a b s t r a c tThis work presents contact angle measurements for CO 2 -water-quartz/calcite systems at general sequestration pressure and temperature conditions (200-3000 psig and 77-122 • F). The effect of drop volume, repeated exposure of the substrates to dense water saturated CO 2 , pressure and temperature on the contact angles is examined. In the 1st measurement cycle, the contact angles for the quartz substrate varied from 46 to 48 • and 47 to 46 • for gaseous (water saturated) CO 2 and liquid (water saturated) CO 2 respectively, at 77 • F. For calcite substrate, these values varied from 45 to 48 • and 42 to 40 • , respectively. Remarkably, this work highlights a characteristic permanent shift in the contact angle data with repeated exposure to dense, water saturated, CO 2 . The contact angle data trends after repeated exposure to the dense, water saturated CO 2 varied from 89 to 91 • and 85 to 80 • for the quartz substrate for gaseous (water saturated) CO 2 and liquid (water saturated) CO 2 respectively, at 77 • F. For calcite substrates, these values varied from 60 to 59 • and 54 to 48 • , respectively. This important observation has serious implications towards the design and safety issues, as a permanent positive contact angle shift indicates lower CO 2 retention capabilities of sequestration sites due to a reduction in the capillary pressure. It is further confirmed that the permanent shift in the contact angle is due to surface phenomena. With an increase in temperature (from 77 to 122 • F), the contact angle shift is reduced from about 45 • to about 20 • for quartz substrates. Other observations in the contact angle data with respect to pressure are in good agreement with the trends reported in the literature.

This work presents interfacial tension (IFT) data for the CO2–water system in the pressure and temperature range of (1.48 to 20.76) MPa and (298.15 to 333.15) K. The IFT evaluation is carried out using the pendant drop method. Inaccuracies observed in the literature such as consideration of pure phase densities and short presaturation time durations have been avoided by utilizing saturated phase densities and long presaturation time durations. The water-rich phase density is evaluated using a literature correlation, and the CO2-rich phase density is evaluated using equation-of-state modeling approach. Also, presaturation times were extended up to 24 h to obtain equilibrated IFT data for the CO2–water system. It is observed that the IFT reduces with pressure when the CO2-rich phase is a gas at both subcritical and supercritical temperatures. Further, the IFT values reached a plateau at about 23 mN·m–1 at higher pressures (13.89 to 20.79 MPa) and for the entire temperature range. A predominant buoyancy effect is observable at higher pressures due to the reduction in phase density differences. Comparatively, the evaluated IFT data trends are about (5 to 7) mN·m–1 lower at high pressures than those reported in most of the literature.

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