Micro-CT imaging and pore-scale modelling have developed rapidly over the last decade by bridging the disciplines of geology, reservoir engineering, image processing, and computational fluid dynamics. They have provided new pathways for understating complex transport phenomena in heterogeneous geological formations. However, direct simulation of flow in these complex three-dimensional geometries can be difficult and time-consuming. Machine learning and Convolutional Neural Networks (CNN), as a part of the broader field of Artificial Intelligence (AI), can be integrated into the framework of pore-scale modelling. We propose a neural network architecture that considers features of the rock geometry as well as the conservation of mass and predicts the velocity distribution on the images. The method can be applied to two or three-dimensional rock images. The reliability of the flow prediction is studied by comparing the predicted permeability versus ground truth values as a bulk measure. Then, we study the accuracy of solute transport modelling. The results show that velocity fields obtained by CNN can have a considerable degree of error and are not suitable for accurate transport simulations. Finally, challenges and opportunities for the development of machine-learning approaches in porous media applications will be discussed.

How to cite: Mostaghimi, P., Wang, Y. D., Chung, T., and Armstrong, R.: Application of machine learning in predicting flow and transport in porous media, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-4072, https://doi.org/10.5194/egusphere-egu23-4072, 2023.

Solute mixing is efficient in a steady three dimensional porous media flow, since filaments of solute elongate exponentially fast in time. This "chaotic" elongation enables molecular diffusion to rapidly distribute solute concentrations. In two dimensional steady flows, such as through thin fractures in rock, existing knowledge indicates that filaments of solute elongate much more slowly than exponentially, meaning the mixing is far less efficient. Here, we present experimental evidence that when porous media flows are instead unsteady, two dimensional mixing becomes chaotic.  Using 3D printed model porous media with steady longitudinal and oscillating transverse flow components, we measure Lyapunov exponents of filament elongation and quantify solute stretching and folding statistics as a function of the frequency and amplitude of the transverse flow. We find resonances in mixing frequency which are consistent with numerical simulations of the model geometry. These findings improve our understanding of mixing in geological systems and provide insights which may be useful to design efficient geologically-inspired mixing devices in the future.

How to cite: Pierce, K., Linga, G., and Moura, M.: Chaos in flatland: mixing in unsteady two dimensional porous media flow, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-11598, https://doi.org/10.5194/egusphere-egu23-11598, 2023.

How to cite: Dell Oca, A. and Dentz, M.: Mechanisms of Solute Mixing in Darcy’s scale Heterogeneous Formations, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-6771, https://doi.org/10.5194/egusphere-egu23-6771, 2023.

The advection-dispersion equation has been a key tool for modelling Darcy-scale solute transport. In the equation, local-scale mixing is expressed by the local dispersion coefficient, which considers mixing by molecular diffusion and pore-scale variability in flow velocity [1]. Mixing is enhanced by velocity variability on the Darcy scale, represented by spatial heterogeneity in hydraulic conductivity (K) [1].

     Observations show that the dispersion coefficient increases with the spatial scale [e.g., 2]. This effect is expressed by the macrodispersion coefficient increasing proportionally to the correlation length of heterogeneity in K [2]. Conventional upscaled advection-dispersion models assume constant macrodispersion coefficients [2], yet they typically overestimate the dispersive effect and can cause problems such as “back dispersion”, an unrealistic spreading of the solute in the direction opposite to the flow when groundwater flows towards a high concentration zone [3]. Explicitly representing local scale medium heterogeneity mitigates the overestimation of dispersion, however, this downscaled approach (hereinafter called the “local dispersion model”) requires the full representation of heterogeneity in K with a high spatial resolution. This comes at a high computational cost in numerical simulation whereas the detailed representation of the full K variability on the field scale is typically not feasible.

