CO2 Fugacity Calculations

Hari Shankar Pandalai


I-Ming Chou


Dear Fellow Fluid-Inclusionists,

I need to compute fugacity of CO2 in a H2O-CO2-NaCL fluid with XCO2=0.2033, and about 6 eq.wt% NaCl (XNaCl = 0.0187) at 250 C and 200 to 400 bars. The system is in the field of immiscibility of the CO2-H2O-NaCl system.

The EOS given by Bowers and Helgeson (1983) is for higher T and P. An EOS based on correspondance states for CO2-H2O-NaCl has been given by Duan, Moller and Weare (1995) which is valid up to 300 C. The computation is however not easy. Others (as I understand) only deal with the CO2-H2O system.

I request members for literature/suggestions for the calculation. An explicit answer to the question is also welcome.

Hari Shankar Pandalai
Department of Earth Sciences
Indian Institute of Technology
Powai, Mumbai 400076
Tel. Off. : (+91) (22) 5767265
Dept.: (+91) (22) 5767251
Res. : (+91) (22) 5770148
Fax Dept.: (+91) (22) 5767253
IIT : (+91) (22) 5783480
e-mail :,


Dear Dr. Pandalai,

If you are referring to the paper of Duan et al. 1995 (Equation of state prediction of phase equilibria and volumtric properties), you are not quite right that the equation is valid up to 300 C. Rather the original formulation on which the paper is based (Anderko and Pitzer, 1993) treats the system only above 300 deg. so that all NaCl can be assumed to be associated and can behave as hard spheres. I think, you can calculate the fugacity coefficient, hence the fugacity, through the DMW equation. I myself have never computed the fugacity coefficient because I have not needed to do it. Correct me if I am wrong.



Department of Geology & Geophysics
I.I.T., Kharagpur (WB) 721302 India
Fax: (91) 3222 55303


Dear Dr. Pandalai:

Dr. Panigrahi was right.

The computer program EOSNHC that Dr. Duan gave me in 1995 was based on the paper by Duan, Moller, and Weare (GCA, 59, 2869-2882, 1995) for the system NaCl-H2O-CO2 for T=300-1000 C, and P=0-6000 bar, NaCl=0-30 wt% (or up to 50 wt% with less accuracy).

I believe the program is still available from Duan (<>), who is traveling in China, and will be back at UCSD soon.


I-Ming Chou


I-Ming Chou
Address: 954 National Center
 U.S. Geological Survey
 Reston, VA 20192
Phone: +1 (703)648-6169
Fax: +1 (703)648-6383 or
 +1 (703) 648-6252