Investigation on Hydrate Growth at the Oil–Water Interface: In the Presence of Wax and Surfactant

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.