     Dentz et al. [4] showed that the effective dispersion coefficient (D) evolves temporally and asymptotically reaches a macrodispersion coefficient. They derived explicit analytical expressions for an idealized setting with an isotropic velocity spectrum in a steady state and constant local dispersion. From this finding, we hypothesise that accounting for the temporal evolution in D can mitigate the overestimation of dispersive processes in the macrodispersion model. Prospecting further applications to complex settings, this study aims to find an empirical formulation of the time-evolving dispersion (TED) coefficient. In this model, D is set to be identical to the molecular diffusion coefficient at the initial stage, and then it increases exponentially over time and asymptotically reaches a value identical to the macrodispersion coefficient after sufficient time has elapsed. We implemented the TED model by modifying the MODFLOW [5] source code and compared the simulation results with those from the macrodispersion and local dispersion models.

     The results from the TED model showed concentration distributions similar to the local dispersion model and less dispersive than those from the macrodispersion model, especially at early times in the simulations. The temporal evolution of D assumed in the TED model well matched that calculated from the spatial variance of the concentration distributions obtained by the local dispersion model. Therefore, the TED model can be an alternative to the conventional models for modelling Darcy-scale solute transport.

References

[1] Dentz, M., Hidalgo, J. J., & Lester, D. (2022). Transport in Porous Media.

[2] Gelhar, L. W. & Axness, C. L. (1983). Water Resources Research, 19(1), 161–180.

[3] Konikow, L. F. (2011). Ground Water, 49(2), 144-159.

[4] Dentz, M, Kinzelbach, H., Attinger, S., & Kinzelbach, W. (2000). Water Resources Research, 36(12), 3591–3604.

[5] Langevin, C., Hughes, J., Banta, E., Provost, A., Niswonger, R., & Panday, S. (2017). MODFLOW 6.

How to cite: Tajima, S., Tokunaga, T., Liu, J., and Dentz, M.: Time-evolving dispersion (TED) model: towards a more realistic representation of Darcy-scale mixing in porous media, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-10148, https://doi.org/10.5194/egusphere-egu23-10148, 2023.

Being the world’s largest freshwater resource, groundwater is at a continuous risk of overabstraction for human water use. Beside substantial drops in groundwater levels that are the consequence of unsustainable groundwater abstraction, which modify the recharge/discharge relationships between large-scale hydrogeological units, this anthropogenic hydraulic forcing is also responsible for changes in thermal regimes within the critical zone. While the impact of global groundwater pumping on the hydrogeological cycle has long been demonstrated, we still have insufficient knowledge on the influence of human activities on groundwater temperatures and, as a consequence, on stream thermal regimes and groundwater quality.

In this contribution we discuss temperature anomalies that develop in the shallow subsurface as a result of localized groundwater extraction. We study different hydrogeological settings, i.e., porous and fractured aquifers, that we explore via numerical modelling and comparison with field observations. In the field, we use repeated temperature-depth borehole profiles separated by decades, the advantage of which is that differencing the temperature logs for individual boreholes yields real temperature change and eliminates steady-state sources of curvature. Thus, it enables us to detect changes in subsurface thermal regimes, resulting from transient conditions, i.e., climate change and changes in groundwater hydrodynamics.

How to cite: Klepikova, M., Bense, V., Bour, O., Guiheneuf, N., and le Borgne, T.: Impact of groundwater abstraction on subsurface thermal regimes, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-16362, https://doi.org/10.5194/egusphere-egu23-16362, 2023.

