Study On Structural Behavior And Start-up Flow Of Waxy Crude Oil By Shearing During The Cooling

The waxy crude oil has complex rheological properties below its abnormal point.Researchers are particularly concerned the yield characteristics and thixotropy of waxy crude under the pipeline restart conditions.They are of great significance for the safety of transportation.However,the current laboratory simulation methods have some differences with the real flow situation under actual working conditions,especially the differences of rheological properties under different cooling modes are not clear.In this study,the laboratory rheometer test method was used to set up the corresponding experimental scheme.The differences of yield characteristics and thixotropy near the gel point of waxy crude oil under dynamic and static cooling mode were studied.In addition,the effect of shearing during cooling on the characteristics of the start-up flow was studied by numerical simulation.The differences of yield characteristics near the gel point of waxy crude oil under dynamic and static cooling mode were studied by the experimental method of linear increase of stress.The experimental results show that the effect of shearing during cooling on the yield stress test results of different waxy crude oils varies from oil to oil.The impact of shearing on the thixotropy and start-up flow characteristics of waxy crude oil were studied with shear rate step experiment by means of thixotropic model and numerical simulation.The results show that the impact of shearing during the cooling process on the thixotropy of waxy oil around the gel point may also be diametrically opposed on the basis of different types of crude oil.The effect of shearing on the minimum starting pressure and the end seeing time of the waxy crude oil restarting varies from oil to oil.When the actual working condition is formulated,specific plans should be made according to the characteristics of actual oil samples.Finally,the new experiments that different shear rates are applied to oil during the cooling process and add the heavy oil to waxy oil were set up to explore the internal mechanism of"The research conclusions may be opposite for different oil".The differences of thixotropy of waxy crude oil subjected to different shear rates in low-viscosity shear range(30 s^-1-100 s^-1)and the change of thixotropy when heavy oil is added were researched with experiments combined with thixotropic models.The research results showed that in the middle and low-viscosity shear range,the effect of shearing will not affected by the increase of shear rate after the shear rate exceeds"critical point".In addition,the addition of heavy oil weakens the thixotropy of waxy crude oil and reducing the effect of shearing at the same time.In summary,the shearing during the cooling process has an effect on the rheology of the waxy crude oil at low temperatures,but the specific impact needs to be analyzed according to the specific analysis of actual oil samples.