Changes in groundwater flow in response to strong earthquakes are widely described in many tectonic environments. For example, a post-seismic discharge variation is often attributed to an increase of bulk permeability due to co-seismic fracturing and/or to a change in the role of faults in acting as conduits/barrier to groundwater flow.

We take as an example the fractured aquifer of the Mts. Sibillini carbonate massif, in Central Italy, which were affected by a strong and prolonged extensional seismic sequence in 2016-17. The sequence was characterized by an M=6.5 event (mainshock), an M=6 event, an M=5.9 event, up to 60 M>4 events and several M>5 earthquakes. The strongest events caused rupturing of the topographic surface for a cumulative length in the order of 30 km and an important portion of aftershocks occurred at depths where groundwater is stored.

As a response to the seismic sequence, the main NNW-directed groundwater flow was diverted to the west and a discharge deficit was observed at the foot-wall of the activated fault system with a relevant discharge increase, accompanied by geochemical variations, at the fault system hanging-wall.

By integrating geo-structural reconstructions, seismological and ground deformation data, artificial tracer tests results and a 4-years discharge and geochemical monitoring campaign data, we show that the observed groundwater variations are due to a combination of permeability increase along the activated fault systems and hydraulic conductivity increase of the hanging-wall block due to fracturing, extension and subsidence, which determined a fast aquifers emptying. Seismicity temporarily triggered a change of the pre-existing predominant along-faults-strike NNW-SSE oriented regional flow to a west-directed flow, perpendicular to faults strike. We discuss the position of the aquifer with respect to the activated faults and how this affected the observed phenomena.

REFERENCE

Cambi, C., Mirabella, F., Petitta, M., Banzato, F., Beddini, G., Cardellini, C., ... & Valigi, D. (2022). Reaction of the carbonate Sibillini Mountains Basal aquifer (Central Italy) to the extensional 2016–2017 seismic sequence. Scientific Reports, 12(1), 1-13. DOI: 10.1038/s41598-022-26681-2

How to cite: Cambi, C., Mirabella, F., Petitta, M., Banzato, F., Beddini, G., Cardellini, C., Fronzi, D., Mastrorillo, L., Tazioli, A., and Valigi, D.: Groundwater flow changes in response to extensional earthquakes: a case study from the 2016-17 seismic sequence in Central Italy, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-7325, https://doi.org/10.5194/egusphere-egu23-7325, 2023.

The Flamborough Head Fault Zone (FHFZ) is a regionally-significant structural zone in northeast England which dissects the Upper Cretaceous Chalk Group, a 500 m thick limestone succession which is a principle aquifer and main source of water supply in the region. The geometry and physical characteristics of the Chalk succession, including the effects of faulting, influence groundwater flow across the region. Consequently, understanding the architecture of the FHFZ is vital to sustainably managing water resources in this area.

The FHFZ marks the southern extent of the Cleveland Basin and the northern margin of the Market Weighton Block and has a complex history of Mesozoic-Cenozoic extension and compression. It is predominantly comprised of east-west trending faults which form a graben that is dissected by north-south trending faults, including the southern extension to the Peak Trough, the Hunmanby Fault. To the west, FHFZ links with the Howardian Fault System and offshore, in the east, it is truncated by the north-south trending Dowsing Fault. The FHFZ is well exposed and described in coastal cliff sections at Flamborough Head but the inland architecture of the faults has hitherto been poorly explored predominantly due to limited inland-exposure.

To address this a multi-faceted approach to geological mapping has been undertaken in the region by the British Geological Survey, in collaboration with the Environment Agency and Yorkshire Water Limited. Remote sensing, targeted field mapping, palaeontological analysis, passive seismic and 2D onshore seismic interpretation have been integrated to understand the inland architecture of the FHFZ in unprecedented detail. Combining these techniques has enabled us to bridge the gap between the surface geology and deeper subsurface structure, increase our understanding of the geology of the region and produce an improved conceptual model at a range of depths which will be used to better manage water resources.

How to cite: Vernon, R., Burrel, L., Ford, J., Haslam, R., Randles, T., McCarthy, D., Woods, M., and Burke, H.: Surface and subsurface mapping of the Flamborough Head Fault Zone to inform groundwater management in the Yorkshire Wolds, UK., EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-6983, https://doi.org/10.5194/egusphere-egu23-6983, 2023.

