The presence of multiple fluid phases enhances heterogeneity at the level of flow, mixing, and reaction in structurally heterogeneous media. This impacts the transport of dissolved substances and fundamentally changes mixing patterns and effective reaction rates, posing major challenges for predictive modeling. Recent theoretical and experimental advances provide unprecedented insights into the pore-scale mechanisms governing these processes and open new opportunities to tackle these challenges.
This session aims to bring together researchers working on fundamental and applied aspects of flow, transport, mixing, and reaction in multi-phase systems across scales. In particular, we encourage submissions relating to experimental, numerical, and theoretical contributions pertaining to the following topics:
- Impact of medium heterogeneity on multiphase flow, from the pore to the continuum scale.
- Impact of multiphase flow patterns on mixing and reaction rates across scales in heterogeneous media.
- Biogeochemical processes in multiphase systems.
- Applications to vadose zone hydrology and geological storage.
Orals: Thu, 7 May, 10:45–12:30 | Room 2.31
Convective mixing in porous media plays a central role in a wide range of geophysical and environmental processes, including geological CO2 storage, groundwater contamination, and reactive transport in subsurface formations. We investigate how fluid properties and boundary conditions control solutal convection and mixing in confined porous media. The system consists of two miscible fluid layers initially separated by a horizontal interface, where density variations are induced by solute concentration. Mixing can locally increase fluid density, triggering buoyancy-driven instabilities that enhance mass transport. The relative importance of convective and diffusive mechanisms is quantified by the Rayleigh-Darcy number. Using high-resolution numerical simulations, we explore mixing dynamics at high Rayleigh-Darcy numbers (O(10,000)) for fluids with different density-concentration relationships, including linear, parabolic, and piecewise non-monotonic laws. These scenarios are representative of realistic fluids encountered in subsurface applications, such as CO2-brine mixtures or chemically reactive solutes. We analyse how (i) the density contrast between the mixed fluid and the initial layers, and (ii) the concentration at which density is maximized relative to the initial conditions, influence the onset and efficiency of convective mixing. Across all cases considered, we find that the mixing process is controlled by the mean scalar dissipation rate, allowing us to develop simple physical models that capture the observed behaviour. We further assess the impact of boundary conditions on the mixing rate and identify configurations that promote efficient mixing. Finally, we compare two- and three-dimensional systems and discuss the implications of our results for predicting and optimizing solute transport in geophysical porous-media flows. Funded by the European Union (ERC, MORPHOS, 101163625). Views and opinions expressed are however those of the author(s) only and do not necessarily reflect those of the European Union or the European Research Council. Neither the European Union nor the granting authority can be held responsible for them.
How to cite: De Paoli, M. and Pirozzoli, S.: Mixing of complex fluids in confined porous media, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-8938, https://doi.org/10.5194/egusphere-egu26-8938, 2026.
Efficient solute mixing in porous media is essential for a wide range of natural processes and industrial applications, including nutrient transport in biological systems, groundwater bioremediation, and carbon dioxide geological sequestration. The extent of mixing directly controls the rates of associated biological and chemical reactions. Although turbulence is widely employed to promote mixing due to its transient and chaotic nature, its effectiveness in porous media is severely limited by the presence of extensive solid boundaries that suppress turbulent fluctuations. In contrast, dispersed two-phase flows—characterized by inherently transient flow features—offer a promising alternative for enhancing mixing efficiency.
Despite substantial research on dispersion and mixing in two-phase flow systems, the majority of existing studies assume static phase interfaces [1]. However, dispersed two-phase flows are intrinsically associated with dynamic and evolving phase interfaces. While recent studies [2, 3] have begun to explore this issue, the pore-scale mechanisms that control solute transport and mixing in porous media under dispersed two-phase flow remain poorly understood.
In this study, we examine transverse solute mixing in porous media under dispersed two-phase flow and steady single-phase flow conditions using microfluidic experiments. The results show that, at a Péclet number of 1000, dispersed two-phase flow leads to a substantial enhancement of transverse mixing relative to single-phase flow. Mixing efficiency, quantified by the dilution index, is approximately doubled under dispersed two-phase flow compared with single-phase flow at identical injection rates. Complementary direct numerical simulations indicate that this improvement originates from transient flow structures, including vortex formation induced by dynamically evolving phase interfaces, which are absent in steady single-phase flow. Together, these findings offer new pore-scale mechanistic insights into solute mixing in porous media and highlight flow-regime modulation as an effective strategy for enhancing mixing performance.
