Solute transport in unsaturated media exhibits a complex, nonmonotonic dependence on fluid saturation and flow rates. Adding to the intricate dependence of multiphase flow and solute transport on the heterogeneity across scales is their coupling: the sensitivity of the concentration fields to the spatial distribution of the fluid phases and their velocity fields.
Here, we study solute transport following partial displacement of one fluid by the other, where the fluids are immiscible and hence solute transport occurs only in one fluid and the fluid-fluid interface acts as barrier for transport. We combine pore-scale simulations (using openfoam) with microfluidic experiments to examine the role of the pore-scale heterogeneity structure (in terms of its spatial correlation) and its evolution with chemical and mechanical erosion. We find that increasing the correlation length in particle size increases fluid connectivity, and thus the solute spreading by reducing the number of advection-dominated regions. Decreasing saturation of carrier fluid (in which dissolved solutes are transported) is found to promote dead-ends (slow flow regions), and thus of diffusion.
We compare two simple forms of erosion in granular media: mechanical where the smallest particles are washed away, vs. chemical where all particles are shrunk by uniform dissolution. We find that mechanical erosion, unlike chemical erosion, alters the pore space morphology toward a multi-modal variation in pore sizes, which shifts transport towards a more non-Fickian spreading. For saturated media, erosion induces a non-monotonic effect on solute spreading, promoting spreading at the diffusion-dominated (low Peclet) regime while suppressing it at higher rates (high Peclet). Under unsaturated conditions, erosion decreases spreading by reducing local velocities through widening available pathways, and enhances mixing by minimizing dead-ends which enhances the relative strength of advection.
How to cite: Holtzman, R., Saeibehrouzi, A., Denissenko, P., and Abolfathi, S.: Impact of heterogeneity and its alteration by erosion on solute transport in unsaturated media, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-12082, https://doi.org/10.5194/egusphere-egu25-12082, 2025.
In a cylindrical capillary or a Hele-Shaw cell with perfectly flat walls, the equilibrium position of the interface between two fluids given the external conditions such as the pressure head is unique. If the external conditions change infinitely slowly (quasistatically), the interface follows this equilibrium, thus, its position is history-independent; there is no energy dissipation in this quasistatic limit. In contrast, in disordered porous and fractured media there are multiple equilibria, leading to history dependence (hysteresis) of the interface evolution even in the quasistatic limit, and Haines jumps of the interface between these equilibria lead to dissipation. An imperfect Hele-Shaw cell (with a gap width randomly varying in space) provides a simple model system in which these phenomena (both in the quasistatic limit and beyond) can be studied, promoting understanding of multiphase flow in a rough fracture as well as providing insights into more complex, 3D porous media. However, even in this simple model the evolution of the interface is nontrivial due to the nonlocality brought about by the resulting fluid flow, which, in principle, requires solving the Stokes equations for the flow in the whole domain even when only the interface evolution is of interest.
We present a novel spectral approach for computing the interface evolution in such a system, based on the Fourier expansion of the interface shape at each time step, confirming its accuracy via comparison to the much more computationally costly numerical solutions of the Stokes equations. We use our approach to study the (microscopic) dynamics of the interface relaxation towards equilibrium, as well as the (macroscopic) pressure-saturation trajectories following drainage/imibibition cycles. We find that even for a single perturbation (“defect”) in an otherwise perfectly uniform cell, interface relaxation dynamics in a Haines jump is a complex, multistage process. Nonetheless, we present a remarkably simple model relying on the concepts of viscous and "dry friction" dissipation, that is able to predict the pressure-saturation cycles in random media. Our findings are a promising step towards an upscaled model of flows in rough fractures, where from the macroscale properties of the roughness one could obtain the averaged interface dynamics.
How to cite: Chubynsky, M. V., Dentz, M., Ortín, J., and Holtzman, R.: Fluid-fluid interface dynamics in an imperfect Hele-Shaw cell: A novel computational method for hysteresis and energy dissipation, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-13767, https://doi.org/10.5194/egusphere-egu25-13767, 2025.
Groundwater flow is subject to transients, due to natural events or human activities (recharge, tides, decontamination, etc.). The occurrence of such temporal fluctuations in the flow field can have significant impact on reactive transport processes, compared to steady flow conditions, especially in reactive fronts. These fronts manifest as localized interfacial regions where chemical reaction occurs in an ambient flow field that brings two or more reactants in contact with each other. Understanding how reaction fronts evolve during transient flows is therefore key to predicting reactive transport in the subsurface.
In these fronts, reaction rates often depend on the local mixing state of the reactants, which in turn is controlled by the interplay between advective and diffusive processes. Under steady flow conditions, the presence of heterogeneity in the permeability fields has been shown to enhance mixing and reaction at the Darcy scale, due to stretching-enhanced mixing. In contrast, it is currently unknown how transient flows would impact reaction rates.
Here, we conduct reactive transport experiments with transient flow in both Hele-Shaw and index-matched porous media cells. A steady mixing front is created inside the cell by two opposing injection points, creating of a stagnation point flow. Transient flow is then imposed by varying the ratio of the injection rates, causing a displacement of the stagnation point and the mixing front. A bimolecular chemiluminescent reaction is used to quantify the effective reaction rate within the mixing front at all times. We observe that transient flows increase reactivity compared to steady state conditions, both in the local maximum of reaction rates and in the size of the reactive front.