The fracture density of rock could create the applying shock waves phase difference at the laboratory scale. For using this technology in determining the stress status along the wave propagating path, removing unnecessary noise is the most crucial task. In this study, a machine learning method with Long short-term memory (LSTM) algorithm to retreat the signals from sophisticated seismograms is proposed. The primary analyzing target is data across the 2022 Taitung, Eastern Taiwan seismic event and another micro-seismic data set associated with a surface crack on a hill of Ping-Tong, southern Taiwan. It is found that there is no phase difference among vertical and horizontal components from the same record, when comparing the difference between two various records then the result is distinct. The detecting sub-surface crack density via phase difference has increased in some seismic data pairs of eastern Taiwan after the rupture of the 2022 Taitung earthquake. The machine learning method with LSTM helps to elevate the data retrieval accuracy which cannot be done by conventional Fast Fourier Transformation (FFT). Records from stations adjacent to the hypocenter offer better agreement in phase difference measurement, the higher signal possibly causes it to noise ratio (SNR) in the such neighborhood.

Keywords: phase difference, machine learning, LSTM, crack density, stress field

How to cite: Yu, T.-T. and Peng, W. F.: Inverting the Subsurface Fracture Density by Detecting the Phase Difference of Various Seismic wave with Machine Learning, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-4868, https://doi.org/10.5194/egusphere-egu23-4868, 2023.

Noble gas release can be used to investigate the timing, location and magnitude of fracture creation.  Here, a numerical model of gas release and transport, resulting from fracturing events, is used to estimate first-order fracture network characteristics after subsurface detonation.  Released radiogenic noble gases after detonation of three different subsurface explosions of varying source characteristics were interpreted.  A broad suite of gases was sampled from 62 discrete sampling intervals in a 3-D array surrounding the explosion location using an automated field sampling system and a capillary inlet quadrupole mass spectrometer.  Gases analyzed include: ⁴He, ³⁶,⁴⁰Ar, ²⁰Ne, N₂, O₂, NO and CO₂/N₂O.  Geogenic gas arrivals were observed in a subset of sampling locations.  All geogenic gas arrivals were observed in ports with explosive-derived gas arrivals.  Helium amount and arrival time were used to estimate fracture network damage using a numerical model which allows dynamic changes in fracture aperture, matrix porosity and permeability.  The amount of fracture damage was significantly different between the three different explosions and consistent with other observations of damage.  These results illustrate how geogenic noble gases can be used to understand damage, transport, and fracture creation in fracture networks, with implications for a variety of subsurface topics including hydraulic fracking, mine failure, earthquake and volcanic monitoring.

How to cite: Gardner, W. P. and Bauer, S. J.: Estimating Fracture Network Damage After a Subsurface Detonation Using Geogenic Noble Gases., EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-12447, https://doi.org/10.5194/egusphere-egu23-12447, 2023.

We study flow and hydrodynamic transport in spatially random fracture networks.
The flow and transport behavior is characterized by first passage
times and displacement statistics, which show heavy tails
and anomalous dispersion with a strong dependence on the injection
condition. The origin of these behaviors is investigated
in terms of Lagrangian velocities sampled equidistantly along particle
trajectories, unlike classical sampling strategies at a constant rate. The
fluctuating velocity series is analyzed by its copula density, the
joint distribution of the velocity unit scores, which reveals a simple correlation
structure that can be described by a Gaussian copula. This insight
leads to the formulation of stochastic particle motion in terms of a
Klein-Kramers equation for the joint density of particle position and
velocity. The upscaled model captures the heavy-tailed first passage
time distribution and anomalous dispersion, and their dependence on the
injection conditions in terms of the velocity point statistics and
average fracture length. The first passage times and displacement
moments are dominated by extremes occurring at the first step.
The developed approach integrates the complex interaction of flow and structure
into a predictive model for large scale transport in random fracture networks.    

How to cite: Dentz, M. and Hyman, J. D.: Large-scale physics of hydrodynamic transport in random fracture networks, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-10078, https://doi.org/10.5194/egusphere-egu23-10078, 2023.

Karst characterizes almost 15% of the worlds terrain, however the mechanics of sediment transport and its prediction in karst river and cave systems remains underdeveloped. Hysteresis analysis has recently been used more to investigate the behaviors of sediments during storm events in surface systems and to some extent in karst systems. Historically, clockwise and counter-clockwise hysteresis typically refer to proximal and distal sourcing for streams. For karst systems, clockwise and counter-clockwise hysteresis has been identified to refer to an saturated and unsaturated aquifer prior to the event.