Keywords: mixing; porous media; dispersed two-phase flow.
Reference
[1] J. Jiménez-Martínez, P.d. Anna, H. Tabuteau, R. Turuban, T.L. Borgne, Y. Méheust, Pore-scale mechanisms for the enhancement of mixing in unsaturated porous media and implications for chemical reactions, Geophys. Res. Lett. 42 (13) (2015) 5316-5324.
[2] J. Mathiesen, G. Linga, M. Misztal, F. Renard, T. Le Borgne, Dynamic Fluid Connectivity Controls Solute Dispersion in Multiphase Porous Media Flow, Geophys. Res. Lett. 50 (16) (2023) e2023GL105233.
[3] X. Zhang, Z. Dou, M. Hamada, P. de Anna, J. Jimenez-Martinez, Enhanced Reaction Kinetics in Stationary Two-Phase Flow through Porous Media, Environ. Sci. Technol. 59 (2) (2025) 1334-1343.
How to cite: Liu, Y., Dentz, M., and Wang, M.: Enhanced mixing in porous media by dispersed two-phase flow, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-10198, https://doi.org/10.5194/egusphere-egu26-10198, 2026.
Effective management of Managed Aquifer Recharge (MAR) systems is strongly influenced by the interplay between geological reservoir features and kinetically controlled geochemical reactions. The former are often approximated by a simple geometrical distribution of hydrofacies, while the latter are approximated as unreactive systems or as systems that always reach geochemical equilibria. Fluid-rock interactions induce modifications of the physical-chemical characteristics of the mineral porous medium, the dissolved gases compositions, and the aqueous solution. This setup induces modifications in preferential flow paths, pollutant residence time, and pollutant persistence in the reservoir. The numerical simulation of such multiphase systems is thus challenging due to the combined nonlinear and time-dependent effects acting on them. The presented results focus on the evaluation of the multifaceted uncertainty through a sensitivity analysis, derived from the quantification of the individual impact of: (i) the adaptive spatial discretization resolution, (ii) the kinetically controlled processes, and (iii) the heterogeneity uncertainty in multiphase reactive transport simulations. A MAR system is modelled over a highly heterogeneous geological section, accounting for reactive processes associated with water-rock-gas interactions. These processes are evaluated through the Transition State Theory. The workflow involves (i) geometric spatial discretization of the reservoir in the form of an unstructured mesh, coupled with geostatistical generation of porosity and permeability fields (as continuous and categorical variables, respectively) using MUSE software (Miola 2025, PhD thesis & EGU25); (ii) segmentation of the domain into homogeneous regions via FSUM (Sorgente et al. 2026, Computers & Geosciences) and localized mesh refinement with an increase of details over hydraulic impedance surfaces; (iii) conversion of stochastic geological models into data formats, and (iv) execution of parallel multiphase reactive transport simulations with PFLOTRAN (Hammond et al. 2014, Water Resources Research). The entire process is managed through EWOPE (Miola et al. 2026, Computers & Geosciences), an open-source computational workflow tracker, which ensures full reproducibility and traceability by recording metadata, enabling the backward reconstruction of computational history and a deep analysis of the single multi-realization computations, the core of the uncertainty evaluation. Simulation results indicate that a MAR can be planned and managed by considering a multi-scenario involving variations in unsaturated medium properties, pollutant arrival times, and variations in the flow patterns, from a probabilistic point of view.
How to cite: Raviola, M., Cabiddu, D., Miola, M., Sorgente, T., Pittaluga, S., and Vetuschi Zuccolini, M.: Evaluation of uncertainty in kinetically controlled and unsaturated heterogeneous reservoirs under wastewater-groundwater mixing , EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-19683, https://doi.org/10.5194/egusphere-egu26-19683, 2026.
Modeling reactive mass transport in porous media systems is often performed using effective-medium approaches due to the difficulties of solving the microscale equations throughout the entire system. Under an effective-medium framework, transport processes at the solid-fluid interface are usually assumed to be quasi-steady with respect to the transport in the bulk phase that saturates the pores of the system. This has led to effective-medium models in which the reaction term is present in the macroscopic mass balance equation, which cannot be used to predict transport at the early stages of the process but rather under steady conditions. To address this issue, this work presents an alternative modeling approach in which transport at the interface is assumed to be unsteady. This leads to a macroscopic model consisting of a set of two coupled partial differential equations that can be used to predict the average concentration in the phase and at the interface under unsteady conditions. These equations are derived using the volume averaging method, which also allows for predicting the associated effective-medium coefficients by solving the corresponding closure problems in periodic unit cells. The model is validated through comparisons with direct numerical simulations under several transport and reaction conditions. From this analysis, and by comparison with a previously derived interface-steady model, specific situations in which the two-equation model excels compared to previous approaches are identified. The results of this work are relevant in many water resources, chemical, and biological systems involving the transport and adsorption of reactive species under unsteady conditions.