In the Hele-Shaw cell, the enhancement can be up to 3 times compared to steady conditions. The evolution of the reaction front to the new steady state occurs in a time much shorter than that required for Taylor-Aris dispersion, indicating that the reaction front remains in the ballistic shear regime when the reactivity enhancement is observed. Using the lamellar theory for sheared fronts, we find that the maximum reaction rate should scale with the transient flow strength to the power of 3/4, a prediction that compares well with the experimental observations (0.76±0.03).
In the porous media cell, we also observe a power law scaling between the reaction rate enhancement and the transient flow magnitude, with an exponent of 0.58±0.01. In contrast to the Hele-Shaw case, we argue that the mixing enhancement is due to longitudinal hydrodynamic dispersion. Solving the advection-dispersion-reaction equation for the reaction front near the stagnation point yields a theoretical exponent of 1/2 , which agrees well with experimental observations.
These results indicate that an important part of the biogeochemical activity in the subsurface can occur during transient events. The proposed modeling framework provides a quantitative prediction of such reactive transport dynamics.
How to cite: Karan, P., Izumoto, S., Le Borgne, T., and Heyman, J.: Impact of Transient Flow on Reactive Fronts in Porous Media, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-21286, https://doi.org/10.5194/egusphere-egu25-21286, 2025.
Soil and rock formations experience variation in saturation and chemical composition over time that may alter relative saturation of one phase or the other due to change in interfacial tension (IFT) at the pore structure. We can physically describe this process within a porous network hosting two phases where one initially invades the other and then surfactants are introduced to the invading phase and alter the IFT of the interfaces, thus leading to further invasion. This study explores the dynamic interplay between fluid flow and surfactant adsorption in porous media, focusing on the spatio-temporal evolution of invasion patterns in heterogeneous pore networks. We develop a time-dependent pore network model (PNM) to simulate the effects of surfactant-induced IFT reduction on two-phase flow under constant driving pressure. The initial invasion follows invasion percolation theory, and pressure drops across the network are calculated using a random resistor network and mass conservation equations. Node-specific flux and velocity are derived via the Hagen-Poiseuille law. Surfactant adsorption is modeled using Langmuir kinetics, capturing its impact on fluid-fluid and solid-fluid interfaces within the invaded path. Over time, reduced IFT and contact angle alterations trigger secondary invasions, reshaping the invasion patterns. The model investigates how pore-scale heterogeneity and reaction timescales influence this evolution. Results indicate that invasion patterns evolve with surfactant mass transfer and network heterogeneity, scaling with the cumulative Gaussian distribution used for pore allocation. These dynamic patterns align with Kosugi’s quasi-static model of water retention versus capillary pressure, emphasizing the significance of IFT alterations. This work provides theoretical insights into surfactant-driven invasion dynamics in porous media and their dependence on physical and chemical parameters.
How to cite: Bhattacharjee, D., Ramon, G., and Edery, Y.: Dynamic coupling of flow and surfactant adsorption at interfaces in a heterogeneous pore network , EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-775, https://doi.org/10.5194/egusphere-egu25-775, 2025.
Biofilms, complex microbial communities embedded in an extracellular matrix, are significantly influenced by flow-induced shear stress, which creates a competition between biofilm growth and detachment. In this study, biofilms of Pseudomonas fluorescens were grown in a microfluidic channel and exposed to aqueous flow which includes nutrients at varying velocities. Real-time observations using transmitted-light microscopy coupled with a camera revealed that biofilms can adapt to their conditions and grow accordingly. In some cases, intermittent flow-path regimes emerged, maintaining a dynamic balance with biofilm growth. This balance was observed within certain flow velocity ranges, corresponding shear forces, nutrient availability, and biofilm cohesiveness.
- At very low nutrient velocities, biofilm growth was inhibited due to nutrient limitations. However, when nutrient concentration was increased, growth occurred briefly without intermittency, likely because the biofilm adapted to low-shear conditions by forming a highly permeable and porous structure.
- When the mean velocity was sufficiently high for a given nutrient concentration, biofilm growth resumed. Under these conditions, the biofilm adapted to the challenging environment, withstanding shear forces and enabling the formation of intermittent flow paths.
- Adding pore bodies to the flow channel introduced regions of lower shear stress. The biofilm adapted to these low-shear conditions, and grow in the pore bodies but could not survive in the channel, highlighting its adaptability to varying shear environments.
- As the mean velocity of nutrient flow increased further, the frequency of flow paths initially rose but eventually disrupted the dynamic balance by exceeding the critical shear stress. This led to higher detachment rates and ultimately inhibited biofilm growth.
As a result, the intermittent flow-path regime, in dynamic balance with biofilm growth, is defined within specific ranges of flow velocity, nutrient availability, and the ratio of shear stress to the biofilm’s ability to resist these forces, which we also confirm by comparison to a numerical model.
How to cite: Bozkurt, K., Lohrmann, C., Weinhardt, F., Hanke, D., Hopp, R., Holm, C., and Class, H.: Intermittent flow paths in biofilms grown in a microfluidic channel, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-3071, https://doi.org/10.5194/egusphere-egu25-3071, 2025.
