02 Fakultät Bau- und Umweltingenieurwissenschaften
Permanent URI for this collectionhttps://elib.uni-stuttgart.de/handle/11682/3
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Item Open Access Fluid-phase transitions in a multiphasic model of CO2 sequestration into deep aquifers : a fully coupled analysis of transport phenomena and solid deformation(Stuttgart : Institut für Mechanik (Bauwesen), Lehrstuhl für Kontinuumsmechanik, Universität Stuttgart, 2017) Häberle, Kai; Ehlers, Wolfgang (Prof. Dr.-Ing. Dr. h. c.)Item Open Access Reconstruction of μXRCT data sets using the ASTRA toolbox(2020) Voland, PaulItem Open Access Experimental multi-scale characterization using micro X-ray computed tomography(Stuttgart : Institute of Applied Mechanics, 2023) Ruf, Matthias; Steeb, Holger (Prof. Dr.-Ing.)The effective mechanical and hydro-mechanical behavior of porous media, granular solids, and related materials with complex morphologies is intimately linked to their internal microstructure on the pore/grain scale. For microstructural characterization, transmission micro X-Ray Computed Tomography (µXRCT) has emerged as a crucial three-dimensional (3D) imaging technique that can provide structural information from the micrometer to centimeter scale. Due to its non-destructive nature, it can be excellently combined with time-dependent investigations, either ex situ or in situ. In particular, the possibility of coupling mechanical or hydro-mechanical characterization with µXRCT-based 3D imaging in situ allows many physical phenomena to be studied in more detail and consequently understood more comprehensively. For example, the microstructure evolution can be observed under various controlled boundary conditions and linked to measured effective quantities. New insights and improved understanding can ultimately positively influence modeling approaches. In order to be able to perform such multi-scale studies, a modular, open, and versatile lab-based µXRCT system was developed within the scope of this work. It provides a spatial resolution of down to less than 10 µm. The developed system has an integrated universal testing machine that enables in situ compressive, tensile, and torsional studies as well as their combinations, parallel or sequential. Furthermore, hydro-mechanical coupled phenomena can be investigated using appropriate equipment, such as triaxial flow cells. Thanks to the open and modular concept, the developed system can be used in the future for a wide variety of multiphysics research questions and can be considered as an open experimental platform. Employing the established system, various multi-scale phenomena from different material classes are motivated and partly investigated in more detail within this work. For this purpose, classical experimental characterization methods are combined with µXRCT-based 3D imaging ex situ as well as in situ. Among others, 3D imaging is combined with ultrasound wave propagation measurements to investigate the influence of artificially generated crack networks in Carrara marble by different thermal treatment protocols. Load-sequence effects are demonstrated on an open-cell foam sample. An in situ workflow is shown to investigate the not-well-understood effective stiffness behavior of biphasic monodisperse granular packings of stiff and soft particles of different volume fractions at different stress states. The fracturing of a rock sample in a triaxial flow cell shows possibilities of application in the context of fracture mechanics. All resulting data sets, including metadata, are available via the Data Repository of the University of Stuttgart (DaRUS).Item Open Access Diagnosing hydro-mechanical effects in subsurface fluid flow through fractures(2023) Schmidt, Patrick; Steeb, Holger; Renner, JörgHydro-mechanically induced transient changes in fracture volume elude an analysis of pressure and flow rate transients by conventional diffusion-based models. We used a previously developed fully coupled, inherently non-linear numerical simulation model to demonstrate that harmonic hydraulic excitation of fractures leads to systematic overtones in the response spectrum that can thus be used as a diagnostic criterion for hydro-mechanical interaction. The examination of response spectra, obtained from harmonic testing at four different field sites, for the occurrence of overtones confirmed their potential for the hydro-mechanical characterization of tested reservoirs. A non-dimensional analysis identified relative aperture change as the critical system parameter.Item Open Access Fractures in glaciers : crack tips and their stress fields by observation and modeling(2023) Humbert, Angelika; Gross, Dietmar; Sondershaus, Rabea; Müller, Ralf; Steeb, Holger; Braun, Matthias; Brauchle, Jörg; Stebner, Karsten; Rückamp, MartinHigh‐resolution optical camera systems are opening new opportunities to study fractures in ice. Here, we present data obtained from the Modular Aerial Camera System camera