Experimental investigations on hydrate equilibrium conditions in multiphase mixtures incorporating a gas phase, a liquid hydrocarbon (LHC) phase and an excess water phase were performed. Measurements were conducted in a stirred autoclave at pressures up to 12 MPa and a temperature range of 275 to 295 K.

The gas phase consisted of both pure hydrocarbon gases (methane, ethane and propane) and their mixtures. The LHC phase consisted of pure alkanes, cyclo-alkanes, aromatics, their mixtures, and crude oils. In some experiments methanol was added as hydrate inhibitor. The measurements were performed in the hydrate decomposition mode. They aimed at obtaining data for estimating the influence of crude oils on hydrate equilibrium, and at determining their impact on the inhibiting effect of methanol.

For a constant pressure the presence of liquid hydrocarbons leads to decreasing the onset temperature of hydrate decomposition. Generally, their influence on pure gases is insignificant while it is severe on gas mixtures. The equilibrium temperature reduction increases with decreasing molecular weight and with increasing volume of the liquid hydrocarbons. Some cyclo-alkanes were incorporated into the hydrate structure. The inhibition with methanol is not influenced by any of the liquid hydrocarbons; the temperature depression appears to be additive. These findings are interpreted to depend on the preferential solubility of ethane and propane in the oil phase.

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