Review of the thixotropic models for waxy crude

The viscoelastic-thixotropic property is an important rheological property of waxy crude oils. It has important impact on the restart safety and flow recovery of crude oil pipelines. The paper introduces the causes, mechanism, and characteristics of the viscoelastic-thixotropic property, and summarizes the commonly used thixotropic test methods along with their individual advantages and disadvantages. The existing thixotropic models are reviewed, and the characteristics and defects of the existing viscoplastic-thixotropic and viscoelastic-thixotropic models are analyzed in detail. For the structural kinetics models, the problems of using a single scalar parameter to characterize the micro-structure are discussed. And the mathematical characteristics and defects of the commonly used kinetic equations are illustrated, furthermore the improvement methods solving those problems are summarized.