Hydrate phase equilibrium for CH4‐CO2‐H2O system in porous media

Abstract

CO2/CH4 replacement in hydrate exploitation is considered a promising method to enhance natural gas production and mitigate the greenhouse effect. Since the gas concentration in mining hydrate sediment changes with the displacement process, it is crucial to investigate the hydrate formation and dissociation characteristics with the presence of different gas mixtures. To obtain fundamental thermodynamic data, CO2/CH4 gas mixture hydrate phase equilibrium conditions in porous media were experimentally investigated. The experiments were conducted at 276.55–284.85 K and 2.10–6.80 MPa using an isochoric method with different CO2/CH4 gas mixture compositions (CO2 mole fractions were 0.798, 0.499, and 0.199 mol/mol (79.8, 49.9, and 19.9 mol%)). The results showed that gas mixtures with higher CO2 mole fractions had lower hydrate equilibrium pressure (p) under the same temperature (T) according to the experimental data. The two different porous media used in the experiments had a slight influence on gas mixture hydrate phase equilibrium conditions. An improved thermodynamic model was proposed to calculate the CO2/CH4 hydrate phase equilibrium conditions in porous media, and the prediction results fitted closely to the experimental data.