Development and calibration of a high pressure high shear rate capillary rheometer
For the characterization of the viscosity and the flow behavior of heavy and extra heavy oil, a high pressure, high shear rate capillary rheometer has been developed. Due to the commercial rise in the exploitation of heavy and extra heavy oils, non-Newtonian flow behavior becomes relevant. Information on the flow properties of these heavy oils, particularly at high pressure and high shear rates is essential for recovery and processing methods. The capillary rheometer consists of two high-pressure vessels connected by a tube system including a calibrated capillary. Each vessel is equipped with a hydraulically operated metal bellow that can be varied in size to make oil flow from one vessel, through a capillary, into the other one at a controlled rate of flow. From the measured pressure drop the viscosity of Newtonian fluids is calculated with Hagen-Poiseuille's law. The capillary rheometer is designed for ambient operating conditions up to 1000 bar and 200 °C. Fluids with a viscosity between 1 and 100,000 mPas can be measured under high shear rates. The maximum possible shear rate depends on the viscosity of the fluid. For fluids with viscosities under 4000 mPas, shear rates up to 50,000 1/s are possible. Viscosities up to 100,000 mPas still allow shear rates of 4000 1/s. Before being set into operation, the apparatus is calibrated in a range up to 500 bar with viscosity standards that have been independently measured to high-pressure conditions. In this range, the apparatus works with an overall accuracy of about 3%.