High friction losses while pumping emulsified acid in a carbonate stimulation treatment limit the injection rate, which can negatively impact operational efficiency; consequently, reducing friction is highly desirable. This study experimentally investigates the role of dispersed phase (water) fraction on frictional drag in different pipe diameters.

Flow loop experiments were conducted to study the effect of water fraction on the flow characteristics of surfactant-stabilized water-in-oil emulsions. Emulsion physical properties such as stability, type, and rheology measurements were correlated to pressure drop measurements in a flow loop consisting of 1-in and 0.5-in horizontal pipe diameters at constant (ambient) emulsion temperature.

The results demonstrated a shear thinning behavior for the emulsions being investigated. In addition, as water fraction increased emulsion stability increased. Furthermore, a significant reduction in emulsion viscosity and pressure drop with decreasing water fraction was observed. In one case, a decrease of water volume fraction from 0.7 to 0.6 resulted in a 60 to 75% drag reduction, depending on the Reynolds number (Re). Moreover, for a given water fraction, the reduction in drag of stable water-in-oil emulsions was found to be more pronounced in smaller pipe diameter due to the shear thinning effect and became significant at higher values of water fraction and Re.

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