Non-Newtonian steady shear flow characteristics of waxy crude oil

Abstract

The experimental research on the non-Newtonian flow characteristic of a waxy crude oil was conducted through a rotational parallel-plates rheometer system. The test temperature is about 6.5 °C higher than its gel point. The shear stress and viscosity of the waxy crude oil show sophisticate non-Newtonian characteristics in the shear rate of 10⁻⁴–10² s⁻¹, in which the shear stress can be divided into three parts qualitatively, i.e. stress-up region, leveling-off region, and stress-up region. This indicates that there is a yielding process in shearing for the waxy crude oil at the experimental temperature, which is similar to the yield phenomenon in thixotropy-loop test discussed by CHANG and BOGER. Furthermore, the steady shear experiment after the pre-shear process shows that the stress leveling-off region at low shear rate disappears for the waxy crude oil and the stress curve becomes a monotonic climbing one, which demonstrates that the internal structure property presenting through yielding stress at low shear rate can be changed by shearing. The experimental results also show that the internal structure of waxy crude oil presenting at low shear rate has no influence on the shear viscosity obtained at the shear rate higher than 0.1 s⁻¹. The generalized Newtonian model is adopted to describe the shear-thinning viscosity property of the waxy crude oil at high shear rate.

Keywords

waxy crude oil / shear flow / non-Newtonian flow / generalized Newtonian model

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