How to cite: Valdés-Parada, F. and Sánchez-Vargas, J.: Upscaling mass transport with heterogeneous reaction, adsorptionand accumulation in porous media, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-115, https://doi.org/10.5194/egusphere-egu26-115, 2026.
The term diffusiophoresis refers to the phenomenon by which colloids migrate following salt concentration gradients. The strength of this effect actually follows a logarithmic scaling, and thus the diffusiophoretic drift can be very pronounced over small salt concentration variations when those concentrations are low. Therefore, this phenomenon could potentially be engineered for colloid manipulation. In the context of porous media, the emerging colloid transport behaviors that can arise from diffusiophoresis are still not fully understood. Some recent two-dimensional experimental and simulation results have demonstrated upscaled effects of diffusiophoresis in porous media. Depending on the sign of both the diffusiophoretic coefficient and the concentration gradients, diffusiophoresis can lead to either increased retention or increased flushing of colloids in the medium. This is magnified in the presence of pronounced small-scale medium heterogeneities, which are able to support concentration gradients for relatively longer times. Because water velocity fields are a lot more heterogeneous in the presence of air, unsaturated conditions enhance the accumulation or depletion of colloids. How these two-dimensional findings apply to natural three-dimensional porous media is still unclear, since recent work has shown that, compared to their two-dimensional counterparts, water velocity fields in unsaturated three-dimensional media tend to display a markedly lower occurrence of very low velocity regions, and a distinct non-monotonic behavior of mixing as a function of saturation. These features affect solute gradients and are therefore expected to have an impact on diffusiophoretic drift. Hence, the goal of the work presented here is to elucidate the effective behavior of diffusiophoresis in three-dimensional unsaturated porous media. We perform high-performance computing pore-scale simulations of Stokes flow at various saturation degrees and solute–colloid transport with diffusiophoretic drift. We identify the upscaled behaviors and their dependence on parameter configurations, and we compare them to the two-dimensional case. Our results provide new insight into how diffusiophoretic mechanisms operate under realistic three-dimensional unsaturated flow conditions, revealing scenarios in which diffusiophoresis can substantially influence colloid mobility and retention in porous media.
How to cite: Sole-Mari, G., Farhat, S., Bolster, D., and Jotkar, M.: Diffusiophoresis of colloids in partially saturated three-dimensional porous media, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-23109, https://doi.org/10.5194/egusphere-egu26-23109, 2026.
An “imperfect” Hele-Shaw cell (IHSC) with random variations of the aperture provides a useful analogue for a rough fracture. For flow of two immiscible fluids with a single interface between the phases in an IHSC tilted with respect to the horizontal plane, with pressure control at the inlet, there are, in general, multiple equilibrium interface profiles. This leads to hysteresis (history dependence) of the interface evolution and finite energy dissipation even in the limit of infinitely slow (quasistatic) driving, due to Haines jumps between the equilibria.
We use a recently developed spectral method that predicts the interface evolution and energy dissipation in such a system with high accuracy and computational efficiency. We show that, given the inlet pressure, the set of equilibrium interface configurations forms a band with rough boundaries. This constitutes a “sticky region”: an interface starting within it only undergoes minor deformations (maintaining its overall position without moving as a whole), whereas an interface starting outside it advances to the nearest boundary of the region. Drawing analogy between this behaviour and that of an object in a well with dry (Coulomb) friction, we hypothesise — and confirm numerically — that if the motion of the interface is reduced to a single variable, the mean height, then the evolution of this variable follows a simple law akin to a combination of viscous and dry friction. We then proceed to study systematically how the “dry friction” coefficient depends on the properties of the cell’s roughness, such as the aperture variance and the correlation length. Our results may serve as an input to an upscaled model of flow in fractures, replacing the full aperture field (typically unknown) with continuum roughness parameters.
