Waxy crude oil shows complex rheological behavior below gelation temperature

such as viscoelasticity

yield stress and thixotropy

owing to the formation of three dimensional sponge-like interlocking network structure.Traditional thixotropic models for waxy crude do not consider the viscoelastic behavior near and/or before yield point.To address this problem

a new thixotropic model with ten independent parameters was proposed.The new model consists of an equation of state and a structural kinetic equation.The total stress is composed of viscous stress and elastic stress.Elastic stress is assumed to be the product of shear modulus and shear strain

and shear modulus varies proportionally to structural parameter and a non-linear damping function.The evolution of structural parameter is described by a new kinetic equation whose breakdown term is assumed to be dependent on energy dissipation rate

to overcome the shortcoming of the kinetic equation whose breakdown term is assumed to be dependent on shear rate.The proposed model was validated by stepwise shear rate tests and hysteresis loop tests of Daqing waxy crude.The proposed model nicely described the viscoelasticity and thixotropy of waxy crude

and for the two kinds of test

the average absolute deviations(AADs)between fitted and measured values were within 2.0% and 5.0%

respectively.The model was further validated by predicting the transient flow curve of hysteresis loop test with the model parameters obtained from the stepwise shear rate measurement

and the results showed that the agreement between the predictions and measurements is acceptable

with AADs about 16%.