Temperature Dependence of Crude Oil Viscosity within the Unified Scaling Model for Viscosity

Crude oil is a complex system with unique physical and chemical properties. One of the most important physical properties of crude oil is viscosity. This paper demonstrates that the temperature dependence of crude oil viscosity can be described using the universal scaling model for viscosity over a wide temperature range. For the first time, a correlation has been established between the API gravity of crude oil and the fragility index, which is a measure of viscosity change with temperature in the glass transition region. It has been demonstrated that this correlation can be replicated by a linear function: the higher the API gravity the lower the oil density and the poorer the oil forms an amorphous state. The temperature range has been determined, at which molecular cooperation in crude oil can occur. The obtained results allow us to estimate/predict the viscosity of any crude oil at low temperatures, correlated with the glass transition temperature, based on high temperature experimental measurements near the melting point.