However, most interpretation of hysteresis assumes a single dominant water source, for example runoff, and assumes that baseflow is not contributing to the sediment load. One aspect of sediment hysteresis and its interpretation that has received less attention is the occurrence of several, significant water sources, eroding and delivering sediment to the watershed outlet. It is common for both surface stream systems  and karst subsurface systems to have multiple water sources contributing to the total sediment load. Each of the sources carries their own sediment time distribution, and often lead to complex hysteresis looping behavior after mixing. The primary goals of this work are to (1) study how the complex source water-sediment mixing processes impact hysteresis results and (2) to carry out solutions to the water-sediment mixing processes for karst streams, caves, and springs and show the utility and uncertainty of the method.

Several high-resolution sensors have collected data at a karst spring in central Kentucky, USA, for a 2.5 year period. Water unmixing was performed using electrical conductivity as a tracer to separate the groundwater from the surface water and infer sediment sources. Theoretical analyses have shown that not only timing and magnitude of sedigraphs influence the result of the hysteresis loops, but also timing and magnitude of each of the multiple water sources have a strong effect on the resulting hysteresis loop. The groundwater flow shows to have dominant counter-clockwise hysteresis loop, surface water shows to have clockwise loops dominating. Depending on the timing and magnitude of the water sources, the hysteresis loop at the karst spring varies from strictly counterclockwise, to a figure-8 loop, to a complex pattern.

How to cite: Bettel, L., Fox, J., Husic, A., Mahoney, T., Marin, A., Zhu, J., Tobin, B., and Al Aamery, N.: Investigating sediment transport in karst using hydrograph unmixing, sediment transport modeling and multi-source hysteresis, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-9766, https://doi.org/10.5194/egusphere-egu23-9766, 2023.

Saltwater wedge is a natural phenomenon defined as the displacement and retention of saltwater in a freshwater aquifer. This saline intrusion can modify the content of dissolved elements in coastal freshwater aquifers, which can have consequences for water use (drinking or agricultural), on the ecology, the environment, the erosion of coasts, and the stability of coastal structures.

This study focuses on the integration and coupled interpretation of various geophysical and optical data obtained on the ground and by drone to evaluate the intrusion of seawater in a coastal chalk cliff in Sainte-Marguerite-sur-Mer in Normandy, France. The objective is to characterize the freshwater-saltwater interface and describe the internal structure of the formation. To do so, the combination of geophysical (Electrical Resistivity Imaging, ERI), aerial (visible and thermal infrared photogrammetry, IRT), and geotechnical (piezometers) methods was adopted.

The ten ERI profiles (transverse and longitudinal to the cliff) allowed for the mapping of the electrical resistivity distribution. The novel contribution of this study was the highlighting of a marine intrusion under the chalk cliffs visualized using transverse ERI profiles implanted directly on the steep dip of the cliff. The use of a 30m deep piezometer positioned on the plateau of the cliff and intersecting the ERI profiles made it possible to constrain the resistivity values to the measured salinity values. The presence of this saltwater wedge was characterized by low resistivity values. The top of the cliff and the parts close to the outcrop showed significant resistivities, indicating a high level of potential damage (cracks in the outcrop, underground cavities). This allowed for the identification of a zone (about 10m before the main scarp) vulnerable to the risk of collapse.

It has been shown that the difference in groundwater density leads to unstable conditions. We propose that the denser saline water covering the less dense freshwater creates a haline convection of the brackish waters at the base of the cliff and at the level of the rocky shore platform. The IRT was used to identify the wet areas of the cliff and the resurgences of the water table on the platform. Finally, all the data were grouped to propose a conceptual model of saline intrusion under the coastal cliffs.

How to cite: Junique, T., Antoine, R., Costa, S., Beaucamp, B., Guilbert, V., Ledun, C., Maquaire, O., Rejiba, F., and Fauchard, C.: Characteristics of saltwater wedge under the chalk cliffs of Sainte-Marguerite-sur-Mer (Normandy, France) using optical and geophysical methods., EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-9396, https://doi.org/10.5194/egusphere-egu23-9396, 2023.

