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  • Permeability
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  • 1
    Language: English
    In: Journal of Hydrology, January 2016, Vol.532, pp.90-101
    Description: Ground water flow systems of shallow sedimentary basins are studied in general by analyzing the fluid dynamics at the real world example of the Thuringian Basin. The impact of the permeability distribution and density differences on the flow velocity pattern, the salt concentration, and the temperature distribution is quantified by means of transient coupled simulations of fluid flow, heat, and mass transport processes. Simulations are performed with different permeabilities in the sedimentary layering and heterogeneous permeability distributions as well as with a non-constant fluid density. Three characteristic numbers are useful to describe the effects of permeability on the development of flow systems and subsurface transport: the relation of permeability between aquiclude and aquifer, the variance, and the correlation length of the log-normal permeability distribution. Density dependent flow due to temperature or concentration gradients is of minor importance for the distribution of the flow systems, but can lead to increased mixing dissolution of salt. Thermal convection is in general not present. The dominant driver of groundwater flow is the topography in combination with the permeability distribution. The results obtained for the Thuringian Basin give general insights into the dynamics of a small sedimentary basin due to the representative character of the basin structure as well as the transferability of the settings to other small sedimentary basins.
    Keywords: Subsurface Flow and Transport ; Fluid Dynamics in Sedimentary Basins ; Heterogeneity in Permeability ; Density Dependent Flow ; Thuringian Basin ; Opengeosys ; Geography
    ISSN: 0022-1694
    E-ISSN: 1879-2707
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  • 2
    Language: English
    In: Environmental Earth Sciences, 2013, Vol.70(7), pp.3363-3380
    Description: As part of the HG-A experiment in the Mont Terri Rock Laboratory, large-scale in situ water/gas injection experiments was conducted in a microtunnel. This research work focuses on the numerical analysis of the experimental data and the in situ observations. Concerning a temporary change of the hydromechanical properties of Opalinus Clay during experimental operations, three phases were numerically interpreted. These included the generation of excavation damaged zone during tunnel excavation, in which highly permeable flow paths around the tunnel have been formed; the self-sealing effect during water tests; and the pressure evolution during a long-term gas injection test. A coupled two-phase flow and mechanics model, taking into account the strong anisotropic properties of Opalinus Clay, was developed to interpret the measured data. The hydraulic anisotropy was described by a transversely isotropic permeability tensor. An elasto-plastic model was established to consider both stiffness anisotropy and strength anisotropy. Anisotropic plasticity was studied using the microstructure tensor method.
    Keywords: HM coupling ; Anisotropy ; In situ injection experiment ; Mont Terri Rock Laboratory ; EDZ
    ISSN: 1866-6280
    E-ISSN: 1866-6299
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  • 3
    Language: English
    In: Transport in Porous Media, 2011, Vol.90(2), pp.545-573
    Description: Predicting fluid replacement by two-phase flow in heterogeneous porous media is of importance for issues such as supercritical CO 2 sequestration, the integrity of caprocks and the operation of oil water/brine systems. When considering coupled process modelling, the location of the interface is of importance as most of the significant interaction between processes will be happening there. Modelling two-phase flow using grid based techniques presents a problem as the fluid–fluid interface location is approximated across the scale of the discretisation. Adaptive grid methods allow the discretisation to follow the interface through the model, but are computationally expensive and make coupling to other processes (thermal, mechanical and chemical) complicated due to the constant alteration in grid size and effects thereof. Interface tracking methods have been developed that apply sophisticated reconstruction algorithms based on either the ratio of volumes of a fluid in an element (Volume of Fluid Methods) or the advective velocity of the interface throughout the modelling regime (Level set method). In this article, we present an “Analytical Front Tracking” method where a generic analytical solution for two-phase flow is used to “add information” to a finite element model. The location of the front within individual geometrical elements is predicted using the saturation values in the elements and the velocity field of the element. This removes the necessity for grid adaptation, and reduces the need for assumptions as to the shape of the interface as this is predicted by the analytical solution. The method is verified against a standard benchmark solution and then applied to the case of CO 2 pooling and forcing its way into a heterogeneous caprock, replacing hot brine and eventually breaking through. Finally the method is applied to simulate supercritical CO 2 injected into a brine saturated heterogeneous reservoir rock leading to significant viscous fingering and developement of preferential flow paths. The results are compared with to a finite volume simulation.
