Experimental and Theoretical Investigation of the Interaction between Hydrate Formation and Wax Precipitation in Water-in-Oil Emulsions

The study of the interaction between hydrate formation and wax precipitation 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 performed in a high-pressure autoclave. The macro-parametric data, including pressure, temperature, hydrate induction time, hydrate growth amount and rate, were compared and analyzed. Results indicated that the stage behavior of hydrate formation process was not affected by the precipitated wax crystals in W/O emulsions. The mass transfer resistance of hydrate nucleation was enhanced in waxy W/O emulsions. Hence, the hydrate induction time was prolonged and could be estimated by a semiempirical crystallization model developed based on the Freundlich adsorption isotherm theory. Meanwhile, the precipitated wax crystals in W/O emulsions affected the porosity of the hydrate shell, leading to a decrease in the average hydrate growth rate, but the total hydrate growth amount increased compared to the emulsified systems without wax crystals. The effect of hydrate formation and dissociation on the wax precipitation was studied, combined with the data analysis obtained from the polarizing microscopic observation. More wax crystals precipitated in the systems after hydrate dissociation compared to the systems without hydrate formation. The fractal box dimension of the precipitated wax crystals was relatively larger affected by hydrate formation and dissociation, implying that the structure of precipitated wax crystals was more intricate.