As an important unconventional natural gas resource, the charging mechanism of tight gas is of great significance for the accumulation of natural gas. Although previous studies have mainly focused on qualitative evaluation, there is a lack of quantitative evaluation research on the charging process of tight gas. Consequently, this paper uses an example from the tight sandstones of the Upper Triassic Xujiahe Formation, Sichuan Basin, China, by employing physical charging simulation of nuclear magnetic resonance (NMR) coupling displacement, physical property analyses, scanning electron microscopy (SEM), X-ray diffraction (XRD), and high-pressure mercury injection (HPMI) experiments, combined with numerical simulation methods, reveals the tight gas charging mechanism. The principal findings are: (1) The tight reservoirs of the Xujiahe Formation can be classified into four types based on the differences in pore structure. From Type I to IV reservoirs, the distribution of pore sizes (as shown by NMR T2 spectra) gradually transitions from a bimodal shape dominated by large pores to a single peak shape dominated by small pores. (2) Through multi-factor analysis, a tight gas saturation evaluation model is established that considers reservoir types and pressure and can predict the tight gas charging process and gas saturation in different types of tight reservoirs. (3) The charging process of tight gas is controlled by a combination of charging pressure, pore structure, and water film. Higher charging pressure has a significant impact on the gas content of poor reservoirs. Under the same charging pressure, the gas saturation decreases with the decrease in of pore size. As the charging pressure increases, the influence of the water film diminishes. (4) Based on the principles of mechanical equilibrium and material balance, a numerical model for tight gas charging and reservoir formation is established for three types of source-reservoir combinations: “lower-generation and upper-storage type”, “upper-generation and lower-storage type”, and “interlayer reservoir type”. In the “lower-generation and upper-storage” type, the gas saturation gradually improves from bottom to top. As the thickness of the source rock increases, the gas saturation in the middle and lower parts increases rapidly. The thickness of high-quality source rock has a significant impact on the gas-bearing properties of Type I and Type II reservoirs. In the “upper-generation and lower-storage” type, as the thickness of the source rock increases, the gas-bearing stable zone grows until it becomes stable. For the “interlayer reservoir type”, with the increase in the thickness of the interlayer, the gas saturation of the sand bodies in the middle and lower parts of Type I and Type II reservoirs exhibits a downward tendency, and the gas-bearing capacity of the thick interlayer is lower than that of the thin interlayer. This research not only aids in understanding the accumulation process of tight gas but also provides a theoretical foundation for the accurate prediction of tight gas sweet spots.
How to cite: Shao, H. and Wang, M.: Dynamic charging mechanism of tight gas reservoirs based on experimental and numerical simulation, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-3077, https://doi.org/10.5194/egusphere-egu25-3077, 2025.
The evaporation of saline water from porous media is a critical global concern, influencing diverse applications such as water management, subsurface energy storage, construction materials, and agriculture. Understanding this process is essential, as it may lead to salt precipitation within pores that can partially or fully block them. This can alter the hydraulic properties of the porous medium, affecting fluid and solute transport. Most studies dealing with salt precipitation during evaporation have focused on homogeneous porous media, with limited attention to heterogeneous systems. This study addresses this gap by investigating vertical textural contrasts in porous media, specifically sand columns with a distinctive vertical interface between fine and coarse sand. Previous studies dealing with evaporation have shown that in such configurations, water migrates from coarse to fine sand, creating an additional evaporation surface at the vertical interface. This potentially leads to subflorescent salt precipitation at the interface, which can significantly impact transport properties. However, previous characterization methods, such as surface imaging, infrared thermography, and low-resolution medical computed tomography, fail to provide direct visual evidence of these processes within the sand matrix. In this study, we aim to bridge this gap by employing time-lapse micro-computed tomography (µ-CT) to provide high-resolution visualization and quantification of water movement and salt distribution during evaporation. The experiments use a heterogeneous column divided into half fine sand (particle size ~0.1 mm) next to coarse sand (particle size ~1 mm) with a sharp vertical interface. The column was saturated with NaCl solution and underwent evaporative drying at room temperature. µ-CT enabled the characterization of salt distribution on the surface, at the vertical interface, and within the porous media, while mass loss measurements were used to quantify evaporation rates. The spatial and temporal variability of salt precipitation was analyzed to determine its dynamic effects on evaporation and transport processes. Overall, this study enhances the understanding of evaporation and salt precipitation in heterogeneous porous media, offering valuable insights for fields such as soil science, hydrology, and energy storage, where controlling or predicting these processes is crucial.
How to cite: Bakhshi, P., Chaudhry, A., and Huisman, J. A.: Unraveling Salt Precipitation Dynamics in Heterogeneous Porous Media via Time-Lapse Micro-Computed Tomography, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-891, https://doi.org/10.5194/egusphere-egu25-891, 2025.
