Invited speakers

Fundamentals in flow and transport

René Therrien (Université Laval, Québec, Canada): Fundamentals of Flow in Porous and Fractured Media

This lecture covers the basic concepts of fluid flow in porous and fractured media. The material presented is limited to the fully saturated case, where the pores and fracture space are completely filled with water. Variably-saturated media and multiphase systems are therefore not covered. The different scales for quantifying flow in porous media are briefly presented. The continuum approach for flow in porous and fractured media is then presented. It is the approach used for most applications in hydrogeology and is based on the definition of a Representative Elementary Volume (REV). The properties of a continuous porous medium are presented. The lecture then focuses on groundwater flow, which requires the definition of the energy components of groundwater, leading to the definition of hydraulic head. Darcy’s Law is discussed and various forms are presented, from the simple form proposed by Darcy to a fully 3D representation. The continuity equation for flow in a fully-saturated porous media is derived and various simplifications used for specific applications are presented. The lecture concludes with basic concepts describing flow in fractured media, including flow in single fractures and the various conceptual models available to represent fractured porous and non-porous media.

Tomás Aquino (CSIC, Spain): Fundamentals of transport in saturated media

Transport phenomena are at the core of a great many processes in the hydrogeosciences and beyond, ranging from the behavior of nutrient and contaminant plumes to heat transport. This lecture will focus on the basics of solute transport in saturated flows, although the derivations we will cover apply just as well to transport of other scalars such as temperature. We will begin by deriving the advection-diffusion equation as a consequence of mass conservation, followed by the derivation of some fundamental solutions. First, we will consider transport in an infinite, one-dimensional medium following an instantaneous point injection. Next, we will illustrate the importance of the resulting Green's function solution as a building block for more complex problems by considering a continuous injection. Finally, we will treat advection-diffusion in a shear flow. Because shear flow can be seen as a local linearization of the flow field, it also plays an important role in more complex scenarios. We will use this solution to motivate the concept of mechanical dispersion, and, to further make the connection to mixing, we will finish by discussing stretching-enhanced diffusion in terms of the Ranz transform.

Camille Bouchez (University of Rennes, France)

Fundamentals in unsaturated and multiphase flow

Dani Or (ETH, Switzerland): Capillary Processes in Porous Media 

The presentation will introduce concepts of energy state of water in porous media (water potential) and highlight the origins of interfacial processes and capillarity in soil and rocks. We will discuss capillary rise dynamics (including inertial effects) and water retention in angular pores. The phenomenon of water film adsorption and its separate contribution to water retention. The importance of water characteristic curve and its parametric models (van Genuchten, Brooks-Corey) used for modeling and representation of soil hydraulic properties for different soil types and global databases will be presented. We will emphasize the narrow range of hydration conditions that support biological functioning in porous media (water films, connectivity and relative humidity) and mention capillary effects on the mechanical behavior of granular media.

Joaquin Jimenez-Martinez (Eawag and ETH, Switzerland): Solute mixing and chemical reactions in unsaturated and multiphase flows

Understanding chemical mixing and reactions in the unsaturated zone (soil and vadose zone) is critical for life-sustaining resources, protection of groundwater, and remediation efforts. A non-wetting immiscible phase (i.e., air) within the pore space can remain immobile, giving rise to the so-called unsaturated flow or moving, resulting in a multiphase flow. In this lecture, we describe the impact of saturation (fraction of the pore volume occupied by the wetting phase) and multiphase flow (stationary two-phase flow) within the pore space on fluid-fluid (mixing-driven reactions) and fluid-solid (adsorption and dissolution) reactions. Further, microbial life in the unsaturated zone is exposed to a mosaic of fluid flow velocities and an extremely heterogeneous chemical landscape. This abiotic–biotic coupling plays a key role in soil respiration and applications such as biomineralization. In this lecture, we will try to disentangle some of these couplings.