How to cite: Chubynsky, M. V., Dentz, M., Ortín, J., and Holtzman, R.: A “Coulomb friction” model of two-phase flow in a rough fracture, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-14139, https://doi.org/10.5194/egusphere-egu26-14139, 2026.
The immiscible displacement of a wetting fluid by a non-wetting fluid (drainage) in rough-walled fractures is central to subsurface applications such as CO₂ sequestration and underground hydrogen-storage. Predicting displacement outcomes, including residual trapping and invasion morphology, requires understanding how viscous and capillary forces interact with fracture-scale geometric heterogeneity. In horizontal systems, where gravity effects are negligible, this interaction gives rise to complex and spatially variable invasion patterns. In porous media, drainage morphologies are commonly interpreted using the viscosity ratio M and capillary number Ca within the classical framework of [1]. However, even within this framework, the influence of structural heterogeneity on displacement patterns remains unresolved. In rough fractures, aperture variations introduce an additional geometric control that further complicates this picture. The competition between smoothing by in-plane interfacial curvature and roughening induced by out-of-plane aperture variability makes invasion morphologies difficult to predict [2]. As a result, the commonly used roughness measure, the closure δ, is insufficient: fractures with identical δ can exhibit markedly different invasion patterns under identical flow conditions.
A more complete geometric description must therefore account for both the amplitude and spatial organization of aperture variability. The fracture aperture field a(x,y), is characterized not only by its variance σa but also by a lateral correlation length Ic relative to the fracture length L. Focusing on the out-of-plane contribution to capillary pressure, which scales with ,1/a(x,y) we derive a dimensionless geometric parameter quantifying capillary heterogeneity. Introducing Ic as the characteristic lateral scale of variability leads to a dimensionless parameter which links aperture variance and spatial correlation to capillary pressure fluctuations. This formulation revisits the curvature-ratio introduced by [2], while reformulating it in terms of statistically measurable aperture variability, yielding a practical geometric measure of capillary heterogeneity.
Direct numerical simulations of horizontal drainage were performed using a validated Volume-of-Fluid framework [3] for Ca between 10-2 and 10-5 and M=0.1, 0.8. Synthetic self-affine fractures with systematically varied mean aperture, aperture variance, and correlation length were considered. Displacement morphology was quantified using fractal dimension, fluid-fluid interfacial length, and typical finger width. Preliminary results show that fractures sharing similar values of the aforementioned dimensionless parameter, exhibit comparable invasion structures, regardless of how the roughness is generated, indicating that this parameter provides a physically grounded link between fracture geometry and drainage morphology.
[1] Lenormand, R., Touboul, E., & Zarcone, C. (1988). Numerical models and experiments on immiscible displacements in porous media. Journal of fluid mechanics, 189, 165-187.
[2] Glass, R. J., Rajaram, H., & Detwiler, R. L. (2003). Immiscible displacements in rough-walled fractures: Competition between roughening by random aperture variations and smoothing by in-plane curvature. Physical Review E, 68(6), 061110.
[3] Krishna, R., Méheust, Y., & Neuweiler, I. (2024). Direct numerical simulations of immiscible two-phase flow in rough fractures: Impact of wetting film resolution. Physics of Fluids, 36(7).
How to cite: Krishna, R., Méheust, Y., and Neuweiler, I.: A geometric parameter linking aperture heterogeneity and drainage morphology in rough fractures, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-23099, https://doi.org/10.5194/egusphere-egu26-23099, 2026.
The sound quantification of the flow distribution in heterogenous groundwater systems is
a cornerstone for the prediction of solute dispersion and solute travel times with implications
for the assessment of the vulnerability and management of groundwater resources.
A broad distribution of flow velocities leads to a broad distribution of mass transfer times,
which is at the root of non-Fickian transport features such as strong tailings of solute breakthrough curves.
The relation between the medium structure and the distribution of flow rates and flow velocities
is a missing link that would allow to estimate solute dispersion directly from the hydraulic medium
properties. While the structure-flow relation is well known for simple stratified
and composite medium geometries, it remains an open question for flow in heterogeneous pore,
fracture and karst networks. To decipher this relation, we analyze flow rate and velocity statistics
across heterogeneous networks of different connectivities and conductance distributions. We quantify
the average flow in terms of the effective conductivity and the full statistics in terms of the
probability density function of flow rates and flow velocities, which are the key quantities for
the prediction of solute transport. The analysis of the conditional flow statistics reveals that
flow in random networks is organized in distinct substructures of different hydraulic
behaviors. These structures can be delineated using percolation theory. The flow distribution can
then be quantified by the interaction between these structures using a random aggregation approach.
