Interfacial Interactions between Reservoir Brine and CO₂at High Pressures and Elevated Temperatures

In this paper, an experimental technique has been developed to study the interfacial interactions of the reservoir brine−CO 2 system at high pressures and elevated temperatures. Using the axisymmetric drop shape analysis (ADSA) for the pendant drop case, this new technique makes it possible to determine the interfacial tension (IFT) and visualize the interfacial interactions between the reservoir brine and CO 2 under practical reservoir conditions. More specifically, the dynamic IFT between the reservoir brine and CO 2 is measured as a function of pressure at two different temperatures. It is found that the dynamic IFT gradually reduces to a constant value, which is termed as the equilibrium IFT. The equilibrium IFT decreases as the pressure increases, whereas the same parameter increases as the temperature increases. The major interfacial interactions observed in this study include interface disappearance, the swelling effect, the shrinking effect, and wettability alteration. At an elevated temperature ( T = 58 °C), the pendant brine drop cannot be observed in the CO 2 phase at a pressure of P ≥ 12.238 MPa. It is also found that CO 2 solubility in the brine phase, which is measured using the PVT system, approaches its maximum value under the same conditions. Further increases in pressure do not noticeably increase the CO 2 solubility in the brine phase. The brine swelling effect is observed at all the pressures and temperatures tested, whereas the brine shrinking effect occurs only at high pressures and a lower temperature ( T = 27 °C). In addition, the wettability of the reservoir brine−CO 2 system changes from the hydrophilic case to the hydrophobic case when the CO 2 changes from the gas phase to the liquid phase.