Rheology of cyclopentane hydrate slurry in a model oil-continuous emulsion

Abstract

Liquid cyclopentane (CP)-based hydrate slurry is prepared at atmospheric pressure from a density-matched water-in-oil emulsion by quenching it to a lower temperature at a fixed shear rate. Viscosity increases by several orders of magnitude and is indicative of hydrate formation on the dispersed water droplets and subsequent agglomeration. A mechanism in which the hairy and porous hydrate growth combined with enhanced agglomeration due to liquid bridges formed by wetted water films leads to the development of a porosity, resulting in greater effective dispersed phase fraction, is proposed. This is supported by experiments performed for water volume fractions ranging from 10 to 45 % at variable shear rates, temperatures, and surfactant (Span 80) concentrations. The observed dependence on the degree of sub-cooling, with lower slurry viscosity obtained at higher sub-cooling, and the possible anti-agglomerant like effect of high Span 80 concentrations, support our proposed mechanism. The hydrate slurries are found to exhibit shear-thinning and a small degree of thixotropy.