Influences of hydraulic boundary conditions on the deep fluid flow in a 3D regional model (central Upper Rhine Graben)

AbstractKnowledge of groundwater flow is of high relevance for groundwater management or the planning of different subsurface utilizations such as deep geothermal facilities. While numerical models can help to understand the hydrodynamics of the targeted reservoir, their predictive capabilities are limited by the assumptions made in their setup. Among others, the choice of appropriate hydraulic boundary conditions, adopted to represent the regional to local flow dynamics in the simulation run, is of crucial importance for the final modelling result. In this work, we systematically address this problematic in the area of the central part of the Upper Rhine Graben. We quantify how and to which degree different upper boundary conditions and vertical cross-boundary fluid movement influence the calculated deep fluid flow conditions in the area under study. Robust results, which are insensitive to the choice of boundary condition, are: (i) a regional groundwater flow component descending from the graben shoulders to rise at its centre and (ii) the presence of heterogeneous hydraulic potentials at the rift shoulders. Contrarily, results affected by the chosen boundary conditions are: (i) calculated flow velocities, (ii) the absolute position of the upflow axis, and (iii) the evolving local flow dynamics. If, in general, the investigated area is part of a supra-regional flow system—like the central Upper Rhine Graben is part of the entire Upper Rhine Graben—the inflow and outflow across vertical model boundaries need to be considered.

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Influence of fluid flow and heat transport on predictions of geothermal potentials in sedimentary layers of Hesse (Germany)

10.5194/egusphere-egu2020-4685 ◽

2020 ◽

Author(s):

Nora Koltzer ◽

Maximilian Frick ◽

Magdalena Scheck-Wenderoth ◽

Björn Lewerenz ◽

Kristian Bär ◽

...

Keyword(s):

Fluid Flow ◽

Heat Transport ◽

Thermal Model ◽

Transport Processes ◽

Heating Power ◽

Upper Rhine Graben ◽

Reservoir Temperature ◽

Rhine Graben ◽

Geothermal Potential ◽

Upper Rhine

For the sustainable utilization of deep geothermal resources it is essential to predict the exploitable potential thermal energy from the subsurface. One main parameter influencing the geothermal potential is the reservoir temperature that may vary locally or regionally in response to fluid flow and heat transport processes.This study aims at combining highly complex 3D thermo-hydraulic numerical simulations of heat transport and fluid flow with predictions of the geothermal potential for the application case of a hydrothermal doublet. Quantifying the influences of conductive, advective and convective heat transport mechanisms on the thermal field and moreover on the predicted heating power requires fundamental numerical investigations. We use the Federal State of Hesse in Germany as study area where heat transport processes have been quantified in recently published studies. There, the heterogeneous geology consists of outcropping Variscan Crust and up to 3.8 km and 1.8 km thick sedimentary deposits of the Upper Rhine Graben and the Hessian Depression, respectively. This geological complexity is expressed by areas of different hydraulic and thermal configurations: in the flat, but tectonically active Upper Rhine Graben high heat flow from below the graben sediments is in contrast to the variable topography of the Hessian Depression with low heat input from the Rhenohercynian Basement.The heating power in the three reservoir units (I) Cenozoic, (II) Buntsandstein and (III) Rotliegend is only predicted to be high in the Upper Rhine Graben. There the reservoir temperature is high enough and varies between 50 &#176;C in the convective thermal model of the Cenozoic reservoir and 170 &#176;C in the conductive thermal model of the Buntsandstein reservoir. Predicted low temperatures in the Hessian Depression lead to negligible low heating power, but as production mass flux is above ~6 kg s-1 investigations should continue to assess the geothermal potential for other applications like seasonal energy storage or low enthalpy geothermal utilization.

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Locating Geothermal Resources: Insights from 3D Stress and Flow Models at the Upper Rhine Graben Scale

Geofluids ◽

10.1155/2019/8494539 ◽

2019 ◽

Vol 2019 ◽

pp. 1-24 ◽

Cited By ~ 2

Author(s):

Antoine Armandine Les Landes ◽

Théophile Guillon ◽

Mariane Peter-Borie ◽

Arnold Blaisonneau ◽

Xavier Rachez ◽

...

