Thermophysical Properties of Pore-confined Supercritical Co2 by Vibrating Tube Densimetry

Properties of fluids confined in pore systems are needed for modeling fluid flow, fluid-rock interactions, and changes in reservoir porosity. The properties of CO2-rich fluids are particularly relevant to geothermal heat mining using carbon dioxide instead of water. While manometric, volumetric, and gravimetric techniques have been used successfully to investigate adsorption of low-density subcritical vapors, the results have not been satisfactory at higher, liquid-like densities of supercritical fluids. Even if the requirements for high experimental accuracy in the neighborhood of the critical region were met, these methods are fundamentally unable to deliver the total adsorption capacity, since the properties (e.g. density) of the adsorbed phase are in general not known. In this work we utilize vibrating tube densimetry for the first time to measure the total amount of fluid contained within a mesoporous solid. The method is first demonstrated using propane at subcritical and supercritical temperatures between 35 °C and 97 °C confined in silica aerogel (density 0.2 g·cm, porosity 90%) that was synthesized inside Hastelloy U-tubes. Sorption and desorption of carbon dioxide on the same solid was measured at 35 °C at pressures to 120 bar (density to 0.767 g·cm). The results show total adsorption increasing monotonically with increasing pressure, unlike excess adsorption isotherms which show a maximum close to the critical density.