Abstract:

This study extends the solubility model developed by Duan and coworkers for pure CO2, CH4, C2H6, and H2S to the
CO2-CH4-N2-C2H6-H2S gas mixture. The DMW92 equation of state (EOS) was extended to the CO2-CH4-N2-C2H6-H2S gas mixture by evaluation of interaction parameters between dissimilar molecule pairs from experimental VLE or PVTx data of binary gas mixtures. The extended DMW92 EOS was used in this model to calculate fugacity coefficients of components in gas mixture. The Pitzer model was used to calculate activity coefficients of gas dissolved in aqueous solutions. Solubility parameters determined by Duan and coworkers for pure CO2, CH4, C2H6 and H2S were followed and solubility parameters for pure N2 were determined in this study. Because this model contains no parameters evaluated from solubility data of gas mixtures, it is predictive for solubility of gas mixtures. Comparison with experimental data available shows that this model can predict solubility of CO2-CH4-N2-C2H6-H2S gas mixtures in aqueous solutions with high accuracy over a wide P-T range (For CO2 and CH4 dominant gas mixtures, the P-T range of this model is from 273 to 523 K and from 0 to 2000×105 Pa). Calculations of this model indicate that the solubility of CO2 decreases with adding small percentage of CH4, N2 or H2S. The homogenization pressure of CO2-H2O-NaCl fluid inclusions will increase with adding CH4. The computer program based on this model can be obtained from the corresponding author.

Key words: solubility, model, gas mixture, aqueous solution, CO2