How to cite: Dentz, M., Gouze, P., and Puyguiraud, A.: Linking flow and structure in heterogenous porous and karstic networks, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-14555, https://doi.org/10.5194/egusphere-egu26-14555, 2026.
Evaporation of brine leads to salt precipitation, which can clog pores and affect further evaporation and reactions. The transport of vapor and liquid, reactions and the intricate feedback of these with change in transport properties are influenced by microstructural heterogeneity at the pore (micron to cm) scale, however their impact is felt at scales of meters and above. Evaporation-induced salt precipitation is of interest to for cultural heritage, as well as mineralization in carbon geosequestration. We present a modeling platform based on a computationally-efficient pore-network approach, that aims to perform this upscaling. The model is trained and validated by laboratory mock-ups: glass bead samples soaked in brine and left to dry under controlled environmental conditions. We apply this to study the impact of the type of salt, initial salt concentration, and the dependence of the vapor pressure on salt concentration, on the amount, location and timing of salt precipitation.
How to cite: Holtzman, R., Habeeb, N.-M., Sahraoui, F.-Z., Chubynsky, M. V., and Goehring, L.: Pore network modeling of drying-induced salt precipitation, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-14901, https://doi.org/10.5194/egusphere-egu26-14901, 2026.
This work investigates steady Stokes flow through a two-dimensional array of circular obstacles. We develop a minimal statistical model for the flow rate distribution based on a mapping of the pore space to a network of Poiseuille-flow tubes. Our work shows that the flow rate at the pore bodies follow a Gamma distribution, and that the flow distribution at the pore throats is fully determined in terms of it. Furthermore, the parameters of this Gamma distribution are satisfactorily linked to the geometrical properties of the the medium. The predictions agree closely with computational fluid dynamics simulations and show better agreement than prior mean-field models, clarifying how local splitting and merging shape flow in disordered porous networks.
How to cite: Arnal, J., Sole-Mari, G., and Aquino, T.: Flow statistics in a 2D disordered pillar array, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-11786, https://doi.org/10.5194/egusphere-egu26-11786, 2026.
Access to clean water is one of today’s major global challenges. Human health, food production and biodiversity all rely on groundwater, yet this vital resource is increasingly exposed to soil pollution. Substances such as pesticides, fertilizers, plastics and industrial chemicals seep into the ground and travel downwards with rainwater. Before reaching groundwater, pollutants must pass through soil layers that act as natural filters. These layers can slow down or transform contaminants, but their effectiveness is uncertain. Predicting whether pollutants stay trapped in the soil or reach aquifers remains a central unresolved problem in environmental science.
A key difficulty is that soils are highly heterogeneous. They contain pores and grains of different sizes, shapes and chemical properties, producing complex flow pathways where some regions transmit water rapidly while others remain stagnant. Most soils are also only partly saturated, with water coexisting alongside pockets of air. These air–water–solid interfaces strongly influence motion and mixing, often causing pollutants to spread in irregular, non-predictive ways. How all these processes combine under partially saturated conditions remains poorly understood.
This work aims at addressing this gap through controlled experiments and advanced simulations. The experimental work, uses a transparent soil analogue known as a Hele-Shaw cell: two glass plates separated by a thin gap and patterned with microstructures that reproduce aspects of natural soil heterogeneity. By injecting water, air, and chemical solutes into the cell and filming their movement with high-sensitivity cameras, I observe pollutant pathways and reactions directly under realistic but fully controlled conditions. Unlike standard column tests, this approach provides real-time visualization over large areas while still resolving fine spatial details.
This poster presents my preliminary work for the study chemical reactions in partially saturated soils, examining how structure and water content affect reaction rates when reactions are fast compared to molecular mixing. These experiments are complemented by detailed simulations using OpenFOAM, more specifically a solver developed by Krishna et al. By reproducing flow patterns in the Hele-Shaw cell and modeling chemical transport within them, the simulations help identify which microscopic processes most strongly control large-scale behavior.
How to cite: Legrand, G., Ortín Rull, J., and Aquino, T.: Chemically Reactive Transport in imperfect Hele-Shaw cell: 2-Phase Flow Experiments and Simulations, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-7734, https://doi.org/10.5194/egusphere-egu26-7734, 2026.