Estimating multiphase flow properties, particularly permeability, is critical for addressing critical challenges in subsurface engineering applications such as CO2 sequestration, efficient oil and gas recovery, and groundwater contaminant remediation. At the sub-core scale, accurate determination of permeability is vital for understanding flow dynamics and reservoir characterization. However, traditional estimation methods, which rely heavily on numerical simulations, are computationally expensive and time-intensive, limiting their scalability for large-scale or real-time applications. Deep Neural Networks (DNNs) have emerged as a promising alternative due to their ability to learn complex input-output relationships, enabling rapid predictions. Despite their potential, standard data-driven deep neural networks (DNNs) encounter substantial challenges when data availability is limited, often resulting in suboptimal performance and unreliable predictions. Additionally, these models heavily rely on the quality of the measurements, making them sensitive to noise and inaccuracies in the dataPhysics-Informed Neural Networks (PINNs), a class of DNNs that incorporate physical laws as soft constraints, have demonstrated exceptional robustness in addressing inverse problems under data-scarce conditions. By embedding the governing equations into the learning process, PINNs bridge the gap between data-driven and physics-based modeling approaches. Nevertheless, the application of PINNs to inverse problems is often scenario-specific, requiring retraining when transitioning to new conditions or settings. While recent studies have begun leveraging PINNs as surrogate models to efficiently solve forward problems across varying conditions, their full potential in generating datasets for coupled systems remains underexplored. In this study, we present an innovative framework that integrates a PINNs-based surrogate model with a data-driven DNN to accurately and efficiently estimate a 1D heterogeneous permeability profile using sub-core saturation measurements. The surrogate PINNs system was pre-trained to solve a 1D steady-state two-phase flow problem, incorporating capillary pressure heterogeneity and spanning a wide range of flow conditions. This pre-trained PINNs system was subsequently employed to generate an extensive dataset for training a DNN, which establishes a direct mapping between permeability, flow conditions, and measured saturations at the sub-core level. By coupling these two systems, our approach enables the rapid prediction of permeability profiles based on observed flow conditions and saturation measurements, bypassing the computational burden of traditional numerical simulations. The coupled framework demonstrated remarkable accuracy and robustness, achieving average misfits below 1% when validated against actual permeability profiles. Its computational efficiency also facilitated the development of a stochastic extension, allowing the system to handle noisy or contaminated data while quantifying uncertainties. This enhanced solution, capable of delivering results in less than 15 seconds, significantly improves the reliability and applicability of the method for real-world scenarios. Furthermore, the approach successfully reconstructed 1D permeability structures from 3D datasets and generated 1D saturation profiles under varying conditions, achieving an average misfit of approximately 3%. These findings highlight the potential of integrating PINNs with data-driven models for high-fidelity, efficient estimation of flow properties in heterogeneous systems. The proposed method offers a powerful tool for advancing subsurface flow characterization, with broad implications for both scientific research and practical applications.
How to cite: Chakraborty, A., Rabinovich, A., and Moreno, Z.: Estimating sub-core permeability using coreflood saturation data: a coupled physics-informed deep learning approach, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-634, https://doi.org/10.5194/egusphere-egu25-634, 2025.
Underground hydrogen storage in saline aquifers offers a promising solution to address seasonal fluctuations in renewable energy supply. Repurposing natural gas storage facilities for hydrogen leverages existing infrastructure; however, the distinct flow behaviors of hydrogen-brine and methane-brine systems, particularly in fractured reservoirs and sealing caprocks, remain poorly understood. This study investigates the microscopic two-phase flow dynamics of hydrogen (H₂), methane (CH₄), and their mixtures in fractured karstic limestone from the Loenhout natural gas storage facility in Belgium. Experiments on primary drainage (gas injection) and imbibition (withdrawal) were conducted under reservoir conditions (10 MPa, 65°C) using three different rock samples to examine the influence of fracture geometry on fluid invasion and recovery efficiency. Our findings reveal that while H₂ and CH₄ reach similar gas saturations after primary drainage, H₂ forms a greater number of smaller ganglia due to its discontinuous invasion in rough fractures. Fracture aperture variability and roughness significantly affect flow dynamics, gas trapping, and recovery. Furthermore, steady-state relative permeability experiments demonstrate that hydrogen’s relative permeability closely matches that of methane but is substantially lower than nitrogen, emphasizing nitrogen’s inadequacy as a proxy for hydrogen in reservoir simulations. These results highlight the importance of precise pore-scale modeling to improve field-scale predictions, ensuring effective and secure hydrogen storage in fractured reservoirs like Loenhout.
How to cite: Manoorkar, S., Kalyoncu Pakkaner, G., Omar, H., Barbaix, S., Ceursters, D., Latinis, M., Van Offenwert, S., and Bultreys, T.: Hydrogen vs Methane: Microscopic Flow Dynamics in Fractured Reservoir Rocks for Energy Storage, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-14592, https://doi.org/10.5194/egusphere-egu25-14592, 2025.
Induced calcite precipitation, where CaCO3 closes voids inside porous media and unconsolidated samples are solidified, is an important technique in geotechnical engineering. To optimize these applications, it is crucial to understand how the dynamics of mineral precipitation affect flow and transport in porous media. The aim of this study is to investigate how different injection strategies affect the spatial and temporal development of calcite precipitation using time-lapse non-invasive imaging with magnetic resonance imaging (MRI) and X-ray microcomputed tomography (µXRCT). These two imaging methods are complementary because µXRCT aims to detect structural changes of the solid matrix, whereas MRI focuses on the liquid phase in the pore space. Together, these methods enable time-resolved observations of the three-dimensional development of porosity, and thus have the potential to offer valuable insights into the spatial and temporal dynamics of the precipitation process.