Anthropogenic impact on groundwater storage depletion has been detected in many places from catchment to global scales, including in our study area, the Bandung groundwater basin, Indonesia. Groundwater abstraction of various magnitudes, pumped out from numerous depths of aquifers, stimulates different changes in hydraulic heads among vertical subsurface stratifications. Such circumstances generate groundwater movement, where it flows from the upper layer storage to underlying aquifers, referred to as aquifer interaction in this study. Meanwhile, remote-sensing products such as GRACE measure the integrated water storage changes over depth and space, making it difficult to capture and derive the storage internal vertical groundwater fluxes from such signals. As an alternative, environmental water tracers (EWT) have been used to investigate subsurface water movement and to gain a conceptual understanding of groundwater flow dynamics. However, quantitative measurement of the rates of fluxes is not often possible, despite being essential to ensure sustainable groundwater resources management.

In this study, we utilize (a) groundwater flow modeling in conjunction with (b) EWT data to quantify the aquifer interaction driven by multi-layer groundwater abstraction in the Bandung groundwater basin, Indonesia. The available environmental water tracers data include major ion elements (Na⁺/K⁺, Ca²⁺, Mg²⁺, Cl^-, So²₄^-, HCO₃^-), stable isotope data (d²H and d¹⁸O), and groundwater age estimates (radiocarbon/¹⁴C content). These measurements are used to qualitatively evaluate the numerical groundwater flow model. The model, forced by recharge calculated using the hydrological model of wflow_sbm, is calibrated by minimizing the difference between the dynamic steady-state simulated and the observed groundwater levels.

We evaluate the groundwater flow model and the EWT-driven analysis from multiple perspectives. The results suggest that the groundwater recharge is uniformly distributed spatially, the groundwater is flowing regionally from the basin periphery inward to the basin’s center following the topographical distribution, and vertical groundwater fluxes are identified. All three deductions, in a qualitative sense, are agreed upon by both the EWT observations and the groundwater flow model. From the groundwater flow model, we quantify that the aquifer interaction is equivalent to, on average, 0.110 m/year, which is highly significant compared to the other groundwater budgets. We also determine the unconfined aquifer storage volume decrease, calculated from the change in the groundwater table, that results in an average declining rate of 51 Mm³/year. This number shows that the upper aquifer storage is dwindling at a rate that is disproportionate to its groundwater abstraction, hugely influenced by the aquifer interaction. The storage lost from only this partition contributes up to 60.3% of the total groundwater storage lost, despite contributing to only 32.3% of the groundwater abstraction. Additionally, we also investigate and examine the correlation between the groundwater level changes and the groundwater abstraction zones. The results of our study confirm that quantification of the aquifer interaction and groundwater level change dynamics driven by multi-layer groundwater abstraction in multi-layer hydrogeological settings is possible by our proposed methods. Applying such methods will assist in deriving basin-scale groundwater policies and management strategies under the changing anthropogenic and climatic factors, thereby ensuring sustainable groundwater management.

How to cite: Rusli, S. R., Weerts, A., Mustafa, S., Irawan, D. E., and Bense, V.: Quantifying aquifer interaction using numerical groundwater flow model evaluated by environmental water tracers data: Application in Bandung groundwater basin, Indonesia, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-12405, https://doi.org/10.5194/egusphere-egu23-12405, 2023.

Transport of solutes in aquifers is controlled by the heterogeneous spatial distribution of hydraulic properties, but the characterization of aquifer heterogeneity is quite challenging with conventional methods. Hydraulic tomography (HT) was developed to define the heterogeneous distribution of hydraulic conductivity (K) and specific storage (S_s). HT involves the emission of a series of hydraulic head perturbations in a stressed well and the recording of this signal at several levels in the stressed and observation wells. All recorded hydraulic head responses are simultaneously analyzed through numerical inversion, which provides the spatial distribution of hydraulic properties at a scale relevant for local site investigations.

This communication reports on a tomographic experiment carried out in a heterogeneous and highly anisotropic granular aquifer at the Saint-Lambert research site near Quebec City, Canada. This site has already been the object of detailed characterizations with multiple hydraulic methods: pumping tests, packer slug tests, flowmeter profiles, vertical interference tests, and slug test tomography. A relatively new approach named oscillatory hydraulic tomography (OHT) was tested, in which multi-frequency oscillatory head perturbations are induced in an interval isolated by packers of the stressed well by a submerged rod that is electronically controlled by a winch system. Hydraulic responses are measured in the stressed intervals and in multiple intervals of an observation well.

This study was primarily aimed at testing, first on an operational level, if the OHT signal could be generated in the stressed well and propagated to the observation well in a highly anisotropic granular aquifer. Second, the study developed a rigorous workflow for the treatment of the measured hydraulic heads. Third, in terms of characterization efficacy, the study aimed to determine if multiple controlled frequencies would allow the assessment of K spatial distribution.

