Densities of CO 2 + decane binary mixtures were measured by using the magnetic suspension balance (MSB) at different CO 2 mole fractions, x 1 = 0.2361, 0.4698, 0.7100, 0.7725, and 0.8690 with temperatures from (303.15 to 353.15) K and pressures from (8 to 19) MPa. Excess molar volumes were calculated from the density data. The experimental results revealed that the density of CO 2 + decane mixtures increases with increasing pressure and decreases with increasing temperature. The density of mixtures increases with increasing CO 2 concentration first and then decreases at higher CO 2 concentration and higher temperature. A crossover phenomenon with compositions is observed, and the crossover pressure increases with temperature. The excess molar volumes of this mixture display more negative values with increasing temperature at 18 MPa and less negative values with increasing pressure at 313.15 K. Moreover, the mixture densities have been predicted with GERG-2008 and a modified Benedict−Webb−Rubin−Starling (BWRS) model. The validities of the two models have been tested by predicting density data in this work and comparing with previous literature.

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Density data of carbon dioxide (CO2) + brine solution from Tianjin reservoir were determined using magnetic suspension balance (MSB). Measurements were performed in the pressure range (10 to 18) MPa and at the temperatures (313 to 353) K. CO2 mass fraction in solution was selected up to 0.040. The experimental results revealed that the density of CO2 + brine solution decreases with increasing temperature and increase with increasing pressure. The density of CO2 + brine solution increases almost linearly with increasing mass fraction of CO2 in solution. The slope of the density vs CO2 mass fraction curves decreased from 0.222 to 0.185 as temperature increased from 313 to 353 K and is independent of pressure. Two regression functions were developed to describe the density data of CO2-free brine and CO2 + brine solution from Tianjin reservoir under sequestration conditions, and the errors between experimental results and prediction were within 0.004% and 0.03%, respectively.

The injection of CO 2 into oil reservoirs (CO 2 enhanced oil recovery, CO 2 -EOR) can result in higher production, and the use of CO 2 as a mining resource can thus be an economic driver for oil production. The thermodynamic properties of CO 2 mixtures are essential for the design and operation of CO 2 -EOR systems. This paper addresses the (p, ρ, T) properties of a CO 2 + tetradecane solution. Experimental densities were measured on a magnetic suspension balance, and experiments were performed at pressures from 10 MPa to 19 MPa, temperatures from 313.15 K to 353.15 K, and CO 2 mole fractions of x 1 = 0, 0.2469, 0.5241, 0.7534, and 0.8773. Solution densities increased with pressure and decreased with temperature over the experimental range. Density versus the CO 2 mole fraction increased at first and then decreased at higher temperatures and higher CO 2 concentrations. The compositions intersect when plotted, and the pressure intersection increased with temperature. The excess molar volumes of the binary mixtures were negative over the entire range of composition, which increased with increasing pressure and became more negative with increasing temperature. The PC-SAFT and tPC-PSAFT equations of state were used to calculate the densities of the binary mixtures. New PC-SAFT parameters for tetradecane were obtained by fitting to experimental densities directly. In both PC-SAFT and tPC-PSAFT, the binary interaction parameter k ij was fitted as a function of the CO 2 mole fraction. The tPC-PSAFT combined with the correlation of k ij gave the best predictions of the CO 2 + tetradecane mixture densities.

The density of carbon dioxide + brine solution under supercritical conditions is a significant parameter for CO 2 sequestration into deep saline formations. This paper has extended our previous study on density measurements of CO 2 + Tianjin brine to the CO 2 −H 2 O−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 °C to 140 °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 CO 2 mass fractions (w = 0, 0.01, 0.02, 0.03). The influences of pressure, temperature, CO 2 mass fractions and NaCl concentration on the CO 2 −H 2 O−NaCl solution density were analyzed. The CO 2 −H 2 O−NaCl solution density increased almost linearly with an increase in the CO 2 mass fraction when the NaCl concentration was less than 4 mol•kg −1 and the temperature was lower than 120 °C. However, at a high concentration of NaCl (C NaCl = 4 mol•kg −1 ), the density decreased with increasing mass fraction of CO 2 when the temperature was over 120 °C. The density of the CO 2 −H 2 O−NaCl solution with a high NaCl concentration decreased after dissolving CO 2 at high temperatures, which caused the solution to float over the saline layer and increased the risk of CO 2 leakage. An empirical model was established to predict the solution density with high accuracy.