The Dynamic Yield Stress of Waxy Crude Oil

Yield stress exists in waxy crude oil when temperature drops to a certain point. The dynamic yield stress is described and is defined as the minimum shear stress necessary for keeping the products flow on. Dynamic yield stress is determined by the extension of the equilibrim rheological characteristics. Having more than one values, it presents the strength of the nonrecover-able, residual structure of the destructed waxy crude oil. Two methods, direct and indirect methods, are usually involved in the measurement of waxy crude oil's dynamic yield stress. Stress relief method is one of the best ways in indirect measurement. The measured dynamic/static yield stresses of the crude oil from Shengli Oilfield depend upon the shear rate selected during pre-shearing, and they differ greatly from the stress values obtained from the extention of equilibrim rheologic characteristics. Introduced arc the applications of dynamic yield stress in low temperature transportation as well as in the course of restart after shutdown of the waxy crude oil transport system.