Improvements in clathrate modelling II: the H ₂O-CO ₂-CH ₄-N ₂-C ₂H ₆ fluid system

This paper is part of the special publication Gas hydrates: relevance to world margin stability and climatic change (eds J.P. Henriet and J. Mienert). Clathrate stability conditions have been modelled for the H 2O-CO 2-CH 4-N 2- C 2H 6 fluid system based on all available experimental data. Optimum Kihara parameters are estimated for pure CO 2, CH 4, N 2 and C 2H 6 gas hydrates from using the most accurate calculation of other parameters involved in clathrate modelling, like fugacities, gas solubilities in H 2O and thermodynamic constants. For mixed gas hydrates of CO 2-CH 4, CH 4-N 2, and CH 4-C 2H 6 excess Gibbs free energy functions are introduced to obtain a good fit to experimental data. The excess Gibbs free energy is described according a modified Margules equation, which depends on mole fraction and temperature.