The coupled flow, transport, and hydro-chemo-mechanical processes in fractured porous media have great relevance for numerous applications including underground water management, hydrocarbon recovery, CO2 sequestration, and geological waste disposal. We developed a novel experimental setup designed to investigate these coupled processes. The setup uses fully matched transparent rectangular fracture blocks. These blocks are created by molding a granite fracture surface with resin. The design of the experimental setup provides controlled shear and normal stresses with simultaneous measurement of the resulting stresses and displacement in both the normal and shear directions. The fluid is injected from the center and flows radially toward the outputs. There are nine discrete outlets per side to provide highresolution measurements of the redistribution of flow and permeability anisotropy at various flow and stress conditions. Moreover, we utilize high-resolution imaging to visualize real-time flow.
The results of shear-flow experiments showed that shear displacement enhances the permeability in the direction perpendicular to the applied shear stress. This anisotropic behavior is the result of the development of preferred flow paths due to the dilation and changes in the geometry of fractures caused by shear.
This experimental setup enables us to study coupled hydraulic, mechanical, and chemical processes, with precise evaluation of permeability anisotropy under a wide range of conditions. In the next step, we will utilize this setup for two-phase flow studies, as it has often been a challenging complexity in fractured porous media.
*This reasearch activity is funded by Hydropore II project (PID2022-137652NB-C42)
How to cite: Sheikhi, S., Ortín, J., and Aquino, T.: Investigating Permeability Anisotropy in a Rough Fracture: A Novel Shear-Flow Setup, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-10467, https://doi.org/10.5194/egusphere-egu26-10467, 2026.
Displacement of a wetting fluid by a non-wetting fluid in fractured media is relevant to many subsurface applications, including fluid storage and groundwater contaminant remediation. Such flows are difficult to predict because they are governed by fracture-scale geometric heterogeneity embedded within complex fracture networks, which sets a large contrast of relevant length scales. The flow is also governed by the coupled action of viscous, capillary, and gravitational forces. These effects are further compounded by wetting films, contact-line dynamics, and spatial variations in wettability. As a result, developing models that are both computationally efficient and faithful to the governing physics remains challenging.
At the scale of individual fractures, two main modeling strategies are commonly employed. Fully resolved three-dimensional direct numerical simulations provide detailed descriptions of interfacial dynamics but are computationally expensive and impractical for extensive parameter exploration. Conversely, continuum-scale approaches offer efficiency but typically neglect aperture-scale hydrodynamic instabilities and geometric controls that govern displacement morphology. Recently, we introduced a two-dimensional depth-integrated model for immiscible two-phase flow in rough fractures [1], which retains the dominant hydrodynamic and capillary effects while substantially reducing computational cost. Although this model has been tested against idealized configurations and numerical benchmarks, its performance against laboratory experiments in realistic rough-walled fractures has not yet been systematically evaluated.
A direct comparison between model predictions and controlled drainage experiments was carried out using transparent fracture analogs and corresponding numerical simulations. The fracture geometry was first generated numerically as a self-affine rough fracture with a Hurst exponent of 0.8 and a domain size of 145 mm by 80 mm. The geometry has a mean aperture of 0.4 mm and a correlation length equal to one eighth of the fracture length, resulting in a strongly heterogeneous aperture field characterized by a relative closure of 0.57. The rough surfaces were fabricated by precision milling into polymethylmethacrylate plates [2]. The experimental fracture geometry was subsequently reconstructed from X-ray tomography and employed directly in the numerical simulations. Drainage experiments were conducted with three immiscible fluid pairs spanning viscosity ratios of 1/200, 1/100, and 70, and capillary numbers between 10−3.0 and 10−7.0, thereby covering viscous-dominated stable and unstable, as well as capillary-dominated, displacement regimes. Two-dimensional depth-integrated simulations were performed under identical flow conditions, enabling direct comparison. Model performance is assessed using quantitative descriptors of invasion dynamics, including displacement morphology, finger width, interfacial length evolution, breakthrough saturation, and longitudinal saturation profiles.
The depth-integrated model reproduces the dominant displacement features observed in the experiments while requiring substantially less computational effort than fully resolved three-dimensional simulations. This demonstrates its suitability as an efficient and physically consistent framework for studying immiscible two-phase flow in rough-walled fractures.
[1] Krishna, R., Méheust, Y. and Neuweiler, I., 2025. A two-dimensional depth-integrated model for immiscible two-phase flow in open rough fractures. Journal of Fluid Mechanics, 1011, p.A43.