Results show that the field experiment provided clear measured hydraulic responses that could be used to obtain the 2D distribution of hydraulic properties from the inversion of OHT measurements. Comparison was made of inversion results using a single oscillatory frequency and multiple frequencies. Under conditions of realistic field measurement noise and uncertainty, it will be valuable in future work to compare the imaging capabilities of oscillatory hydraulic tomography against other tomographic methods. Further investigation is also needed to examine the information content of oscillatory hydraulic tomographic data for characterizing K and Ss heterogeneities through a sensitivity and resolution analysis. This study demonstrates the practical potential for the implementation of OHT experiments in relatively low permeability and highly anisotropic granular aquifers.

How to cite: Nefzi, A., Paradis, D., Lefebvre, R., and Bour, O.: Data acquisition and processing of multi-frequency oscillatory hydraulic tomography in a granular aquifer, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-10693, https://doi.org/10.5194/egusphere-egu23-10693, 2023.

Managed aquifer recharge (MAR) sytems based on water filtration allow to improve recharged water quality and quantity by retaining suspended particles and microorganisms. However, the periodic detection in groundwater of pathogens and other microorganisms that represent a significant risk for human health makes it necessary to study the mechanisms affecting the propagation and fate of microbial populations during the process.

In this work a series of column experiments were performed to characterize bacteria transport in porous media. Two type of columns were built. One using only sand and another using a combination of sand, compost and wood chips. In each column a punctual injection of tracers (rhodamine and amino-G acid) and bacteria consortium collected from the effluent of a wastewater treatment plant were injected. Samples of column outflows were collected to obtain breakthrough curves of the tracers and the different amplicon sequence variants (ASVs) of bacteria to determine the material influence on the retention of bacteria. Bacteria displayed a strong anomalous behavior with late arrival peaks and longer tails than those obtained with the tracers.

A continuous time random walk (CTRW) transport model was developed to interpret the experimental results. The model characterizes transport in terms of mobile-immobile domains. Bacteria are transported with the mean flow and experience transitions from and to low mobility zones with a certain frequency. Transport is described in terms of four parameters, namely, the mean flow velocity, the dispersion coefficient, the trapping rate, and the mean residence time in the immobile zones. The model was able to reproduce satisfactorily the observed breakthrough curves of over 470 measured ASVs. The analysis of the breakthrough curved determined that bacteria form two clusters. The breakthrough curve of one cluster has heavy tails and it is formed by small, motile, gram-negative bacteria. The other cluster displays strong peaks and a relatively weaker tailing. CTRW parameters are able to predict the cluster in which a certain bacteria belongs.

How to cite: Hidalgo, J. J., Piña, B., Valhondo, C., Sanz, C., and Casado, M.: Stochastic modeling of bacterial transport and retention during aquifer artificial recharge, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-13617, https://doi.org/10.5194/egusphere-egu23-13617, 2023.

The standard liquid transport processes in porous media happens through a network of interconnected pore bodies and pore throats (here called the primary network). When a non-wetting phase displaces a wetting phase from a porous sample (drainage), thin films of the wetting phase are bound to be left on the surface of the constituting grains (for example when air displaces water from a porous rock, thin films of water are left behind, covering the rock grains). Under certain conditions, isolated liquid films can eventually merge, forming a secondary network of interconnected films and capillary bridges (see red arrows in the figure) that can effectively enhance the overall connectivity of the medium and act as a new pathway for fluid transport. We have performed experiments using transparent networks with the objective of studying transport processes that are enhanced by film flow. Our setup allow us to directly visualize the secondary network in the sample and we have shown how fluid bodies that are not linked via the primary network can actually be connected via the secondary network. This connection has important consequences for processes such as the dispersion of pollutants in soils and the transport of nutrients to plants in arid regions.

References

Moura, E. G. Flekkøy, K. J. Måløy, G. Schäfer and R. Toussaint, “Connectivity enhancement due to film flow in porous media,” Phys. Rev. Fluids 4, 094102 (2019).

Moura, K. J. Måløy, E. G. Flekkøy, and R. Toussaint, “Intermittent dynamics of slow drainage experiments in porous media: Characterization under different boundary conditions,” Front. Phys. 7, 217 (2020).

How to cite: Moura, M., Reis, P., Schäfer, G., Toussaint, R., Flekkøy, E. G., Rikvold, P. A., and Måløy, K. J.: Thin film flow: fluid transport via thin liquid films in slow porous media flows, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-4020, https://doi.org/10.5194/egusphere-egu23-4020, 2023.