We performed two distinct types of experiments to induce precipitation by simultaneous injection of a cementing solution consisting of 0.5 M CaCl2 and 0.5 M urea and an enzyme solution containing 5.0 g/l of Jack Bean meal into homogeneous sand packings prepared in 30 mm long sample cuvettes with a diameter of 15 mm. Two injection strategies were realized. In a first experiment, a constant flow rate of 0.01 mL/s was maintained during six injection cycles. Pressure development was monitored in parallel. In a second experiment, the solutions were injected at a constant pressure that was increased stepwise during six cycles from initially 50 mbar to 300 mbar to maintain moderate flow rates. Following each cycle, both samples were imaged using XRCT and MRI and the intrinsic permeability was determined.
Imaging results indicate that calcite preciptation occured more strongly close to the inlet, as manifested by water content and relaxation maps from MRI and density maps from XRCT. Only during the last two injection cycles, zones with increased precipitation became visible in the center of the column. The MRI relaxation maps suggest a reduction in pore size due to precipitation, which agreed with increased surface-to-volume ratio of the pores. Vertical porosity profiles derived from XRCT showed an average change of 12 and 11 vol.% for the constant flow and constant pressure inection strategies, respectively, and confirmed the non-uniform distribution observed with MRI. The permeability decreased by two orders of magnitude for both injection strategies. However, this decrease was achieved already after 90 injected pore volumes in case of the constant pressure injection strategy, whereas the constant flow strategy required 165 pore volumes for a comparable decrease. This is attributed to the increased tendency for preferential flow in case of the constant-rate injection strategy, but this needs to be confirmed through a detailed analysis of the variability of calcite precipation within the sample cross-section. Overall, this study showed the feasibility of monitoring induced calcite precipitation using both MRI and XRCT.
How to cite: Emadi, S., Bakhshi, P., Pohlmeier, A., and Huisman, J. A.: Non-invasive imaging of the effect of injection strategy on the spatial and temporal development of enzymatically-induced calcite precipitation, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-7028, https://doi.org/10.5194/egusphere-egu25-7028, 2025.
Fluid/chemical transport in the connected pore network of porous sandstone with variable permeability governs numerous subsurface energetic, environmental, and industrial activities. In this work, we compile a multi-scale pore connectivity evaluation by integrated pore structure characterization involving casting thin section, scanning electron microscope, nuclear magnetic resonance, X-ray computed tomography, and mercury intrusion porosimetries. The pore connected pattern, connective ratio, and connected full-range pore size distribution (CPSD) are obtained by the determination of full-range pore size distribution and empirical correlations between pore size and connective ratio, upon which the across-scale steady-state multiphase flow physics are further explored incorporating physical simulation experiment and numerical analyses. The scale-invariant connective ratio of conventional sandstone with reticular connection pattern stays at around 0.60, that of low-permeability sandstone ranges from 0.53 to 0.60, exhibiting branch-like connection, and it is avg. 0.31 in tight sandstone with local chain-like pattern, of which the ratio can be predicted by its strong dependence on porosity, permeability, and connected median pore radius. With decreasing pore connectivity, the fractional flow of non-wetting phase in steady-state two-phase flow turns from linear deviated flow to power-law flows. The pore-scale interpretations of multiphase mobility and interaction dynamic by incorporating DLVO theory, augmented Young-Laplace equation, and effective hydraulic radius model suggest that the connected full-range pore size distribution determines the wetting phase mobility and non-wetting phase accessibility, controlling the dynamic of multiphase interaction and build of non-wetting phase pathways. Preferential flow path expansions in the connected pores < 1000 nm, leading to strong differences in the resistance for non-wetting phase flow, are the primary reasons for distinctions in flow regimes. The increasing pores of 30-50 nm in the non-wetting phase flow paths are responsible for the TPG, pressure disorders, and fluid snap-offs, resulting in the power-law flow deviations. A dynamic fractional flux prediction model for non-wetting phase is proposed by modifying the fractal-based Hagen-Poiseuille equation considering flow physics, pore heterogeneity, and critical percolation length scale variations along with flow path expansion in the connected pore system. Comparative analysis indicates that the determination of hydraulic flow diameter should follow the percolation threshold theory and reliable of porous sandstone is at round R40 of the connected flow pathway.
How to cite: Qiao, J., Zeng, J., Jiang, S., and Chen, D.: Pore-scale understandings for steady-state two-phase flow in porous sandstone from full-range pore connectivity quantification, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-15356, https://doi.org/10.5194/egusphere-egu25-15356, 2025.
Nitrate contamination in groundwater is a pervasive environmental issue with significant ecological and potential human health implications. Emulsified vegetable oil (EVO) has shown promise for nitrate plume remediation through simulation of indigenous denitrifying populations, but the potential for secondary effects such as nitrous oxide emissions and discharge of dissolved carbon are not well understood. This study is the first adaptation of an electron competition model with steady-state biomass developed for modeling denitrification in wastewater treatment facilities to denitrification in the subsurface environment with biomass growth. The goal of the model is to quantify carbon and nitrogen emissions over the lifetime of a treatment. The model integrates EVO hydrolysis with substrate availability and electron carrier dynamics, incorporating microbial interactions between hydrolyzers and denitrifiers. Key findings reveal that nitrous oxide emissions are significantly influenced by the balance between oxidized and reduced electron carriers, modulated by biomass activity and carbon substrate availability. The hydrolysis of EVO is identified as the rate-limiting step in sustaining denitrification, but incomplete denitrification can occur even at high carbon availability. This research advances the understanding of microbial-mediated denitrification mechanisms and provides insights for identifying the conditions that favor nitrous oxide emissions in Permeable Reactive Barriers (PRBs) for nitrate-contaminated groundwater remediation.
