Surfactant Adsorption and Interfacial Tension Investigations on Cyclopentane Hydrate

Abstract

Gas hydrates represent an unconventional methane resource and a production/safety risk to traditional oil and gas flowlines. In both systems, hydrate may share interfaces with both aqueous and hydrocarbon fluids. To accurately model macroscopic properties, such as relative permeability in unconventional systems or dispersion viscosity in traditional systems, knowledge of hydrate interfacial properties is required. This work presents hydrate cohesive force results measured on a micromechanical force apparatus, and complementary water-hydrocarbon interfacial tension data. By combining a revised cohesive force model with experimental data, two interfacial properties of cyclopentane hydrate were estimated: hydrate-water and hydrate-cyclopentane interfacial tension values at 0.32 ± 0.05 mN/m and 47 ± 5 mN/m, respectively. These fundamental physiochemical properties have not been estimated or measured for cyclopentane hydrate to date. The addition of surfactants in the cyclopentane phase significantly reduced the cyclopentane hydrate cohesive force; we hypothesize this behavior to be the result of surfactant adsorption on the hydrate-oil interface. Surface excess quantities were estimated for hydrate-oil and water-oil interfaces using four carboxylic and sulfonic acids. The results suggest the density of adsorbed surfactant may be 2× larger for the hydrate-oil interface than the water-oil interface. Additionally, hydrate-oil interfacial tension was observed to begin decreasing from the baseline value at significantly lower surfactant concentrations (1-3 orders of magnitude) than those for the water-oil interfacial tension.