An assessment of the accuracy of isochore location techniques for H2O-CO2-NaCl fluids at granulite facies pressure-temperature conditions

doi:10.1016/0016-7037(92)90134-5

Geochimica et Cosmochimica Acta

Volume 56, Issue 1, January 1992, Pages 295-302

https://doi.org/10.1016/0016-7037(92)90134-5 Get rights and content

Abstract

Synthetic H₂O-CO₂-NaCl fluid inclusions with XCO₂ compositions ranging from 0.10–0.51 and relative salinities ( $r-s = wt NaCl (wt NaCl + wt H_{2} O$ )) of 6 to 23.9 wt% have been produced in spontaneously nucleated forsterite, diopside, and orthopyroxene hosts. Molar volumes of the fluids at the pressure and temperature of formation have been calculated using microthermometric data from the fluid inclusions. These P-V-T data are used to compare the accuracy of published methods of isochore location for H₂O-CO₂-NaCl fluids at elevated pressures and temperatures. The results of these analyses show that isochores calculated with the MRK equation of Bowers and Helgeson (Geochim. Cosmochim. Acta, vol. 47, 1247–1275, 1983) reproduce the trapping pressures and temperatures well for fluids with XCO₂ ≤ 0.3 and up to 23.9 wt% NaCl. For a fluid with XCO₂ = 0.49 and relative salinity of 15%, however, the agreement is poor. For these fluid compositions, the observed molar volume is larger than that predicted from the MRK equation of Bowers and Helgeson and, if not corrected, will give isochores that are too low in pressure for a given temperature. The ideal geometric mixing model of Brown and Lamb (Geochim. Cosmochim. Acta, vol. 53, 1209–1221, 1989) provides less satisfactory results for the fluid compositions studied.

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Determination of the homogenization temperatures and densities of supercritical fluids in the system NaCl-KCl-CaCl₂-H₂O using synthetic fluid inclusions
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Binary mixtures of volatile compounds

Cited by (12)

