Rheological properties of heavy & light crude oil mixtures for improving flowability

The rheological properties of heavy crude oil and its mixture with light crude oil were investigated experimentally. These rheological properties include steady flow behavior, yield stress, transient flow behavior, thixotropy behavior, and viscoelastic behavior. A RheoStress RS100 rheometer was employed in all of the rheological examination tests. The heavy crude oil exhibits a non-Newtonian shear thinning behavior over the examined shear rate range of 0.1-750 s(-1). The viscosity of the heavy crude oil decreases considerably with temperature over the range of 25-65 degrees C. The addition of 10% light crude oil to the heavy crude oil, to form 10% HLCO mixture, causes a strong reduction in the heavy crude oil viscosity from 10 Pa.s to 1.2 Pa.s at 25 degrees C. An even higher viscosity reduction from 10 Pa.s to 0.375 Pa.s at 25 degrees C can be achieved in the presence of 20% light crude oil. The yield stress of the heavy crude oil reaches 0.7 Pa at a room temperature of 25 degrees C and it decreases to 0.4 Pa at 65 degrees C. The tested samples of heavy crude oil, 10% HLCO mixture, and 20% HLCO mixture exhibit time independent flow behavior. The heavy crude oil shows a thixotropic area of 321.65 kPa/s at 25 degrees C and decreases to 118.62 kPa/s at 65 degrees C. The presence of the light crude oil eliminates the thixotropic behavior of the heavy crude oil. The complex modulus of the heavy crude oil decreases significantly with temperature. The addition of 10% of the light crude oil strongly reduces the values of the complex modulus of the heavy crude oil. From the comparison of the storage and loss moduli values for the heavy crude oil, it is found that the heavy crude and its blends flow in a viscous liquid behavior. The 10% and 20% of the HLCO mixtures display viscous behavior as well. The storage and loss moduli of the heavy crude oil decrease significantly by the addition of 10% light crude oil. (C) 2011 Elsevier B.V. All rights reserved.