Back diffusion of chlorinated solvents from low permeability media remains a challenge to remediation of contaminated groundwater in heterogeneous subsurface environments. Naturally occurring abiotic dechlorination of trichloroethene (TCE) has shown potential as a viable natural attenuation mechanism, particularly at sites where in-situ remediation technologies have generated reducing conditions favorable for the generation of reduced iron minerals. These abiotic processes may occur under anaerobic conditions or aerobic conditions when oxygen is introduced to reduced sediments. Quantification of aerobic/anaerobic abiotic dechlorination rate constants to date has generally been performed using bench-scale batch experiments with low solids to water ratios and well-mixed conditions, confounding extension of the results to the field where mass transfer limitations dominate.  To address this knowledge gap, bench-scale experiments were conducted to evaluate diffusive transport of TCE and coupled aerobic/anaerobic abiotic dechlorination. The natural clays used in this study were collected from several chlorinated solvent impacted sites and characterized for geochemical parameters including ferrous iron content, electron shuttle mediated oxidation-reduction potential (ORP), and mineralogy via X-ray diffraction (XRD). Clays were packed into gas-tight serum bottles under anaerobic conditions to a saturated bed depth of 4 centimeters, and TCE was injected at the top of the clay beds. For the aerobic experiments, a slug of oxygenated water was introduced at the top of the clay immediately prior to spiking with TCE. Headspace and aqueous samples were periodically collected and monitored for reduced gases and organic acids associated with abiotic transformation of TCE in the presence of ferrous minerals. ¹⁴C-radiolabeled TCE was used for select experiments to facilitate detection of dechlorination products at low concentrations indicative of conditions near a dilute solvent plume.   Accumulation of expected TCE dechlorination products under aerobic (organic acids) and anaerobic (primarily acetylene) conditions was observed in the diffusion experiments. Detection of ¹⁴C dechlorination products served to clearly distinguish compounds originating from TCE. A one-dimensional coupled reaction and diffusion model was developed to describe diffusive transport of TCE and dechlorination products into and out of the clay bed. First order abiotic dechlorination rate constants were determined by fitting profiles of reduced gas and organic acid generation over time, using literature values for molecular diffusion coefficients and clay tortuosity. Following conclusion of the experiments, depth-discrete ORP measurements of the packed clay beds from the aerobic diffusion experiments will be conducted, providing further insight into the effect of oxidative TCE transformation on local geochemistry near the groundwater table and the relative contribution of aerobic abiotic degradation. The results of this study elucidate the capacity for abiotic natural attenuation to reduce TCE mass flux out of clays in dilute plumes under a variety of geochemical conditions.

How to cite: Werth, C., Blount, T., Kearney, K., Tran, D., and Schaefer, C.: Impact of Abiotic Attenuation Reactions on Chlorinated Solvent Fate in Diffusion-Limited Clay Lenses, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-111, https://doi.org/10.5194/egusphere-egu23-111, 2023.

The movement of solute or chemical species into the subsurface has been a concern of groundwater quality variation due to its hazardous and severe health-related effects. To understand and reliably predict the migration and fate of contaminants in the subsurface, modeling is necessary. In this study, the experiment is carried out to investigate the contaminant migration through porous media, particularly the solutes emerging through the pesticides. A soil column experiment is setup to trace the particles and their behavior is analyzed, which is validated using the numerical model. This model uses the advection-dispersion equation (ADE), taking the application of effective dispersivity in order to account for the local heterogeneity. The implicit finite difference technique has been incorporated into the numerical model. The implication of macrodispersivity provides a plentiful assay in delineating the transport process and a perspective for large-scale heterogeneities. Results exhibit the concentration profiles of pesticides in the function of depth and time that can be employed to identify the areas with higher contaminant loading in the groundwater, posing a severe threat to groundwater and human health. This necessitates the experimental and numerical model to predict the contaminant migration process and to lay down changes in policy-making, monitoring of harmful chemicals, adoption of good agricultural practices, and execution of water safety regulations which, in turn, can be incorporated in determining the emerging contaminants, PFASs, etc.,  in the groundwater.

How to cite: Gupta, K. R. and Sharma, P. K.: Unraveling the leaching of pesticide transport through porous media with an experimental and numerical study, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-640, https://doi.org/10.5194/egusphere-egu23-640, 2023.

