Interfacial tension measurements are reported for the (H2O + CO2) system at pressures of (1 to 60) MPa and temperatures of (298 to 374) K. The pendant drop method was implemented using a high-pressure apparatus consisting of a view cell, fitted with a high-pressure capillary tube for creating pendant H2O drops in the CO2 bulk phase. The reported results have a relative standard deviation in most cases of less than 1.0 % and are in good agreement with literature values at low pressures. However, at higher pressures (up to 45 MPa), there is a significant scatter in the published data; the reasons for this are discussed. Measurements in the present work extend the pressure range of available data up to pressures of 60 MPa.

During imbibition, initially connected oil is displaced until it is trapped as immobile clusters. While initial and final states have been well described before, here we image the dynamic transient process in a sandstone rock using fast synchrotron‐based X‐ray computed microtomography. Wetting film swelling and subsequent snap off, at unusually high saturation, decreases nonwetting phase connectivity, which leads to nonwetting phase fragmentation into mobile ganglia, i.e., ganglion dynamics regime. We find that in addition to pressure‐driven connected pathway flow, mass transfer in the oil phase also occurs by a sequence of correlated breakup and coalescence processes. For example, meniscus oscillations caused by snap‐off events trigger coalescence of adjacent clusters. The ganglion dynamics occurs at the length scale of oil clusters and thus represents an intermediate flow regime between pore and Darcy scale that is so far dismissed in most upscaling attempts.

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[1] For subsurface flow, the correct definition for the balance of viscous and capillary forces, the so-called capillary number (Ca), which predicts the mobilization of nonwetting phase, has been a long-standing controversy. The most common microscopic definition results in nonwetting phase mobilization at Ca~10 À5, which is counterintuitive. Rather, mobilization should occur at Ca ≥ 1. As demonstrated herein, by using fast synchrotronbased X-ray computed microtomography and averaging of thereby accessible pore-scale parameters to macroscale values, a macroscale Ca definition is validated and shown to correctly describe mobilization at Ca~1. The presented methodology provides a connection between desaturation and pore-scale fluid topology and gives insight into when and how Ca changes with system size. The broader implication implies that it makes a difference whether desaturation is driven by an increase in flow rate or viscosity or decrease in interfacial tension since Ca incorporates nonwetting phase cluster length, which is process-dependent.

The interfacial tension between H2O and [(1 – x)n-decane + xCO2] was investigated for three different compositions of CO2 in the alkane-rich phase, of mole fractions x = (0.0, 0.2, and 0.5), along several isotherms at temperatures up to 443 K and pressures ranging from the miscibility state points for (n-decane + CO2) up to 50 MPa. The pendant drop method was implemented using a high pressure apparatus consisting of a view cell, fitted with a high pressure capillary tube for creating pendant H2O drops in the [n-decane + CO2] bulk phase. The conditions investigated cover a wide range relevant to carbon storage, providing information as to how the variation of the CO2 content in hydrocarbon fluids affects their interfacial tension with aqueous phases, which influences the trapping potential of underground formations. The results were compared to literature values where possible. A thermodynamic analysis of the dependence of the interfacial tension on CO2 composition, as well as on temperature, was discussed with respect to the Gibbs surface excess concentration and the enthalpy of interface formation, respectively. The present work provides novel interfacial tension data for the ternary system and addresses possible reasons for the observed discrepancies in literature values for the binary (H2O + n-decane) system observed over the range of conditions investigated. The reported results have a relative average standard deviation of 1.7 %.