The self-preservation effect experiments in water + diesel oil dispersion systems for methane hydrate were carried out with the particle size ranging from tens to more than 100 μm. The influence of water cuts (low water cuts of 10, 20, and 30 vol % or high water cuts of 95, 99, and 100 vol %) and types of inhibitors (tetra-n-butylammonium bromide or Lubrizol) on the dissociation kinetics in oil and water suspensions were examined. The addition of surfactants, especially those able to lower the size of droplets or hydrate particles in low water cut suspension systems, could remarkably hinder the self-preservation effect by surface adsorption and alterations in structures and morphologies of ice film. For higher water cut systems with or without surfactants, the enhanced self-preservation effect was observed in comparison to lower water cuts. Systems with oil exhibited a declined effect in contrast to pure water systems. The ice-shielding mechanism for hydrate dissociation is supported by the effects of surfactants and water cuts on dispersion and agglomeration properties as well as the size of hydrate particles.
Hydrate plugging is the major challenge in the flow assurance of deep-sea pipelines. For water-in-oil emulsions, this risk could be significantly reduced with the addition of anti-agglomerants (AAs). Hydrates often form from water-in-oil emulsions and the measurement of emulsion and slurry viscosity constitutes the basis for the application of hydrate slurry flow technology. In this work, using a novel high-pressure viscometer, emulsion and slurry viscosity with different AAs for water content ranging from 5% to 30% was obtained. The viscosity-temperature curves of emulsions were determined and correlated. The variation of system viscosity during hydrate formation from water-in-oil emulsions was examined, the sensitivity of stable slurry viscosity to water cut and the effects of temperature on annealed slurry viscosity were investigated. The results indicated that the variation of viscosity during hydrate formation relies on the conversion ratio. It also implied that the sensitivity of slurry viscosity to change in its water cut or temperature was reduced with AA addition.
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