Jenna Poonoosamy (Forschungszentrum Jülich GmbH, Germany): Rationalizing hydro-geochemical processes at the pore scale

Hydro-geochemical processes such as transport-induced mineralization are important processes governing the evolution of many subsurface systems. These processes can lead to an alteration of permeability, diffusivity, and other physical characteristics of the rock matrix that can have significant effects on subsurface solute and gas transport. Understanding these phenomena at the pore scale is a prerequisite for the development of predictive conceptual approaches for a “close to reality” description of the evolution of the subsurface. Our lab-on-a chip concept, which combines microfluidic experiments and reactive transport modeling diagnostics (Poonoosamy et al., 2019, 2020, Prasianakis et al., 2020) has proven to be a powerful tool for rationalizing these processes. In this work, we present an overview where we have successfully applied this methodology to: (i) evaluate the kinetic and thermodynamic controls on crystallization processes in confined porous media (Poonoosamy et al., 2023); (ii) decode oscillatory zoning exhibited by solid solutions crystallizing in porous media (Poonoosamy et al., 2021), and (iii) parameterize porosity-diffusivity relationships with respect to coupled mineral dissolution-precipitation reaction(Poonoosamy et al., 2022, Loenartz et al., 2023) as well as further opportunities for this approach.

Sophie Roman (Université d'Orléans, France): Microfluidics for geosciences to study the interplay between flow, geochemistry, and colloidal transport in porous media

There is strong interest in understanding hydrogeochemical processes at the pore-scale with application to reservoir engineering, subsurface hydrology, and CO₂ sequestration. The mechanisms and consequences of local processes, such as interfacial jumps, contact-line dynamics, or the coupling between mineral dissolution and flow properties are largely unexplored and not well understood. Using microfluidic experiments, we explore pore-scale mechanisms and their consequences on the upscaling of rock and transport properties. Micromodel systems are transparent pore networks that allow direct and in situ visualizations of pore-scale dynamics. We investigate different two-phase flow invasion mechanisms, and discuss the flow regimes relevant to CO₂ sequestration systems. I will present the couplings between surface chemical reaction and fluid flow by investigating the dissolution of solid minerals. Finally, we show that in the presence of negatively charged particles, these colloids tend to aggregate around a dissolving mineral forming a passivation layer that slows down the reaction process. This could be used to deliver healing materials toward target regions of a porous formation for remediation.

Environmental sensing and hydrogeophysics

Thomas Hermans (University of Gent, Belgium): Hydrogeophysics – Non-invasively sensing water in the subsurface

Electric and electromagnetic geophysical methods are sensitive to the electrical conductivity of the subsurface. The latter is directly influenced by the distribution of fluids in the pore space (water content or saturation), the fluid salinity and temperature, the porosity and tortuosity as well as the composition of the subsurface (presence of clay and organic matter). This makes these geophysical methods ideal to study water-related phenomena in the subsurface. In this lecture, we will review the basic principles of electric and electromagnetic methods, the inversion process required to interpret the data including advanced approaches, with a special focus on monitoring applications (time-lapse). At the end of the lecture, participants should have a feeling about when and how these techniques can be applied, what are their limitations, and if they are relevant to their own project.

John Selker (Oregon State University, USA)

Reactive transport at the interface of rocks, life and water

Jennifer Druhan (University of Illinois Urbana-Champaign, USA): Fundamentals of reactive transport across water-rock-life interfaces

Peter Kang (University of Minnesota, USA): Inertia effects on mixing and reaction in porous and fractured media: From mixing-induced chemical reactions to mineral dissolution and precipitation

Mixing and reaction in porous and fractured media control a variety of natural and engineering processes, including carbon mineralization, cave formation, geothermal energy, contaminant transport, and microfluidics. Subsurface systems commonly contain fractures and conduits that are highways for fluid flow. Typical flow velocities in these systems are sufficiently fast to create inertial flows, which manifest complex flow topologies. However, due to the common perception that porous media and microchannel flows are slow, the effects of fluid inertia are often overlooked in studies of mixing and reaction. In this lecture, I will discuss fundamental concepts for characterizing inertia effects on mixing and reaction, and then focus on unraveling how hydrodynamic conditions control mixing and reaction, including mineral dissolution and precipitation. My lecture will demonstrate how fluid inertia fundamentally changes mixing-induced reactions at the pore scale and how such effects manifest at larger scales. Finally, I will show how improved understanding can lead to engineered solutions for critical problems such as carbon mineralization and fracture sealing.

