Modeling the steady-shear rheological behavior of dilute to highly concentrated oil-in-water (o/w) emulsions: Effect of temperature, oil volume fraction and anionic surfactant concentration

Abstract

Oil-in-water (o/w) emulsions having different internal phase concentrations have been encountered in the petroleum industry during production, transportation and storage operations. The present study deals with the rheological behavior of o/w emulsions of varying internal phase (oil) concentrations (10–80%) at different temperatures (25–50 °C). A controlled stress rotational viscometer was used with shear rates ranging from 1 to 100 s−1. The emulsions were prepared with an anionic surfactant sodium dodecyl benzene sulfonate (SDBS) and the concentration of the surfactant was varied from 0.5 to 2 w/v %. The emulsions exhibited typical shear thinning behavior and described well by the power law relationship between shear stress and shear rate. Different viscosity models were tested and fitted with the experimental rheological data using rigorous-linear regression analysis. The emulsion viscosity and pseudoplasticity were found to increase with an increase in oil concentration and decrease with an increase in temperature. Droplet size distribution and surface tension (SFT) measurements showed that both droplet size and SFT of emulsions decreased with an increase in the oil concentration, which significantly influenced the emulsion rheology. The effect of oil concentration on the apparent viscosity of emulsions was correlated by an exponential and a polynomial model. Further, a correlation was proposed for the combined effect of volume fraction and temperature on viscosity of emulsions. At higher concentrations of SDBS, the emulsion showed yield stress to flow. The Herschel–Bulkley model described the rheological data significantly well.