Effect of Wax Crystals on Nucleation during Gas Hydrate Formation

Abstract

Hydrate formation and wax deposition pose great flow assurance challenges to subsea oil pipes, especially when the two phenomena co-occur. Wax crystals can have a significant impact on hydrate nucleation and growth kinetics, but this phenomenon has not been studied in great detail. Here, the effect of wax crystals on hydrate nucleation was investigated using both molecular dynamics simulation methods and experiments conducted using a custom-designed high-pressure autoclave equipped with an on-line viscometer. Both the simulation and the experimental results demonstrated that the presence of wax crystals inhibits hydrate nucleation. The simulations showed that water droplets tend to approach and adsorb on wax crystals prior to nucleation, thus inhibiting the formation of hydrate cages. The experiments demonstrated that water cut and stirring rate play a significant role in determining the hydrate nucleation rate. In addition, adding more wax increased the viscosity of the emulsion, which limits mass transfer of gas to the oil–water interface.