Macropores have important beneficial impacts on the hydrological cycle, since they reduce risks of waterlogging, surface runoff, soil erosion and flooding. On the other hand, macropore flow is also associated with significant ecosystem disservices, since it can dramatically accelerate the leaching of contaminants to surface water and groundwater. Several approaches to model preferential macropore flow have been developed. One approach is to use the kinematic wave equation, in which the kinematic exponent should depend on the exponent in a power law relationship between wetted macropore surface area and macropore saturation. Most model applications have relied on calibration of model parameters against measured data on water flow. This makes critical testing of the underlying model concepts difficult and raises the question of whether the model is matching the data for the right reasons or not. In this study, we used X-ray tomography to quantify water and air distributions in macropores at varying steady-state flow rates in two topsoil and two subsoil columns (diameter 9 cm) sampled from a clay soil. We collected sufficient data to derive the kinematic wave exponent from the image data for the two topsoil samples. We found that the wetted macropore surface area and macropore saturation were indeed related by a power law for the first three irrigation intensities, corresponding to kinematic exponents of 1.22 and 1.26, respectively. These promising results need to be verified in future experiments that should be conducted on soil samples with smaller diameters to achieve better image resolutions and signal-to-noise ratios.

How to cite: Koestel, J., Schwenk, A., Jarvis, N., and Larsbo, M.: Quantitative three-dimensional imaging of macropore flow in undisturbed soil under different irrigation intensities, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-14697, https://doi.org/10.5194/egusphere-egu23-14697, 2023.

Plant roots and bacteria release in soils polymeric blends of substances which alter the physics of soil water flow and support life in soils. They adsorb water, decrease the surface tension of the soil solution and increase its viscosity, and, more generally, they change the soil solution into a non-Newtonian liquid with viscoelastic properties. A theory of drying of polymer solutions in porous media is missing and it is needed to understand the feedback between physics of porous media and life in soils. It was observed that during drying polymer solutions are deposited as thin surfaces spanning multiple pores and that these depositions are associated with a decrease in evaporation rate. Here, we provide a physical explanation of surface formation. The modeling framework includes Darcian flow across the polymeric network driven by a gradient in water potential. As the polymer dries and air invades the pore space the polymer network is stretched. The stretching causes a stress in the polymer network that alters the relation between water potential and polymer concentration: the more stretched is the polymer network the smaller is the spacing between the polymers at a given water potential, and the lower is the permeability of the network. The model predicts that at a critical point during evaporation there is an asymptotic increase in polymer concentration at the gas-gel interface corresponding to the deposition of solid-brittle interfaces. The onset of this glass transition depends on flow rate and pore size, with earlier deposition for fast high evaporative fluxes and small pores. The model explains why evaporation is suppressed much earlier and more significantly when the polymer solution dries into a porous medium, in comparison to the case when the polymer solution is free to dry outside a porous medium.

How to cite: Carminati, A., Benard, P., and Lehmann, P.: Theory of drying of polymer solutions in porous media, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-15772, https://doi.org/10.5194/egusphere-egu23-15772, 2023.

We study the upscaling of pore-scale solute transport in partially saturated porous media at different saturation degrees. The interaction between structural heterogeneity, phases distribution and small-scale flow dynamics induces complex flow patterns and broad probability distributions of flow. In turn, this spatial distribution of flow velocities, at the pore scale, induces irregular (non-Fickian) transport of dissolved substances (e.g., contaminants), causing an earlier arrival and longer tailing, which may have grave consequences in underestimating risk assessments and prolonged cleanup times of contaminated sites.

Here, we suggest an integrated continuous time random walk (CTRW) modeling framework, which accounts for also the entrapping of particles in zones of low flow velocities, to estimate the resident times of solutes in the media. Furthermore, comparing the results of the CTRW model to a well-established numerical simulation method allows a phenomenological evaluation of the model's physical parameters for different conditions (i.e., volume of entrapped air, mean water flow rate, or solute molecular diffusion coefficient).   

In this study we show that entrapped air promotes preferential solute transport and solute trapping in low flow regions. Moreover, we demonstrate that the trapping frequency and trapping time depend on the interaction between advection and diffusion (i.e., the Péclet number). An integrative CTRW model captures the effects of trapping in stagnant regions and preferential transport on non-Fickian dispersion of solutes.

