Volumetric Properties Of The Carbon Dioxide-Water-Sodium Chloride Systems: Data Assessment And Modeling

Accurate knowledge of pressure–volume–temperature–composition(PVTx) properties of the CO2-H2O-Na Cl system is crucial for simulation and safety evaluation of CO2 geological storage. In addition, the simulation of many other geological processes and the simulation, design and control of many industrial processes also need accurate data of these properties. Thus, the following work was conducted:(1) Assessed fourteen sets of experimental PVTx data(274.15–513.15 K, 0–120 MPa) of pure water and the Na Cl-H2 O, CO2-H2 O and CO2-H2O-Na Cl solutions reported in recent years. The assessment adopted some reference models that are accurate in their applicable ranges, which include a highly accurate thermodynamic model of water and some accurate models for the PVTx properties of aqueous solutions or the solubility of CO2. The contents of assessment include the uncertainties and systematic deviations of data, the distribution features of deviations(including the correlations of deviations with P-T-x conditions), the consistency between data of different sources, and error sources during measurements. It is found that only few sets of data(or a part of them) have high precisions, which are usually companied by systematic deviations; whereas most sets of data have remarkable or obvious uncertainties, and systematic deviations as well, whose size and correlations with P-T-x conditions vary with the measurement conditions.(2) Corrected the systematic deviations of some data with small uncertainties.(3) Established a highly accurate model for the molar volume of liquid water. The accuracy of this model is close to the high-precision reference model of water(IAPWS-97), but it has simpler form and fewer parameters, and can be extended moderately to higher temperatures and pressures.(4) Proposed a new model for the molar volumes of aqueous CO2 solutions. In this model, the molar volume of water is used as a reference, and the contribution of CO2 to molar volume is treated as a quadratic function of composition, whose coefficients are polynomials of T and P, where the parameters were fitted with high-precision density data high(including corrected data) of aqueous CO2 solutions. This new model can be used in a wider range of pressure and CO2 concentration, and is more reliable at intermediate to temperatures(below the critical temperature of water).