Effect of doped emulsifiers on the morphology of precipitated wax crystals and the gel structure of water-in-model-oil emulsions

Waxy crude oils can easily form water-in-oil (W/O) emulsions in submarine gathering and transportation pipelines. When the temperature becomes lower than the wax appearance temperature (WAT), wax crystals will gradually precipitate and the emulsions will thus change to a gel state. This paper aims to uncover the effect of wax crystal morphology on the gel structure of W/O emulsions. Experiments were performed on the crystallization exothermic characteristics, viscoelasticity, and yield stress of the different emulsifier-doped model oils and their emulsions with different wax crystal microstructures. The structural strength of the emulsion gels was mainly correlated with the morphology of the precipitated wax crystals, and also related to the water cut. The needlelike wax crystals could easily overlap with each other and form a compact and solid network structure. In this case, the wax crystals played a leading role in forming the emulsion gels. Therefore, as the water cut decreased, more wax crystals were there to be precipitated, leading to a stronger structural strength of the emulsion gels. On the contrary, when the precipitated wax crystals aggregated into large flocs, it was hard to build a network on their own, so they could enhance the structure by adsorbing at the dispersed water droplets. In this case, the water droplets played a leading role in the formation of the network structure. Therefore, as the water cut increased, the structural strength of the emulsion gels became stronger, mainly due to the increase in the number of water droplets. These findings are of great significance to the safe operation of waxy crude oil gathering and transportation systems under low-temperature subsea environments.