How to cite: Ben-Noah, I., Hidalgo, J. J., Jimenez-Martinez, J., and Dentz, M.: Evaluating solute-Trapping Induced Non-Fickian Transport in Partially Saturated Porous Media, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-2274, https://doi.org/10.5194/egusphere-egu23-2274, 2023.

Reaction fronts are widespread in nature and are encountered frequently in the geological context. Examples include contaminant spread, neutralization-based reservoir decontamination, biogeochemical phenomena, and many more. The complex porous structures of subsurface formations renders the flow geometry incredibly complex, which in turn can, and often does, lead to interesting and peculiar reactive transport. For instance, the stretching and folding of the reaction front due to flow shear can enhance the effective reactivity, and flow stagnation spots can serve as sites for accummulation of reactants.

At the Darcy scale, the spreading of the front is controlled by hydrodynamic dispersion, which is a continuum scale manifestation of the pore scale interaction between heterogeneous advection and molecular diffusion. When the flow field is uniform, the consequence of dispersion is only a quantitative enhancement of diffusion. However, if the flow field varies in space, as may occur for example during aquifer remediation by injection of a neutralizing agent, the effect of hydrodynamic dispersion will lead to qualitative modifications in reactive transport dynamics as compared to hypothetic scenarios where the only diffusive mechanism is molecular diffusion. Yet, despite the ubiquity of dispersion, its impact on reactive fronts in porous media has not been addressed for flows with an axisymmetrical geometry, which are typical of well injection scenarios.

Therefore, we study the impact of hydrodynamic dispersion on reactive transport in cylindrically-advected bimolecular reaction fronts. We show that, in the reaction-limited regime at early times, mechanical dispersion is the dominant transport process and augments the reaction front’s advancement (which scales as t^1/3, t being the time), the reaction rate (which scales as t^2/3) and the product mass (which scales as t^5/3), in comparison to a dispersion-free scenario (for which, the reaction front advancement, the reaction rate and the product mass scale as t^1/2, t¹ and t² respectively). On the other hand, depending on the strength of hydrodynamic dispersion, we may encounter a dispersion-dominated, mixing-limited, regime of the reactive front at large times, which exhibits a declining reaction rate. This bevahior is significantly different from the dispersion-free scenario where a declining reaction rate is never encountered. Lastly, at sufficiently long times (longer for stronger dispersion), the reaction front transitions to a behavior akin to that seen in the dispersion-free scenario, wherein the differences between the dispersive and the dispersion-free scenarios become negligible.

How to cite: Karan, P., Ghosh, U., Méheust, Y., and Le Borgne, T.: Early Time Effective Reactivity of Reactive Transport in Cylindrically-Advected Reaction Fronts is enhanced by Hydrodynamic Dispersion, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-17037, https://doi.org/10.5194/egusphere-egu23-17037, 2023.

Fate and transport of colloids and bio colloids in structurally heterogeneous porous media are known to exhibit anomalous behaviours such as non-Gaussian breakthrough curves. Classical approaches, like Colloid Filtration Theory, relies on spatial averaged quantities, neglecting flow topology heterogeneity brought about by both local pore scale surface irregularities and broad pores size distribution: two potential triggers for super diffusive effects and broad trapping time distributions. Recent theoretical work has tried to address these deficiencies by modeling deposition and flow variations as stochastic processes (Miele et al., Phys. Rev. Fluids 2019; Bordoloi et al., Nat. Commun. 2022). However, experimental evidence to demonstrate its validity for 3D geologic structures is still lacking. We thus design a novel experimental set-up to assess colloid fate transport under realistic structural heterogeneity with controlled laboratory conditions. Heterogeneous pore structures are first obtained from X-ray tomography of field samples and are subsequently 3D-printed at high resolution. Column transport experiments with gold (Au) nanoparticles are then conducted at different flow regimes, from which effluent concentration (at the macro scale) and colloid deposition (at the pore scale) are collected. These empirical data are complemented with pore network analysis that parametrizes the co-presence of preferential channels and stagnant cavities and, further, validates the stochastic model of interest. The findings shed light on the main drivers and structural hotspot for colloid filtration in realistic porous media.

How to cite: Miele, F., Patino, J., and Morales, V.: Surface Induced Anomalous Transport of Nanoparticle in 3D Printed Structurally Heterogeneous Soils: coupling experiments and stochastic models, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-16451, https://doi.org/10.5194/egusphere-egu23-16451, 2023.