system operated onboard of Alfred Wegener Institute Helmholtz Centre for Polar and Marine Research (AWI) polar aircraft in northeast Greenland in 2022. In addition, we are using optical and radar satellite imagery. The study area is the 79°N Glacier (Nioghalvfjerdsbræ, 79NG), an outlet glacier of the Northeast Greenland Ice Stream. We found that crack tips are exhibiting additional isolated cracks ahead of the main crack. Subsequent crack propagation is starting from those isolated cracks, leading to an advance of the crack, with bridges between crack faces. The bridges provide information of the episodic crack propagation. Fractures have typically a length scale of kilometers and the distance of crack faces is in the order of meters to tenths of meters. Fracture modes will be inferred from stress fields computed by an inverse modeling approach using the Ice Sheet and Sea Level System Model. To this end, a surface velocity field derived from satellite remote sensing is used for the optimal control method that constrains model parameters, for example, basal friction coefficient or rheology.Item Open Access Experimental evaluation of fluid connectivity in two‐phase flow in porous media during drainage(2022) Vahid Dastjerdi, Samaneh; Karadimitriou, Nikolaos; Hassanizadeh, S. Majid; Steeb, HolgerThis study aims to experimentally investigate the possibility of combining two extended continuum theories for two‐phase flow. One of these theories considers interfacial area as a separate state variable, and the other explicitly discriminates between connected and disconnected phases. This combination enhances our potential to effectively model the apparent hysteresis, which generally dominates two‐phase flow. Using optical microscopy, we perform microfluidic experiments in quasi‐2D artificial porous media for various cyclic displacement processes and boundary conditions. Specifically for a number of sequential drainage processes, with detailed image (post‐)processing, pore‐scale parameters such as the interfacial area between the phases (wetting, non‐wetting, and solid), and local capillary pressure, as well as macroscopic parameters like saturation, are estimated. We show that discriminating between connected and disconnected clusters and the concept of the interfacial area as a separate state variable can be an appropriate way of modeling hysteresis in a two‐phase flow scheme. The drainage datasets of capillary pressure, saturation, and specific interfacial area, are plotted as a surface, given by f (Pc, sw, awn) = 0. These surfaces accommodate all data points within a reasonable experimental error, irrespective of the boundary conditions, as long as the corresponding liquid is connected to its inlet. However, this concept also shows signs of reduced efficiency as a modeling approach in datasets gathered through combining experiments with higher volumetric fluxes. We attribute this observation to the effect of the porous medium geometry on the phase distribution. This yields further elaboration, in which this speculation is thoroughly studied and analyzed.Item Open Access Hydro-mechanical coupling of flow in deformable high-aspect ratio fractures(Stuttgart : Institute of Applied Mechanics, 2022) Schmidt, Patrick; Steeb, Holger (Prof. Dr.-Ing.)Underground flow processes in fractured porous media possess a great significance regarding the optimization of energy production based on natural resources. Energy is stored in form of liquids, respectively heat in the underground and its excavation is highly impacted by discontinuities of the porous medium's transport characteristics such as induced by discrete fractures or fracture networks. Throughout the exploitation flow processes might become fairly complex, since fractures do not simply increase the permeability and induce preferential flow paths within the reservoir, they also reduce the stiffness of the surrounding rock mass. Therefore, the objective of this thesis is to derive a numerically efficient hydro-mechanical model for flow in fractured porous media in which the reduction of the fracture flow domain by one dimension increases the computational performance. The derived model is then applied to data obtained from field-scale pumping operations in fractured reservoirs to contribute to a better understanding of hydro-mechanical processes under in-situ conditions.Item Open Access Digital Rock Physics : a geological driven workflow for the segmentation of anisotropic Ruhr sandstone(2021) Balcewicz, Martin; Siegert, Mirko; Gurris, Marcel; Ruf, Matthias; Krach, David; Steeb, Holger; Saenger, Erik H.Over the last 3 decades, Digital Rock Physics (DRP) has become a complementary part of the characterization of reservoir rocks due to the non-destructive testing character of this technique. The use of high-resolution X-ray Computed Tomography (XRCT) has become widely accepted to create a digital twin of the material under investigation. Compared to other imaging techniques, XRCT