Combined effects of shear and flow improvers: the optimum solution for handling waxy crudes below pour point

Abstract The effect of shear on the viscosity of Umbarka waxy crude during cooling is investigated via viscometric measurements. The viscosity-time dependence throughout cooling is measured. The influence of a commercial flow improver (FI) on the rheological parameters of the tested crude oil during static and dynamic cooling is determined. Results showed that the flow behaviour of the crude is Newtonian above the pour point, and becomes non-Newtonian below it. When applying the shear effect the non-Newtonian flow behaviour is delayed to lower temperatures below the pour point. It also serves to decrease viscosity below the pour point, but has almost no effect above it. Thus, shear counteracts the adverse flow effect of cooling into two successive forms. First, a decrease in viscosity up to the yield stress of the crude gel structure at which a viscosity peak value is attained. Secondly, a decline of viscosity with time when the accumulated structural deformation exerted by shear overcomes the cooling effect. The used flow improver demonstrated a high potential in improving the cold flow properties of the crude on static cooling. However, the combined effects of flow improver and shear further decrease gel strength and viscosity up to several orders of magnitude. They also lead to a more steady and regular decrease of viscosity at low additive concentration.