Cyclopentane Hydrate Crystal Growth Behavior at the Three-Phase Interface with the Presence of Fine-Grained Sediments

To provide evidence for hydrate occurrence states in marine sediments, cyclopentane (CP) hydrate crystal growth at interfaces of water–CP, water–silica–CP, and water–kaolin–CP was observed through a perfluoroalkoxy ethylene (PFA) tube. The effect of water salinity on the growth of CP hydrate crystals in silica sand and kaolin was also investigated. It was found that the growth of CP hydrate crystals caused the migration of sediment particles, but the migration of kaolin particles was not obvious. The measurement results of the growth length of the hydrate crystal surface showed that the addition of sediments increased the growth of the hydrate crystal, and the growth rate of the hydrate crystal in the silica sand was larger than that in the kaolin. The increased growth rate of hydrate crystals implied that CP and water could react quickly to form hydrates, resulting in smaller crystal size and a rougher crystal surface. The growth rate of hydrate crystals became slower after adding NaCl into the water phase, NaCl also changed the growth pattern of hydrate crystals, making the crystal surface rough. The difference in growth behavior and morphology of hydrate crystals in fine-grained sediments is believed to be closely related to the surface properties of silica sand and kaolin, and a possible growth mechanism of CP hydrate crystals at the multiphase interface with fine-grained sediments was proposed.