technology allows a location-dependent resolution of the individual material particles in volume. However, there are still challenges in assigning physical properties to a particular voxel within the digital twin, due to standard histogram analysis or sub-resolution features in the rock. For this reason, high-resolution image-based data from XRCT, transmitted-light microscope, Scanning Electron Microscope (SEM) as well as geological input properties like geological diagenesis, mineralogical composition, sample’s microfabrics, and estimated sample’s porosity are combined to obtain an optimal spatial segmented image of the studied Ruhr sandstone. Based on a homogeneity test, which corresponds to the evaluation of the gray-scale image histogram, the preferred scan sample sizes in terms of permeability, thermal, and effective elastic rock properties are determined. In addition, these numerically derived property predictions are compared with laboratory measurements to obtain possible upper limits for sample size, segmentation accuracy, and a geometrically calibrated digital twin of the Ruhr sandstone. The comparison corresponding gray-scale image histograms as a function of sample sizes with the corresponding advanced numerical simulations provides a unique workflow for reservoir characterization of the Ruhr sandstone.Item Open Access Simulation of flow in deformable fractures using a quasi-Newton based partitioned coupling approach(2022) Schmidt, Patrick; Jaust, Alexander; Steeb, Holger; Schulte, MiriamWe introduce a partitioned coupling approach for iterative coupling of flow processes in deformable fractures embedded in a poro-elastic medium that is enhanced by interface quasi-Newton (IQN) methods. In this scope, a unique computational decomposition into a fracture flow and a poro-elastic domain is developed, where communication and numerical coupling of the individual solvers are realized by consulting the open-source library preCICE. The underlying physical problem is introduced by a brief derivation of the governing equations and interface conditions of fracture flow and poro-elastic domain followed by a detailed discussion of the partitioned coupling scheme. We evaluate the proposed implementation and undertake a convergence study to compare a classical interface quasi-Newton inverse least-squares (IQN-ILS) with the more advanced interface quasi-Newton inverse multi-vector Jacobian (IQN-IMVJ) method. These coupling approaches are verified for an academic test case before the generality of the proposed strategy is demonstrated by simulations of two complex fracture networks. In contrast to the development of specific solvers, we promote the simplicity and computational efficiency of the proposed partitioned coupling approach using preCICE and FEniCS for parallel computations of hydro-mechanical processes in complex, three-dimensional fracture networks.Item Open Access GeomInt : geomechanical integrity of host and barrier rocks : experiments, models and analysis of discontinuities(2021) Kolditz, Olaf; Fischer, Thomas; Frühwirt, Thomas; Görke, Uwe-Jens; Helbig, Carolin; Konietzky, Heinz; Maßmann, Jobst; Nest, Mathias; Pötschke, Daniel; Rink, Karsten; Sattari, Amir; Schmidt, Patrick; Steeb, Holger; Wuttke, Frank; Yoshioka, Keita; Vowinckel, Bernhard; Ziefle, Gesa; Nagel, ThomasThe present paper gives an overview of the GeomInt project “Geomechanical integrity of host and barrier rocks - experiment, modelling and analysis of discontinuities” which has been conducted from 2017–2020 within the framework of the “Geo:N Geosciences for Sustainability” program. The research concept of the collaborative project is briefly introduced followed by a summary of the most important outcomes. The research concept puts geological discontinuities into the centre of investigations- as these belong to the most interesting and critical elements for any subsurface utilisation. Thus, while research questions are specific, they bear relevance to a wide range of applications. The specific research is thus integrated into a generic concept in order to make the results more generally applicable and transferable. The generic part includes a variety of conceptual approaches and their numerical realisations for describing the evolution of discontinuities in the most important types of barrier rocks. An explicit validation concept for the generic framework was developed and realised by specific “model-experiment-exercises” (MEX) which combined experiments and models in a systematic way from the very beginning. 16 MEX have been developed which cover a wide range of fundamental fracturing mechanisms, i.e. swelling/shrinkage, fluid percolation, and stress redistribution processes. The progress in model development is also demonstrated by field-scale applications, e.g. in the analysis and design of experiments in underground research laboratories in Opalinus Clay (URL Mont Terri, Switzerland) and salt rock (research mine Springen, Germany).