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Institut für Wasserbau - IWS

Selected Topics and International Network Lectures (WS 2005/06)


noch laufendeSS-2008WS-2007/08SS-2007WS-2006/07SS-2006WS-2005/06SS-2005WS-2004/05(vor WS-2004/05)

16:00 Uhr
Dr. Adam Szymkiewicz, Institute of Hydroengineering of the Polish Academy of Sciences

Generalized macroscopic model for unsaturated water flow in binary porous media

Binary porous media are composed of two materials having different hydraulic properties. According to the asymptotic homogenization theory, the unsaturated flow in such type of media is described with various models, depending on the ratio of the hydraulic diffusivity of the two components and the connectivity of the most conductive component. It can be shown that a continuous passage between various models exist. It is also possible to deduce a generalized model, suitable for the entire range of the diffusivity ratio. The obtained results are compared with other models that can be found in the literature.

16:00 Uhr
Dr.-Ing. Arne Färber, Universität Stuttgart, Institut für Wasserbau, Lehrstuhl für Hydrologie und Geohydrologie

Thermal In-situ-Remediation Principles for Contaminated Soils: Do Processes or Structures Prevail

Thermal In-Situ remediation techniques are increasingly used to clean up soils from contaminants. Compared to most other "enhanced" methods, they dispose of a significant advantage, improving their efficiency substantially: heat conduction helps to "crack down" the "diffusion-limit-problem", which acts in many practical cases as the unsurmountable barrier for ordinary in-situ methods. Thus these methods may help to save a lot of time (and money). Nevertheless the limits for thermal technologies are evident as well. The presentation will show this by some experimental examples. Although the role of heterogeneous structures is apparent and for thermal methods can sometimes be considered by very simple approaches in order to predict the clean-up process, yet a thorough and consistent analysis is difficult to obtain due to the complex interaction between the various dominating processes and the structures involved. Thus the question in the title can be answered according to Radio Eriwan.

16:00 Uhr
Maarten Felix, Universität Stuttgart, Institut für Wasserbau, Lehrstuhl für Hydromechanik und Hydrosystemmodellierung

Dilution of sediment gravity currents, or: the generation of turbidity currents from debris flows

Abstract: Sediment gravity currents are a subclass of density currents, which are currents driven by the density difference with the ambient fluid. In sediment gravity currents this density difference is caused by sediment. Such flows occur in many different environments, both subaerially and subaqueously, but the flows considered in this talk will be subaqeous only. Sediment concentration in sediment gravity flows can range from dense (debris flows with 60-70 % volumetric concentration of sediment) to dilute (turbidity currents with less that 1 % sediment). Several mechanisms have been suggested to explain how dense flows can transform into dilute flows, but none appear to be entirely satisfactory. In this talk, results will be presented from laboratory experiments, numerical simulations and from field work, aimed at gaining a better understanding of dilution/transformation processes.

16:00 Uhr
Dr. Sebastian Geiger, ETH Zürich, Institute of Isotope Geochemistry and Mineral Resources

Hydrodynamic and thermodynamic modelling of NaCl-H2O fluids: Groundwater flow below volcanoes

Abstract: Many important geological processes in the shallow Earth's crust are related to the simultaneous, often buoyancy driven, movement of heat and dissolved salt (NaCl) in water-rich fluids. These processes encompass the formation of large metallic ore deposits below volcanoes, the cooling of new-formed oceanic crust along mid-ocean ridges, convection in sedimentary basins, or heat transported by fluid flow in geothermal systems. The hydrodynamic and thermodynamic behavior of NaCl-H2O fluids in permeable rocks is fundamentally different from that of pure H2O. During thermohaline convection, so-called double-diffusive and double-convective flow patterns can evolve, because heat diffuses at a higher rate than salt while salt is advected at a faster rate than heat. NaCl-H2O fluids can also separate into two fluid phases, a high-density, high-salinity brine and low-density, low-salinity vapor, at pressures and temperatures well above the critical point of pure H2O (374oC, 221 bar), which is likely a key driver for the formation of the world's major ore deposits of Cu, Mo, Au and other important metals. Previous numerical studies of thermohaline convection have either assumed that the fluid is incompressible and the Boussinesq approximation applies or, in the case of phase separation, that the fluid is pure water. This, however, does not account for the full complexity of thermohaline convection including phase separation at high-temperature and high-pressure. This talk will discuss new numerical approaches for modelling the hydrodynamics and thermodynamics of NaCl-H2O fluid flow and present results related to the formation of economic ore deposits.

