# Experimental Study and Numerical Simulation of W/O Emulsion in Developing Heavy Oil Reservoirs
## 3 Results and Discussion
### Effect of water cut of emulsion  
Figure 7 displays the effect of water cut on the stability of the emulsion. Figure 8 shows the effect of water cut on the viscosity of the emulsion.  
Figure 5: Effect of temperature on emulsion stability.  
Figure 6: Influence of temperature on emulsion viscosity; the viscosity of oil is provided as a reference.  
As shown in Figure 7, the water bleeding rate of the emulsion increased with the increase in water cut for the same residence time, indicating that a lower water cut led to better stability of the emulsion. When the water cut was less than 50%, there was little change in emulsion stability. An increase in water cut, i.e., an increase in the concentration of the inner phase, increased the total area of the oil-water interface, reduced the amount of emulsifier adsorption per unit area, reduced the strength of the interfacial film, reduced the coalescence resistance of the dispersed droplets, and reduced the stability of the emulsion [30].  
As shown in Figure 8, for water cuts of 10% to 60%, the viscosity of the emulsion increased with the increase in water cut, whereas, when the water cut was greater than 60%, the viscosity decreased as the water cut increased. The viscosity ratio of the emulsion with 60% water cut to crude oil could reach 2.4. The viscosity of the emulsion with 90% water cut was lower than that of crude oil. This was due to the increase in water cut and the increase in the viscosity of the emulsion, which made the mutual shear interaction between the dispersed droplets stronger, benefitting the deformation, elongation, and fracture of the droplets and, thus, forming smaller droplets. At the same time, the increase in viscosity weakened the interaction of dispersed phase droplets in the static position, and the settling process of droplets under the action of gravity was also inhibited. At a certain timepoint, the emulsion emulsified rapidly and the viscosity decreased.  
As shown in Figure 9, with the increase in mineralization degree, the water bleeding rate of emulsion increased slightly, indicating that a lower mineralization degree leads to a better stability of the emulsion. Due to the existence of an electro-double structure at the oil-water interface, ions with opposite electrical properties of dispersed droplets acted as emulsifiers. For the W/O emulsion, negative ions contributed to demulsification, whereas positive ions mainly deformed the water droplets and promoted the destruction of the emulsion structure, thus making the stability of the emulsion worse.  
As shown in Figure 10, the viscosity of the emulsion decreased with the increase in mineralization degree. The viscosity of the emulsion was 1.2-2.3 times that of oil, and a higher mineralization degree led to a lower emulsion viscosity.  
As shown in Figure 11, the emulsion had the highest water bleeding rate and the lowest stability at pH 7.11, indicating that the emulsion had good stability. This is because, when the pH value was neutral, the oil-water interface tension was highest, whereas the interfacial tension decreased rapidly with the increase or decrease in pH value. When the pH was too low, it stimulated the charging of natural active substances in the crude oil and increased their activity. This made it easier to adsorb on the oil-water interface, resulting in a decrease in oil-water interfacial tension and an increase in interfacial film strength, thus increasing the stability of the emulsion [31].  
As shown in Figure 12, the emulsion had the lowest viscosity at pH 7.11. The viscosity of the emulsion showed an increasing trend, being 1.1-2.4 times that of crude oil when the pH value was less than or greater than 7.