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Wettability is a primary factor controlling how fluids flow in porous media during multiphase flow and yet we still know relatively little about how wettability affects the two-phase relative permeability (kr) of both the wetting and nonwetting phases. An integrated experimental methodology was used to measure how wettability (ranging from hydrophilic to hydrophobic behavior of the porous medium) controls water relative permeability (krw) and air relative permeability (kra) of two well characterized quartz sands over a wide range of water saturation (Sw) levels. For this research, two experimental devices were manufactured to provide precise, steady-state measurements of both krw and kra during controlled main drainage and imbibition cycles. The vertical column setup (ID=3 cm, L=20 cm) used for krw measurements includes a TRIME PICO TDR probe for localized water-content measurements and dual pressure transducers to monitor hydraulic gradients in real time. It allows accurate quantification of water relative permeability and in situ water retention curves (Pc–Sw). Moreover, it offers a significant advantage over the typical steady-state method of measuring krw, which assumes a constant unit hydraulic gradient. The air relative permeability (kra) was measured using a dedicated horizontal column (ID=3 cm, L=15 cm) containing hydrophobic porous membranes that prevented water from breaking through the membranes and thus ensured that air was allowed to flow only through the porous medium. The use of suction-controlled boundary conditions during drainage and imbibition cycles enabled continuous air-flow monitoring and allowed for precise determination of kra values in partially water saturated porous media.
Experiments were conducted on two well-sorted sands (fine sand P100 and coarse sand P2040) conditioned to hydrophilic and hydrophobic states and their mixtures, allowing a systematic assessment of wettability effects of both the wetting and non-wetting phases. The results indicate that wettability affects both the shape and magnitude of the hysteresis of the kr-Sw relationships. For water-wet sands, the krw curve exhibits minimal hysteresis, and the predicted Mualem-van Genuchten model accurately reproduces the krw curve based on independent values of α and n obtained from water retention measurements. In contrast, the kra curve is strongly dependent on wettability. Oil-wet and mixed-wet sands contain a larger amount of non-wetting connectivity, particularly in the studied coarse sand (P2040), where long gas pathways develop during the imbibition process and result in large kra plateaus followed by steep declines upon reaching high water saturation. Fine sand (P100) exhibits a more gradual transition from high to low kra values due to both better continuity of wetting films and lack of significant non-wetting connectivity and shows a lower degree of hysteresis. The characteristics of pore size and grain wettability determine how phases are interconnected, water and air saturations are distributed, and how film flow interacts with percolation pathways.
Finally, numerical two-phase flow modeling at the pore level using OpenFOAM in combination with X-ray microtomography images enabled us to scale up the two-phase pressure and flow fields computed at the pore level to resulting relative permeabilities at the macroscopic level and compare them with our experimental results.
| References | Ayaz, M., R. Toussaint, G. Schäfer and K. Jørgen Måløy, “Gravi- tational and finite-size effects on pressure saturation curves during drainage”, Water Resour. Res. 56 (2020), no. 10, article no. e2019WR026279 DiCarlo, D. A., “Drainage in finite-sized unsaturated zones”, Adv. Water Resour. 26 (2003), no. 12, pp. 1257–1266 Dury, O., U. Fischer and R. Schulin, “Dependence of hydraulic and pneumatic characteristics of soils on a dissolved organic compound”, J. Contamin. Hydrol. 33 (1998), no. 1–2, pp.39–57 Dury, O., U. Fischer and R. Schulin, “A comparison of relative nonwetting-phase permeability models”, Water Resour. Res. 35 (1999), no. 5, pp. 1481–1493 Fischer, U., R. Schulin and M. Keller,“Experi mentaland numer ical investigation of soil vapor extraction”, Water Resour. Res. 32 (1996), no. 12, pp. 3413–342 Haines, W. B., “Studies in the physical properties of soil. V. The hys- teresis effect in capillary properties, and the modes of moisture distribution associated therewith”, J. Agric. Sci. 20 (1930), no. 1, pp. 97–116. Løvoll, G., M. Jankov, K. J. Måløy, R. Toussaint, J. Schmittbuhl, G. Schäfer and Y. Méheust, “Influence of viscous fingering on dynamic saturation–pressure curves in porous media”, Transp. Porous Media 86 (2011), no. 1, pp. 305–324. Schäfer, G., R. Di Chiara Roupert, A. H. Alizadeh and M. Piri, “On the prediction of three-phase relative permeabilities using two-phase constitutive relationships”, Adv. Water Resour. 145 (2020), article no. 103731. Schäfer, G., K. H. Perez, P. Hulsurkar, M. Ibrahim Youssif, F. Lehmann and M. Piri, “Influence of wettability on water reten- tion curves in unconsolidated porous media”, J. Contamin. Hy- drol. 269 (2025), article no. 104502. Stauffer, F. and W. Kinzelbach, “Cyclic hysteretic flow in porous medium column: model, experiment, and simulations”, J. Hy- drol. 240 (2001), no. 3–4, pp. 264–275. Toussaint, R., K. J. Måløy, Y. Méheust, G. Løvoll, M. Jankov, G. Schäfer and J. Schmittbuhl, “Two-phase flow: structure, up- scaling, and consequences for macroscopic transport proper- ties”, Vadose Zone J. 11 (2012), no. 3, article no. vzj2011.0123. Van Genuchten, M. Th., “A closed-form equation for predicting the hydraulic conductivity of unsaturated soils”, Soil Sci. Soc. Am. J. 44 (1980), no. 5, pp. 892–898 |
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| Country | France |
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