Research On The Characteristics And Control Of Surge And Swab Pressure In The Long Distance Of Oil And Gas Crossing Pipelines

As the main method of long distance oil and gas multiphase flow in modern civilized industries,the long-distance crossing transmission pipelines(LCTP)have many advantages such as low one-time investment&transmission cost,large amount of transport and high security.Comparing with the regular pipelines,the parameters of LCTP like gas holdup,gas slippage and pressure wave velocity change significantly with the migration of fluid.Meanwhile,it is much harder for LCTP Oil and gas multiphase flow research when considering the factors such as the interaction between oil and gas,gas drift,gas-liquid density and difference in viscosity.Because the calculation of surge and swab pressure in oil-gas LCTP is closely related to the movement law of oil-gas fluid,gas-liquid density and pressure wave velocity,it is important to get not only the clear definitions of boundary conditions,but also the exact parameters like gas holdup,change under steady pressure and pressure wave velocity.This paper focuses on the movement law of oil-gas fluid,pressure wave velocity,pressure response and pressure fluctuation,laying a foundation for the subsequent research on pipeline design and surge and swab pressure of Oil and gas multiphase flow.This paper first established multiphase flow mathematical model?multiphase pressure wave velocity model and multiphase surge and swab pressure hydraulic system,the corresponding calculation module is developed for the model,obtain multiphase flow parameters(Pressure,temperature,gas holdup,etc),get the wave velocity in the pipe,on the basis of obtaining multiphase flow parameters and pressure wave velocity parameters,finally solve the multiphase surge and swab pressure,through experiments the correctness of the model,put forward the corresponding surge and swab pressure control methods.The main contents of this paper are as follows:(1)Study on multiphase migration rule:To establish a model of LCTP oil and gas multiphase flow migration,analyze the effect of parameters such as gas solubility characteristic,pipe gas holdup and pipe outlet pressure on transport law during LCTP oil-gas transporting.(2)Study on pressure wave velocity:On the basis of solving the mixed pressure and gas holdup,through the improvement of the solving process of the two-fluid model,A two-phase pressure wave velocity model considering virtual mass force is proposed,thus establish pressure wave velocity model of oil-gas mixing,and analyse the effect of parameters such as Mixed throughput and outlet pressure of mixed pipeline on pressure wave velocity.(3)Study on surge and swab pressure:Taking into account the influence of some factors such as the elasticity of the two-phase flow in the pipeline,Poisson's ratio of pipe and change of pressure wave velocity in pipe,put forward the surge and swab pressure model of oil-gas mixing,with the aid of finite difference and other mathematical methods,a multiphase surge and swab pressure model is established,obtain the valve and the variation law of the surge and swab pressure along the pipeline which caused by valve action.(4)Computational software development:based on the oil and gas multiphase flow migration model pressure wave velocity model,surge and swab pressure model that previous established,Developed the oil and gas multiphase flow rule and surge and swab pressure analysis system for LCTP,The software can be used to analyze the solubility characteristics of oil and gas multiphase flow,influence of gas mixture and oil-water mixture ratio on gas holdup,effect of pressure and temperature on pressure wave velocity,effects of oil-gas mixing,gas mixing and valve closing time on surge and swab pressure.(5)Experimental verification:In the third stage multiphase flow test field of Southwest Petroleum University,carry out the experimental research on fluctuating pressure of oil-gas multiphase flow,The experiments show the true law of the oil-gas multiphase flow in the process of valve regulation.Comparison of multiphase phase surge and swab pressure and oil phase surge and swab pressure,The amount of gas mixing has a significant influence on surge and swab pressure,this is related not only to the frictional resistance of gas relative to the wall of the pipe,but also to the energy dissipation of the gas during the propagation of the surge and swab pressure.In the process of mixed transportation,the surge and swab pressure caused by the valve action cannot be ignored,During the first cycle,the maximum surge and swab pressure appears at the valve.(6)Control method:From the angle of controlling surge and swab pressure,three new methods to control surge and swab pressure are put forward,respectively as set up the movement path model of the valve under the limited pressure condition,reduce the surge and swab pressure through the series of two valves,and adopt a double connecting device designed to reduce the surge and swab pressure.