THEORETICAL AND PRACTICAL ASPECTS OF DIFFERENTIAL PARTITIONING OF GASES BY CLATHRATE HYDRATES IN FLUID INCLUSIONS

Clathrate hydrates may form in aqueous, gas-rich fluid inclusions during low-temperature microthermometric analysis. Gases are differentially partitioned between the clathrate and residual fluid as a function of temperature, pressure, and bulk composition. Of particular concern in multicomponent gas-bearing inclusions is the fact that the selective partitioning of individual gases into clathrate hydrate can strongly affect the interpretation of microthermometric data. The absolute extent of depletion of gases (consumed by clathrate) in the residual fluid is dependent upon both the composition of the gas and the relative proportions of H2O and gas-rich fluid. The equilibrium phase relations in clathrate systems may be modeled in order to correct for the presence of clathrates. Quantitative modeling of CO2CH4H2O, and consideration of CO2N2H2O, N2CH4H2O, and H2SCH4H2O indicates th and extent of differential partitioning of gases and the temperature-pressure-composition stabilities of clathrates. For instance, under a geologically reasonable range of pressure, H2S and CH4 will partition into clathrate more strongly than N2, whereas the direction of partitioning between CO2 and CH4 and between CO2 and N2 changes as a function of temperature, pressure, and the relative proportions of the components. Comparison of experimental data for unary- and binary-gas systems and the model of John et al. (1985) indicates that the model correctly predicts clathrate stabilities and is useful for fluid inclusion studies. © 1990.