Rheological behavior of high-pour-point oil: Insights into viscosity–temperature prediction and viscoelastic-yielding transition

Abstract

The rheological characteristics of high-pour-point (high-PPT) oil are crucial for its economical and safe production and transportation. However, current research on the viscosity–temperature prediction and viscoelastic-yielding transition of high-PPT oil is insufficient. The Arrhenius formula faces challenges in accurately depicting the viscosity–temperature relationship, and there is a lack of a quantitative description of the viscoelastic-yielding transition behavior in gelled high-PPT oil. This study addresses these gaps through a series of rheological experiments. The results reveal that the viscosity–temperature relationship of high-PPT oil can be classified into three regions, each associated with a sequentially increasing activation energy Ea. Introducing two characteristic parameters, T0 and n, yields a modified Arrhenius formula with an extended range of applicability. Thixotropy and gelation process experiments demonstrate an exponential increase in thixotropic strength with a decreasing temperature below the wax appearance temperature, while an optimum cooling rate maximizes the gelation degree of high-PPT oil. A brittleness index BI was defined to quantitatively describe the fracture mode of gelled crude. Critical characteristic strains and BI exhibit a decrease with an increase in the reciprocal of the average free degree 1/wfree, where the diminishing trend of BI follows a robust power-law form. This comprehensive investigation contributes valuable insights into the rheological behavior of high-PPT oil, offering a foundation for more accurate modeling and control strategies in its production and transportation.