Basic Research On One-Dimensional Simplification Of Restart Model Of Gelled Crude Oil Pipeline

In order to avoid the occurrence of malignant condensate accident after the shutdown of low temperature waxy crude oil and ensure the safe and economic operation of waxy crude oil pipeline,it is necessary to accurately grasp the pipeline pressure and start-up wave speed of the crude oil pipeline during restart process.The restarting mathematical model of the gelled crude oil pipeline is an important means to get the restarting pressure and the start-up wave speed.Compared with the two-dimensional and three-dimensional mathematical model,one dimension mathematical model is more suitable for industrial application because of its small calculation and simple model.In the process of simplification of two-dimensional starting model to one-dimensional model,two problems will be faced.: the effect of fluid radial velocity field on the unsteady process during the restarting process of gelled crude oil pipeline;how to apply one-dimensional restarting model based on indoor loop experiment to industrial pipelines.Since gelled crude oil shows obvious viscoelastic thixotropic characteristics during restart process,the Burgers viscoelastic fluid and viscoelastic-thixotropic fluid with damage variables are taken as study objects,and the unsteady Poiseuille flow characteristics in the pipe under the constant pressure boundary condition and from 0 linearly increasing pressure boundary condition are studied.The relative measured strain and stability time are used as the characterization of unsteady process.By establishing Burgers viscoelastic fluid and viscoelastic-thixotropic fluid unsteady Poiseuille flow numerical models respectively,the rules of dimensionalless measured strain and stability time are given.The results show: during the unsteady Poiseuille flow process of Burgers viscoelastic fluid and viscoelastic thixotropic fluid under both boundary conditions,relative measured strain curves show different forms of oscillation and attenuation,the parameters of the fluid constitutive model,the diameter and the boundary pressure have different degrees of influence on the relative measured strain and the stability time.Relative measured strain changes in a small range.The measurement strain corresponding to the unsteady flow and the uniform flow is at the same order of magnitude.The influence of the velocity distribution on the unsteady state process is negligible,and the one-dimensional simplification of the two-dimensional model is reasonable.In this paper,based on the indoor multi diameter crude oil loop experimental device,a constant flow restart experiment was carried out for Sultan GNPOC waxy crude oil with pour point depressant,and the multi diameter association law of starting yield stress/ start-up wave speed is established,and what is more,the theoretical basis for enlarging the small diameter pipe test results to the large diameter pipe in the field is provided.Through the loop experiment,it is found that: under the experimental conditions,the starting yield stress is approximately linearly increased with the start flow rate,but an inverse proportional function to the pipe diameter.The start-up wave speed increases approximately linearly with the starting flow,and the start-up wave speed first increases and then decreases with the increase of the pipe diameter.The start-up wave speed is mainly determined by the additional medium filling efficiency of the pipeline.