Phase transition characteristics of heavy oil-viscosity reducer-water emulsion systems

Abstract

Heavy oil reservoirs can be feasibly developed using viscosity reducer (VR), by which the heavy oil is emulsified to form a less viscous oil-in-water (O/W) emulsion. As the formed emulsion is unstable, we studied the phase transition characteristics of the heavy oil-VR-water emulsion system. First, we used an emulsifier to prepare the heavy oil-VR-water emulsion system. The microscopic properties of the emulsion system were investigated using a microfluidic test system and laser particle size analyzer after the emulsion system reached phase equilibrium. To measure the conductivity of the emulsion system, a conductivity meter was used. The effects of different concentrations of VR, salinities, and oil-water ratios on the type of emulsion were determined. The results indicated that an O/W emulsion occurred when the VR concentration was greater than 0.3 wt%, the oil-water ratio was lower than 1:1, and the salinity was less than 10,000 mg/L. Higher VR concentrations reduced the droplet size to the micron scale. A water-in-oil emulsion was formed when the VR concentration was less than 0.3 wt%, the oil-water ratio was higher than 1:1, and the salinity was higher than 10,000 mg/L. The parameters of heavy oil recovery using VR can be adjusted upon obtaining the critical values of the factors influencing the change in the type of emulsion. These findings can help better understand the phase transition characteristics of heavy oil-VR-water emulsion systems.