The formation and aggregation of hydrate in W/O emulsion containing different compositions: A review

Flow assurance is the most important issue during the deep-sea oil/gas production. Hydrate formation is one typical flow assurance problem which draws much attention. In the flow system, the wax, asphaltene, scale, sand and other solid deposits may coexist. They can facilitate the formation of hydrate and worsen its slurry flow, thus heightening the risk of pipeline plugging and threatening the production safety. Therefore, it is of vital significance to probe the effect of one or more compositions on the formation and aggregation of hydrate into consideration. This review summarizes the recent development of hydrate formation and aggregation in water-in-oil (W/O) emulsions containing wax crystals, asphaltenes, and solid particles. Additionally, the synergistic effect among these compositions is also stressed. The large interfacial area in the emulsion system contributes to the formation of hydrate. When the interfacially-active wax crystals, asphaltenes and solid particles adsorb at the oil–water interface, they will reduce the effective interfacial area, increase the mass transfer resistance, and thus inhibit the hydrate formation. However, they can also act as heterogeneous nucleation sites to promote hydrate formation as their content increases. Besides, their adsorption at the hydrate shell surface can change the wettability into hydrophobic, reducing the probability of collision and aggregation among the hydrate particles. According to the current research status, some suggestions are put forward for further study.