Influences of asphaltene subfractions with different polarities on hydrate growth at water/oil interface

As a kind of typical natural surface-active substance, asphaltenes can not only lead to deposition and plugging accidents, but also affect the formation and slurry flow of hydrate during deep-sea oil and gas transportation process. This paper investigates the polarity effects of the asphaltene subfractions on the growth process of hydrate particles at oil–water interface. First of all, four asphaltene subfractions with different polarities were extracted by the solvent precipitation method. Then, the dynamic interfacial tension and dilational viscoelastic properties were measured to characterize the oil–water interfacial films adsorbed with the different asphaltene subfractions. Following that, the hydrate growth experiment was carried out using a self-designed atmospheric visualization unit. Specifically, the transformation process of a single droplet into a hydrate particle in oil phase containing asphaltenes was studied to determine the influence of asphaltene subfractions on hydrate growth. The change degree of particle morphology and the growth rate of hydrate shells were used as two analysis indexes. The results show that the change degree of particle morphology and the growth rate of hydrate shells were both affected by the dispersion state and interfacial adsorption amount of the asphaltene subfractions. Under the combined action of migration and surface covering, the asphaltene subfractions have different effects on hydrate growth process at various concentrations. At the concentration of 0.01 mg/g and 0.1 mg/g, a looser interfacial adsorption layer will result in a large effective interfacial area, i.e., a weaker mass transfer hindrance. At this time, the structural strength of the interfacial film is low. At the concentration of 0.2 mg/g, however, the transformation rate of the hydrate shells is accelerated owing to the trapped oil phase, so the structural strength of the interfacial film is enhanced. Therefore, with the increase of the asphaltene concentration, the hydrate particles are easier to maintain their original state.