    Keywords: Two-phase flow ; Hybrid analytical numerical ; CO sequestration ; Caprock integrity ; Front tracking
    ISSN: 0169-3913
    E-ISSN: 1573-1634
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  • 4
    Language: English
    In: Environmental Earth Sciences, 2011, Vol.62(6), pp.1197-1207
    Description: The present work compares the performance of two alternative flow models for the simulation of thermal-hydraulic coupled processes in low permeable porous media: non-isothermal Richards’ and two-phase flow concepts. Both models take vaporization processes into account: however, the Richards’ model neglects dynamic pressure variations and bulk flow of the gaseous phase. For the comparison of the two approaches first published, data from a laboratory experiment are studied involving thermally driven moisture flow in a partially saturated bentonite sample. Then a benchmark test of longer-term thermal-hydraulic behavior in the engineered barrier system of a geological nuclear waste repository is analyzed (DECOVALEX project). It was found that both models can be used to reproduce the vaporization process if the intrinsic permeability is relative high. However, when a thermal-hydraulic coupled problem has the same low intrinsic permeability, only the two-phase flow approach provides reasonable results.
    Keywords: Non-isothermal two-phase flow ; Richards’ approximation ; Porous media ; CTF1 experiment ; DECOVALEX task D
    ISSN: 1866-6280
    E-ISSN: 1866-6299
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  • 5
    Language: English
    In: Computational Mechanics, 2010, Vol.45(4), p.263(18)
    Description: In this paper we present an uncertainty analysis of thermo-hydro-mechanical (THM) coupled processes in a typical geothermal reservoir in crystalline rock. Fracture and matrix are treated conceptually as an equivalent porous medium, and the model is applied to available data from the Urach Spa and Falkenberg sites (Germany). The finite element method (FEM) is used for the numerical analysis of fully coupled THM processes, including thermal water flow, advective-diffusive heat transport, and thermoelasticity. Non-linearity in system behavior is introduced via temperature and pressure dependent fluid properties. Reservoir parameters are considered as spatially random variables and their realizations are generated using conditional Gaussian simulation. The related Monte-Carlo analysis of the coupled THM problem is computationally very expensive. To enhance computational efficiency, the parallel FEM based on domain decomposition technology using message passing interface (MPI) is utilized to conduct the numerous simulations. In the numerical analysis we considered two reservoir modes: undisturbed and stimulated. The uncertainty analysis we apply captures both the effects of heterogeneity and hydraulic stimulation near the injection borehole. The results show the influence of parameter ranges on reservoir evolution during long-term heat extraction, taking into account fully coupled thermo-hydro-mechanical processes. We found that the most significant factors in the analysis are permeability and heat capacity. The study demonstrates the importance of taking parameter uncertainties into account for geothermal reservoir evaluation in order to assess the viability of numerical modeling. Keywords Geothermal reservoir analysis * Uncertainty assessment * Thermo-hydro-mechanical (THM) coupled processes * Sequential Gaussian simulation * Monte-Carlo simulation
    Keywords: Finite Element Method – Analysis ; Finite Element Method – Models ; Finite Element Method – Usage ; Geothermal Resources – Analysis ; Geothermal Resources – Models ; Geothermal Resources – Usage ; Hydraulic Flow – Analysis ; Hydraulic Flow – Models ; Hydraulic Flow – Usage ; Permeability – Analysis ; Permeability – Models ; Permeability – Usage ; Monte Carlo Methods – Analysis ; Monte Carlo Methods – Models ; Monte Carlo Methods – Usage
    ISSN: 0178-7675
    Source: Cengage Learning, Inc.
