Emulsions of Heavy Crude Oils. I: Influence of Viscosity, Temperature, and Dilution

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Twenty‐seven crude oils of different origin have been systematically analyzed with regard to viscosity, density, molecular weight, and SARA (saturates, aromatics, resins, asphaltenes) fractionation. Emulsion stability of water‐in‐oil emulsions of the different crude oil samples have been measured by the critical electric field technique (E‐critical). In addition, droplet size distributions for some of the water‐in‐oil emulsions have been determined by NMR self‐diffusion. Rheology measurements show that some of the crude oils have Bingham plastic type flow behavior at temperatures below 20°C, indicating content of waxes. Analysis of the critical electric field measurements shows that the E‐critical value depends on the applied electric field gradient. At low applied electric field gradients, the droplets are given more time to organize into water‐continuous bridges, resulting in a lower E‐critical value than when the applied electric field gradient is higher. The value of E‐critical also increases as the volume of the water phase decreases, due to the increased distances the droplets must move to form linear chains between the two electrodes. E‐critical measurements of emulsions of diluted crude oils show that, in general, the emulsion stability decreases with increased dilution of the oil phase. However, some systems show regions where the emulsion stability is independent of the dilution ratio or viscosity of the crude oil. Here the coalescence rate controls the level of emulsion stability. Viscosity and emulsion stability for water‐in‐oil emulsions were measured for the complete crude oil matrix (27 crude oils), and in general there is an increase of the emulsion stability as the viscosity increases. However, viscosity also correlates well with the SARA data of the crude oils. E‐critical shows a temperature dependence according to the Arrhenius law.