Modelling of phase equilibria involving mixed gas clathrates; application to the determination of molar volume of the vapour phase and salinity of the aqueous solution in fluid inclusions
Modelling of phase equilibria involving mixed gas clathrates; application to the determination of molar volume of the vapour phase and salinity of the aqueous solution in fluid inclusions (in Proceedings of the Eleventh European symposium on Fluid inclusions research (ECROFI XI), Benedetto De Vivo (editor) and Pierfranco Lattanzi (editor))
European Journal of Mineralogy (October 1992) 4 (5): 873-884
Modelling of clathrate stability in single component gases (CO (sub 2) , CH (sub 4) , N (sub 2) , H (sub 2) S and C (sub 2) H (sub 6) ) and of mixtures in systems with or without NaCl is described, and then applied to fluid inclusions in which the dissociation of clathrate occurs in the presence of a vapour phase. The chemical potential of the water component in clathrate is calculated. The Langmuir constants have been recalculated to obtain the best fit of the available experimental data on single gas systems. The dependence of the activity of water on the salt concentration in the aqueous solution is described by the model of Pitzer. P is calculated with an uncertainty of < 10% along the dissolution curve of clathrate for single component gas systems and gas mixtures. The bulk salinity, expressed in equivalent NaCl concentration, can be derived from the melting T of ice in the presence of clathrate + vapour phase + aqueous solution, but is shown to be a function of the volume fraction of the vapour phase. The fugacity coefficient of the gas components and the molar volume of the vapour phase are computed from the Soave equation of state.