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  • 6
    Language: English
    In: Computational Mechanics, March, 2010, Vol.45(4), p.263(18)
    Description: Byline: Norihiro Watanabe (1,2), Wenqing Wang (1), Christopher I. McDermott (3), Takeo Taniguchi (4), Olaf Kolditz (1,2) Keywords: Geothermal reservoir analysis; Uncertainty assessment; Thermo-hydro-mechanical (THM) coupled processes; Sequential Gaussian simulation; Monte-Carlo simulation Abstract: In this paper we present an uncertainty analysis of thermo-hydro-mechanical (THM) coupled processes in a typical geothermal reservoir in crystalline rock. Fracture and matrix are treated conceptually as an equivalent porous medium, and the model is applied to available data from the Urach Spa and Falkenberg sites (Germany). The finite element method (FEM) is used for the numerical analysis of fully coupled THM processes, including thermal water flow, advective--diffusive heat transport, and thermoelasticity. Non-linearity in system behavior is introduced via temperature and pressure dependent fluid properties. Reservoir parameters are considered as spatially random variables and their realizations are generated using conditional Gaussian simulation. The related Monte-Carlo analysis of the coupled THM problem is computationally very expensive. To enhance computational efficiency, the parallel FEM based on domain decomposition technology using message passing interface (MPI) is utilized to conduct the numerous simulations. In the numerical analysis we considered two reservoir modes: undisturbed and stimulated. The uncertainty analysis we apply captures both the effects of heterogeneity and hydraulic stimulation near the injection borehole. The results show the influence of parameter ranges on reservoir evolution during long-term heat extraction, taking into account fully coupled thermo-hydro-mechanical processes. We found that the most significant factors in the analysis are permeability and heat capacity. The study demonstrates the importance of taking parameter uncertainties into account for geothermal reservoir evaluation in order to assess the viability of numerical modeling. Author Affiliation: (1) Department of Environmental Informatics, UFZ-Helmholtz Centre for Environmental Research, Permoserstrasse 15, 04318, Leipzig, Germany (2) Applied Environmental System Analysis, Dresden University of Technology, Helmholtzstrasse 10, 01069, Dresden, Germany (3) Edinburgh Collaborative of Subsurface Science and Engineering (ECOSSE), School of Geoscience, University of Edinburgh, West Mains Road, Edinburgh, EH9 3JW, Scotland, UK (4) Graduate School of Environmental Science, Okayama University, 1-1, Tsushima-Naka, 3-chome, Okayama, 700-8530, Japan Article History: Registration Date: 03/11/2009 Received Date: 30/03/2009 Accepted Date: 30/10/2009 Online Date: 18/11/2009
    Keywords: Monte Carlo Methods ; Geothermal Energy ; Geothermal Resources ; Hydraulic Flow ; Reservoirs (Water) ; Finite Element Method ; Universities And Colleges ; Permeability
    ISSN: 0178-7675
    Source: Cengage Learning, Inc.
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  • 7
    Language: English
    In: Geological Society, London, Special Publications, 2015, Vol.415(1), pp.203-212
    Description: To investigate gas-migration processes in saturated low-permeability argillaceous rocks, gas-injection tests under different injection pressures were carried out at different scales: on core samples at the laboratory scale; in the packed-off section of boreholes at the borehole scale (HG-B); and in the sealed microtunnel at the tunnel scale (HG-A) - a 1:2 scale experiment at the Mont Terri Rock Laboratory, Switzerland. All three tests at the Mont Terri Rock Laboratory involved Opalinus Clay. A fully coupled hydromechanical model has been developed that takes account of elastic and plastic anisotropies, anisotropic two-phase flow based on the van Genuchten function, and permeability changes when evaluating the experimental data. Two different flow regimes were studied: two-phase flow under low gas-injection pressure and dilatancy-controlled gas flow under high gas-injection pressure above the confining pressure in the laboratory experiment or the minimal principal stress in situ. When dealing with the dilatancy-controlled gas-flow regime, special consideration was made by applying two permeability approaches in which (i) the permeability change was pore-gas-pressure dependent and (ii) where the permeability change was deformation dependent. Using the parameter values determined by laboratory data, the in situ borehole tests obtained under well-defined hydromechanical conditions could be analysed accordingly. The gas-flow regime in large-scale experiments, as in the case of HG-A, is mainly governed by experimental circumstances: in this case, the excavation-induced fractures around an opening with a permeability four order of magnitude higher than that in the undisturbed rock mass.
    Keywords: Engineering Geology ; Anisotropy ; Argillite ; Boreholes ; Boundary Conditions ; Capillary Pressure ; Central Europe ; Clastic Rocks ; Confining Pressure ; Cores ; Cracks ; Deformation ; Dilatancy ; Disposal Barriers ; Equations ; Europe ; Excavation Damaged Zone ; Experimental Studies ; Failures ; Fluid Flow ; Fractures ; Gas Injection ; Gas Migration ; Gaseous Phase ; Hydromechanical Models ; In Situ ; Jurassic ; Laboratory Studies ; Liquid Phase ; Mechanical Properties ; Mechanics ; Mesozoic ; Methods ; Microcracks ; Microtunnels ; Models ; Numerical Models ; Opalinus Clay ; Permeability ; Pore Pressure ; Porous Materials ; Rupture ; Saturation ; Sedimentary Rocks ; Simulation ; Slug Tests ; Solute Transport ; Strain ; Stress ; Switzerland ; Testing ; Transport ; Underground Installations ; Underground Storage ; Waste Disposal ; Waste Management ; Water Pressure;
    ISSN: 0305-8719
    E-ISSN: 2041-4927
