Measurement of Interfacial Tension of CO₂ and NaCl Aqueous Solution over Wide Temperature, Pressure, and Salinity Ranges

Abstract

Interfacial tension data and models are of great importance to the storage of CO2 in deep saline aquifers. In this study, the pendant-drop method combined with axisymmetric drop shape analysis was used in the interpretation of the interfacial behavior of CO2 and brine. Extensive experimental measurements of the interfacial tension between CO2 and an NaCl solution were acquired for pressures ranging from 3.0 to 12.0 MPa, temperatures from 300 to 353 K, and NaCl molalities from 0 to 1.8 mol·kg–1, for a total of 1,254 valid data points. All experiments were conducted in a pressure cell fitted with a capillary tube to create pendant droplets in a CO2-rich atmosphere. The experimental results indicated that interfacial tension decreased with increasing pressure and increased with temperature and salinity. As pressure increased to a certain point, the interfacial tension reached a plateau. At a given temperature, the CO2–aqueous system reached a plateau for different salinities under nearly the same pressure. However, the plateau pressure increased with temperature. The plateau interfacial tension value slightly increased with temperature and salinity. We also found a linear relationship between the change in interfacial tension and the molality concentration of brine. An empirical model was also proposed based on the Parachor model for the prediction of interfacial tension. Most results of this model deviated by less than ±5% from our experimental results, indicating that the model was a good fit to our experiments.

Effects of Na+, K+, Ca2+, and Mg2+ cations on CO2–brine interfacial tension under offshore storage conditions

“…In our previous work, we developed a combined model based on the Parachor model and linear relationship between interfacial tension and NaCl molality to predict CO 2 –NaCl interfacial tension values . However, this model could not fit our new data quite well, especially for the brine containing divalent cations.…”

“…Figure shows the deviations Δγ (mN·m −1 ) of the interfacial tension using empirical equations under the same conditions as that used for the experiment. The empirical equation was also used to fit our previous data . The plot shows that the deviations ranged from −4 to +4 mN·m −1 .…”

“…The pendant‐drop experimental apparatus is shown in Fig. ; it has been described in detail in our previous work . The measuring system mainly consists of a pressure vessel with two windows, pressure control pump, temperature controller, image capture camera, and data acquisition and processing computer.…”

“…The interfacial tension between CO 2 and pure water systems was mainly measured at pressures and temperatures ranging from 0.1 to 20 MPa and 5°C to 62°C . Later, NaCl solutions with different salinities were used for interfacial tension measurements for temperatures ranging from 298 K to 423 K and pressures up to 69.51Mpa, and salt molalities up to 4.28 mol·kg −1 . All authors reported that the interfacial tension of the CO 2 –brine system increases with temperature and salinity and decreases with pressure until it asymptotically reaches a pseudo‐plateau value.…”

“…[9][10][11] Later, NaCl solutions with different salinities were used for interfacial tension measurements for temperatures ranging from 298 K to 423 K and pressures up to 69.51Mpa, and salt molalities up to 4.28 mol·kg −1 . 5,8,[12][13][14][15][16][17][18][19] All authors reported that the interfacial tension of the CO 2 -brine system increases with temperature and salinity and decreases with pressure until it asymptotically reaches a pseudo-plateau value. However, doubt remains about the accuracy of interfacial tension data based on the different experimental methods used to determine the thermodynamic equilibrium.…”