How to cite: Gonsalez, V., Ramsburg, C. A., and Muller, K.: Modeling enhanced denitrification in groundwater through electron competition among nitrogen species to identify N2O emissions, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-17828, https://doi.org/10.5194/egusphere-egu25-17828, 2025.
CO2 sequestration is a promising method to mitigate anthropogenic CO2 emissions. When CO2 is injected into a saline aquifer, its buoyancy leads to the formation of a gravity current that migrates laterally, while CO2 dissolves into the underlying brine, creating a high-density mixture that can trigger fingering instabilities. In this study, we investigate the migration of this gravity current and the mixing of CO2 with brine in heterogeneous porous media. Heterogeneity is modeled using horizontally stratified media and multi-Gaussian log-normal permeability fields, characterized by the variance of the log-permeability and its correlation length. We examine how heterogeneity influences the time-evolution of the gravity current and CO2-brine mixing by analyzing factors such as dissolution fluxes, residual buoyant mass, the length of the CO2-brine interface, interface width, and mixing volume. Additionally, we explore the impact of different Rayleigh numbers, correlation lengths, and variances on mixing behavior. Our findings aim to enhance the understanding of CO2 storage in geological formations.
How to cite: Jiménez-Ramos, A., Dentz, M., and Hidalgo, J. J.: Heterogeneity effects on gravity current migration and mixing in porous media, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-11315, https://doi.org/10.5194/egusphere-egu25-11315, 2025.
A hyperbolic description of the problem of solute transport using a deterministic and Lagrangian formulation that combines characteristics of the classical formulations based on the Fokker-Planck (FP) and Langevin equations is developed. This formulation is based on a Liouville master equation, whose hyperbolicity allows for tracing the concentrations along characteristic lines in the augmented phase space composed by solute particle locations and a set of (time-independent) random coefficients used to define a source term that introduces the noise added to the system, in lieu of (time-dependent) stochastic processes. This circumvents the use of stochastic calculus and eliminates the diffusive term of the master equation, at the expense of increasing the dimensionality of the joint probability density function (PDF) of solute particle locations. The characteristic lines define flow maps for the joint PDF and its support such that all one-point space-time statistical information to study mixing and dispersion respectively is contained in them. Therefore, diffusion is modeled with kinematics parametrically dependent on random coefficients. This approach can be combined with numerical algorithms to solve ordinary differential equations (ODEs), that are unaffected by the Courant-Friedrichs-Lewy (CFL) stability condition, do not suffer from Gibbs oscillations, do not require (order-reducing) filtering and regularization techniques, and do not rely on standard Monte Carlo sampling. Because of these reasons this formulation offers more accuracy and a lower computational cost in comparison to Eulerian grid-based and Lagrangian particle tracking solvers. To find the proper noise term to add, we impose that averaging the Liouville equation over the coefficients must lead to the FP equation, which leads to a classical closure problem for the moments of the joint PDF. However, assuming a local linearization in concordance with the Ranz transform used in the lamellae description, a simple closure based on truncated central moments becomes exact and so does this hyperbolic description, which accounts for diffusion in all directions. In this talk, I will discuss the methodological advantages of using a hyperbolic description of mixing, and show how it can be used to construct a numerical lamellae method for arbitrarily shaped initial concentration profiles.
How to cite: Dominguez-Vazquez, D. and Aquino, T.: A numerical lamellae method based on flow maps, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-13723, https://doi.org/10.5194/egusphere-egu25-13723, 2025.
Saline water evaporation from porous media with the corresponding surface salt crystallization patterns play a vital role in many environmental and engineering applications. While the impact of factors such as type and concentration of salt, particle size and angularity, and ambient temperature and humidity are relatively well characterized [1]–[3], the influence of wind and aerodynamic conditions on saline water evaporation and salt crystallization is not fully understood. We conducted a series of laboratory experiments in a wind tunnel to systematically investigate the effect of wind flow on saline water evaporation and dynamics of salt crystallization. Cylindrical sand columns (D: 5 cm – H: 20 cm) were placed in the test section of the wind tunnel. Surface of the samples were exposed to uniform mean wind velocities of 0.5 and 5 m/s. To keep samples fully saturated during the evaporation experiments, sand columns were supplied from Mariotte bottles containing 10, 15, and 20% NaCl solutions. Evaporation rates were monitored by measuring mass losses from Mariotte bottles, while salt crystallization patterns were captured using an optical camera positioned above the surface of columns. Preliminary results indicate that variation in aerodynamic conditions and turbulence patterns, driven by changes in wind velocity and surface roughness (due to crystal growth), significantly alter evaporation rates and salt crystallization process. Distinct crystallization patterns were observed with variation of wind velocity with possible influences on the evaporative fluxes. Using the measured data, we will identify the key effects of air flow regimes coupled with the salt concentration on evaporative losses and the evolution of crystallized salts at the surface, which will be important for a wide range of environmental and hydrological applications.
[1] S. M. S. Shokri‐Kuehni, B. Raaijmakers, T. Kurz, D. Or, R. Helmig, and N. Shokri, “Water Table Depth and Soil Salinization: From Pore‐Scale Processes to Field‐Scale Responses,” Water Resour. Res., vol. 56, no. 2, Feb. 2020, doi: 10.1029/2019WR026707.