A predictive model for the PVTx properties of CO<inf>2</inf>-H<inf>2</inf>O-NaCl fluid mixture up to high temperature and high pressure
2015, Applied Geochemistry
Citation Excerpt :
In particular, the isochores of CO2–H2O–NaCl fluid inclusions, along which the fluid inclusions were trapped, are often calculated from the pressure–volume–temperature–composition (PVTx) models (Bakker, 1999; Brown and Lamb, 1989; Duan et al., 2008; Mao et al., 2010; Sun and Dubessy, 2012). In the near decades, there have been some experimental studies for the PVTx properties of CO2–H2O–NaCl fluid mixture (Gehrig et al., 1986; Johnson, 1992; Li et al., 2004; Nighswander et al., 1989; Schmidt and Bodnar, 2000; Schmidt et al., 1995; Song et al., 2005, 2013; Teng and Yamasaki, 1998; Yan et al., 2011). However, these data are very scattered, and most of them cover a limited temperature–pressure–composition space that is only valid for CO2 sequestration environments, and they are inconvenient and inadequate for fluid inclusion research.
A predictive thermodynamic model is constructed to calculate the pressure–volume–temperature–composition (PVTx) properties of CO₂–H₂O–NaCl fluid mixtures by the Helmholtz free energy model of CO₂–H₂O fluid mixtures. The new model uses no other mixing parameters but those of the CO₂–H₂O system, because the Helmholtz free energy of H₂O–NaCl fluid at a given composition is equivalently converted into that of pure H₂O by a scaled temperature redefined at the same pressure. In addition, the parameters developed by Driesner (2007) in the PVTx model of H₂O–NaCl fluid system are refitted by the IAPWS-95 formulation. Comparisons with experimental data available show that the model can reproduce the single-phase PVTx properties of H₂O–NaCl and CO₂–H₂O–NaCl fluid mixtures of all compositions from 273 to 1273 K and from 0 to 5000 bar, within or close to experimental uncertainty in most cases (with slightly lower accuracy at 5000–10,000 bar). The isochores of CO₂–H₂O–NaCl fluid can be obtained from this model by a bisection algorithm, and an application example is given to analyze some natural CO₂–H₂O–NaCl fluid inclusions in quartz from a wolframite deposit. Computer program code for calculation of molar volume of the CO₂–H₂O–NaCl fluid as a function of temperature, pressure and composition can be obtained from the corresponding author ([email protected]).
A model for single-phase PVTx properties of CO<inf>2</inf>-CH<inf>4</inf>-C<inf>2</inf>H<inf>6</inf>-N<inf>2</inf>-H <inf>2</inf>O-NaCl fluid mixtures from 273 to 1273K and from 1 to 5000bar
2010, Chemical Geology
A thermodynamic model explicit in Helmholtz free energy is constructed to calculate the single-phase PVTx properties of the CO₂–CH₄–C₂H₆–N₂–H₂O fluid mixtures. Parameters of the binary CO₂–H₂O, CH₄–H₂O, C₂H₆–H₂O and N₂–H₂O mixtures are regressed from assessed experimental data. On the basis of the binary mixture parameters, the model can be used to predict the single-phase volumes of the CO₂–CH₄–C₂H₆–N₂–H₂O–NaCl fluid mixtures with a simple approach. Comparison with a large number of experimental data shows that the model can reproduce the single-phase PVTx properties of the CO₂–CH₄–C₂H₆–N₂–H₂O–NaCl fluid mixtures from 273 to 1273 K and from 1 to 5000 bar, with or close to experimental accuracy. Online calculations can be made on the website: www.geochem-model.org/.
Experimental determination of the activity-composition relations and phase equilibria of H<inf>2</inf>O-CO<inf>2</inf>-NaCl fluids at 500°C, 500 bars
2004, Geochimica et Cosmochimica Acta
An understanding of the activity-composition (a-X) relations and phase equilibria of halite-bearing, mixed-species supercritical fluids is critically important in many geological and industrial applications. We have performed experiments on H₂O-CO₂-NaCl fluids at 500°C, 500 bar, to obtain accurate and precise data on their a-X relations and phase equilibria. Two kinds of experiments were performed. First, H₂O-CO₂-NaCl samples were reacted at fixed activities of H₂O = 0.078, 0.350, 0.425, 0.448, 0.553, 0.560, 0.606, 0.678, 0.798, 0.841, and 0.935 to define the tie lines of known H₂O activity in the halite-vapor and vapor-brine fields. Results indicate that fluids with all but the last of these H₂O activities lie in the vapor-halite two-phase region and that a fluid with a_H₂O = 0.841 has a composition close to the three-phase (vapor + brine + halite) field. A second set of experiments was performed to determine the solubility of NaCl in parts of the system in equilibrium with halite. Data from these experiments suggest that the vapor corner of the three-phase field lies at H₂O contents above X_H₂O = 0.58 and X_NaCl = 0.06, and below X_H₂O = 0.75 and X_NaCl = 0.06, which is a significantly more H₂O-rich composition than indicated by existing thermodynamic models.
Synthetic fluid inclusions: XVI. PVTX properties in the system H<inf>2</inf>O-NaCl-CO<inf>2</inf> at elevated temperatures, pressures, and salinites
2000, Geochimica et Cosmochimica Acta
