Visual Studies of Methane Hydrate Formation on the Water-Oil Boundaries

Visual studies of the growth of methane hydrate at the interface of water with three kinds of methane-saturated crude oils were performed at supercooling ∼20 °C. The results were compared with the growth of methane hydrate at the interfaces of water-methane and water-methane-saturated decane or toluene. The average rates of hydrate film growth measured for the water-oil interfaces vary within the range of 0.8-1.0 mm s^-1, which is somewhat lower than the average growth rate at the water-methane and water-decane (toluene) interfaces (1.6 mm s^-1). It was found that in some cases hydrate nucleation proceeded not on the water-oil boundary but at the walls of the cell. Spontaneous intrusion of oil formations (drops, serpentlike formations) into the aqueous phase was observed in some experiments. These formations are likely to originate from oil catching by the bundles of needlelike hydrate crystals due to the capillary effect. Intense growth of the hydrate on the walls of the cell was observed for two kinds of crude oils. It was demonstrated that one of the factors blocking hydrate growth on the cell walls may be the presence of naphthenic acids (natural surface-active substances) in the oil phase.