Rheological investigation of methane hydrate formation with biodegradable emulsifiers as anti-agglomerants

In the present study, the hydrate anti-agglomerant (AA) performance of three biodegradable emulsifiers (Span 80, lecithin, and lanolin) was evaluated in oil-dominated systems using high-pressure rheological tests. The viscosity variations of the fluid systems were examined depending on the concentration of the emulsifiers and water cut during the entire hydrate formation process. The biodegradable emulsifying AAs prevented the drastic increase in the viscosity of the CH4 hydrate slurry in mineral oil and significant hydrate agglomeration. The AA performance decreased in the following order: Span 80, lecithin, and lanolin. These biodegradable AAs create W/O (water-in-oil) emulsions, namely, small water droplets in mineral oil, by which more water is converted to hydrate that is well dispersed in the oil phase than in the cases without the AAs. The hydrate aggregates formed in the absence of the AAs contain more unconverted water that acts as a capillary bridge for hydrate aggregation or that is confined at the core of the hydrate particles by the partial conversion of water. The density of the dispersed hydrate particles in the AA tests is lower than that of the hydrate aggregates formed in the absence of the AAs. This is due to the unconverted water confined in the aggregates. Therefore, the AAs not only prevent hydrate agglomeration but also reduce the hydrate bedding risk by increasing the conversion of water to hydrate.