The ternary system H₂O-NaCl-CO₂ is one of the most important fluid systems in geochemistry and petrology. However, there is little information on the phase equilibrium and PVT properties in this system at salinities above 6 wt.% NaCl. In this study, PVTX data were obtained experimentally by using the synthetic fluid inclusion technique in conjunction with conventional microthermometry and a hydrothermal diamond–anvil cell.
Solvi (liquid-vapor boundaries) and lines of equal homogenization temperature (approximating lines of constant density) were determined for pressures between about 100 and 500 MPa, temperatures of 300°C to 800°C, and compositions up to 40 wt.% NaCl and 20 mol.% CO₂, both relative to water. Critical temperatures were obtained for ternary compositions ≤ 20 wt.% NaCl and ≤ 20 mol.% CO₂, both relative to water.
For a constant homogenization temperature, the dP/dT slopes of lines of equal homogenization temperature become steeper along pseudobinaries with both increasing carbon dioxide concentration and increasing NaCl. At constant salinity, the high-pressure portion of the solvus shifts to higher pressures and temperatures with increasing CO₂ concentration. Addition of carbon dioxide causes the critical point to migrate towards higher pressures and slightly lower temperatures. For concentrations less than 20 wt.% NaCl and less than 20 mol.% CO₂, the main effect of an increase in salinity at a fixed H₂O/CO₂ ratio is a sharp rise in the critical temperature, coupled with a moderate shift of the critical point towards higher pressures. The addition of CO₂ and NaCl causes the solvus to migrate to high temperatures and pressures, reaching granulite–facies conditions for moderate to high concentrations of CO₂ and NaCl. The results of this study are combined with literature data to construct P-T sections, with lines of constant homogenization temperature, for various compositions in the H₂O-NaCl-CO₂ ternary, and the results are compared with results predicted by a recently published equation of state.
Adaptation of the Bowers and Helgeson (1983) equation of state to the H<inf>2</inf>O-CO<inf>2</inf>-CH<inf>4</inf>-N<inf>2</inf>-NaCl system
1999, Chemical Geology
The equation of state developed by Bowers and Helgeson ([Bowers, T.S., Helgeson, H.C., 1983. Calculation of the thermodynamic and geochemical consequences of nonideal mixing in the system H₂O–CO₂–NaCl on phase relations in geological systems: equation of state for H₂O–CO₂–NaCl fluids at high pressures and temperatures. Geochim. Cosmochim. Acta, 47, 1247–1275.] and [Bowers, T.S., Helgeson, H.C., 1985. Fortran programs for generating fluid inclusion isochores and fugacity coefficients for the system H₂O–CO₂–NaCl at high pressures and temperatures. Computers and Geosciences, 11, 203–213.]), which was originally designed for H₂O–CO₂–NaCl fluids, has been extended to CH₄ and N₂ bearing fluids. Available experimental P–V–T–X data in the H₂O–CO₂–CH₄–N₂–NaCl fluid system are accurately reproduced by this equation of state, and, therefore, isochores and fugacity coefficients can be accurately calculated up to 1000 MPa and 1300 K. This equation of state cannot be used in and near immiscibility regions and critical points, like any modified Redlich–Kwong equation of state. The empirical modifications allow isochore construction for realistic geological fluid systems which are often found in fluid inclusions, and which involve several gases and salts.
Synthetic fluid inclusions: XIII. Experimental determination of PVT properties in the system H<inf>2</inf>O+ 40 wt % NaCl + 5 mol% C0<inf>2</inf> at elevated temperature and pressure
1995, Geochimica et Cosmochimica Acta
The location of the liquid + vapor → liquid phase boundary and the P−T slopes of iso-Th lines were determined for a constant composition of 40 ± 0.1 wt% NaCl and 5 ± 0.15 mol% C0₂ (both relative to H₂O) at high density. Synthetic fluid inclusions with this composition were formed in cold-seal pressure vessels at pressures of 2 and 4 kbar and temperatures between 350° and 700°C. The inclusions were analyzed on a gas-flow heating/cooling stage to determine the temperatures of halite dissolution [Tm_{(H+L+V→L+V)}] and total homogenization [Th_(L+v→L)].
Addition of 40 wt% NaCl to an aqueous solution containing 5 mol% C0₂ causes a significant shift of the liquid + vapor → liquid boundary towards higher pressures. The slopes of the iso-Th lines decrease from 29.5 bars/°C for Th_(L+V→L) of 400°C, to 6.4 bars/°C for Th_(L+v→L) = 600°C. Addition of 5 mol% C0₂ to an aqueous solution containing 40 wt% NaCl results in halite dissolution temperatures that are slightly higher (TM_{(H+L+V→L+V)} ≈ 332°C) than the literature value of 323†C for the vapor-saturated liquidus of an H₂O-40 wt% NaCI mixture.
Calculated molar volumes for 40 wt% NaCl + 5 mot% C0₂ solutions at 2 and 4 kbar show trends that are similar to those of other compositions in the ternary system H₂OCO₂NaCl at the same pressures and temperatures. In the P−T range of this study, all excess volumes are negative and lie between the values for the compositions H₂O5 mot% C0₂ and H₂O40 wt% NaCl.

