Viscoelastic-thixotropic properties of gelled waxy crude oil

The earlier thixotropic model of waxy crude oil was basically a viscoplastic model, in which the contribution of viscoelasticity was not considered, and the influence of viscoelasticity was not taken into account in the numerical simulation of pipeline shutdown and restart accordingly. Therefore, the viscoelastic-thixotropic model with 9 unknown parameters was established based on the principle of mechanical analogy and the characteristics of "viscoelasticity-yieldthixotropy" of waxy crude oil. The model was verified by experimental data of two waxy crude oils with different physical properties under three typical loading modes of shear rate step, shear rate hysteresis loop and constant shear rate near the solidification point. The results show that the average relative deviations between the fitting values of the three testing models and the measured values are 4.6%, 6.6% and 4.2%, respectively, which realizes a complete and accurate description of the rheological response of waxy crude oil during the full loading process with one model, and provides important basic data for the hydraulic characteristics of the oil pipeline during the shutdown and restart process and the safe operation of the pipeline.