Study On Static Structure Recovery And The Influence Of Pressure On Starting Characteristic Of Waxy Crude Oil In Pipeline

On the basis of pipe flow loop experiments,some researches were carried out on the structure recovery of waxy crude oil in pipeline and the effect of pressure in the characteristics of pipeline start-up,in this paper.The article mainly consists of these parts:the pipeline pressure characteristic of the gelled structure recovery when the waxy crude oil pipeline shutdown at constant temperature;further improve the solving method of start-up yield stress of waxy crude oil pipeline;effect of shutdown pressure on restart characteristics of gelled crude oil pipeline.(1)When pipeline shutdown,there exists the phenomenon of volume shrinkage during the recovery of gel structure,and the characteristic of shrinkage is correlated with gelled structure.Based on this characteristic,using the pipe flow loop experiment to research the gelled structure recovery by controlling different time of airtight experiment pipeline at static structure recovery at constant temperature,getting the pressure change caused due to formation.Using non-dimensional approach,getting the variation of the relative pressure during structure recovery with standing time.Using the relative pressure to define the relative degree of crystallinity,and analyzed the process of structure recovery by using method of isothermal kinetics.Meanwhile,we analyzed the effect of these factors on characteristics of static structure recovery of crude oil in pipeline,including pre-shear rate,cooling rate.We found: the smaller pre-shear rate,the bigger cooling rate,the bigger recovery rate of gelled structure,the greater of pressure because of the structure recovery.(2)Based on the propagation of yield front during start-up of gelled crude oil pipeline,we made pipeline microcell division and combine the least squares principle,using particle swarm algorithm with cross factor seek the optimal solution to solve the parameters in the thixotropic model as well as start-up yield stress.This paper we proposed the calculate method of start-up yield stress based on experimental data,we using polynomial to fitting the starting pressure distribution in the start time at the end of the pipeline to calculate the wall shear stress in the start time,and the maximum wall shear stress is the start-up yield stress.(3)In this paper,we found the effect of pressure in pipeline start-up of gelled crude oil in different pressurization ways by buffer tank when pipeline shutdown.And we found: the shear stress not only correlation with gelled structure,but also with the compressible of crude oil,and we found the transient pressure will decrease the compressible of oil and the yield stress will increase with pressure increase;when applied constant pressure at inlet when pipeline thermostatic standing,the pressure on the one hand will decrease the compressible of oil,and on the other hand,the constant pressure will damage the gelled structure,combined this two factors,the yield stress increases at first then decreases as the pressure increases.