Study on the viscoelastic-thixotropic characteristics of waxy crude oil based on stress loading

High waxy crude oil occupies an important proportion in oil resources, and its output is increasing year by year. At the temperature below the wax precipitation point, the wax in crude oil will precipitate and cross-link to form a spatial network structure, resulting in the gelation of crude oil. Once crude oil is gelled, it will exhibit viscoelastic-thixotropic characteristics, which will seriously affect the safety of crude oil pipeline transportation. In this paper, based on the principle of mechanical analogy, the elasticity, viscosity and structural strength of the gelled crude oil are characterized by springs, viscous pots, and structural parameters, respectively. On this basis, the viscoelastic-thixotropic model of waxy crude oil with 9 parameters is established. Meanwhile, the model applicability is verified by experimental data using two waxy crude oils under constant shear stress, shear stress step increase and shear stress hysteresis. Compared with the models in literatures, our model has clear physical meaning, relatively few parameters and high prediction accuracy.