Effects of paraffin wax content and test temperature on the stability of water-in-model waxy crude oil emulsions

Waxy crude oil is important fossil energy containing both paraffin wax and some asphaltene. The interactions between paraffin wax and asphaltene not only affect the crude oil rheology, but also the stability of crude oil emulsion. To further understand the influences of paraffin waxes on the W/O emulsion stability, in the course of this work, the effects of paraffin wax content and test temperature on the stability of W/O emulsions (with fixed asphaltene concentration of 0.5 wt%) were investigated grounded on the physical property tests of the oils, macroscopic stability measurement of the emulsions, microscopic observation of the emulsions and oil-water interfacial properties test. The results indicated that increasing the paraffin content enhances the WAT of the oils but weakens the asphaltene stability in the oil phase thus leading to the aggregation of asphaltene into a bigger size. The rheology of the model waxy oils deteriorates greatly with increasing the content of paraffin wax. The emulsion stability is outstandingly affected by the test temperature. At 30 °C (much more than the WAT), increasing the paraffin wax content benefits the asphaltene adsorption at the oil-water interface, which then reduces the interfacial tension but increases the strength of the asphaltene film formed at the interface, this facilitates the formation of smaller water droplets and improves the stability of the emulsion to some extent. At a test temperature of 15 °C (well below the WAT), increasing the content of paraffin wax also facilitates the formation of a stronger network structure of wax crystals, which dramatically improves the emulsion stability by immobilizing water droplets in the network. Meanwhile, the water droplets in the emulsion containing 15 wt% paraffin wax have the smallest size and largest number, and can efficiently act as the wax crystal nucleators thus dramatically changing the precipitated wax crystals into very small particles and facilitating the development of a wax crystal film around the droplets. This film also helps to improve the stabilization of the emulsion.