02 Fakultät Bau- und Umweltingenieurwissenschaften
Permanent URI for this collectionhttps://elib.uni-stuttgart.de/handle/11682/3
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Item Open Access Investigations into the opening of fractures during hydraulic testing using a hybrid-dimensional flow formulation(2021) Schmidt, Patrick; Steeb, Holger; Renner, JörgWe applied a hybrid-dimensional flow model to pressure transients recorded during pumping experiments conducted at the Reiche Zeche underground research laboratory to study the opening behavior of fractures due to fluid injection. Two distinct types of pressure responses to flow-rate steps were identified that represent radial-symmetric and plane-axisymmetric flow regimes from a conventional pressure-diffusion perspective. We numerically modeled both using a radial-symmetric flow formulation for a fracture that comprises a non-linear constitutive relation for the contact mechanics governing reversible fracture surface interaction. The two types of pressure response can be modeled equally well. A sensitivity study revealed a positive correlation between fracture length and normal fracture stiffness that yield a match between field observations and numerical results. Decomposition of the acting normal stresses into stresses associated with the deformation state of the global fracture geometry and with the local contacts indicates that geometrically induced stresses contribute the more the lower the total effective normal stress and the shorter the fracture. Separating the contributions of the local contact mechanics and the overall fracture geometry to fracture normal stiffness indicates that the geometrical stiffness constitutes a lower bound for total stiffness; its relevance increases with decreasing fracture length. Our study demonstrates that non-linear hydro-mechanical coupling can lead to vastly different hydraulic responses and thus provides an alternative to conventional pressure-diffusion analysis that requires changes in flow regime to cover the full range of observations.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 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 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).