Dependence of rheological behavior of waxy oils on wax composition and cooling and shear histories

The dependence of the rheological properties of model wax–oil mixtures is studied for two wax compositions using two cooling/shear/measurement protocols: the “temperature arrest measurement” protocol by Harris et al., J. Rheol. 67, 1073–1089 (2023) and the “preshearing” protocol by Geri et al., J. Rheol. 61, 427–454 (2017). These protocols are applied at different cooling, stresses, and shear rates during cooling to waxes used in both the work of Harris et al. and Geri et al., with wax concentration varied from 5 to 40 wt. %. Our study shows for the first time that rheological results on waxy oils measured in one laboratory, those of Geri et al., can be replicated in another laboratory (ours), with only minor discrepancies attributed to subtle variations in composition, thermal history, or experimental conditions. It is found that very long time scales, at least up to 48 h, are required to achieve a nearly steady-state stress at a given shear rate when the shear rate is less than 1 s−1. Also, the rate of cooling to the final temperature has significant effects on subsequent stress versus shear rate behavior, showing extreme difficulty in attaining “steady-state” flow curves that are independent of previous stress and temperature histories. The extensive data sets reported here contribute to a broader understanding of waxy crude oil rheology and can be used in future efforts to develop thixotropic constitutive models for waxy oils that account for both shear and temperature history. The work also has implications for efficient transport, processing, and wax deposition mitigation strategies in the petroleum industry.