Evaluation Of Viscoplastic Thixotropic Model Based On Stress Loading

This paper is funded by the national natural science fund project(No.51404072)and(No.51534004).Thixotropy is an important rheological property of crude oil and its emulsions,and is an important basis for assessing pumpability.In this paper,the thixotropic properties of waxy crude oil and its W/O emulsion under different stress loading conditions were studied,and the viscoplastic thixotropic model was evaluated.The shear rates of the waxy crude oil and its W/O emulsions were studied,under the three typical stress loads which is constant shear stress,stress step rise,and linear increase and decrease of stress.The shear rates varies with water content,loading stress,and the temperature.The rules of hysteresis loop generation and change are summarized.According to the experimental results,the empirical formula of the relationship between the hysteresis loop area and the shear stress change rate is summarized.Based on the experimental data of waxy crude oil and W/O emulsion in three loading modes,the existing viscoplastic thixotropic model was used to evaluate the thixotropic characteristics of waxy crude oil and its W/O emulsion.The results show that the lower the temperature,the worse the curve fit.The higher the water content is,the worse the model is.Chen Hongjian model and Zhao Xiaodong model fit the best for constant shear stress loading and different water content emulsions under stress loading.Relatively speaking,Jia Banglong model is the least applicable.When the stress is in linear increase and linear decrease of the hysteretic loop loading,Zhao Xiaodong model has the best fitting result,but Guo Liping model is not suitable for the control in stress of hysteretic loop mode.The results show that the Zhao Xiaodong model and the Houska model have similar structural parameters in the cusp,which can reflect the structural state of waxy crude oil and its emulsion.