Viscoelastic characteristics of heavy crude-oil-water two-phase dispersed mixtures

Abstract

The viscoelastic characteristics of unstable heavy crude-oil-water dispersed mixtures are investigated to improve pipeline transportation. The effects of temperature, dispersed phase volume fraction, and droplet size distribution are considered on experiments. And, the unstable characteristics of heavy crude-oil-water dispersed mixtures, which display the similar droplet size distribution as the two-phase pipeline flow, is emphasized in this study. As a result, the mixing of water into heavy crude oil does not considerably affect the storage modulus that maintains a constant value even with the changing oil volume fractions. The loss modulus increases with the increased oil volume fractions of the oil-in-water dispersed mixtures. It increases to its maximum value when the oil volume fraction increases to the phase inversion point of oil-water mixtures. After the phase inversion point, the loss modulus decreases as the oil volume fraction increases which can be described by the modified Mooney model accurately. The viscoelastic parameters decrease with increasing temperature because the mechanical strength of the interfacial film and the ability to resist droplet deformation due to shear force decrease when the temperature increases. The storage modulus, loss modulus, and complex viscosity increase as the median diameter decreasing with the approximate exponent behaviors. This is because the link force between two droplets is increased by a smaller distance through a longer stirring time which will decrease the median diameter. Also, the smaller droplet, which is more difficult to deform by shear stress, can increase the values of the viscoelastic parameters. Furthermore, the critical elastic dominant and viscous dominant are investigated through the critical frequency. In conclusion, the unstable heavy crude-oil-water dispersed mixture displays the great different viscoelastic characteristics compared to the normal crude-oil-water emulsions. The unstable characteristics must be considered in the design of the heavy crude oil and water two-phase dispersed flow system. It is important for understanding the pipeline transportation system of heavy crude-oil-water mixtures.