-Water-in-oil (W/O) emulsions are complex mixtures generally found in crude oil production in reservoirs and processing equipment. Sedimentation studies of water-oil emulsions enable the analysis of the fluid dynamic behavior concerning separation of this system composed of two immiscible liquids. Gravitational settling was evaluated in this article for a model emulsion system consisting of water and a Brazilian crude oil diluted in a clear mineral oil as organic phase. The effects of water content and temperature were considered in the study of sedimentation velocity of water-oil emulsions. Water contents between 10% and 50 % and temperatures of 25, 40 and 60 °C were evaluated, and a Richardson-Zaki type correlation was obtained to calculate settling velocities as a function of the process variables investigated. Water contents and average droplet sizes were monitored at different levels in the settling equipment, thus enabling identification of the effect of these variables on the phenomena of sedimentation and coalescence of the emulsions studied. The results showed that the emulsion stability during sedimentation was governed by the emulsion water content, which yielded high settling velocities at low water contents, even when very small droplets were present. A quantitative analysis of the combined effects of drop size and droplet concentration supports the conclusion that a stronger effect is produced by the higher concentration of particles, compared with the relatively smaller effect of increasing the size of the droplets.
During the crude oil production, stable water-in-oil (W/O) emulsions are generally found along the pipeline between the reservoir and surface facilities. The main objective of this work is discussing about the influence of the salinity (with NaCl at 0, 50, and 100 g·L–1), pH (2, 6, and 10 values), and water content (variations between 8% and 65%) upon the rheological behavior of water-in-crude oil emulsions. Tests including the rotational and oscillatory rheology for assessment of profiles of viscosity, elastic and viscous modulus for the different cases were performed. Semi-theoretical models and available empirical literature models have been successfully used to fit the rheological data, enabling a better understanding of the interactions between the constituents of the samples at a colloidal level. Results presented here show that the emulsion loss modulus calculated from bulk rheological tests does not respond differently for acid, quasi-isoelectric point and alkaline aqueous phase; this modulus also has a salt content-independent behavior for crude oils with different content of resins and asphaltenes. The presence of electrolyte in the emulsions may decrease the storage modulus, once the concentration of resins and in special asphaltenes were low. For higher content of these molecules, the attractive electrostatic forces are not enough to change the interfacial tension between the macromolecules.
Molecular dynamics simulations have been performed on the interface between linear saturated hydrocarbons and water in the presence of an asphaltene molecule by measuring the properties such as mean square displacement, radial distribution function, density profile using ave/spatial command, and interfacial tension (IFT) by OPLS and TIP3P FF (force fields). The box of simulation contained one particle of asphaltene, 100 linear saturated hydrocarbons molecules, and 300 water molecules in mixture with interfacial appropriate positioning. The main results show that a small amount of asphaltene in the interface does not significantly alter the data of IFT and that the aliphatic and aromatic groups have preferred orientation.
A radial distribution analysis of pairs between the constituent atoms of protic ionic 2-(hydroxy)ethylammonium acetate was performed with molecular dynamics technique (MDT). The ionic liquid structure will help us in different engineering applications, as emulsification process (petroleum industry). The results presented here show that the development of force field to predict the high interaction behaviour between the cation and the anion, as well as the formation of ion-pair dispersed aggregates. These results can contribute to help the different applications of ionic liquids.
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