11:00 Uhr
Philip Binning, Associate Professor in Subsurface Hydrology and Numerical Modelling, Institute of Environment & Resources, Technical University of Denmark

A catchment scale model for assessing the risk associated with point source contaminated sites

Point sources are one of the main threats to groundwater quality. It is essential that remediation efforts are prioritised to ensure that the point sources which constitute the largest groundwater risk are remediated first. Currently, no systematic procedure is available for evaluating and comparing the contamination risk associated with various point sources within a catchment area. Here a simple method is presented that provides the basis for a ranking of point sources according to their impact on groundwater quality. The method is designed for real catchments where data availability is a major limitation on risk assessment. The model consists of two components: a source model and a large scale transport model. The source model describes the discharge of contaminant from a polluted site where the source of contaminant is located both in the unsaturated zone and in a secondary aquifer. It includes separate phase organics and degradation processes. The transport model applies particle tracking for simulating groundwater flow and residence time in the aquifer. The solute transport description includes sorption effects as well as transformation processes. Degradation is spatially variable and depends on the redox conditions in the aquifer. The risk assessment concept was tested at a contaminated site, Østerparken 5-7, located in Tåstrup, Denmark. The site is heavily contaminated with TCE, where residual phase in a hot spot in the unsaturated zone and the secondary aquifer is present. The simulations performed with the developed models show that the contamination at Østerparken 5-7 poses a large risk for the groundwater resource both locally and at the catchment scale. This risk will be present for an extended period of time. Sensitivity- and scenario analyses were performed to identify the most critical parameters for the risk assessment of Østerparken. Comparisons with existing risk assessment tools were also made.

11:00 Uhr
Birgitte Eikemo und Helge Dahle, University of Bergen, Norway

A discontinuous Galerkin Method for Computing Flow in Porous Media

We consider a discontinuous Galerkin scheme for flow in heterogeneous media. An efficient solution of the resulting system of unknowns is possible by taking advantage of a priori knowledge of the direction of flow. By arranging the elements in a suitable sequence, the full system need not be assembled and one may compute the solution in an element by element fashion. We demonstrate this procedure on boundary-value problems for time of flight and tracer flow.

11:00 Uhr
Dr. Hans Bruining, TU Delft, Faculty of Civil Engineering and Geosciences / Dept. of Geotechnology

Upscaled model, derived from homogenization, for water drive recovery in fractured reservoirs

Zusammenfassung: Homogenization is a powerful method to obtain upscaled equations in situations where a clear separation of scales is possible. The ratio of the small scale with respect to the large scale is denoted by e. The method has been used successfully for a variety of porous media flow problems, e.g. for reactive convection diffusion flows, two phase flow in heterogeneous media, non-Newtonian flow and flow in fractured reservoirs. In this contribution our interest is in water drive recovery from water-wet fractured reservoirs. Our approach follows the ideas of T. Arbogast (TIPM). However, the emphasis in this contribution is on (1) the physical assumptions used in the derivation of the upscaled equation to leading order of e, (2) the use of dynamic constitutive relations (capillary pressures and relative permeabilities) proposed by Barenblatt et al. to obtain the matrix imbibition contribution and (3) the correct implementation of the imbibition contribution in the combined fracture-matrix model. The numerically computed results are compared to the results obtained with the semi-empirical dual-porosity-transfer function method conventionally used by petroleum engineers in their simulators. The advantages of using homogenization for the derivation of transfer functions are discussed.

