(669b) Surfactant Effect on Hydrate Crystallization at Oil-Water Interface

Clathrate hydrates are solid crystalline compounds with cage-like structures of water molecules. Hydrates have found important applications in many areas, including flow assurance of oil and gas lines, potential sources of natural gas from permafrost and deep-sea hydrate deposits, and use as a medium for energy storage and transportation. Plugging of transport pipelines due to hydrate formation is a major concern in the oil and gas industry which spends over US $200 M annually to prevent hydrate formation and aggregation to maintain flow assurance. Blockage of the oil and gas lines not only affects production but is also a major safety concern due to possible pressure buildup upon hydrate agglomeration. Anti-agglomeration is perhaps the most effective approach for flow assurance. Anti-agglomerates are surfactants which prevent the formation of the hydrate crystalline structure. Over the past several decades, even though significant knowledge has been gained regarding properties of hydrates, many aspects still remain puzzling or simply unknown. Among these aspects is the mechanism for destabilization of hydrates by surfactants. In this study a novel approach using interfacial rheology was applied to understand cyclopentane clathrate hydrate formation in the presence of nonionic surfactants. The hydrate inhibiting performance of low(<CMC), medium (~CMC), and high (>CMC) concentrations of Span 20, Span 80, Pluronic L31, and Tween 65 at 2^oC on a 2μL water droplet showed a morphological shift in crystallization mechanism from planar shell growth to conical growth. Monitoring the internal pressure of a droplet undergoing planar hydrate crystallization provided a strong correlation of decreasing interfacial tension to the shrinking area of the water cyclopentane interface. In the case of conical growth, interfacial tension measurements showed oscillations. These oscillations result from the cycling growth and release of the crystals from the interface to the bulk. This study provides a first hard evidence of the formation of different crystallization morphologies depending on the concentration and structure of the surfactant molecules. The results of this study can lead to the design of more effective, eco-friendly surfactants which will have broad applications in offshore natural gas production and seabed oil capture.