The petrophysical properties of cap rocks and intraformational barriers can constrain the CO₂ containment volumes of potential geosequestration sites. Characterization of regional seals and intraformational barriers requires an understanding of the seal capacity of the cap rock or barrier. Seal capacity is the capillary pressure (or column height) at which a trapped fluid commences to leak or move through a seal rock. Seal rocks are effective because of very fine pore and pore-throat sizes that result in low porosities and permeabilities, which in turn generate high capillary threshold pressures. These high threshold pressures, together with wettability and interfacial tension (IFT) properties, determine the final column height that a seal can hold. A review is presented on the function of wettability and IFT in the geological storage of CO₂ and its effect on seal capacity (CO₂ column height) with respect to capillary pressure, the potential for the movement of CO₂ through the seal, and the effect on reservoir storage volumes.

Mercury injection capillary pressure analysis has been used extensively in the petroleum industry to determine the effectiveness of the top seal in relation to hydrocarbon column height retention. With the burgeoning interest in geological storage of CO₂, this technology can be applied to establish the suitability of a top seal for containment of CO₂; however, the function of IFT and wettability in the CO₂-water-rock systems is not well understood. How supercritical CO₂ (scCO₂) affects these two properties is unclear, especially as the waterfront becomes saturated with scCO₂ and may eventually become miscible with the scCO₂ at reservoir conditions.

To date, literature shows that the wettability and IFT of the CO₂-water-rock system may be more significant than in the hydrocarbon-water-rock systems and that calculated CO₂ column heights based on nonwetting assumptions could result in column heights being as much as 50% less than otherwise predicted.