Study On Wax Deposition Rule Of Qingha Oil Pipeline Under The Condition Of Qing-russia Oil Mixed Transportation

In recent years,the new line of Qingha oil pipeline began to transport Daqing crude oil and Russian mixed crude oil.However,the physical properties of Russian crude oil and Daqing crude oil are quite different.The rheology and waxing characteristics of Russian crude oil and Daqing crude oil have changed greatly after mixing,and the wax deposition rule of pipeline transportation process is more complicated.These unknown characteristics will bring great challenges to the pipeline transportation of mixed crude oil.Therefore,it is necessary to study the pipeline transport characteristics and wax deposition rule of Daqing and Russian crude oil after mixed transportation in Qingha oil pipeline,and establish a prediction model of wax deposition rate for pipeline mixed crude oil.The prediction and analysis of wax deposition rule of Qingha oil pipeline under different working conditions is of great significance for guiding the safe operation of Qingha oil pipeline after transporting Daqing and Russian mixed crude oil.The specific studies are as follows:Firstly,the basic physical properties of mixed crude oil are studied experimentally.The density and freezing point of Daqing and Russian mixed crude oil in different proportions were measured according to the relevant standards.The wax precipitation point and peak temperature of mixed crude oil were measured by differential scanning calorimeter.The wax content was obtained by processing and analyzing the experimental data.The viscosity and temperature characteristics of mixed crude oil were tested by rotary rheometer.According to the data obtained from viscosity test,five kinds of viscosity calculation models of mixed crude oil were verified.The double logarithmic model,which has the highest precision,is selected as the viscosity calculation model of Daqing and Russian mixed crude oil.After that,the existing theoretical models and experimental methods of wax deposition are sorted out and summarized,and the mechanism,parameter determination methods,experimental precision and so on are screened.Differential pressure method and wax deposition tendency coefficient method are selected as the experimental method and theoretical model of this study.A small indoor loop was designed to simulate the wax deposition.The factors affecting the wax deposition characteristics of mixed crude oil were divided into four factors: mixing ratio of mixed crude oil,oil temperature,oil wall temperature difference,oil flow rate.Twenty-four groups of experiments were designed by using single factor analysis method.The waxing rule of different factors on oil products was analyzed and the action rule of different factors was clarified.On the basis of this,27 groups of experiments were designed based on orthogonal design method.Based on range analysis and variance analysis,the main and secondary factors affecting wax deposition of mixed crude oil in Qingha oil pipeline were analyzed.According to the analysis result,the influence degree of each influence factor is obtained.Finally,based on the experimental data,two prediction models of wax deposition rate are established.One is based on the method of wax deposition propensity coefficient and the other is based on the least square to regress model parameter.The other one is based on the least squares support vector machine to predict the wax deposition rate.In a large number of experiments,19 groups of data were selected as regression data of wax deposition rate prediction model and 8 groups of data were used to test the accuracy of the prediction model.The accuracy of the model was illustrated by error comparison and correlation analysis.From the analysis results,the prediction model based on least squares support vector machine algorithm is more accurate.Three groups of production data of actual operation of Qingha oil pipeline are selected,and the wax deposition rate under three working conditions is calculated by using the optimized wax deposition rate model.The results show that the relative error is less than 20% compared with the actual wax deposition rate.It accords with the requirement of model precision.Thus the wax deposition rate model predicted by the least square support vector machine algorithm is used as the wax deposition rate model of mixed crude oil in Qingha oil pipeline,and the wax deposition rule under certain working conditions is analyzed.