COMBINED EFFECTS OF SHEAR AND FLOW IMPROVERS - THE OPTIMUM SOLUTION FOR HANDLING WAXY CRUDES BELOW POUR POINT

The effect of shear on the viscosity of Umbarka waxy crude during cool ing is investigated via viscometric measurements. The viscosity-time d ependence throughout cooling is measured. The influence of a commercia l flow improver (FI) on the rheological parameters of the tested crude oil during static and dynamic cooling is determined. Results showed t hat the flow behaviour of the crude is Newtonian above the pour point, and becomes non-Newtonian below it. When applying the shear effect th e non-Newtonian flow behaviour is delayed to lower temperatures below the pour point. It also serves to decrease viscosity below the pour po int, but has almost no effect above it. Thus, shear counteracts the ad verse flow effect of cooling into two successive forms. First, a decre ase in viscosity up to the yield stress of the crude gel structure at which a viscosity peak value is attained. Secondly, a decline of visco sity with time when the accumulated structural deformation exerted by shear overcomes the cooling effect. The used flow improver demonstrate d 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. (C) 1998 Elsevier Science B. V.