Synthetic fluid inclusions: IX. Critical PVTX properties of NaCI-Hz0 solutions

Critical PVTX properties of NaCl-Hz0 fluids having compositions ofO-30 wt% NaCl have been determined using the synthetic fluid inclusion technique. Critical temperatures and pressures increase from 374. I “C and 220 bars for pure H20, to 820°C and 1574 bars for 30.0 wt% NaCl. Critical specific volumes decrease from 3. I 1 to 1.44 cm3/g over this same salinity range. Critical temperatures of NaCl-Hz0 fluids over the range O-30 wt% NaCl are described by the equation 7’= 374.1 + 8.800@ + 0.1771+ 0.02113~-‘+ 7.334. lO-4# where Tis the critical tempemture in degrees Celsius (+4.O”C) and Cp is fluid com~sition in weight percent NaCl. The critical pressure, determined from the intersection of the critical isochore with the critical temperature in P-T space, is expressed as a function of the critical temperature according to the relationship P = 2094 20.56T + 0.06896T2 8.903 X IO-‘T3 + 4.214. 10-8T4 where P is the critical pressure in bars (f21 bars) and T is the critical temperature in degrees Celsius. The critical specific volume is given as SV = 3.106 0.59679 O.O1066’P* + 0.01267@ where SV is the critical specific volume in cm’/g (?O.OZ cm’/g) and YI is related to the salinity as