A large fraction of greenhouse gases (about 60%) released into the atmosphere are due to CO₂ emissions from industrial processes and the burning of fossil fuels [1]. One of the strategies employed to reduce the emissions is rapping them securely in the subsurface [2-4]. Dissolution trapping, in particular, involves injection of CO₂ into the subsurface where the supercritical CO₂ (sCO₂) dissolves in the aquifer brine and forms a CO₂ enriched layer within solution. The interface between the high density CO₂ rich brine on the top and the ambient low density aquifer water below results in destabilization of the aforementioned layer [2-4]. This leads to a gravitational instability which then causes a natural convection of CO₂ rich brine to lower layers, thereby accelerating further dissolution of the sCO₂ into the fresh brine.

The study of Brouzet et al. shows that traditional continuume scale, Darcy law-governed, models underestimate the timescales of the convective dissolution’s dynamics, owing to local heterogeneity in the pore-scale flow, and that it may thus be necessary to take pore-scale fluctuations into account [5]. We present here a 2D experimental study using miscible analog fluids with a contrast in densities to understand the convective transport of the dissolved sCO₂. The fluids and the granular media are refractive index matched, which renders the medium transparent and helps in accurate quantification of experimental findings at various Rayleigh (Ra) and Darcy numbers (Da). Darcy scale simulations are used to complement the two-dimensional experimental measurements and it was found that Darcy scale simulations underpredict the experimental findings by several orders of magnitude, which is consistent with the findings by Brouzet et al. We investigate convective dynamics for various values of the number by changing the density of fluids, the properties of the granular medium (permeability, size of the granular medium) which determines the size of the instability with respect to pore size. When that number is much smaller than 1, obvious causes for the failure of the continuum scale description can be excluded, yet discrepancies remain between the experimental results and the simulations.

References:

[1] Contribution of Working Group III to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change, IPCC 2014.

[2] Emami-Meybodi, H., Hassanzadeh, H., Green, C. P., & Ennis-King, J. (2015). Convective dissolution of CO₂ in saline aquifers: Progress in modeling and experiments. International Journal of Greenhouse Gas Control, 40, 238-266.

[3] Pau, G. S., Bell, J. B., Pruess, K., Almgren, A. S., Lijewski, M. J., & Zhang, K. (2010). High-resolution simulation and characterization of density-driven flow in CO₂ storage in saline aquifers. Advances in Water Resources, 33(4), 443-455.

[4] Meunier, P., & Nadal, F. (2018). From a steady plume to periodic puffs during confined carbon dioxide dissolution. Journal of Fluid Mechanics, 855, 1-27.

[5] Brouzet, C., Méheust, Y., & Meunier, P. (2022). CO₂ convective dissolution in a three-dimensional granular porous medium: An experimental study. Physical Review Fluids, 7(3), 033802.

How to cite: Ashraf, S., Dhar, J., Nadal, F., Meunier, P., and Méheust, Y.: Experimental characterization of Rayleigh-Taylor convection in granular media for CO2 sequestration by dissolution trapping, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-17523, https://doi.org/10.5194/egusphere-egu23-17523, 2023.

The displacement of one fluid by another in porous media is of interest in reservoir engineering, groundwater remediation, and subsurface heat recovery. In several instances, i.e. in coarse or macro porous media, or in heavily fractured rocks, the threshold Reynolds number is exceeded and inertial effects cannot be neglected. Consequently, the Forchheimer extension of Darcy’s law describes the motion, and a novel quantity, the Forchheimer or inertial coefficient, enters the picture, entailing implications on several coupled phenomena. We study plane gravity currents propagating in a homogeneous porous medium of given permeability saturated with a lighter fluid, but results are also valid for the displacement of a heavier ambient fluid (brine) by a lighter one advancing below the roof of a porous layer such as in CO₂ injection. The injected fluid volume is given by a global conservation of mass and varies as a power-law function of time. Under the lubrication approximation, the pressure gradient is hydrostatic and the one-dimensional transient problem governing the current depth, when expressed in dimensionless form, depends uniquely by a pure number equal to the combination of a Reynolds number multiplied by a Forchheimer number and divided by the square of a densimetric Froude number. We explore the two limit cases of dominating inertial effects or prevailing viscous effects and demonstrate that in both cases the governing equations are amenable to a semi-analytic similarity solution governed by the aforementioned pure number. For a current with constant volume, the solution takes a closed form. 

How to cite: Di Federico, V., Lenci, A., and Majdabadi Farahani, S.: Forchheimer gravity currents in porous media, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-15397, https://doi.org/10.5194/egusphere-egu23-15397, 2023.