Modelling and characterisation of diluted and concentrated water-in-crude oil emulsions: comparison with classical behaviour

Water-in-oil type emulsions can be formed during the crude oil production process. The presence of natural surfactants in oil (asphaltenes, resins) and mechanical stirring (piping/well system) produce emulsions, the stability and rheological behaviour of which depend mainly on the chemical composition of the oil and the internal phase concentration. In this work, water (brine 8 g NaCl/cm³) in oil (crude oil) emulsions were prepared and characterised by varying the internal phase concentration (5–80%). Rheological properties are discussed according to the composition of the oil and the temperature of the system. Relative viscosity was modelled following the classical models of Mooney and Krieger and Dougherty, but the best-fitting model for the experimental results was found with an exponential type equation between relative viscosity and volume fraction, as proposed by Richardson. Moreover, we observed that the plastic behaviour determined through the yield stress determination depended not only on the internal phase concentration but also on the temperature. Quantitative analysis of the emulsions’ viscoelastic parameters (storage and loss modulus) was made. In the case of concentrated emulsions (containing over 70% of internal phase), Princen’s theory of the high internal phase ratio emulsions (HIPRES) was verified.