A combined analysis was conducted to understand nitrogen loading to a deep (~ 80 m below ground level (bgl)) bedrock aquifer, including hydrochemical, isotopic, microbiological, hydrogeological, and geophysical investigation. The studied site, located in a suburban area, had been used to grow fodder crops for cattle and fertilized with cattle manure. The geology consists of Gyeonggi gneiss complex, fine-grained granite, and alluvium, while the surface is covered by loess deposits. Four boreholes (BH-1~4) were installed in 2018-2019, and geological, hydrogeological and geophysical surveys were conducted. Then hydrochemical, isotopic and microbiological properties were quarterly studied for 4 years at both shallow (~ 30 m bgl) and deep (~ 80m bgl) groundwater in each borehole as well as a pre-existing well. Groundwater levels were automatically monitored using levelogger. The initial depth to groundwater was 20.4 – 24 m bgl. As a result, high concentrations of nitrate were consistently observed in deep groundwater (35.3±16.0 mg/L; n=59) as well as shallow groundwater (50.9±16.8 mg/L; n=60) and a pre-existing well (44.3±6.8 mg/L; n=16). Based on N isotopes of nitrate (8.9-19.0‰; n=27), nitrogen mainly came from manure or sewer. The enrichment of ¹⁵N along with decreasing dissolved oxygen and nitrate in deep groundwater indicated denitrification in deep subsurface. Meanwhile ammonium and nitrite were exceptionally high in two deep groundwaters (BH-1d; BH-4d) where fecal coliforms were also occasionally detected. δ¹⁵N of ammonium were 9.2 and 14.0‰ in BH-1d and BH-4d, respectively. The hydrochemical, isotopic and microbiological results indicate that the vertical transport of contaminants from surface to deep groundwater is significant in the study area, probably through permeable fractures, given that the integrated interpretation of seismic data and electricity resistivity with geological data suggested fractures in deep weathered soil zones (down to 48 m bgl) and soft rocks. In addition, the borehole logging identified permeable fractures in hard rocks at high dips particularly in BH-1 and BH-4 in the west (up to 72. 9 degree). The natural gamma ray and P-wave velocity were higher in the west, indicating the different geology from the east (BH-2 and BH-3). Besides, the groundwater levels were fluctuated at BH-1d and BH-4d, due to groundwater extraction nearby. This combined examination of hydrochemical, isotopic, microbiological, hydrological, and geophysical characteristics suggests a scenario of contaminant transport from surface to deep subsurface through permeable fractures, which is enhanced by groundwater pumping. The integrated analysis is expected to be useful for subsurface characterization in crystalline bedrocks. <Acknowledgement> This study was supported by the basic research project of Korea Institute of Geoscience and Mineral resources (KIGAM) funded by the Ministry of Science and ICT of Korea (No. 23–3411) and by the Korea Environment Industry & Technology Institute (KEITI) through the Subsurface Environment Management Research Project (No. 2021002440003).

How to cite: Yu, S., Kim, H.-S., Shin, J., and Yun, S.-T.: A combined analysis of hydrochemical, isotopic, microbiological and geophysical characteristics for assessment of nitrogen loading to a deep crystalline bedrock aquifer, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-17347, https://doi.org/10.5194/egusphere-egu23-17347, 2023.

The aim of the present work is to extend the existing overlay and index method for aquifer vulnerability assessment to groundwater transport. This novel procedure falls into the category of “hybrid” methods since it combines the overlay and index methods, that considers only vertical transport through the vadose zone, with the horizontal transport through groundwater. Based on a simple probabilistic analysis, we can use any overlay and index method for the assessment of the probability that the contaminant reaches the groundwater then such probability is propagated within the aquifer using the piezometric surface as proxy of the groundwater flow. For this purpose, geomorphological methods, usually available in Geographic Information Systems (GIS) software, were used. This study leads to the definition of a new index called combined vulnerability index υ which considers the transport of the contaminant from soil surface that takes care of both transport in the vadose zone and the aquifer. The procedure is applied to a groundwater catchment area in the Campania region (Southern Italy) with the use of QGIS software. The method is independent from the index and overlay method used and the hydraulic characteristics of the aquifer. Furthermore, this procedure is simple as it requires a few data and it can be used to analyze large areas, demonstrating its effectiveness in assessing the intrinsic vulnerability of groundwater.