[2] S. Jannesarahmadi, M. Aminzadeh, R. Helmig, D. Or, and N. Shokri, “Quantifying Salt Crystallization Impact on Evaporation Dynamics From Porous Surfaces,” Geophys. Res. Lett., vol. 51, no. 22, pp. 1–10, Nov. 2024, doi: 10.1029/2024GL111080.
[3] M. Norouzi Rad and N. Shokri, “Effects of grain angularity on NaCl precipitation in porous media during evaporation,” Water Resour. Res., vol. 50, no. 11, pp. 9020–9030, Nov. 2014, doi: 10.1002/2014WR016125.
How to cite: Jannesarahmadi, S., Aminzadeh, M., Helmig, R., Oesterle, B., and Shokri, N.: The Role of Wind Velocity in Saline Water Evaporation from Porous Media and Surface Salt Crystallization Dynamics, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-3537, https://doi.org/10.5194/egusphere-egu25-3537, 2025.
The relative permeability–saturation (kr–s) relationship is a macroscopic representation of microscale flow characteristics between multiphase immiscible fluids, governed by the interplay among capillary, viscous, and gravitational forces. Previous studies on two phase fluid flow have primarily derived the kr–s relationship from horizontal core-flooding experiments while neglecting the influence of gravity. However, frequent advent of vertical flows caused by conditions such as macroscale heterogeneity, brine extraction, and CO2 injection through horizontal well, emphasizes non-negligible gravitational effects varying with the direction of displacement. This study aims to provide experimental evidence of anisotropy on kr–s relationship induced by gravitational forces, contributing to a deeper understanding of gravity’s role in multiphase flow systems. Steady-state relative permeability tests using a 1-meter acrylic column tightly packed with glass beads and two immiscible fluids were performed under various flow directions. In addition, several total flow rates and beads sizes were used to adjust dimensionless capillary and bond number, which indicate different interplays among three governing forces. Our experiments revealed the differences in the kr–s relationship between upward and downward flow directions, suggesting that the isotropic kr–s assumption may not fully capture these dynamics. Under conditions of higher bond number, such as in the finer glass beads, the anisotropy on kr–s relationship were weaker, indicating the influence of gravitational forces on its anisotropy. This study underscores the need to account for anisotropy on kr–s relationships under dynamic flow conditions.
Project Acknowledgement
This work was supported by Korea Institute of Energy Technology Evaluation Planning (KETEP) grant funded by the Korea government (MOTIE) (20212010200010, Technical development of enhancing CO2 injection efficiency and increase storage capacity)
How to cite: Lee, C., Ha, S.-W., and Lee, K.-K.: Anisotropy on relative permeability curve under the influence of gravity, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-5358, https://doi.org/10.5194/egusphere-egu25-5358, 2025.
Understanding the probability distributions of flow velocities in heterogeneous porous media is crucial for the study of transport phenomena, as velocity variability controls residence times and dispersion phenomena. However, our knowledge of velocity distributions and their relation to medium structure remains incomplete, especially under partially-saturated conditions, where phase heterogeneity plays a key role in determining the flow structure. In addition, the distributions of shear (the spatial rate of change of velocity transverse to the flow) are essential for understanding the impact of flow on mixing processes, because they represent a key control on solute plume deformation and its interplay with diffusion. Yet, these distributions are far less explored, particularly at the pore scale and under unsaturated conditions. This gap limits our ability to predict the impact of microscopic dynamics on macroscopic plume structure.
In this work, we focus on pore-scale velocity and shear distributions in unsaturated systems. Velocity fields are obtained through numerical simulations based on experimental data for the structure of the medium and fluid-phase distributions. The media are quasi-two-dimensional, with cylindrical pillars of variable radii and different correlation structures, and the flow conditions are such that the spatial phase distributions are time-independent. We characterize velocity and shear distributions and use this information to parameterize Continuous Time Random Walk (CTRW) models to predict solute transport and mixing.
How to cite: Arnal, J., Sole-Mari, G., Borgman, O., Le Borgne, T., and Aquino, T.: Pore-scale shear distributions in unsaturated porous media and their role in transport and mixing, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-6197, https://doi.org/10.5194/egusphere-egu25-6197, 2025.
Geochemical reactions in porous rocks are typically scaled up using effective reaction parameters derived under well-mixed conditions. Such well-mixed conditions are often absent in natural settings. While conventional transport theories based fundamentally on diffusion and dispersion processes can not fully capture the state of mixing, several lines of evidence point to the dominance of chaotic solute mixing. Yet, proving the existence of chaotic mixing in porous rocks remains unresolved mostly due to the limitations in directly observing pore-scale processes. In this work, we present direct evidence of chaotic microscale trajectories in porous rock samples by performing fast high-resolution X-ray tomography at the European Synchrotron Radiation Facility (ESRF). We utilize a custom-designed core holder and highly permeable sandstone and sand pack samples to achieve notably high Peclet numbers during the co-injection of two miscible, highly viscous mixtures of glycerin and brine. These high Peclet numbers are crucial for visualizing chaotic trajectories within the rock pores, as they allow the deformation of fluid fronts to dominate before molecular diffusion blurs the patterns. The existence of such trajectories could significantly enhance microscale concentration gradients, potentially leading to chemical reaction rates that differ from conventional reactive transport model predictions. This difference underscores the need to update kinematic models to incorporate the coupling between chaotic mixing and chemical reactions in porous media for a better understanding and quantification of transport and storage processes in the subsurface.
