(201f) Investigation of the Interaction between Wax Precipitation and Hydrate Formation in Water-in-Oil (W/O) Emulsions

The hydrate blockage and wax deposition may exist simultaneously in the transport system, which will pose a great threat to the safety of pipelines and enhance the safety hazards of subsea production system. Therefore, the study of interaction between wax precipitation and hydrate formation in water-in-oil (W/O) emulsions, is of great significance for the security of development in deep-water waxy oil and gas fields. Experiments of natural gas hydrate formation in W/O emulsions containing wax crystals were carried out in the high-pressure autoclave. The macro-parametric data such as pressure, temperature, hydrate induction time, hydrate formation amount and rate was compared and analyzed. Besides, the effect of hydrate formation and dissociation on wax precipitation was studied combined with the microscopic data analysis obtained from the polarized light microscopic observation. The results indicated that wax crystals had no influence on the stage behavior of natural gas hydrate formation process. Wax crystals were absorbed on the surface of water droplets under the synergistic effect of surfactant, increasing the mass transfer resistance of hydrate nucleation, hence prolonging the hydrate nucleation induction time. An empirical model for predicting hydrate nucleation induction time in W/O emulsion systems containing wax crystals was developed based on the Freundlich adsorption isotherm. The precipitated wax crystals in W/O emulsions would affect the structure of the hydrate shell, causing gas hydrate to grow at a lower rate, but the total hydrate formation amount was increased compared to the emulsified systems without wax crystals. More wax crystals precipitated in the systems after the formation and dissociation of natural gas hydrate compared to the systems without hydrate formation. The box dimension of wax crystals was relatively larger due to hydrate formation and dissociation, implying that the structure of precipitated wax crystals was more intricate. The findings of this work provide a preliminary insight into the interaction behavior of hydrate and wax, which is an on-going research topic of flow assurance in deep-water offshore fields.