Thermodynamic Calculation And Simulation Of H₂O, H₂O NaCi And CO₂-H₂O-NaCl Fluid Inclusions

H₂O, H₂O-NaCl and CO₂-H₂O-NaCl fluids can approximately represent manykinds of geological fluids, which play an important role in geological activities. Oncethese fluids are trapped and sealed by ores, fluid inclusions will form. Thecorresponding physical-chemical parameters can be obtained from the studies of thethermodynamic properties of these fluid inclusions, and some physical-chemicalphenomena and laws in geological activities can be explained well. On the basis ofprevious experiments and updated thermodynamic models, some thermodynamicproperties of H₂O, H₂O-NaCl and CO₂-H₂O-NaCl fluid inclusions are calculated inthis study.For unary H₂O system, a reliable and highly efficient calculation method basedon the IAPWS-95formulation (the national standard equation of fluid water with avalid P-T range of273.16-1273K and0-1000MPa) proposed by Wagner and Pru (2002) is presented here for the saturated properties of water so that the formulationcan be conveniently applied in the study of fluid inclusion, e.g., calculatinghomogenization pressures, homogenization densities (or molar volumes), volumefractions and isochores.For binary H₂O-NaCl system, according to different homogenization modes,salinities are simulated based on phase-transition temperatures duringmicrothermometric process by using the best thermodynamic models up to now. Forthe high-salinity H₂O-NaCl inclusions in which liquid-vapor homogenization occursfirst, this paper suggested that salinities can be accurately calculated from theexperimentally measured liquid-vapor homogenization temperatures and the halitedissolution temperatures by combining equation proposed by Driesner and Heinrich(2007) with that of Becker et al.(2008). In addition, solid-liquid curve, vapor-liquidcurve, triple point and critical point at certain salinity, isochore and moral volume arecalculated for this system.For ternary CO₂-H₂O-NaCl system, this work focused on solving the problem ofsalinities, which are determined by the phase-transition parameters in combination with Raman spectroscopy method. CO₂-H₂O-NaCl inclusions usually have two orthree phases at room temperatures. For the three-phase inclusions (CO₂liquid+CO₂vapor+aqueous liquid), CO₂clathrate will form during cooling, so salinities can bedetermined by the dissociation temperatures of CO₂hydrates during heating. For thetwo-phase inclusions at room temperatures, two methods can be used to determine theinclusion salinities. One is to calculate NaCl contents by the dissociation temperatureof CO₂hydrate and the partial homogenization temperature of CO₂phases (higherthan the hydrate nucleation temperature); the other method utilizes the relationshipbetween CO₂density and the split shift of Fermi diad at the dissociation temperatureof CO₂hydrate in combination with the equation of state of CO₂and thermodynamicmodel of CO₂hydrate to obtain the NaCl contents of CO₂-H₂O-NaCl inclusions.Corresponding discussions are made for the CO₂contents and isochores ofCO₂-H₂O-NaCl inclusions.Furthermore, online calculation for the thermodynamic properties of H₂O,H₂O-NaCl and CO₂-H₂O-NaCl inclusions is programmed in Fortran95language, freeuse for the domestic and foreign inclusion researchers.