Ran Holtzman (Coventry University, UK)

Temperature : a critical environmental variable and source of energy

Peter Bayer (Martin Luther University of Halle-Wittenberg, Germany): Spatial and temporal trends of shallow groundwater temperatures 

Worldwide, shallow groundwater temperatures are rising due to the thermal coupling of the subsurface with the warming atmosphere, leading to substantial changes in previously stable thermal regimes. These changes impact groundwater-dependent ecosystems, geothermal potential, and groundwater quality. This lecture will delve into the causes of spatially variable groundwater warming patterns, particularly in urban settings. We will explore both observed and simulated long-term trends of subsurface warming. Building on this understanding, we will learn about opportunities for shallow geothermal use and various technological options.

Qinghua Lei (Uppsala University, Sweden): Multiphysics coupling in geothermal reservoirs

Geothermal energy is recognised as an important contributor to green energy transition. It is of central importance to develop predictive understanding of the multiphysical processes in geothermal reservoirs for ensuring safe and sustainable heat extraction from the Earth. In this lecture, I will first present an overview of the fundamental thermo-hydro-mechanical-chemical processes in fractured crystalline rocks, which are commonly utilised for the development of enhanced geothermal systems. I will discuss the relevant governing and constitutive equations as well as different solution schemes. Then, through a series of application examples, I will demonstrate how a deep understanding of the coupled multiphysical processes could help us explain and predict the performance of enhanced geothermal systems during the stimulation and production stages. The lecture will end with a discussion of the current challenges and future directions.

Maria Klepikova (University of Rennes, France): Impact of anthropogenic forcings on the subsurface thermal regimes

Groundwater is under simultaneous threat from increasing anthropogenic activity such as human water consumption and tunneling as well as from human induced climate change. Besides negative impacts on the hydrogeological cycle, these ongoing forcings are also responsible for changes in thermal regimes of groundwater systems and, as a consequence, on groundwater quality. The major scientific obstacle that prevents accurate understanding of the impact of these forcings on the subsurface thermal dynamics is a dire lack of field observations, i.e., repeated temperature profiles collected over decades. In this presentation, I will present new temperature data series illustrating the complex interplay of climate warming and human-modified (e.g., by abstraction or tunneling) groundwater flow. I will show (1) that hydraulic forcings may have a significant impact on the thermal regime of the critical zone (i.e., the shallow subsurface where the water, element, energy and biological cycles interact), and (2) that depending on hydrogeological conditions and the natural geothermal gradient, this impact might be even more important than that of climate change.

Life supporting functions of porous media

Maciej Zwieniecki (UC Davis, USA)

Trees are natural masters of microfluidics, dwarfing any man-made structures. In a single tree, the number of conduits can exceed hundreds of millions, with a total length of hundreds of kilometers. A large tree can lift hundreds of liters of water from the soil to the leaves per day without any moving parts and over a vertical distance of tens to even a hundred meters. In this lecture, we will focus on the structure and function of these conduits. We will discuss the physics that underlies water transport through plants, which, while not exotic, when applied to the microfluidic wood matrix results in transport regimes operating far outside our day-to-day experience. During the associated practicum, we will examine wood structure and set up experiments to investigate the properties of the porous nature of wood.

Andrea Schnepf (Forschungszentrum Jülich, Germany)

This lecture will introduce models of root architecture, its growth, its structure and function, as well as structure-function relationships. It will discuss the role of plant roots in terrestrial water cycles and follow the flow of water from soil through plants into the atmosphere with the potential gradient as the driving force and regulated by hydraulic conductivities between the compartments of the system. Details of the different parts along this path will be discussed individually, including radial water flow from soil into the root as influenced by the root anatomy, and axial water flow within the xylem as influenced by the anatomy as well as the occurrence of embolism. An additional resistance to water flow may be caused by a drying rhizosphere. Finally, we will combine root and soil hydraulics in macroscopic representations of root water uptake in soil models.

