Pressure drop reduction of stable emulsions: Role of aqueous phase salinity

Emulsified acids are a common matrix treatment method for carbonate plays. High frictional pressure losses limit the rates at which these fluids can be pumped especially in small diameter or coiled tubing. A method to effectively reduce friction factor will positively impact pump horsepower needed to place the treatment. This experimental study investigates the role aqueous phase salinity has on frictional drag of emulsions at different pipe diameters. Flow loop experiments were conducted to study the effect of aqueous phase salinity on the flow characteristics of surfactant stabilized emulsions with volumetric oil to water ratio of 30/70. The emulsions' stability, type, droplet size distribution, shear dependent viscosity and interfacial 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) temperature. At low aqueous phase salinity (< 10 kppm), oil-in-water emulsions were created and emulsion stability decreased with increasing salinity. Conversely, water-in-oil emulsions were produced and emulsion stability increased as the salinity increased at high aqueous phase salinity (> 20 kppm). In addition, the results showed a significant reduction in emulsion viscosity as well as pressure drop, in both pipe diameters, with decreasing water salinity, especially for water-in-oil emulsions (salinity > 20 kppm). These results were explained in terms of droplet size distribution as well as interfacial rheology.