How to cite: Pomarico, I., Fiori, A., Zarlenga, A., Catani, V., and Leone, G.: The combined vulnerability: a novel hybrid index for the aquifer vulnerability assessment, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-1013, https://doi.org/10.5194/egusphere-egu23-1013, 2023.

Simulating hydrodynamic reactive transport processes in heterogeneous systems is required
in various research fields and applications including environmental remediation, geological
storage, and energy production. Developing reliable numerical tools for these environmental
issues requires to consider both the structural heterogeneities encountered in the natural
environment, and the complexity of the (bio)geochemical reactions associated with each
application. The former is very often modeled at the expense of the latter, in particular when
studying large-scale heterogeneous systems such as fractured rocks for which most of the
modeling effort focuses on the multi-scale structural heterogeneities. These features are
responsible for anomalous transport behavior that is well reproduced by particle-based (PB)
methods with optimized computational cost. After introducing PB methods that are usually
used for modeling reactive transport in fractured rocks, I will present a new random walk
approach that is designed for complex (bio)geochemical reactions and upscaling purpose.

How to cite: Roubinet, D.: Reactive transport models in heterogeneous systems from pore to reservoir scale, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-17468, https://doi.org/10.5194/egusphere-egu23-17468, 2023.

Convection and chemical dissolution in porous media are observed in many hydrogeological processes such as seawater intrusion in coastal aquifers, CO₂ sequestration in saline aquifers and heat transport in geothermal reservoirs. When a porous medium is infiltrated by a fluid contaminated with a reactive solute, convection is accompanied by dissolution of the porous matrix through chemical reactions between the solute and minerals contained in the porous solid, generating reaction products. Here we study how density-driven convection and reactive infiltration affect the transport of the solute and products in the porous medium. Convection and dissolution are modelled by coupled equations describing flow, transport of the solute and products, and mineral dissolution in a two-dimensional rectangular domain with a solute source located along half of the upper boundary. We quantify the average solute flux from the source in unsteady flows and analyze its development towards a steady-state value computed in [1]. Numerical experiments on the temporal development of convective flow and concentration fields are reported (see [2] for more details). The full numerical solutions are augmented with asymptotic analysis in a weakly convective and reactive regime performed in the limit of small Rayleigh and Damköhler numbers.

Acknowledgement:

This work was supported by the Slovak Research and Development Agency under the contract no. APVV-18-0308, and the VEGA project no. 1/0339/21 and the GUK project no. UK/355/2023.

References:

[1] van Reeuwijk, M., Mathias, S. A., Simmons, C. T., and Ward, J. D.: Insights from a pseudospectral approach to the Elder problem, Water Resources Research, 45, W04416, https://doi.org/10.1029/2008WR007421, 2009.

[2] Hurtiš, R., Guba, P., and Kyselica, J.: Simulation of reactive groundwater flow and salinization in carbonate-rock aquifers, 2022 International Conference on Electrical, Computer and Energy Technologies (ICECET), Prague, Czech Republic, 20–22 July 2022, pp. 1–4, https://doi.org/10.1109/ICECET55527.2022.9872944, 2022.

How to cite: Hurtiš, R., Guba, P., and Kyselica, J.: Density-driven convection and chemical infiltration in saturated porous media, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-14696, https://doi.org/10.5194/egusphere-egu23-14696, 2023.

