Norbert Klitzsch

Monitoring and Modeling the Terrestrial System from Pores to Catchments: The Transregional Collaborative Research Center on Patterns in the Soil–Vegetation–Atmosphere System

AbstractMost activities of humankind take place in the transition zone between four compartments of the terrestrial system: the unconfined aquifer, including the unsaturated zone; surface water; vegetation; and atmosphere. The mass, momentum, and heat energy fluxes between these compartments drive their mutual state evolution. Improved understanding of the processes that drive these fluxes is important for climate projections, weather prediction, flood forecasting, water and soil resources management, agriculture, and water quality control. The different transport mechanisms and flow rates within the compartments result in complex patterns on different temporal and spatial scales that make predictions of the terrestrial system challenging for scientists and policy makers. The Transregional Collaborative Research Centre 32 (TR32) was formed in 2007 to integrate monitoring with modeling and data assimilation in order to develop a holistic view of the terrestrial system. TR32 is a long-term research program ...

Electro-osmotic flow in clays and its potential for reducing clogging in mechanical tunnel driving

Clogging during mechanical tunnel driving is not only a serious technical issue, but also an economic one. The costs of a tunnel excavation can easily rise and disputes between the awarding authorities and the executive companies may occur. Although the literature is full of cases describing the clogging in clayey soils and despite countermeasures being available, clogging still occurs. This study proposes an alternative method to diminish adhesion of clays on TBMs. Electro-osmotic flow experiments, spectral induced polarisation tests and Zeta-potential simulations were performed on kaolinite and smectite, mixed with several pore fluids under one critical consistency index. The results showed that the electrical parameters were not only influenced by the clay mineralogy per se, but also by the pore fluid chemistry. To apply the laboratory findings in in situ conditions, several theoretical considerations have been taken into account. Although further research is required, the study indicates electro-osmosis may be a new and revolutionary approach to deal with the clogging of TBMs.RésuméLe colmatage lors du creusement d’un tunnel est non seulement un grave problème technique, mais aussi une question économique. Ce travail de recherche propose une méthode alternative pour diminuer l’adhérence des sols argileux sur les tunneliers. Des expériences d’écoulement électro-osmotique, des essais de polarisation induite spectrale (SIP) et des simulations de potentiel zêta ont été effectués avec de la kaolinite et de la smectite, mélangées avec plusieurs fluides pour un indice de consistance critique. Les résultats ont montré que les paramètres électriques étaient non seulement influencés par la minéralogie de l’argile, mais aussi par la chimie du fluide interstitiel. Pour appliquer ces résultats de laboratoire aux conditions in situ, plusieurs considérations théoriques ont été prises en compte. Bien que des études supplémentaires soient nécessaires, on conclut que l’électro-osmose pourrait constituer une approche nouvelle et révolutionnaire pour traiter du problème du colmatage des tunneliers.

Impact of arid surface megacracks on hydrocarbon reservoir properties

The megacrack pattern of the ephemeral north Panamint dry lake, California, United States, is characterized by variably sized polygons with diameters ranging from hundreds of meters to meters. The evolution and subsurface extent of this polygonal pattern and a probable tectonic link are examined by ground resistivity measurements and surface mapping. Crack development is initiated by the shrinking of clays caused by changes in water content near the surface. For crack evolution, the following processes are proposed: Cavities develop at approximately 1-m (3-ft) depth during a subsurface phase, followed by the collapse of the overburden into the existing cavities to form the surface cracks. Cracks are filled by wind-blown sand and dried-out lake sediments from collapsing crack walls. Following burial, differences in competence between crack-fill and surrounding playa-lake sediments provide zones of structural weakness that might channelize stress release and faulting. Ground resistivity measurements confirmed the extent of the cracks to a depth of more than 3 m (9 ft). The megacrack pattern is compared to a Rotliegende (Upper Permian) tight gas field, located in the southern Permian Basin of northwestern Germany, situated in a comparable geologic setting. There, a multidirectional polygonal pattern is recorded on horizon slices of three-dimensional seismic data and compares well to our observations from the Panamint Valley. The Rotliegende pattern is associated with low-offset faults, which are proposed to be responsible for subtle reservoir compartmentalization.

