Rheology of water-in-oil emulsions for a medium crude oil

An experimental study was conducted to investigate the rheology of water-in-crude oil emulsions. Experiments were carried out on a medium crude oil (API gravity of 29.6, and 1.97% by weight sulfur content) at room temperature. Emulsion samples were prepared using fresh and salt water (3.8% NaCl w/v). The water concentration ranged from 5% to 60% by volume. Tests revealed that water-in-crude oil emulsions showed a shear thickening non-Newtonian behavior. Emulsions prepared using fresh water showed an increase in the emulsion viscosity as water concentration increased until phase inversion occurred, after which the viscosity dropped and then leveled out. However, for emulsions prepared using salt water, viscosity continued to increase beyond the phase inversion point with the increase in water concentration. For the same water concentration, fresh water emulsions had lower viscosity than salt water emulsions and were able to take up to 30% water, while salt water emulsions were able to take up to 15% water only. The emulsions, classified as meso-stable, showed a viscosity increase of less than one order of magnitude greater than that of the starting oil. Water salinity caused a slight increase in the non-Newtonian behavior of the oil emulsions.