Geomaterials are multi-phase materials composed of solid skeletons and pore fluids. Along the solid-fluid interfaces, chemical dissolutions might occur which tends to weaken the strength of geomaterials and can potentially cause catastrophic failures. As the ionic species in the pore fluid evolve during dissolution, we introduce the mass fractions of all the ionic species as independent state variables into the hydrodynamic procedure and develop a mathematically rigorous and thermodynamically consistent modeling framework to address the impact of solid dissolutions on the constitutive properties of poroelastic geomaterials. The development is foundational in that it focuses only on saturated poroelastic systems without accounting for particle crushing, localized plasticity, and surface tensions. However, the theory can be further expanded to deal with such inelastic features under various saturation regimes. For simplicity, the density-dependent linear elasticity is adopted whereby the stiffness degrades as the solid skeleton dissolves and pore fluid pressure is governed by both osmolarity and compressibility. The developed model can naturally recover fluid-related dynamics of Darcy's law, Fick's law, and the law of chemical kinetics. Finally, experimental observations of debonding tests of calcarenite under both oedometric and unconfined conditions are used to validate the model performance.

How to cite: Chen, Y., Guillard, F., and Einav, I.: A hydrodynamic model for chemical dissolution of poroelastic materials, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-17007, https://doi.org/10.5194/egusphere-egu23-17007, 2023.

This study attempts to give some answers on how the electrical signal is impacted by conduit formation in limestone due to calcite dissolution, and how the electrical properties can be related to evolving structural parameters. Ensuring sustainable strategies to manage water resources in karst reservoirs requires a better understanding of the mechanisms responsible for dissolution features in the rock mass. The dissolution of carbonate core samples caused by CO2 or acid solution injection has already been well studied in the laboratory to understand the formation of conduits and their intricate coupling with transport properties such as permeability and porosity. However, these experiments generally rely on image analysis, an accurate technique that cannot be used in the field. Additionally, in a subsurface context, chemical analysis of the pore water can be quite intrusive, providing only restricted and spatially limited information. Thus, studying large-scale heterogeneities such as karst environments can benefit from the use of non-invasive tools such as the ones proposed in hydrogeophysics. In particular, geoelectrical methods are good candidates to detect the emergence of karstification related to the heterogeneous dissolution of large volumes since they present a high sensitivity to the physical and chemical properties of both porous matrix and interstitial fluids. We monitored the electrical conductivity, porosity, and permeability of two limestone core samples during controlled dissolution experiments driven by acid injection at atmospheric conditions under different flow rates creating preferential conduits. These two samples were also characterized before and after the acid percolation with laboratory methods and CT scan imaging. First, we confront the electrical conductivity variations to the evolution of permeability with time. We show that monitoring electrical properties allows us to sense the impact of dissolution in the porous medium long before the sample is percolated. This result is a key finding to highlight the great interest that electrical properties can represent in monitoring reactive percolation in karst systems. Then, we interpret the monitored electrical conductivity of the acid percolation with a physics-based model. This model describes the porous medium as a fractal cumulative distribution of tortuous capillaries with a sinusoidal variation of their radius. According to the model description, the sample electrical conductivity is interpreted in terms of effective structural parameters which are tortuosity and constrictivity. Confronting the model with the experimental results shows that the electrical signature of calcite dissolution is more impacted by the evolution of constrictivity than by tortuosity, while most of the literature focuses on the tortuosity and even neglects constrictivity when describing the pore space complexity with electrical conductivity measurements. Finally, based on our experimental results and data sets from the literature, we show that the characteristic Johnson length is a valuable structural witness of calcite dissolution impact linking electrical and hydrological properties. This small-scale approach to heterogeneous dissolution is an analog of the natural processes involved in forming conduits by dissolution leading to karstification. The results of this study are transferable to large-scale applications such as the survey of karst formation, CO2 geological storage, and geothermal energy recovery.

How to cite: Rembert, F., Leger, M., Jougnot, D., and Luquot, L.: Assessing karst formation at the laboratory scale by confronting geoelectrical and hydro-chemical monitoring, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-9735, https://doi.org/10.5194/egusphere-egu23-9735, 2023.

