Measurements of CO2-H2O-NaCl Solution Densities over a Wide Range of Temperatures, Pressures, and NaCl Concentrations

The density of carbon dioxide + brine solution under supercritical conditions is a significant parameter for CO2 sequestration into deep saline formations. This paper has extended our previous study on density measurements of CO2 + Tianjin brine to the CO2-H2O-NaCl solution by using a magnetic suspension balance (MSB). The measurements were performed in the pressure range (10 MPa to 18 MPa) at a range of temperatures (60 degrees C to 140 degrees C) with different concentrations of NaCl (C-NaCl = 1 mol.kg(-1), 2 mol.kg(-1), 3 mol.kg(-1), 4 mol.kg(-1)) and different CO2 mass fractions (w = 0, 0.01, 0.02, 0.03). The influences of pressure, temperature, CO2 mass fractions and NaCl concentration on the CO2-H2O-NaCl solution density were analyzed. The CO2-H2O-NaCl solution density increased almost linearly with an increase in the CO2 mass fraction when the NaCl concentration was less than 4 mol.kg(-1) and the temperature was lower than 120 degrees C. However, at a high concentration of NaCl (C-NaCl = 4 mol.kg(-1)), the density decreased with increasing mass fraction of CO2 when the temperature was over 120 degrees C. The density of the CO2-H2O-NaCl solution with a high NaCl concentration decreased after dissolving CO2 at high temperatures, which caused the solution to float over the saline layer and increased the risk of CO2 leakage. An empirical model was established to predict the solution density with high accuracy.