Natural gas hydrates can readily form in deep-water–oil production processes and pose a great threat to subsea pipeline flow assurance. The usage of surfactants and hydrate antiagglomerants is a common strategy to prevent hydrate hazards. In water/wax-containing oil systems, hydrate coexisting with wax could lead to more complex and risky transportation conditions. Moreover, the effectiveness of surfactants and hydrate antiagglomerants in the presence of wax should be further evaluated. In this work, for the purpose of investigating how wax and surfactants could affect hydrate growth at the oil–water interface, a series of microexperiments was conducted in an atmospheric visual cell where the nucleation and growth of hydrates took place on a water droplet surrounded by wax-containing oils. On the basis of the experimental phenomena observed using a microscope, the formation of a hydrate shell by lateral growth, the collapse of a water droplet after hydrate initial formation, and the formation of hollow–conical hydrate crystals were identified. These experimental phenomena were closely related to the concentration of wax and surfactant used in each case. In addition, it was shown that the effectiveness of the surfactant could be weakened by wax molecules. Moreover, there existed a critical wax content above which the effectiveness of the surfactant was greatly reduced and the critical wax content gradually increased with increasing surfactant concentration. This work could provide guidance for hydrate management in wax-containing systems.

In deepwater oil and gas transportation processes, natural gas hydrates (NGHs) can form easily in pipelines considering the suitable temperature and pressure conditions and therefore lead to pipeline plugging. In water- and wax-containing oil systems, waxes can coexist with hydrates and thus contribute to even more severe challenges to deepwater pipeline flow assurance. In the present work, to investigate the effects of wax on hydrate growth at the oil–water interface, several micro experiments were performed in an atmospheric visual cell. According to the micro experimental phenomena, the morphology, porosity, wetness, and growth rate of the hydrate shell were studied and the effects of wax on hydrate growth were investigated. In experiments, two kinds of hydrate shells with different morphologies, porosities, and amounts of wetness were observed. Wax was found to have little effect on the morphology of the hydrate shell. However, wax molecules could remarkably influence the shape of the hydrate shell when the wax content ranged from 1 to 2 wt %. Moreover, wax molecules and crystals can influence the hydrate shell growth rate in terms of interfacial tension, medium concentration, mass/heat transfer resistance, and nucleation sites. The results in this work could provide guidance for hydrate management in wax-containing systems.