Micro-mechanism analysis of the rheological properties of water-in-waxy-crude-oil emulsion under pipe flow

Abstract

Flowing experiments with different water contents in water-in-waxy-crude-oil emulsions were performed in a flow loop apparatus. The real-time variations of rheological properties and microscopic distributions of the emulsions over time during pipe flow were quantitatively analyzed. It was found that the emulsification effect of the emulsion is enhanced due to shear effect, resulting in an increase of gel point and viscosity over time. The average increments in the gel point are approximately 1.5 °C, 1.7 °C and 1.9 °C for the emulsions with water contents of 10%, 20% and 30%, respectively. During the experimental period from 0.5 h to 18 h, the average viscosities measured at the emulsion temperature increase by 31%. Characterization parameters of number-averaged diameter (d 1,0), specific surface area (SA) and polydispersity (PDI) were applied to reflect the microstructure of emulsions from the perspectives of droplet size, dispersity and nonuniformity. The water droplets become smaller and uniformly dispersed as the pipe flow goes on. The Gibbs free energy increases as the emulsion flows through the pipe, which is mainly caused by the shear of the pipe wall. The van der Waals force increases from −0.0678 × 10−21 J to −1.7657 × 10−21 J as the emulsion’s water content changes from 10% to 30%. The water droplets can promote crystallization of wax crystals by offering the necessary nucleus surface. Furthermore, the coexistence of water droplets and wax crystals creates a synergistic effect, which can augment the total energy and structural strength of the emulsion system.