Pietro de Anna (UNIL, Switzerland): Transport and mixing-limited processes in confined and heterogeneous media

Permeable systems are host to a high density and diversity of substances, suspensions and microorganisms: even deep-earth porous rocks provide a habitat for active microbial communities. In these environments, substances transport is controlled by complex flow and govern a broad range of natural and engineered processes, from biochemical cycling to remineralization, bioremediation and filtration. A key property of most porous systems is the underlying heterogeneity that may occur due to non-uniformity in size or shape of the constitutive grains. Here, I will discuss laboratory experiments (based on microfluidics and time-lapse video-microscopy) and numerical models to investigate the microscopic processes of mixing, microbial transport and growth that take place within the confined space of heterogeneously distributed pores. Based on such multi-scale observations, we build new theoretical models to unravel the link between microscopic-scale processes and their macroscopic consequences.

Porous media in the decarbonization

Ruben Juanes (Massachusetts Insitute of Technology, USA): Man-made Earthquakes and the Energy Transition (InterPore’s Kimberly-Clark Distinguished Lecture)

Earthquakes occur when faults slip. While the most devastating earthquakes are of tectonic origin, human activities have been associated with the triggering of earthquakes that have caused substantial economic damage and societal concern. The demonstration that fluid injection can cause earthquakes dates back to the 1970s, but critical gaps remain in our ability to understand and, more importantly, mitigate, the occurrence of induced earthquakes. Here I will discuss some of our recent work employing contrasting approaches to help fill these gaps: from minimal-ingredients spring-slider models that account for poroelasticity to sophisticated multiphysics computational models that integrate disparate datasets and have succeeded at setting management strategies that prevent earthquakes while allowing subsurface operations in a tectonically active field. I will discuss how the lessons learned from these analyses may inform subsurface climate-change mitigation technologies like geological carbon sequestration and hydrogen geostorage.

Samuel Krevor (Imperial College London, UK)

Maartje Boon (University of Stuttgart, Germany)

Biogeochemical exchanges at hydrological interfaces

Audrey Sawyer (The Ohio State University, USA): Biogeochemical Exchanges at Hydrological Interfaces

The exchange of water, chemicals, and heat across aquatic interfaces affects water quality and ecological processes in both surface water and groundwater. Here, I focus on two aquatic settings: rivers and beaches. I discuss the hydrologic forces at work in each environment that shape exchange fluxes across scales. I also highlight opportunities to combine measurement and modeling approaches in order to understand biogeochemical and ecological processes at aquatic interfaces in rivers and beaches. A wide variety of methods exist for quantifying surface water-groundwater interactions and their related biogeochemical and ecological processes, including combinations of geophysical, tracer, and modeling techniques. Indeed, one of the challenges of investigating the hydrology of aquatic interfaces is understanding how to select and combine methods from this “grab bag” of options, as each approach has limited suitability for specific aquatic settings or scales of interest. Interpreting data from multiple techniques can be challenging due to scale effects, heterogeneous hydrogeological conditions, and sediment variability. I offer guidance on selecting observational and modeling approaches and discuss some of the challenges with upscaling. I also offer perspectives on new frontiers in the hydrology and biogeochemistry of aquatic interfaces.

Yves Méheust (University of Rennes, France)

Charles Harvey (Massachusetts Insitute of Technology, USA)

Tropical peat domes are formed through the interaction of hydrologic and ecological processes. These peatlands contain enormous stores of carbon and now emit enormous fluxes of CO₂ to the atmosphere. I will describe a unique field program in Borneo, one of the last undisturbed peat forests in Southeast Asia, where we characterize coupled ecological and hydrological processes — the positive feedback between peat accumulation and water table rise that enables organic carbon from rain forests to accumulate over millennia into gently-curved domes of peat, tens of kilometers across, and tens of meter thick. I will discuss how networks of drainage canals have broken this feedback, exposing peat to fire and microbial oxidation, and releasing huge fluxes of CO₂ to the atmosphere. I will describe a new mathematical formulation of the strong coupling between hydrologic and ecological processes. We combine hydrologic, carbon-flux, radiocarbon, and LIDAR data with model simulations to show how peat ecosystem approach a steady-state where: (1) The curvature of the land surface is described by a single parameter, a spatially-uniform Laplacian value which is predicted by rainfall statistics; (2) Water table dynamics are uniform across the peat; the water table responds to rainstorms in the same way everywhere; (3) Uptake and loss of carbon is balanced; and (4) Hydraulic parameters can be determined directly by combining groundwater hydrographs with the dome curvature. Finally, analysis of peatlands, from the arctic to southern New Zealand, show that this model applies to peatlands across the globe. With our mathematical framework, we also show how tropical peatlands are an ideal ecosystem to deploy “nature-based solutions” to limit greenhouse gas emissions. First, the flux of carbon out of, or into, peat domes can be reliably controlled by “adjusting just one knob”, the depth to the water table.  Second, carbon stores and emissions are easily verified by mapping surface elevation because shifts in the surface of the peat correspond directly to carbon loss or gain, since peat is composed almost entirely or organic carbon. 

