Surfactant Adsorption and Interfacial Tension Investigations on Cyclopentane Hydrate

Gas hydrates represent an unconventionalmethane resource and a production/safety risk to traditionaloil and gas flowlines. In both systems, hydrate may shareinterfaces with both aqueous and hydrocarbon fluids. Toaccurately model macroscopic properties, such as relativepermeability in unconventional systems or dispersion viscosityin traditional systems, knowledge of hydrate interfacialproperties is required. This work presents hydrate cohesiveforce results measured on a micromechanical force apparatus,and complementary water−hydrocarbon interfacial tensiondata. By combining a revised cohesive force model with experimental data, two interfacial properties of cyclopentane hydratewere 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 todate. The addition of surfactants in the cyclopentane phase significantly reduced the cyclopentane hydrate cohesive force; wehypothesize this behavior to be the result of surfactant adsorption on the hydrate−oil interface. Surface excess quantities wereestimated for hydrate−oil and water−oil interfaces using four carboxylic and sulfonic acids. The results suggest the density ofadsorbed surfactant may be 2× larger for the hydrate−oil interface than the water−oil interface. Additionally, hydrate−oilinterfacial tension was observed to begin decreasing from the baseline value at significantly lower surfactant concentrations (1−3orders of magnitude) than those for the water−oil interfacial tension.