Density Measurement and Modeling of CO₂-Brine System at Temperature and Pressure Corresponding to Storage Conditions

The densities of CO2 solution of the brine from Teikoku Oil Field located at Niigata Prefecture in Japan are measured by a magnetic suspension balance at temperatures from 303.15 to 323.15 K, pressures from 10 to 20 MPa, and CO2 mole fractions of 0, 0.0038, 0.0040, 0.0087, 0.0100, and 0.0160. Results show that the densities of CO2–brine solution increase to 0.86% from that of brine and linearly increases with pressure at a gradient of 0.411 kg·m–3·MPa–1 and with CO2mole fraction at an average gradient of 514 kg·m–3·mol–1 at a temperature of 303.15 K. On the other hand, the density of CO2–brine solution decreases with increasing temperature at an average rate of −0.377 kg·m–3·K–1 under our experimental conditions. The ePC-PSAFT model is applied to predict the data obtained from this study and those from literature. It is demonstrated that the model works well with average relative deviation (ARD) of 0.27%. A correlation of density ratio of CO2–brine solution to brine is provided and validated by data used in the ePC-PSAFT model, which is convenient for engineering application in comparison with that by the ePC-PSAFT. The ARDs for density ratio predicted by ePC-PSAFT and correlation are 0.075% and 0.019% for this work, respectively.