| In the pipeline transportation of crude oil,it is inevitable to encounter the stoppage condition.In the subsequent restart process,in order to ensure the smooth start of the pipeline,the pressure in the pipeline must reach the minimum pressure required to damage the crude oil structure,and this pressure is closely related to the thixotropic characteristics of crude oil.In view of the actual situation of a new thermal insulation crude oil pipeline in northeast China to convey mixed crude oil of qingji,the steady state test,circulation test and dynamic test of crude oil were carried out by using a rotatory rheometer,and the influence of the experimental results on the thixotropy of crude oil was analyzed.Houska model regression method was compared,and Matlab was used to regression model parameters.Finally,the influence of crude oil aging on thixotropy is studied to provide a scientific basis for hydraulic calculation of pipeline shutdown and restart.The research results are as follows:?1?the physical properties of crude oil were measured by a multifunctional low-temperature tester,DSC differential scanning calorimeter and DHR rotational rheometer.It includes basic physical properties,thermodynamic parameters and rheological properties of crude oil.Igawa auspicious mixed crude oil solidifying point is obtained by measurement of31?,pour point is 34?,35?45?oil density respectively 851kg·m-3848 kg·m-3,related point temperature is 44.38?,the wax content is25.76%,the viscosity-temperature curve,the rheology curve drawing,the use of Matlab to return to the crude oil rheological property parameters,through testing the viscoelasticity,made detailed analysis on the rheological properties of sample.?2?according to the regression of Houska model,the lower the temperature of crude oil is,the higher the fitting rate is,and the higher the shear rate is,the better the fitting effect will be in the range from the temperature at the loss point to the temperature at the abnormal point.?3?according to the cold finger experiment and the cyclic shear hysteresis loop experiment,with the increase of deposition time,the temperature difference of the cold finger hot bath increases and the thixotropy of the deposited sample increases.The increase of wax content makes the area of hysteresis loop fluctuate rather than increase.The comparison between field experiment and cold finger experiment with a deposition time of 7 days shows that the thixotropy is enhanced when the wax content in the sample increases,and the influence of different deposition time on the thixotropy is also different under the same wax content.According to the aging mechanism,the content of paraffin wax molecules with high carbon number in wax crystal also affects the thixotropism. |
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