Experimental measurement and thermodynamic modeling of equilibrium condition for natural gas hydrate in MEG aqueous solution

Comprehensive information about the hydrate formation and dissociation conditions is necessary for design and operation of different processes in the petroleum industry. This study investigated the natural gas hydrate equilibrium conditions in the presence of mono ethylene glycol aqueous solution as a widely used thermodynamic hydrate inhibitor in the oil and gas industries. Stepwise heating method was used for the hydrate formation and dissociation tests in a 250 cm3 stainless steel equilibrium cell. To validate and verify the performance of the apparatus and the method used, methane hydrate equilibrium data were measured and compared to a number of selected experimental data in the literature. This verification showed that the experimental procedure was accurate. The equilibrium temperatures of synthetic natural gas (SNG) hydrates in the absence of MEG aqueous solutions at various pressures of 3.95, 4.49, 5.36, 6.50, 6.85, and 8.20 MPa were 289.9, 290.9, 291.7, 293.1, 293.5 and 294.5 K, respectively. The equilibrium data for natural gas hydrate in the presence of 0.10 and 0.20 mass fractions of MEG in the water for pressure range of 3.90-8.20 MPa were also comparatively measured. The results showed that the natural gas hydrate equilibrium temperature decreased about 2.5 and 5 K in the presence of 0.10 and 0.20 mass fractions of MEG, respectively. The modified statistical thermodynamic model based on van der Waals and Platteeuw solid solution theory and the PVTsim software were applied to predict and evaluate hydrate equilibrium conditions. Thermodynamic model predictions matched reasonably well with the experimental results.