accumulation.Based on the steady-state liquid accumulation model,the effects of liquid accumulation and liquid volume flow at the terminal of the pipeline network on gas field production and downstream equipment processing were studied considering the pipeline network commissioning and the gas station shutdown-restart.It can be concluded that liquid accumulation balance time decreases with the increase of flow rate for pipeline network commissioning.The liquid accumulation in downstream pipe sections should be seriously detected and the pigging period should be adjusted after gas gathering station shutting down.Liquid volume flow on the terminal point rises sharply for restarting.Mitigations,such as restoring the flow rate in stage by stage,increasing the starting operation time of each stage,and slightly shortening the interval time of each stage in the low-flow rate area,should be adopted to lower the maximum liquid volume flow.A rational pigging period was designed by simulating the pigging period in regular criterion,and pigging parameters were determined by studying the pigging flow rate variations and pig bypass rate variations with different operational data in the terminal large drop pipeline with the severest liquid accumulation.In the end,for the 4 trunk pipelines with the severer liquid accumulation and greater pigging sensitivity,pigging schemes were formulated subjected to lower liquid volume flow at the terminal of the pipeline network and shorten pigging duration,which can provide technical guidance for field management.