Density Measurement of CO2 + Deionized Water in Warm Formations by a Magnetic Suspension Balance

摘要

The densities of CO2-deionized water were investigated by a magnetic suspension balance (MSB) at the practical conditions of CO2 geologic sequestration with pressures range from 10 to 18 MPa, temperatures from 333.15 to 413.15 K, and CO2 mole fractions up to 0.0126 according to the solubility of CO2 in water. The experimental results of CO2-free deionized water and CO2-deionized water with different CO2 mole fractions revealed that the density of deionized water in contact with CO2 is higher than that of pure water. The density of the CO2 aqueous solution increases with increasing pressure and CO2 concentration almost linearly, while decreases with increasing temperature. And the slope of the density curves is almost the same for different concentrations at the same temperature within experimental error. The slope of the density versus CO2 mole fraction decreases from 0.442 to 0.257 as the temperature increases from 333.15 to 413.15 K. The slope will be zero or negative value at about 510 K for the system of CO2-water according to this trend. In other words, the density values of CO2- deionized water may be lower than CO2-free deionized water at about 510 K. According to this trend, the mixture solution will migrate upward due to buoyancy-driven at about 510 K, which is not benefit to CO2 geologic sequestration. Therefore, the density of CO2 aqueous solution has an important effect on the safety of CO2 sequestration. An empirical model for the densities of liquid CO2-deionized system was developed on the basis of measured densities. The average deviation (AD) between the model and the experimental data is 0.00001%, the maximum deviation is 0.018%. The empirical model could accurately represent the experimental data and be appropriate for assessing the CO2 geologic sequestration.