Groundwater : a life sustaining resource

Ying Fan Reinfelder (Rutgers University, USA)

In this lecture, I will start with the scientific and societal imperative to understand fluids in the upper lithosphere at the whole Earth scale. The upper km of the continental lithosphere is our largest freshwater reservoir, and the top 10s of meters is the foundation of the terrestrial biosphere. Within this large-scale context, I will pose some simple questions: How deep does the rain regularly infiltrate into the ground and what drives it?  Do plant roots follow? How deep is the water table and what drives it? Do plants notice it?  What is the depth of the lithosphere that supplies ET fluxes to the atmosphere? What is the depth of the lithosphere that is flushed by modern rain hence participates in silicate weathering and long-term biogeochemical cycles? Through synthesis of site studies to understand processes, aided by global model simulations to explore global structures, I show that (1) we don’t have good answers to these questions, and (2) it is critical that our community create a global vision of the upper lithospheric structure, so that Earth System Models can meaningfully represent the life-supporting functions of the largest porous media, the Earth’s upper continental crust.

Christian Moeck (EAWAG, Switzerland): Quantifying Groundwater Recharge: Challenges and Insights in the Context of Climate Change – from the field to global level

In this lecture, I will explore the critical role of groundwater recharge in sustainable water management, emphasizing its challenges in quantification within the water balance framework. I will present a case study from a high-resolution, small-scale study area to illustrate the impacts of climate change on groundwater recharge, highlighting the complexities and uncertainties involved. This discussion will include an examination of model simplifications that significantly affect the simulation of climate change effects. Additionally, I will discuss the utility of global datasets in enhancing the accuracy of regional and global models. These datasets not only allow for a comprehensive study of recharge processes from multiple perspectives but also aim to bridge current knowledge gaps, encouraging further research and data sharing to refine recharge predictions. The presentation will also address the variability of natural recharge rates globally, based on a synthesis of field-estimated data across six continents, and the implications of these findings for the sustainability of groundwater resources in the face of changing climate conditions.

Camille Vautier (University of Rennes, France)

Upscaling : bridging the gap between microscale and macroscopic processes

Marco Dentz (CSIC, Spain): Solute transport in heterogeneous media across scales

Philippe Davy (University of Rennes, France): Lecture on the DFN methodology

Discrete Fracture Networks is a (rather old) way to model the fractured rock masses, where the fracture network is a population of 2D objects embedded in a volume, defined by a position, a shape (generally simple disks with size and orientation), and a set of surface properties (hydraulic transmissivity, mechanical apertures, shear or normal stiffnesses, etc.). The population is either statistically constrained from observations of fracture traces in boreholes, tunnels, or outcrops, and/or deterministically defined from 3D geophysical images. The statistical description compensates for the lack of direct and exhaustive observations in the subsurface. The DFN representation allows discussion of the scales that contribute to the rock properties of interest, whether mechanical or hydraulic.
The DFN methodology is new, evolving, and virtually untaught, although its potential for modeling fractured systems far exceeds that of continuous approaches. The method is integrative in the sense that the model is enriched by all information that can be collected, whether geological, hydraulic or mechanical. The lecture gives the basics for the application of the DFN methodology to site investigation or theoretical work, e.g. the difference between GEO-DFN, HYDRO-DFN and why not MECA-DFN, the stereological issue (how to compute statistics from partial field observations), the definition of (statistical) fracture domain, the different DFN generation models, etc. It illustrates how to calibrate DFN models from pumping and tracer tests, and how to use DFN to understand the theoretical nature of flow and transport in fractured rocks.