Calcium carbonates precipitation plays an important role in several geological, biogeochemical and engineered processes. It has been extensively studied for its application in remediation of contaminated groundwater, enhancing oil and gas recovery, improving geological carbon storage, reducing leakage in tunnel buildings and also to understand dissolution processes in coastal karst aquifers. Most of these works are based on theoretical formulations,  numerical simulations or batch/column experiments and little experimental evidence under transport conditions are reported in the literature. In this work through mixing-induce precipitation experiments we propose the visualization and characterization of the dynamic of precipitation processes focused on the understanding of its influence in solute breakthrough. We performed the experiments in a transparent horizontal cell flow made of plexiglass with 26 x 20 x 1 cm dimensions. The tank was disposed horizontally and filled with glass beads of 2 millimeter. The flow-cell was initially saturated with double-deionized water. In the experimental investigation, two different chemical solutions containing 0,1 M CaCl₂ and 0,1 M NaCO₃ were injected in two separate inlet ports. Color tracer tests consisted on fluorescein were injected before and after the precipitation experiment with the objective of visualizing and quantifying the impact of precipitation in solute transport. We evaluated the effectiveness of the standard solute transport equation to represent precipitation processes and developed new mechanistic transport models.

How to cite: Gonzalez-Subiabre, G., Fernàndez-Garcia, D., Trabucchi, M., and Reales-Nuñez, D.: Precipitation of CaCO3 through induced mixing and its impact on solute breakthrough, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-6162, https://doi.org/10.5194/egusphere-egu23-6162, 2023.

Advent of pre-exascale and exascale computers opens possibility for much higher resolution simulations of porous media flows. During the launch phase of the LUMI supercomputer, a number of simulations of wormhole growth commenced with an aim to use as much spatial information as possible with up to 1e9 DOFs. The goal was to investigate if properties of growing wormholes could be recovered if sufficient resolution is assured. Samples used in this study underwent experimental studies. They were scanned before and after the experiment, as well as during the dissolution. This 4D tomographic data provided necessary input for high-res simulations as well as validation framework.

Since dissolution fingers dramatically increase permeability of the rock, wormholing is important both for industrial applications and in hydrogeological studies. The main problem in modeling of wormholing is a multi-scale character of this process, with flow and transport near a wormhole tip strongly coupled to the macroscopic geometry of the emerging structures. The ability to perform large scale parametric and sensitivity studies of wormholing constitutes thus an important addition to experimental studies, hence the need for a high throughput simulator. 

We test our numerical predictions against the data from time-lapse dissolution experiments in an aim of constructing a predictive model capable of recovering time evolution of 3D wormhole shape based on the initial X-ray tomography data. 

How to cite: Dzikowski, M., Szymczak, P., and Sharma, R.: Empowering pre-exascale computers for Darcy-Brinkman simulation of wormhole growth based on X-CT data - can we recover experiments?, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-739, https://doi.org/10.5194/egusphere-egu23-739, 2023.

The Northern Alpine Foreland Basin (NAFB) in southwest Germany is home to more deep geothermal plants than any other region in the country. The upper Jurassic, its main aquifer, consists of permeable carbonates which bear waters with temperatures of up to 150 °C on the southern border, and total dissolved salts values of up to 2 g/L. Geothermal applications in the NAFB include medical spas, geothermal district heating and power generation.

In the case of heating and power generation, cooled-off waters are reinjected underground where rock-fluid interactions can lead to changes in the rock matrix and flow pathways. These interactions are thus an important factor to consider in the maintenance of geothermal plants. In carbonate systems, a decrease of temperature after heat extraction leads to an undersaturation of the previously equilibrated waters with regard to the host formation. The injected water dissolves the rock matrix along the borehole and the flow paths into the reservoir. This can increase the risk of a thermal breakthrough between injection and production well and possibly affect the borehole integrity. While the overall amount of dissolution has been monitored and modelled previously, the microscopic changes to the flow paths are still under investigation.

