Research On Pigging Technology Of Marine Condensate Natural Gas Pipeline

Traditional pigs tend to form severe slugs and increase the instability of the pipeline system.Studying new jet pigs and their movement rules is of great significance for ensuring the safe and efficient operation of subsea pipelines.This article has conducted in-depth research on the pigging rules of the jet pig.The main research contents and conclusions are as follows:The main structure of the jet pig is designed.It consists of leather bowls and fasteners,a bypass channel and a main body steel shaft.The type of pig is optimized for the pig steel shaft pig.The bypass channel is provided with a jet single-hole form with stronger blow-off capability and wider influence range.The jet nozzle type is preferably a tapered jet nozzle with a longer range and a wide core area.The influences of four factors,such as the inclination of the pipeline,the diameter of the pipeline,the interference of the pig,and the change of the gas-liquid ratio on the pig pigging process,were analyzed.The results show that for pipelines with an inclination angle of less than 45 °,attention should be paid to the movement of the pig at the bottom of the riser to prevent the speed of jet pig from falling too low and blocking.When formulating a pigging plan,pay attention to fluctuations in the operation of the pig in a pipeline with an inclined angle greater than 75 °.The smaller the diameter,the higher risk of gas hydrate formation at the bottom of the riser.For pipeline engineering design,the small-diameter pipe is helpful to reduce the amount of liquid accumulated in the pipe,and also to reduce the amount of pipe material.The pigging process with 3% interference is more stable.The pig with an interference of 2% and 3% can ensure that the maximum liquid flow rate of the terminal is within a reasonable range.When the gas-liquid ratio is 8,the terminal equipment is less impacted when the pig is shooting out of the pipeline.At low gas-liquid ratio and high gas-liquid ratio,attention should be paid to the operation of the terminal receiving and processing equipment to prevent the equipment from being overloaded.Taking a pipeline in the Liuhua Gas Field in the South China Sea as the research object,the effects of the bypass rate on the speed of the jet pig,the pressure of the pipeline,the terminal plug flow,the liquid holding rate and the flow pattern were analyzed,and the optimal bypass rate range was determined.The results show that the pigging time increases with the increase of the bypass rate,changes slowly at low bypass rates,and changes faster at high bypass rates.When the bypass rate is less than 10%,the change of the bypass rate has a significant effect on reducing the pressure peak,and when the bypass rate is greater than 10%,the pressure peak decreases slowly with the increase of the bypass rate.With the increase of the bypass rate,the maximum terminal liquid plug flow decreases rapidly when the bypass rate is less than 14%,and decreases slowly when the bypass rate greater than 14%.As the bypass rate increases,the duration of the bubbly flow increases,and the duration of the slug flow decreases first and then becomes longer.Considering the influence of various factors,the final recommended bypass rate ranges from 14% to 16%.Hydrate simulation predictions were made for the steady-state working conditions,pigging working conditions,and blocking working conditions of the pipeline,and the influence of MEOH injection amount on hydrate formation under different operating conditions was obtained,and the MEOH injection amount was determined.The results show that under steady-state conditions,when the MEOH injection amount is greater than 0.5,as the MEOH injection amount increases,the hydrate formation mass becomes smaller and smaller,and the effective amount of MEOH injected to suppress the formation of natural gas hydrate is 0.73.Under pigging conditions,the effective amount of MEOH injected to suppress the formation of natural gas hydrate is 0.75.Under blocking working conditions,the effective amount of MEOH injected to suppress the formation of gas hydrate is 0.76.Based on the conclusions of various working conditions,the MEOH injection amount is finally determined to be 0.76.