EQUATION OF STATE FOR THE NACL-H2O-CO2 SYSTEM - PREDICTION OF PHASE-EQUILIBRIA AND VOLUMETRIC PROPERTIES

An equation of state (EOS) has been developed for the NaCl-H2O-CO2 sys tem which consistently predicts various properties including PVTX, imm iscibility or phase equilibria, solubilities, and activities with an a ccuracy close to that of experimental data from 300 to about 1000 degr ees C and 0-6000 bar with NaCl concentrations to about 30 wt% of NaCl (relative to NaCl + H2O) or to about 50 wt% with less accuracy. The EO S predicts that excess volumes can be over 30% of the total volume und er some T-P conditions. Adding NaCl to the H2O-CO2 system dramatically increases the T-P range of immiscibility. The immiscibility field is minimal around 400-500 degrees C. Above or below this temperature, it expands for a constant pressure. A moderately saline brine can evolve into a very saline brine by phase separation at high temperatures. The presence of NaCl can substantially decrease the activity of H2O and i ncrease that of CO2, thus affecting decarbonation and dehydration reac tions. Compared to the EOS of Bowers and Helgeson (1983a), the EOS of this study is more reliable in the calculation of volumetric propertie s particularly in the low pressure range. In addition, BH EOS cannot p redict phase equilibria.