Determination of the homogenization temperatures and densities of supercritical fluids in the system NaClKClCaCl 2H 2O using synthetic fluid inclusions

Abstract

Synthetic fluid inclusions were experimentally produced by equilibrating small fractured prisms of quartz with aqueous solutions at temperatures from 300° to 700°C and pressures of 1000, 2000 and 3000 bar. Solution compositions included: 0.500, 2.000 and 4.500 molal NaCl; 0.500, 2.000 and 4.500 molal KCl; 0.50 and 2.00 molal CaCl 2; and H 2O. The homogenization temperatures of the synthetic fluid inclusions were analyzed by microthermometry. Plots of homogenization temperatures as a function of experimental temperature and pressure indicate that lines of constant homogenization temperature are linear and intersect the liquid-vapor curve at the homogenization temperature. For each of the four chemical systems, a relatively simple function was developed by which the homogenization temperature can be related to the temperature (°C) and pressure (bar) of inclusion formation and the composition ( m) of the trapped fluid: P=A 1+A 2T A 1=6.100·10 −3 + (2.385·10 −1−a 1)T h−(2.855·10 −3+a 2)T 2 2−(A 3T h+a 4T 2 h)m A 2=a 1+a 2T h+9.888·10− 6T 2 h+(A 3+A 4T h) m where m is the molality; T h is the homogenization temperature; and a 1, a 2, a 3 and a 4 are constants fit to the data sets of each of the four chemical systems. Ten-parameter polynomial regressions are given for the densities of the solutions on their liquid-vapor surfaces as functions of temperature and composition. These functions combined with the above equations permit calculation of the density as a function of temperature, pressure, solute and solute concentration in the supercritical region. A function is also given which permits calculation of isochores for fluids containing more than one solute. The results of these experiments compare favorably to previously published ones.