[2] Amin Rezaei, Francesco Gomez Serito, Insa Neuweiler, Yves Méheust. Dynamic Displacement of Wetting Fluids by Non-Wetting Fluids in a Geological Fracture: An Experimental Study. American Geophysical Union Annual Meeting 2024 (AGU24), Dec 2024, Washington DC, United States. pp.H53K-1232
How to cite: Neuweiler, I., Krishna, R., Amin, R., Borgman, O., Gomez, F., and Méheust, Y.: Experimental validation of a depth-integrated model for immiscible two-phase flow in rough fractures, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-10914, https://doi.org/10.5194/egusphere-egu26-10914, 2026.
Under unsaturated conditions, the coexistence of air and water generates complex, dynamically evolving interfacial structures, whose impact on solute mixing, residence times, and reactivity remains poorly understood at the pore scale. Substances transported in the water phase can interact with the air phase at the fluid-fluid interface. In particular, per- and polyfluoroalkyl substances (PFAS) are emerging contaminants of concern that are known to preferentially accumulate at air–water interfaces, where interfacial processes control their retention and mobility in the vadose zone. Darcy-scale models and experimental observations suggest that transient hydrological conditions and interfacial area dynamics can strongly influence PFAS fate. However, the pore-scale mechanisms governing transport toward air–water interfaces and the resulting mixing-limited reactivity remain largely unexplored even under steady flow. This gap limits the development of models capable of upscaling pore-scale interfacial mixing processes and predicting solute fate at larger spatial and temporal scales. We investigate these mechanisms using a Lagrangian particle-tracking approach to resolve solute transport in steady two-dimensional pore-scale flow fields under partial saturation. Solute trajectories are governed by advection, diffusion, and interactions with both fluid–fluid (air–water) and fluid–solid interfaces, enabling direct quantification of interfacial encounter statistics and residence-time distributions. These metrics provide natural descriptors of mixing-limited regimes, in which effective reaction rates are controlled by transport toward interfacial zones rather than intrinsic kinetics, and allow identification of pore-scale features that control the large-scale evolution of solute transport. This study contributes to ongoing efforts to connect pore-scale physical processes with effective models of solute transport in the vadose zone, with direct implications for predicting the fate of reactive contaminants under transient unsaturated conditions.
How to cite: Dominguez Vazquez, D., Wang, H., Hanna, K., Sole-Mari, G., Borgman, O., Heyman, J., Le Borgne, T., Méheust, Y., and Aquino, T.: The role of reactive air–water interfaces in contaminant transport in the vadose zone, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-14619, https://doi.org/10.5194/egusphere-egu26-14619, 2026.
Hydraulic tomography (HT) is a high-resolution method for identifying aquifer hydraulic property heterogeneity. Despite decades of development that have led to the relative maturation of HT, the influence of prior boundary information on HT estimations remains insufficiently explored. In this study, HT methods were applied to a synthetic heterogeneous aquifer to examine the impacts of boundary condition types, boundary sizes, and prescribed head values on parameter estimation. The results indicate that boundary size has a limited impact on HT outcomes, regardless of data adequacy, whereas boundary condition type plays a critical role in HT inversion. Increasing the boundary size can mitigate errors arising from incorrect assumptions about boundary type. The SimSLE-HCA iterative algorithm effectively estimates optimal boundary head values when sufficient HT survey data are available. For practical applications, when the boundary size is unknown, a moderate expansion of the simulation domain is recommended. When the boundary type is uncertain, specifying a constant-head boundary is a practical and robust choice.
How to cite: Su, X. and Yeh, T.-C. J.: Optimal strategies for assigning prior boundary settings in Hydraulic Tomography analysis, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-16493, https://doi.org/10.5194/egusphere-egu26-16493, 2026.
We numerically analyze the impact of the porous media heterogeneity in the mixing, migration and spreading of a CO2 gravity current in a saline aquifer. Heterogeneity is represented by multi-Gaussian log-permeability fields of varying correlation length and variance of the log-permeability. We characterize the dynamics of the gravity current using the quantity of buoyant mass, the scalar dissipation rate, and the mixing interface width and length. The results show that, at initial times, heterogeneity favors mixing because of increased the interface length and tortuosity. CO2 gets trapped in low permeability regions and dissolves faster due to high concentration gradients. At later times, low permeability regions prevent the formation and proliferation of fingering instabilities and mixing is similar to homogeneous media. Only for large anisotropy ratio or high variance permeability fields, we observe a more efficient mixing in heterogeneous media compared to the homogeneous media.
