Effect of wax on hydrate formation in water-in-oil emulsions

Gas hydrates are non-stoichiometric crystalline compounds that can block pipelines, representing a significant threat to subsea flow assurance. In addition, wax precipitation is also a common issue in subsea pipelines. Since the multiphase flow is transported under low temperature and high-pressure conditions, formation of gas hydrates and wax precipitation may occur simultaneously, potentially posing greater challenges to subsea pipelines. The presence of wax complicates the hydrate formation issue. In this work, the influence of wax on hydrate formation was experimentally investigated in a high-pressure autoclave equipped with an online viscometer. Since natural surfactants are common in crude oil, Span 80 was used to simulate the presence of natural surfactants, and the effect of this compound on hydrate formation was considered. The presence of wax or Span 80 was observed to increase the difficulty of the hydrate formation at similar temperatures. The wax shell structure was found to grow at the water/oil interface based on the microscopic observation. Wax was also found to increase the hydrate induction time significantly. By associating the microscopic observation, a possible mechanism based on the mass transfer resistance was proposed to clarify the influence of wax on hydrate nucleation. Moreover, in the absence of Span 80, the amount of hydrate formed was observed to increase with the amount of wax in the emulsions.