Aging of water-in-crude oil emulsions: Effect on water content, droplet size distribution, dynamic viscosity and stability

The production of crude oil containing emulsified water presents problems, for example the corrosion of transport systems and the poisoning of catalysts during the refining stage. The ease of separating water from petroleum varies with the aging of the emulsion; however, this issue has not been explored extensively in the literature. This study aims to evaluate the relationship between aging and stability of emulsions, to assess the contribution of certain variables such as asphaltene content and the variation in the size of water droplets in the emulsion, as well as the dynamic viscosity of the oily phases and emulsions. The effect of aging on the performance of a commercial demulsifying product was also evaluated. To this end, synthetic emulsions were prepared from Brazilian crude oil and from the dispersion of asphaltenes in different oily phases. The emulsions were evaluated immediately after preparation and every 15 days for a 60 days period. It was found that a high performance demulsifier can become inefficient in the treatment of aged emulsions causing serious damage to the petroleum treatment. The most significant effect of aging probably occurs because of changes in the internal structure of the emulsion, more specifically in the interfacial film, since there are no significant changes in the emulsified water content, in the droplet size distribution and in the dynamic viscosity of emulsions with the aging of the emulsion. The influence of the asphaltene content on the stability of emulsions was confirmed by the variation of the properties of the model emulsions containing different asphaltenes contents.

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► Asphaltenes in crude oil play an important role in water/oil emulsions stabilization.
► The stability of petroleum emulsions is significantly affected by aging.
► Demulsifiers presenting good performance can became inefficient after emulsion aging.
► Water content, drop size distribution and dynamic viscosity are not affect by emulsion aging.
► Asphaltenes behavior is closely related to their interactions with other oil fractions.