The System Water—Carbon Dioxide—Sodium Chloride to 773 K and 300 MPa

Abstract

Experimental results are reported for fluid‐fluid phase equilibria of the ternary system H2OCO2NaCl. Measurements were extended to 773 K and pressures to 300 MPa. A “synthetic” method was used: Known quantities of the three components were filled into an autoclave at room temperature. The autoclave with a sapphire window and variable volume is described. Transition points to homogeneous one‐phase conditions could be determined from recorded p—T‐curves at constant volumes and from visual observation. From the transition points p—T‐curves on the three‐dimensional phase equilibrium boundary surface at constant compositions, “isopleths”, were obtained. Data for 20 isopleths with CO2‐concentrations between 0.2 and 85 mol% and with 6 weight YO of NaCl are presented together with a few additional results for higher salt concentrations. Molar volumes were measured at the phase boundary surface and within the one‐phase region. Excess molar volumes are given. In comparison with the binary H2O‐CO2 system, the addition of NaCl shifts the range of partial immiscibility to higher temperatures by up to 100 K; for example from 573 to 673 K at 100 MPa for 48 mol% CO2. Results are in agreement with earlier data of Takenouchi and Kennedy. Considerations of the ternary phase diagram H2OCO2NaCl within a wide range of conditions are given.

A Phase-Partitioning Model for CO2–Brine Mixtures at Elevated Temperatures and Pressures: Application to CO2-Enhanced Geothermal Systems

“…6 and 7). As evidenced by earlier investigations (Tödheide and Frank 1963;Takenouchi and Kennedy 1965;Gehrig et al 1986), the presence of dissolved salts significantly raises the critical line of the CO 2 -H 2 O mixture.…”

“…Because these authors do not consider gas-phase compositions, our model cannot be compared with theirs regarding water content in compressed CO 2 . Note that we could not reproduce the high-CO 2 concentration data of Gehrig et al (1986) (close to critical compositions), and consequently, excluded these data from our fits. At elevated temperatures, the effect of dissolved salts on the water solubility in CO 2 is small in comparison to the effect on aqueous CO 2 solubility (Figs.…”

Fluids in the Continental Crust

“…In addition, many studies of fluid PVTX properties were being conducted in the Soviet Union, although this work was not widely known in the West. Other studies focused on determination of the volumetric properties (density or molar volume) of H 2 O-NaCl (Hilbert, 1979) and H 2 O-NaCl-CO 2 (Gehrig, 1980;Gehrig et al, 1986) at elevated temperature and pressure. A detailed summary of available experimental data on the PVTX and other properties of fluids is provided by Valyashko (2008).…”

“…Some ternary phase diagrams, spanning the range from metamorphic to magmatic conditions, are available to interpret the phase equilibrium properties of crustal fluids, and representative diagrams that span a range of crustal PT conditions are shown in Figure 2.6. Data for the densities of multicomponent systems are scarce, with the work by Gehrig (Gehrig, 1980;Gehrig et al, 1986) being the only PVTX data for the ternary system H 2 O-CO 2 -NaCl that covers a significant region of crustal PTX space. Numerical models, such as those of Duan et al (1995) and others provide an effective framework for predicting PVTX behaviour in PT regions where experimental data are lacking.…”

Temperatures and Oxygen Isotopic Compositions of Hydrothermal Fluids for the Takatori Tungsten-copper Deposit, Japan

“…The experimental results of Gehrig et al (1986) are regressed by the same procedure with that for the H 2 O-NaCl binary system. The apparent molar volumes of NaCl from Equation (2) and those of CO 2 from Equation (5) are substituted into Equation (1) for the regression analyses.…”