Rheological properties of non-Newtonian crudes

An investigation of the non-Newtonian, time-dependent, flow properties of crudes at or below their pour points is reported. Experimental observations were made in cone-and-plate and Couette geometries under various shear rate and temperature conditions. The observations provided the basis for the development of a kinetic and rheological model which quantitatively describes the shear degradation and equilibrium behavior exhibited by these materials. The structure "reaction" is characterized by a second order equation and the rheological equation of state is written in terms of a Newtonian stress and structural stress component, the latter involving a yield stress and a non-Newtonian plastic viscosity. The equilibrium behavior as represented by the equilibrium viscosity is found to show a modified Herschel-Bulkley type dependence on shear rate, also involving an infinite shear rate viscosity. Preliminary data on the effects of thermal history and aging are also reported, showing the relative importance of these factors to the rheological properties.