Improving archaeological site analysis: a rampart in the middle Orkhon Valley investigated with combined geoscience techniques

The Orkhon Valley in the Central Mongolia was included in the World Heritage list in 2004. It hosts multiple archaeological sites from Palaeolithic to recent times, which can contribute to the reconstruction of settlement history in this part of the Eurasian Steppe landscape. Almost 100 archaeological sites from prehistoric and historic times including ramparts and khirigsuurs were investigated in five field campaigns from 2008 to 2010 in the middle and upper Orkhon Valley. One site, MOR-2 (Dorvolzhin), proved especially difficult to date due to the lack of sufficient archaeological surface finds, and its role within a manifold of walled enclosures from different times in the study area remained unclear. Therefore, different techniques of archaeology, geophysics and geoarchaeology were combined at MOR-2 in order to determine a comprehensive picture about its timing, archaeological meaning, and environmental history. Information on topographical setting and morphometry of the rampart was gathered by an octocopter equipped with a high-resolution range finder camera. We achieved a high-resolution DEM that allowed us to map the rampart in detail and this served as a base map for all other investigations. SQUID magnetometry, ground-penetrating radar, and electric resistivity measurements (capacitive coupled geoelectrics) were subsequently used to detect archaeological remains and to characterize the sediment distribution of the inner part of the enclosure and the ramparts themselves. The data show that the construction of the walls is similar to well-known Uighur neighbouring sites. Man-made sub-surface structures or bigger finds could not be detected. Sediment cores were drilled in a nearby meander, covering 3000 years BP. The analysis of the strata in terms of elemental composition (P, N, Mn, Fe, etc) revealed an increase of organic content in Medieval times, whereas the allochthonous filling of the back water must have started around the beginning of the 6th century AD. Using geophysical, archaeological and geological observations, we assume a dating in the Turk/Uighur period (6th–9th century AD) and a re-use under Mongolian reign (12th–17th century AD). This would mean that this site is the furthermost walled structure in the peri-urban area of Khar Balgas. However, the specific usage of this walled enclosure remains unclear and needs further analysis.

Joint numerical microscale simulations of multiphase flow and NMR relaxation behavior in porous media using Lattice Boltzmann methods

Nuclear magnetic resonance (NMR) relaxometry is a useful tool to estimate transport and storage properties of rocks and soils. However, as there is no unique relation between the NMR signal and these properties in rocks, a variety of empirical models on deriving hydraulic properties from NMR relaxometry data have been published. Complementary to laboratory measurements, this paper introduces a numerical framework to jointly simulate NMR relaxometry experiments and two-phase flow on the micrometer scale. Herein, the NMR diffusion equations were tied to an established Lattice Boltzmann algorithm used in computational fluid dynamics. The numerically simulated NMR data were validated for both surface-limited and diffusion-limited relaxation regimes using analytical solutions available for fully and partially water-saturated simple pore geometries. Subsequently, simulations were compiled using a complex pore space derived from three-dimensional computer tomography (CT) data of an unconsolidated sand and the results were compared to respective NMR T1 relaxometry data. The NMR transients simulated for different water saturations matched the measured data regarding initial amplitudes (i.e., porosity and saturation) and relaxation behavior (i.e., distribution of water-saturated pores). Thus, we provide a simulation tool that enables study of the influences of structural and physicochemical properties, such as pore connectivity and pore coupling, surface relaxivity, or diffusivity, on partially saturated porous media, e.g, rocks or soils, with NMR T1 relaxometry data.

Numerical study on CO2 leakage detection using electrical streaming potential data

We study the feasibility of detecting carbon dioxide (CO2) movement in the overburden of a storage reservoir due to CO2 leakage through an abandoned well by self-potential measurements at the surface. This is achieved with three-dimensional numerical (SP) modeling of two-phase fluid flow and electrokinetic coupling between flow and streaming potential. We find that, in typical leakage scenarios, for leaky and/or injection wells with conductive metal casing, self-potential signals originating from injection can be identified at the surface. As the injection signal is also observed at the leaky well with metal casing, SP monitoring can be applied for detecting abandoned wells. However, leakage signals are much smaller than the injection signal and thus masked by the latter. We present three alternatives to overcome this problem: (i) simulate the streaming potential of the non-leaky scenario and subtract the result from the measured streaming potential data; (ii) exploit the symmetry of the injection signal by analysing the potential difference of dipoles with the dipole center at the injection well; or (iii) measure SP during periods where the injection is interrupted. In our judgement, the most promising approach for detecting a real-world CO2 leakage is by combining methods (i) and (ii), because this would give the highest signal from the leakage and omit signals originating from the injection well. Consequently, we recommend SP as monitoring method for subsurface CO2 storage, especially because a leakage can be detected shortly after the injection started even before CO2 arrives at the leaky well. This article is protected by copyright. All rights reserved.