    Source: CrossRef
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  • 8
    In: Journal of Geophysical Research: Solid Earth, July 2018, Vol.123(7), pp.5609-5627
    Description: This work focuses on the interaction between pressure solution creep and contact area expansion under hydrothermal conditions and proposes an innovative process‐based approach for describing contact area expansion by fracture closure. The formulation is established in the physical context of pressure solution creep and represents the dynamic process of enhanced mineral dissolution over grain contacts, which moves toward equilibrium as a result of decrease of mineral solubility by pressure drop. Then, a theoretical maximum of the contact area ratio is obtained from the formulation whose existence demonstrates that pressure solution is with an energy threshold for activation rather than spontaneously taking place under any circumstances. Based upon the formulation, a 1‐D reactive transport model is developed and applied to investigate dissolution‐induced permeability evolution of a granite fracture under crustal conditions. The applicability of the developed model to a polymineralic system is examined against the experimental measurements reported in Yasuhara et al. (2011, ). This investigation reconfirms the significance of pressure solution creep in fracture permeability evolution under low and moderate temperatures and provides a justified interpretation for the unusual experimental observation that fracture permeability reduction does not necessarily lead to apparent increases of effluent element concentrations. The surface topography of fracture channels markedly affects hydraulic feedback on chemical compaction in terms of both magnitude and rate of change. Temperature elevation contributes to accelerating the progression of pressure solution creep. An innovative process‐based approach is proposed for describing contact area expansion by fracture closure The established formulation represents the dynamic process of mineral dissolution at grain contacts in response to pressure drop Pressure solution has a minimum energy requirement for activation rather than spontaneously taking place under any circumstances
    Keywords: Fracture Permeability Evolution ; Pressure Solution Creep ; Contact Area Expansion ; Water‐Granite Interactions ; Reactive Transport Modeling ; Opengeosys
    ISSN: 2169-9313
    E-ISSN: 2169-9356
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  • 9
    Language: English
    In: Environmental Earth Sciences, 2017, Vol.76(21), pp.1-13
    Description: Numerical modelling of coupled physical processes in bentonite–sand mixtures under the geological conditions is significant for designing and constructing sealing systems in deep underground repositories for highly radioactive nuclear waste. Within the framework of DECOVALEX 2015, Task A, this work presents the model validation of OpenGeoSys by numerical modelling of coupled hydromechanical (HM) processes in bentonite–sand mixtures. Parameters used in the HM model were determined by modelling the laboratory tests of the sealing experiment (SEALEX). Afterwards these parameters were applied for the modelling of a small-scale mock-up test considering the influence of technological gap and incidental fail of the seal in the sealing system. In order to investigate the availability of employing these HM parameters and numerical models directly to field predictions, the modelling results and measured data of an in situ SEALEX experiment were analysed comparatively. The modelling results reproduced well the main features in HM behaviour of the compacted bentonite–sand mixture, which denotes that the adopted HM models and parameters are adequate for describing the HM processes in the sealing system. It is necessary to take the elastoplastic behaviour and evolution of the permeability of bentonite–sand mixtures into account when using the adopted models to reproduce the HM processes of a sealing system.
    Keywords: Hydromechanics ; SEALEX ; Bentonite–sand mixture ; DECOVALEX ; OpenGeoSys
    ISSN: 1866-6280
    E-ISSN: 1866-6299
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  • 10
    Language: English
    In: Environmental Earth Sciences, 2017, Vol.76(12), pp.1-14
    Description: Fluid–mineral interaction has an irreversible impact on the fracture permeability evolution in the life span of deep geological reservoirs. To investigate the impact, a preliminary study on water–granite interaction in an undeformable fracture under confining pressure is conducted. A 1-D flow and reactive transport model is therefore developed and validated against the experimental data in Yasuhara et al. (Appl Geochem 26(12):2074–2088, 2011). The model takes free-face dissolution on pore walls as well as enhanced dissolution at asperity contacts into account, together with a nested well-equipped geochemical system. The simulation is implemented by FEM-based simulator OpenGeoSys with a plugin module of IPhreeqc for speciation calculation. After calibration, the predictions of effluent element concentrations are in good agreement with the measurements. The study indicates the high effluent concentrations arise from enhanced mineral dissolution at asperity contacts. Pressure solution at anorthite contacts may not take effect under experimental conditions because of the high-level energy barrier to interpenetration, and Al-bearing secondary minerals such as gibbsite may be formed in the current near-equilibrium aqueous system. The sensitivity analysis suggests that contact area ratio is a paramount parameter in determining the surface reactivity and reactive surface area at contacts.
    Keywords: Water–granite interaction ; Pressure solution ; Fracture ; Reactive transport modeling ; OpenGeoSys ; DECOVALEX
    ISSN: 1866-6280
    E-ISSN: 1866-6299
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