How to cite: Vafaie, A., Kivi, I. R., Manoorkar, S., Darraj, N. M., Saleh, M., Gomez, F., Lamblin, M., Cordonnier, B., Bihannic, I., Le Borgne, T., Krevor, S., and Heyman, J.: How does imaging help unveil chaotic mixing in porous rocks?, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-9531, https://doi.org/10.5194/egusphere-egu25-9531, 2025.
Displacement of a wetting by a non-wetting fluid in fractured media is a process with relevance for many applications, such as fluid storage in the subsurface or oil and gas exploitation. How to capture the flow in open rough-walled fractures on the large length scales required for such applications is an open question. It is highly questionable if the two-phase flow equations can be simplified to continuum approaches, such as established for porous media, which would allow for coarse spatial resolutions of a model. For this reason, it is necessary to develop a good understanding of how flow regimes and fracture geometry influence the properties of the fluid distributions during a displacement process that determine the macroscopic behavior. Such properties are, for example, fluid that is immobilized behind the displacement front. While there has been extensive investigation of this question in the context of porous media, studies on rough fractures are relatively scarce.
It is well established that in horizontal settings, the displacement is governed by capillary and viscous forces, resulting in the emergence of various displacement patterns (compact, viscous fingering or capillary fingering). Numerical simulations of the flow process could be helpful to relate the flow conditions and geometrical properties of the aperture field to characteristics of fluid distributions. However, such numerical simulations are not straight forward, as capturing the fluid-fluid surfaces and contact lines requires very fine grids and poor representations of the interfaces can cause large numerical errors. It is thus crucial to validate numerical models with well controlled experiments. As it is necessary to have well controlled conditions for boundary conditions and precise knowledge of the geometrical properties of the fracture aperture, such experiments are challenging.
In this contribution, we compare numerical results to recent results from experiments carried out in a setup featuring a fracture flow cell with self-affine rough walled surfaces and a precisely controlled mean aperture. Different viscosity ratios are obtained by altering the viscosities of both the displacing and the displaced fluids and different capillary numbers are obtained by varying the flow rate imposed through the cell. We compare the experimental findings to Direct Numerical Simulation (DNS) results obtained by solving the Navier–Stokes equations within the fracture pore space, employing the Volume of Fluid (VOF) method to track the evolution of the fluid-fluid interface. We systematically confront the numerical predictions to the experimental results, in terms of various morphological properties of the displacement patterns such as Euler number, cluster size distribution, interfacial length, typical finger width, trapped cluster size distributions or fluid-fluid interface length. From this we infer a range of capillary numbers and viscosity ratios for which the numerical model can be validated as properly predicting the experiments.
How to cite: Neuweiler, I., Krishna, R., Rezaei, A., Borgman, O., Gomez, F., and Méheust, Y.: Drainage in Open Rough-walled Fractures – Comparison of experimental and numerical results, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-20497, https://doi.org/10.5194/egusphere-egu25-20497, 2025.
Low-emission hydrogen accounted for less than 1 % of global hydrogen production by 2023, but will have to increase more than 100-fold by 2030 according to the International Energy Agency’s net-zero emission scenarios for 2050. Proton exchange membrane water electrolyzers are particularly suitable to produce hydrogen from renewable energy sources, yet the currently available technological combinations are considerably more expensive than producing hydrogen from fossil fuels (by 65 % to 810 % according to the International Renewable Energy Agency’s 2021 report). To reduce costs, the materials and dynamic operating conditions in electrolyzers must be optimized, amongst other things with regard to low oxygen concentrations (waste product) at the catalysts. We use a first-principle microscale model for oxygen transport to complement experimental optimization efforts, which are generally expensive and limited by measurement accuracies.
The model deploys the volume of fluid method and accounts for (1) uncertain transport processes in the catalyst layer, (2) numerically challenging two-phase at capillary numbers as low as 2.1 · 10-7 and (3) bubble detachments in channels. The model is validated with respect to flow patterns in microfluidic experiments as well as to pressure drops and bubble velocities within minichannels (30% and 20% match regarding the latter two). The model is numerically stable at operando conditions with at least 0.5 A/cm2 current density in a stochastically reproduced porous transport layer. Uncertain catalyst-side solute transport and nucleations are implicitely accounted for, yet their spatial variations are found to negligibly affect the conditions inside the porous transport layer. Operando gas saturation measurements are locally matched within a 20% margin and are qualitatively matched across the entire porous transport layer.
The simulated bubble detachment in flow field channels occur at pore throats that agree with porosimetry and microfluidic experiments. The gaseous phase pressure fluctuates greatly according to the detachment throat size and the bubble diameter immediately before detachment. The model allows the prediction of nucleation and detachment sites and can be further utilized to optimize porous transport layers as well as to predict boundary conditions when modeling catalyst layers and flow fields.
How to cite: Schmidt, G. and Neuweiler, I.: Volume of Fluid Modeling of Capillary-Dominated Flow Patterns and Bubble Detachment in PEM Water Electrolyzers , EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-21948, https://doi.org/10.5194/egusphere-egu25-21948, 2025.