How to cite: Hidalgo, J. J. and Jiménez-Ramos, A.: Dynamics of gravity currents in heterogeneous porous media, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-20332, https://doi.org/10.5194/egusphere-egu26-20332, 2026.
Heterogeneous porous media saturated with two liquid phases represent a complex system that can be observed in many natural and engineering processes. The transport of passive solutes in this type of environment is at the centre of our research whose final aim is to quantify and mathematically describe the physical mechanisms that regulate the displacement of the solute, such as twisting and stretching. To analyse and quantify the dynamics of the solute mixing and dispersion, we rely on numerical simulations where a passive solute is transported by two fluids through a heterogeneous porous media, such as a reservoir or an aquifer. Based on the mutual miscibility of the fluids two main scenarios are identified, one where the fluids that transport the passive solute are miscible and one where they are immiscible. In both cases the passive solute can freely cross the interface between the two fluids. The setup for the numerical experiment is a three-dimensional flow and transport domain where permeability is represented by an indicator multi-Gaussian random field whose continuous parent fields are characterised by exponential covariance function. We prescribe the mean flow while periodic conditions are applied to the permeability on the lateral boundaries. The injection of the less viscous fluid into the domain saturated with a more viscous fluid happens along a control plane perpendicular to the mean flow direction. The consequent displacement of the more viscous fluid by a less viscous fluid leads to fingering instabilities. The flow fluctuations are governed by the unstable displacement of the two fluids and the spatial heterogeneity. To study the mixing of a passive solute in this flow, we consider an instantaneous solute injection over the control plane at time zero. For both scenarios, the solute dispersion is quantified in terms of the spatial moments of the solute distribution while mixing is measured through the scalar dissipation rate, dilution index, and the probability density function of concentration point values. Mixing metrics that show regular trends are fitted using power and exponential laws. Compared to the constant viscosity case, it is observed that the viscosity difference between the liquid phases enhances the mixing of the passive solute.
How to cite: Pescimoro, E., Dentz, M., Hidalgo, J. J., and Municchi, F.: Solute Mixing Under Unstable Two-Phase Flow in Heterogeneous Porous Media, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-7844, https://doi.org/10.5194/egusphere-egu26-7844, 2026.
Water infiltration in the vadose zone is a transient and unstable process influenced by several factors, including the non-linearity of soil hydraulic properties, rapidly changing boundary conditions, root growth, hysteresis, and soil heterogeneity. As a result, infiltration is often non-uniform and develops into preferential flow. This complex phenomenon, commonly manifested as gravity fingers, originates from wetting-front instabilities and saturation overshoot, the latter being a prerequisite for finger formation.
Experimental studies have consistently shown that infiltration into both homogeneous and heterogeneous soils frequently produces preferential pathways in the form of fingers. However, simulations of unsaturated flow typically rely on the Richards equation, which accounts only for local capillary pressure and therefore fails to reproduce preferential flow patterns. Alternative formulations have been proposed to overcome this limitation, such as the model by Cueto-Felgueroso et al. (2020), which incorporates non-local capillary effects.
In this work, we investigate unsaturated flow under infiltration–evaporation cycles, explicitly considering soil heterogeneity and the formation of gravity fingers. Our objective is to improve the modeling of infiltration and evaporation processes in soils, to better predict water flow behavior, and to characterize the impact of soil heterogeneity, non-linear properties, and gravity fingers on these processes. We are comparing two modeling approaches: the traditional Richards equation and the fourth-order spatial derivative model proposed by Cueto-Felgueroso et al. (2020). Flow is solved using the finite element library FEniCS, and soil heterogeneity is represented by Gaussian random permeability fields with varying correlation lengths and variances.
Keywords: infiltration and evaporation cycles, unsaturated flow, heterogeneity, gravity fingers, finite element method.
References
Luis Cueto-Felgueroso, Marı́a José Suarez-Navarro, Xiaojing Fu, and Ruben Juanes. Numerical simulation of unstable preferential flow during water infiltration into heterogeneous dry soil. Water, 12(3):909, 2020.
How to cite: Castillo, Y., Hidalgo, J., and Dentz, M.: Influence of Soil Heterogeneity and Gravity Fingers on Unsaturated Flow During Infiltration–Evaporation Cycle, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-13355, https://doi.org/10.5194/egusphere-egu26-13355, 2026.
