Fill the form below to run the program.

How this works:

1. Select which of pressure, temperature or salinity will be allowed to vary

This program calculates the density and viscosity of water and carbon dioxide, and the composition of their mixture where the two phases are in equilibrium (between 10 and 380°C, 0.1 to ∼400 MPa and for NaCl concentrations up to 25 mol NaCl/kg H₂O). It uses published thermodynamic and physical models. It has been formatted for iterative use and error propagation, where the thermodynamic model is the main source of uncertainties.

Simplified phase diagram for CO2-H2O mixtures. The solid black curve separates pressure-temperature domains where H2O and CO2 are fully miscible (``one-phase domain'' on the right-hand side) from domains where CO2-rich and water-rich phases may coexist. Note that pressure is on a logarithmic scale. T&F 1963: measurements of Todheide and Franck (1963). T&K 1964: measurements of Takenouchi and Kennedy (1964). H&P 2003: model of Holland and Powell (2003), valid above 300°C and 300 MPa (open circles) but not below (small red circles). The stability fields of high pressure - low temperature solid phases (ices and clathrates) are not represented. Adapted from Dubacq et al. (2013).

In the figure above, the green field (``two-phase domain'') indicates pressure-temperature conditions for which the program is supposed to calculate the solubility of CO₂ in water (or NaCl-brine) and that of H₂O in the CO₂-rich phase. The program estimates the density and viscosity of H₂O and CO₂ in both two-phase and one-phase domains (green and pale pink).
The thermodynamic model has not been parametrized above ∼400 MPa (i.e., in the white domain) as experimental results in this range are sparse.

2. Specify conditions and choose the output:

Indicate the number of points (up to 50) for the calculation, the range of the varying variable (minimum and maximum temperature, pressure or salinity) and constant values for the fixed variables. Choice is given between several outputs:

• solubility only: gives the composition of the water-rich and CO₂-rich phases
• solubility and phase properties: gives compositions and adds density and viscosity of CO₂ and H₂O (not of their mixture)
• full thermodynamic output: all the above plus activity coefficients (γ), interaction parameters (the Ws and αs of the DH-ASF formalism of Holland and Powell, 2003; and Evans and Powell, 2006) and NaCl dissociation.

The solubility model is limited to the green field of the above figure.

References:

• Dubacq, B., Bickle, M. J., Evans, K. A. (2013) An activity model for phase equilibria in the H₂O-CO₂-NaCl system. Geochimica et Cosmochimica Acta 110, 229 - 252. doi: 10.1016/j.gca.2013.02.008
• Evans, K., Powell, R. (2006) A method for activity calculations in saline and mixed solvent solutions at elevated temperature and pressure: A framework for geological phase equilibria calculations Geochimica et Cosmochimica Acta 70, 22, pp. 5488-5506. doi: 10.1016/j.gca.2006.08.032
• Holland, T. J. B., Powell, R. (2003) Activity-composition relations for phases in petrological calculations: an asymmetric multicomponent formulation. Contributions to Mineralogy and Petrology 145, 4, 492-501. doi: 10.1007/s00410-003-0464-z
• Takenouchi, S., Kennedy, G. C. (1964) The bynary system H₂O-CO₂ at high temperatures and pressures. American Journal of Science 262, 1055-1074
• Todheide, K., Franck, E. U. (1963) Das Zweiphasengebiet die kritische Kurve im System Kohlendioxid-Wasser bis zu Drucken von 3500 bar. Zeitschrift für Physikalische Chemie (Neue Folge) 37, 387 - 401