Visualisation of the Electrical Resistivity Distribution of Reinforced Concrete

The electrical resistivity of concrete is a characteristic property correlating with different durability related parameters, e.g. the degree of water saturation, the corrosion rate of the reinforcement or the chloride diffusion coefficient. On structures the resistivity can be determined non-destructively by using a Wenner setup. The analysis is based on the assumption of a homogeneous semi-infinite concrete element. Based on the heterogeneous structure of reinforced concrete (e.g. reinforcement bars, moisture differences) the electrical field is deformed which may lead to misinterpretations.

Tomographische Widerstandsmessungen an Stahlbetonbauteilen

Due to the requirements regarding the maintenance of structures the demand for non-destructive methods increase steadily. The electrical resistivity of concrete is a parameter which can be correlated with different durability aspects of reinforced concrete structures (e.g. porosity, saturation degree, diffusion coefficients, corrosion rate). But the typical methods for determining non-destructively the resistivity on concrete structures are not reliable in cases of heterogeneous resistivity distributions (e.g. reinforcement bars, saturation gradients). Within this paper a geophysical method is presented to determine resistivity tomograms. To study the application on concrete structures measurements are carried out on reinforced concrete specimens. An electrode setup according to Wenner is compared with the dipol dipol setup in order to identify heterogeneities in reinforced concrete.

Linking Thermal and Elastic Properties in Sandstones Reservoir Rocks

Summary Although not measurable at the field scale, thermal properties of reservoir rocks at depth are important for many applications. Motivated by the fact that field-scale elastic properties may be obtained from measurements at the surface, a new physics-based theoretical model has recently been developed to link thermal and elastic properties through their common dependences in rocks. The model aims to ultimately predict thermal properties from elastic ones. But verifying this model with existing datasets obtained from different rock samples measured under different experimental conditions proves to be challenging. New joint measurements of thermal and elastic properties acquired on reference sandstone samples at identical experimental conditions allow an improved assessment.

JOINT NUMERICAL MICRO-SCALE SIMULATIONS OF MULTI-PHASE FLOW AND NMR RELAXATION BEHAVIOR IN POROUS MEDIA

In addition to the classical experimental approaches to derive flow and transport properties of rocks and soils - in particular for the vadose zone - Computational Fluid Dynamics (CFD) has proven to be a viable complementary tool for analyzing and predicting complex transport systems. In nuclear magnetic resonance (NMR), the measured relaxation signals originate from the pore spaces filled with NMR-active fluid (e.g., water, oil) and gas (e.g. methane) phases. The rate of NMR relaxation - of the wetting phase - is sensitive to the pore size and physicochemical properties of the rock-fluid/-gas interfaces (i.e., surface relaxivity), as well as the concentration of paramagnetic ions in the bulk phases (bulk relaxivity). Thus, the method can be applied to derive hydraulic parameters such as pore size distributions or (relative) permeability. To improve the fundamental understanding of the pore scale processes necessary to translate measured NMR relaxometry signals into soil structural and state properties, numerical simulations of the NMR relaxation (i.e., Bloch equation) and multi-phase flow on a pore scale dimension have been implemented using Lattice Boltzmann methods. To jointly study the transport and NMR behavior of partially saturated soils we carry out sequential CFD simulations using a modified Rothmann-Keller (RK) model for multi phase flow modeling (i.e., de-saturation) and due to its improved efficiency, high accuracy and stability an advection/diffusion model developed by Ginzburg is used to subsequently calculate the NMR relaxation signals at different saturation states. Simulations have been compiled for synthetic as well pore systems derived from microCT images of porous ceramics (reference samples) and natural unconsolidated sediments. The simulations have been validated by (1) using analytical and finite element models for simple geometries and (2) corresponding joint pressure-curve and NMR measurements on fully and partially saturated reference and soil samples. In a next step we aim to further advance the model by implementing simulations of Induced Polarization (IP) responses in the time and frequency domain that are complementary to NMR data. Based on these simulations we aim to develop a joint interpretation scheme for combined NMR and (Spectral) IP measurements in order to assess structure, state and thus flow properties of partially saturated soils.