We used rock samples coated with a 2-component paint and produced one microfracture in the coating to overcome experimental restrictions due to a limited fluid volume of the autoclave. The experiments were run at typical injection temperatures between 40°C and 75°C. The CO₂ partial pressure wasadjusted to the measured values in the injection borehole. Microscopic and Raman images were taken before and after the exposition of the rock to the undersaturated waters and complemented by hydrochemical analyses.

The dissolution of the limestones picked up microstructures and led to a heterogeneous development of the flow path. In an early stage of the injection, an underprediction of the increase of the hydraulic conductivity is thus expected.

These assessments allow insights into the kinetics taking place at the artificial disturbance, which will make it possible to characterize and quantify the 3-dimensional pattern of calcite dissolution at a localized scale which is important for the development of the hydraulic properties, and affects further dissolution.

How to cite: Dietmaier, A. and Baumann, T.: Local effects of the injection of undersaturated waters in geothermal applications, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-6329, https://doi.org/10.5194/egusphere-egu23-6329, 2023.

Mineral carbonation (MC) has long been suggested as a potential way to permanently store CO₂ captured from smaller/medium emitters, as alternative to conventional geological sequestration in depleted oil and gas fields. MC consist in CO₂ reacting with calcium-, magnesium- and iron-rich minerals to form carbonates.  MC is a promising option in terms of available resources and security of permanent storage. Nevertheless, this technology, tested in laboratories and small projects, has not yet taken off on a large scale. In situ large scale projects can contribute in reducing the knowledge gaps on MC fundamentals and allowing cost analyses and optimization. Since almost a decade CO₂ is injected in Icelandic basalts, providing a field scale laboratory for testing MC. 

The DemoUpStorage, together with its partner project DemoUpCARMA, is a pilot project by ETH Zurich (http://www.demoupcarma.ethz.ch), EAWAG, EPFL and University of Geneva that aims to demonstrate the implementation and scale—up of CO₂ geological storage using MC. The project investigates the fate of CO₂ transported from an emitter in Switzerland to Helguvik (Iceland), where it is then mixed with oceanic water and injected in basalts at a depth of c.a. 400m.  The monitoring involves a combination of technologies that independently but synchronously observe changes in underground. In particular time-lapse acquisitions of different physical parameters (electrical resistivity, seismic P- and S-wave velocity, attenuation factor Q) will be conducted in parallel with fluid geochemistry monitoring and dissolved gas sampling in boreholes. Repeated cross-hole Vertical Seismic Profiling (VSP) will be performed across an array of three boreholes, of which one is the injection and two are monitoring boreholes. Fiber optic technology will be used in parallel to conventional hydrophones. Additionally, a dense, regular grid of seismic sensors will be deployed at the surface during VSP acquisitions with the goal to provide a high-resolution 3D imaging of the subsurface at the reservoir scale. Downhole Electrical Resistivity Tomography logs in one of the two monitoring wells will be repeatedly performed to constrain the build-up of CO₂-related resistivity signatures in conjunction with CO₂ saturation levels monitored by regular fluid sampling. A portable mass spectrometer connected to a borehole will provide continuous gas analysis to determine the temporal evolution of the local fluid dynamics, to validate permanent storage and to monitor for potential leakage.  Risk mitigation actions comprise monitor the background seismicity before, during and after the whole injection operations. Laboratory observations on rock samples from the Helguvik area complete the set of observation and offer the possibility to model at small scale porosity changes due to MC.  Predictive numerical simulations at reservoir scale are performed and will be continuously updated with the acquisition of the data. The start of the injection is foreseen in Spring 2023. 

How to cite: Zappone, A. and Wiemer, S. and the DemoUpStorage Team: The DemoUpStorage Project: monitoring mineral carbonation in Icelandic basalts, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-14256, https://doi.org/10.5194/egusphere-egu23-14256, 2023.