The Yielding of Waxy Crude Oils

Abstract

The yielding process of statically cooled waxy crude oil was examined in detail. Three direct measurementsa controlled stress test, a creep−recovery test, and an oscillatory testwere employed using a controlled stress rheometer to investigate the yielding of two distinctly different statically cooled waxy crude oils. The results showed that yielding of waxy crude oil occurs by an initial elastic response, followed by viscoelastic creep and a final fracture. A model with an elastic-limit yield stress, a static yield stress, and a dynamic yield stress was introduced to describe the yielding process. The three yield stresses were determined by means of different techniques. The effect of the time scale in different measurements on the three yield stresses was studied. It was shown from both the creep−recovery and oscillatory tests that the elastic-limit yield stress was independent of the time scale. The static yield stress was found to be dependent on the time scale in the three tests. The dynamic yield stress measured only with the controlled stress test was also found to be dependent on the time scale of the yielding. Good reproducibility can be obtained in these tests by strictly controlling the thermal and shear history of the samples.

Experiment Study on Yield Stress Using Curve Extension Method and Vane Method

“…[6]. Extending the shear stress-rate curves to the stress axis, intersection point is taken as the curves extension yield stress.…”

“…Suspensions are also prevalent in a number of natural settings such as debris flow, lava flow, and flood waves carrying extremely high concentration of sediments. The yield stress is a key rheological parameter of thick paste and critical design parameter of a high pressure pipeline system [1], but the parameters is inaccurate obtained by the experiment [2], and now the opinions about how to get the yield stress are different [3][4][5][6]. Generally, dynamic yield stress is defined as the intersection of flow curve extension and shear stress axis [7].…”

Crude Oil Transportation: Nigerian Niger Delta Waxy Crude

“…At low stress, the elastic deformation takes place, which disappears when the applied stress is released (Guozhong and Gang , 2010 ). Chang et al, (1998) yielding behavior of a waxy crude oil as having three distinct characteristics-an elastic response, a creep and a fracture. The shear stress at the point of fracture is the value of practical importance and is usually taken as the yield stress.…”

Experimental Investigation on Yield Stress of Water-in-Heavy Crude Oil Emulsions in Order to Improve Pipeline Flow

“…The yield stress is one of the most important rheology characteristics since the fluids cannot be transported when external force is less than its yield stress. [1][2][3] Here, the yield stress can be defined as a limit stress below which the sample behaves like a solid, but above the value of yield stress, the application of stress undergoes unlimited deformation to cause the fluid flow. [4][5][6] To start the heavy crude oil flow in pipeline, the theoretical minimal pressure drop (DP min ) could be given by the following correlation [7] :…”