Solubility measurements of (methane + ethane + propane) mixtures in the aqueous phase with gas hydrates under vapour unsaturated conditions

• The study focuses on mixed hydrates formed from a ternary hydrocarbon gas mixture.
• Establish equilibrium conditions between mixed gas hydrate and aqueous phase, in the absence of the vapor phase.
• Study the effect of temperature, pressure and salinity on the equilibrium concentrations of the dissolved gases.
• Similar trends of measured and predicted concentrations of the dissolved gases with temperature, pressure, salinity.
• Predicted concentrations were found systematically inferior to the measured ones.

The equilibrium concentrations of two ternary mixtures of methane, ethane and propane in the aqueous phase with gas hydrates were measured at pressures from 6 MPa to 20 MPa and temperatures from 274 K to 299 K at different salinity levels. These conditions for the gas mixtures selected were well inside the hydrate formation envelope so that the vapour phase could not coexist in equilibrium. A laboratory procedure was developed for the formation of homogeneous mixed hydrate crystals in the absence of a vapour phase. The compositional results generated in this work were compared against experimental data reported in the literature as well as against the predictions of the CSMGem thermodynamic model (Sloan and Koh, 2008; Ballard, 2002) [1] and [2].