Rheological behavior of wax deposited through pipeline transportation

摘要

The wax deposit causes flow problems in oil production and transportation. Viscosity's of waxy crude oils have been measured in presence and absent of surfactants mixture for different wax content 9-28%, temperature ranges between 45 degreesC and 65 degreesC and shear rates ranging from 30 to 300 s(-1). The behaviors of waxy crude oils before, during, and after an application of shear force have been studied. The results of this study reveal that the viscosity of the waxy crude oil decreases as the temperature increases. The results also indicated that the rheological behavior of waxy crude oils has a pronounced effect by the concentration of wax and dispersants. In addition the viscosity of waxy crude oil at low shear rate behave as Non-Newtonian (shear thickening) flow behaviors at low shear rate and as Newtonian fluid at high shear rate up to 18% wax content. Meanwhile, at higher wax content and low shear rate they behave as Non-Newtonian (Dilatant-shear thickening), and as pseudoplastic fluids (shear thinning) at high shear rate. This implies that it is safe to pumping the waxy crude oil up to 18 wax% without causing problem when trying to start up a pipeline after a shutdown. The results reveal by increasing wax concentration up to 23-28%, a significant problems begin to appear thereby, a certain amount of force must be applied to the fluid before any flow is induced. On the other hand, the surfactants mixture have been evaluated at 5% and 10% as pour point depressant. Unfortunately, the surfactants mixture give poor results as pour point depressant. For this reasons it was found a major difficulties to measure the theological dynamic viscosity blew the wax appearance temperature or even at the pour point of waxy crude. Consequently, all data are measured above the wax appearance temperature.