Keyword(s):

Fluid Flow ◽

Transport Processes ◽

Upper Rhine Graben ◽

3D Flow ◽

Geothermal Resources ◽

Thermal Anomalies ◽

Rhine Graben ◽

Upper Rhine ◽

Fault Network

To be exploited, geothermal resources require heat, fluid, and permeability. These favourable geothermal conditions are strongly linked to the specific geodynamic context and the main physical transport processes, notably stresses and fluid circulations, which impact heat-driving processes. The physical conditions favouring the setup of geothermal resources can be searched for in predictive models, thus giving estimates on the so-called “favourable areas.” Numerical models could allow an integrated evaluation of the physical processes with adapted time and space scales and considering 3D effects. Supported by geological, geophysical, and geochemical exploration methods, they constitute a useful tool to shed light on the dynamic context of the geothermal resource setup and may provide answers to the challenging task of geothermal exploration. The Upper Rhine Graben (URG) is a data-rich geothermal system where deep fluid circulations occurring in the regional fault network are the probable origin of local thermal anomalies. Here, we present a current overview of our team’s efforts to integrate the impacts of the key physics as well as key factors controlling the geothermal anomalies in a fault-controlled geological setting in 3D physically consistent models at the regional scale. The study relies on the building of the first 3D numerical flow (using the discrete-continuum method) and mechanical models (using the distinct element method) at the URG scale. First, the key role of the regional fault network is taken into account using a discrete numerical approach. The geometry building is focused on the conceptualization of the 3D fault zone network based on structural interpretation and generic geological concepts and is consistent with the geological knowledge. This DFN (discrete fracture network) model is declined in two separate models (3D flow and stress) at the URG scale. Then, based on the main characteristics of the geothermal anomalies and the link with the physics considered, criteria are identified that enable the elaboration of indicators to use the results of the simulation and identify geothermally favourable areas. Then, considering the strong link between the stress, fluid flow, and geothermal resources, a cross-analysis of the results is realized to delineate favourable areas for geothermal resources. The results are compared with the existing thermal data at the URG scale and compared with knowledge gained through numerous studies. The good agreement between the delineated favourable areas and the locations of local thermal anomalies (especially the main one close to Soultz-sous-Forêts) demonstrates the key role of the regional fault network as well as stress and fluid flow on the setup of geothermal resources. Moreover, the very encouraging results underline the potential of the first 3D flow and 3D stress models at the URG scale to locate geothermal resources and offer new research opportunities.

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Regional hydraulic model of the Upper Rhine Graben

Advances in Geosciences ◽

10.5194/adgeo-49-197-2019 ◽

2019 ◽

Vol 49 ◽

pp. 197-206

Author(s):

Nora Koltzer ◽

Magdalena Scheck-Wenderoth ◽

Mauro Cacace ◽

Maximilian Frick ◽

Judith Bott

Keyword(s):

Groundwater Flow ◽

Flow System ◽

Hydraulic Head ◽

Upper Rhine Graben ◽

Groundwater Dynamics ◽

Rhine Graben ◽

Southern Half ◽

Rhine Valley ◽

Upper Rhine ◽

Regional Groundwater

Abstract. In this study we make use of 3-D hydraulic simulations to investigate the regional groundwater flow in the Upper Rhine Graben. The modeling is based on an existing detailed 3-D structural model covering the whole Upper Rhine Graben from the surface down to 14 km of depth. The overall goal of this study is to provide some quantitative analysis on the role of the hydraulic head topology in shaping the underground hydrodynamics by taking into account interactions with the heterogeneous subsurface sedimentary configuration of the basin system. Therefore, the main question addressed by this study can be summarized as follows: does the deep graben flow follow the topographic gradient and the flow direction of the river Rhine from the Alps northward to the northernmost area of the Upper Rhine Graben? Our results demonstrate the presence of a regional subsurface flow in the sedimentary rocks aligning from the graben flanks towards its center and in the southern half of the graben from south to north. The graben-parallel flow velocity is found to be about 1 order of magnitude lower than the velocity predicted perpendicular to the main graben axis. Besides these general trends, the modeling highlights local heterogeneities in the shallow 3-D flow field. Those arise from the interaction between regional groundwater flow and the heterogeneous sedimentary configuration. Within the Cenozoic sediments forming the uppermost aquifer in the model, groundwater flows are driven by imposed hydraulic gradients from recharge areas located at higher elevations in the Black Forest and Vosges Mountains to the discharge region at a lower elevation in the Rhine valley. The presence of a regional aquitard (Keuper) separating the shallow and the deeper aquifer system (Muschelkalk, Buntsandstein, and Rotliegend) hinders hydraulic connection among the two aquifer systems. This is exemplified by the development of a flow system in the deeper aquifers, which shows a more continuous graben-parallel south–north direction. Based on these results we can conclude that both the hydraulic head topology and the level of structuration of the sedimentary sequence exert a 1st-order role in shaping the regional flow system at depth. The regional model predicts a heterogeneous flow system within the upper 4 km of the Upper Rhine Valley, where flow velocities in the graben valley can reach up to 45 mm yr−1 in the upper and lower aquifers. Back to the current conceptual hydrogeological model, the results question the presence of a graben through northward flow, being limited to the southern half of the graben. In the north, the groundwater dynamics turn out to be more complex, being structurally linked to the local geology. This calls for additional studies with a higher level of both structural and stratigraphic attributes in order to arrive at a better quantification of the local to the regional groundwater dynamics in the area.