16:00 Uhr
Prof. Christoph Clauser, Institut für Angewandte Geophysik, RWTH Aachen

Simulation von reaktivem Transport und Permafrost in porösen und geklüfteten Reservoiren

16:00 Uhr
Dr. Ivan Lunati, Inst.f. Hydromechanik u. Wasserwirtschaft, ETH Zürich

A Multiscale Finite-Volume Framework for Modeling Multiphase Flow

A multi-scale finite-volume (MSFV) method for solving multiphase flow problem in highly heterogeneous media was recently developed. In contrast with classical upscaling techniques, the goal of multiscale methods is not simply to capture the large-scale effects of the fine-scale heterogeneity, but to provide an efficient tool for solving large flow problems with fine-scale resolution. The MSFV is based on a fractional flow formulation of the problem: first an equation for the total velocity is solved, then a fine-scale velocity field is reconstructed, finally the phase-saturation distribution is obtained by solving the nonlinear transport equations. In addition to the original fine grid the MSFV method employs an imposed coarse grid and a dual coarse grid. The first step is to compute the effective parameters that have to be used for solving the global flow problem on a coarse grid. This is done by means of a set of basis functions, which are numerical solutions computed on the cells of the dual grid. From these basis functions, the fluxes across the coarse-block boundaries are computed and the transmissibilities are extracted. Then the conservative fine-scale total-velocity field is reconstructed by solving a local flow problem in each coarse cell.

16:00 Uhr
Prof. Peter King, Department of Science and Engineering, Imperial College London, U.K

Entropy-mediated structure-permeability relations in skeletal porous materials

The aim of this paper is to formulate a new framework for characterisation of porous materials and for obtaining first-principles structure-permeability relaions. The formaslism is based on a representation of the porous medium in skeletal form and involves several steps. First, the skeleton is characterised by a new fabric tensor that describes the local pore structure. Second, the fabric tensor is used to construct a configurational entropy of the porous medium, based on Edwards??? compactivity concept. Both the fabric tensor and the entropic analysis are initially illustrated in two-dimensions and are then extended to three-dimensional systems. Third, the local pore-scale permeability is expressed in terms of the structure of the skeleton and the degrees of freedom that comprise the phase space of configurational states. Fourth, the pore-scale permeability is calculated as an expectation value over the partition function. We propose that the same procedure can be used to find the conductivity of the porous medium when it is filled with brine water. This makes it possible to derive a theoretical relation between these two transport properties.

16:00 Uhr
Dipl.-Math. Stefan Rief, Fraunhofer ITWM, Strömung und komplexe Strukturen, 67657 Kaiserslautern

Nonlinear Flow in Porous Media - Numerical Solution of the Navier-Stokes System with Two Pressures and Application to Paper Making

10:00 Uhr
Majid Hassanizadeh, Professor of Environmental Hydrogeology, Department of Earth Sciences, Utrecht University

150 Years of Darcy's Law - A critical look at the theories of two-phase flow in porous media

Darcy's law was proposed in 1856 to describe the flow of constant-density water in homogeneous, isotropic, non-deformable sand under isothermal conditions. Since then, that simple formula has been "extended" to be valid for flow of more fluids, with variable density, in heterogeneous, anisotropic, deformable sand under non-isothermal conditions. The extension has been achieved by adding bells and whistles to the simple equations that was proposed by Darcy.

In this presentation, we briefly describe this metamorphosis of Darcy's law and show that no real physics is actually introduced into the extended versions. In particular, we study the models of capillary effects in traditional multi-phase (and unsaturated) flow theories. Commonly, we assume that there is an algebraic relationship between capillary pressure and saturation. This relationship is based on measurements made under static conditions. This static relationship is then used to model dynamic conditions. However, it is a known fact that there is no unique relationship between capillary pressure and saturation. There are both hysteretic and non-equilibrium effects. We discuss new capillarity theories which are potentially devoid of hysteresis and include an additional term accounting for dynamic (or non-equilibrium) capillarity effects. There is compelling experimental evidence reported in the literature that the non-equilibrium effect is observable, quantifiable, and significant. In this presentation, we provide theoretical and experimental evidences of the validity of new theories. We then focus on the dynamic effect and use pore-scale and continuum scale simulation results to show the possible significance of the dynamic effect at various scales. We also investigate how the extended capillary equation affects mathematical models of unsaturated and two-phase flow models.