Contact angle measurements on cyclopentane hydrates

Abstract

The wetting characteristics of clathrate hydrates influence their behavior in flow assurance situations, but these properties are not well-characterized. In this work, a new experimental method is proposed for measuring the contact angle of various liquids on cyclopentane hydrate, a structure II clathrate hydrate that forms at atmospheric pressure. This method includes a protocol to obtain a smooth flat hydrate surface, followed by standard image-based contact angle measurements. The protocol involves a succession of flipping and resting steps of a solid block, initially ice, immersed in liquid cyclopentane and subject to temperature variations around water freezing point, in order to allow progressive transformation to cyclopentane hydrate. Contact angle measurements on the flat hydrate surface were conducted for two sets of systems. First, water drops immersed in cyclopentane or various oils were observed to fully wet the hydrate surface. This result agrees with the surface tension values estimated by Aman et al. (2013) for the cyclopentane/hydrate/water system. Second, the contact angle of halogenated organic (dichloromethane, dichloroethane, and chloroform) drops immersed in brine was measured on cyclopentane hydrate and ice. Both the hydrate and ice surfaces were found to be water-wetting. Finite contact angles in the range of 125⩽θ⩽149° were obtained on the hydrate substrate. The ice substrate however, was observed to be fully wetted by the aqueous phase. Using the measured contact angles and interfacial tension of the liquid pairs, the work of adhesion for the hydrate surface and each of the halogenated organics was determined, and is comparable to values found in the work of Asserson et al. (2009) on freon hydrates.