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The south-western Black Forest and the Upper Rhine Graben Main Border Fault: thermal history and hydrothermal fluid flow

International Journal of Earth Sciences ◽

10.1007/s00531-008-0391-3 ◽

2008 ◽

Vol 99 (2) ◽

pp. 285-297 ◽

Cited By ~ 6

Author(s):

H. Dresmann ◽

N. Keulen ◽

Z. Timar-Geng ◽

B. Fügenschuh ◽

A. Wetzel ◽

...

Keyword(s):

Fluid Flow ◽

Thermal History ◽

Hydrothermal Fluid ◽

Upper Rhine Graben ◽

Black Forest ◽

The South ◽

Rhine Graben ◽

Border Fault ◽

Upper Rhine

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The southeastern border of the Upper Rhine Graben: a 3D geological model and its importance for tectonics and groundwater flow

International Journal of Earth Sciences ◽

10.1007/s00531-005-0501-4 ◽

2005 ◽

Vol 94 (4) ◽

pp. 580-593 ◽

Cited By ~ 29

Author(s):

Ina Spottke ◽

Eric Zechner ◽

Peter Huggenberger

Keyword(s):

Groundwater Flow ◽

Upper Rhine Graben ◽

Geological Model ◽

Rhine Graben ◽

3D Geological Model ◽

Upper Rhine

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Isotopic and hydrochemical studies of groundwater flow and salinity in the Southern Upper Rhine Graben

International Journal of Earth Sciences ◽

10.1007/s00531-005-0500-5 ◽

2005 ◽

Vol 94 (4) ◽

pp. 565-579 ◽

Cited By ~ 6

Author(s):

Michael Bauer ◽

Lorenz Eichinger ◽

Philippe Elsass ◽

Wolfram Kloppmann ◽

Gunther Wirsing

Keyword(s):

Groundwater Flow ◽

Upper Rhine Graben ◽

Rhine Graben ◽

Hydrochemical Studies ◽

Upper Rhine

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Characterization of conditions and fluid flow paths in the Buntsandstein Gp. sandstones reservoirs, Upper Rhine Graben

BSGF - Earth Sciences Bulletin ◽

10.1051/bsgf/2021027 ◽

2021 ◽

Author(s):

Claire Bossennec ◽

Yves Géraud ◽

Johannes Böcker ◽

Bernd Klug ◽

Luca Mattioni ◽

...

Keyword(s):

Fluid Flow ◽

Fracture Network ◽

Fluid Inclusion Study ◽

Upper Rhine Graben ◽

Isotopic Ratios ◽

Rhine Graben ◽

Basin Scale ◽

Wide Range ◽

Upper Rhine

Deeply buried sandstone reservoirs are targeted in the Upper Rhine Graben (URG) for geothermal and hydrocarbon resources. These reservoirs, which are located at the top of the geothermal convective cells, have a complex diagenetic and structural history recorded by paragenesis. Here the focus is made on the characterization of carbonates and barite cementations which trace paleo geothermal circulations within the fracture network affecting the sandstones. These mineralizations are studied with a double approach on geochemistry and structural, faults and associated fracture network, to characterize fluid-flow episodes on different structural positions in the rift basin and its shoulders. Barite sulphur isotopic ratios suggest a common signature and source for all the locations. REE patterns, oxygen isotopic ratios, and fluid inclusion study suggest though two regimes of fluid flow forming barite, depending on their location. On the graben shoulders the barite have a higher content in total REE and contain non-saline fluids inclusions, suggesting that fluid circulations at the graben border faults interact with sulphate rich layers, and precipitate at high temperatures .In -deep-seated sandstones, fluid inclusions in barites show a wide range of salinities, suggesting a higher contribution of sedimentary brines, and precipitation at lower temperatures. These barite mineralizations are associated with carbonates and apatite with a diagenetic origin, according to their REE signature. These data are used to build a model for fluids circulation within the graben: Fast and deep down- and up-flows are taking place along the major border faults, which are leaching evaporitic horizons, and precipitates from geothermal fluid during fault activity. A part of these deep-down meteoric waters is reaching the centre of the basin. In this central part of the basin, fluid circulation is slower and restricted to the bottom of the basin, where fluid-mixing with sedimentary brines occurs. This new understanding of fluid pathways in the targeted reservoir brings new insights on the compartmentalization of geothermal circulations at the basin scale.

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