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^☆: Presented at PACROFI III, Third Biennial Pan-American Conference on Research on Fluid Inclusions, held in Toronto, Canada, May 20–22, 1990.

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Geochimica et Cosmochimica Acta

Abstract

References (27)

Synthetic fluid inclusions in natural quartz. II: Application to PVT studies

Geochim. Cosmochim. Acta

Calculation of the thermodynamic and geochemical consequences on nonideal mixing in the system H₂O-CO₂-NaCl on phase relations in geologic systems: Equation of state for H₂O-CO₂-NaCl fluids at high pressures and temperatures

Geochim. Cosmochim. Acta

P-V-T properties of fluids in the system H₂O ± CO₂ ± NaCl: New graphical presentations and implications for fluid inclusion studies

Geochim. Cosmochim. Acta

Synthetic H₂O-CO₂ fluid inclusions in spontaneously nucleated forsterite, enstatite, and diopside hosts: The method and applications

Geochim. Cosmochim. Acta

Synthetic fluid inclusions IX. Critical PVTX properties of NaCl-H₂O solutions

Geochim. Cosmochim. Acta

Synthetic fluid inclusions in natural quartz I. Compositional types synthesized and applications to experimental geochemistry

Geochim. Cosmochim. Acta

Determination of the homogenization temperatures and densities of supercritical fluids in the system NaCl-KCl-CaCl₂-H₂O using synthetic fluid inclusions

Chem. Geol.

Experimental determination of the compositional limits of immiscibility in the system CaCl₂-H₂O-CO₂ at high temperatures and pressures using synthetic fluid inclusions

Chem. Geol.

Carbon Dioxide

High pressure and temperature equation of state and calculation of the thermodynamic properties of gaseous carbon dioxide

Amer. J. Sci.

The properties of hydrates of chlorine and carbon dioxide

The thermodynamics and composition of carbon dioxide hydrate

Binary mixtures of volatile compounds

Cited by (12)

A predictive model for the PVTx properties of CO<inf>2</inf>-H<inf>2</inf>O-NaCl fluid mixture up to high temperature and high pressure

A model for single-phase PVTx properties of CO<inf>2</inf>-CH<inf>4</inf>-C<inf>2</inf>H<inf>6</inf>-N<inf>2</inf>-H <inf>2</inf>O-NaCl fluid mixtures from 273 to 1273K and from 1 to 5000bar

Experimental determination of the activity-composition relations and phase equilibria of H<inf>2</inf>O-CO<inf>2</inf>-NaCl fluids at 500°C, 500 bars

Synthetic fluid inclusions: XVI. PVTX properties in the system H<inf>2</inf>O-NaCl-CO<inf>2</inf> at elevated temperatures, pressures, and salinites

Adaptation of the Bowers and Helgeson (1983) equation of state to the H<inf>2</inf>O-CO<inf>2</inf>-CH<inf>4</inf>-N<inf>2</inf>-NaCl system

Synthetic fluid inclusions: XIII. Experimental determination of PVT properties in the system H<inf>2</inf>O+ 40 wt % NaCl + 5 mol% C0<inf>2</inf> at elevated temperature and pressure

An assessment of the accuracy of isochore location techniques for H2O-CO2-NaCl fluids at granulite facies pressure-temperature conditions☆

Abstract

Geochim. Cosmochim. Acta

Geochim. Cosmochim. Acta

Geochim. Cosmochim. Acta

Geochim. Cosmochim. Acta

Geochim. Cosmochim. Acta

Geochim. Cosmochim. Acta

Chem. Geol.

Chem. Geol.

Carbon Dioxide

High pressure and temperature equation of state and calculation of the thermodynamic properties of gaseous carbon dioxide

Amer. J. Sci.

The properties of hydrates of chlorine and carbon dioxide

The thermodynamics and composition of carbon dioxide hydrate

Binary mixtures of volatile compounds

An assessment of the accuracy of isochore location techniques for H₂O-CO₂-NaCl fluids at granulite facies pressure-temperature conditions☆