Thermokinematic memory and the thixotropic elasto-viscoplasticity of waxy crude oils

The effect of thermal and shear history on the rheology of waxy crude oils is studied in detail. A protocol sequence is presented, which enables us to systematically extract the main thixotropic features of a model waxy oil by a series of steady state and transient experiments at different temperatures. The importance of the underlying microstructure formed by a loosely aggregated and percolated network of wax crystals is discussed and quantified through differential scanning calorimetry and rheological measurements. The microstructural morphology can be described by relevant concepts used previously in the literature for concentrated suspensions of fractal aggregates and is augmented with evolution equations to capture the transient rearrangement of the microstructure, resulting in a thermokinematic memory of the shearing history and thermal history of the sample. Finally, a complete constitutive framework is derived that is able to quantitatively describe and predict a number of rheological features of ...