Experimental Investigation of Entrapped Water Droplets in Wax Deposition from Water-in-Oil Emulsion Considering Wax Crystals Adsorption at the Oil-Water Interface

The presence of water in wax deposition from water-in-oil emulsion for petroleum transportation in pipelines has received much attention in recent years. This study investigated the formation of wax deposition with water droplets, considering interfacial adsorption by wax crystals. The prepared 20 vol % water-in-oil emulsion was used for the wax deposition experiment with an analysis of deposition mass/thickness and water volume fraction in deposition, determining that the water content in deposition during the whole deposition duration was constant and equaled to the water content in emulsion. Moreover, a polarizing microscope was employed to observe the microstructure of wax deposition, revealing that some water droplets were covered with wax crystals due to interfacial adsorption, while some droplets were enclosed by the network of wax crystals. Depending on these findings, two kinds of entrapment of water droplets in deposition were proposed. One contained the formation and growth of a crystal network accompanied with these wax-covered water droplets themselves; another one indicated that water droplets were surrounded by a crystal network, resulting in the movement of these droplets being limited and therefore the droplets settling in deposition. Furthermore, a comparison of the distribution of water droplets in deposition using a microscope and that in emulsion by focused-beam reflectance measurement was presented. It was observed that these small droplets were more likely to be incorporated into deposition in contrast with these large ones. The largest size measured for an entrapped water droplet was 115 mu m, which was in accordance with the previous research claiming that the general diameter of water droplets incorporated into deposition was no more than similar to 100 mu m. Interfacial adsorption of wax crystals provides an additional insight to investigate water droplets in wax deposition.