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

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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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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Reconstructing Paleofluid Circulation at the Hercynian Basement/Mesozoic Sedimentary Cover Interface in the Upper Rhine Graben

Geofluids ◽

10.1155/2019/4849860 ◽

2019 ◽

Vol 2019 ◽

pp. 1-30 ◽

Cited By ~ 3

Author(s):

Chrystel Dezayes ◽

Catherine Lerouge

Keyword(s):

Sedimentary Cover ◽

Upper Rhine Graben ◽

Fluid Circulation ◽

Tectonic Events ◽

Rhine Graben ◽

Tectonic Environment ◽

Convective Circulation ◽

Geothermal Wells ◽

Upper Rhine ◽

Fault Network

In this paper, we focus on paleocirculation at the Hercynian basement/sedimentary cover interface in the tectonic environment of the Upper Rhine graben. The goal is to increase our understanding of the behavior of the fracture-fault network and the origin of the hydrothermal fluids. We studied orientations, mineral fillings, and fluid origins of fractures that crosscut the Hercynian granitic basement and the Permo-Triassic formations in relation to the major tectonic events. Because the Mesozoic formations and the Hercynian basement on the graben flanks and inside the graben do not have the same evolution after uplift, our study includes 20 outcrops on both graben flanks and cores of the Soultz-sous-Forêts geothermal wells located inside the graben. The Hercynian granitic basement and Permo-Triassic formations were affected by several brittle phases associated with fluid circulation pulses related to graben formation during the Tertiary. We distinguished at least four stages: (1) reactivation of Hercynian structures associated with pre-rift tectonics during the early Eocene and descending meteoric waters, characterized by shearing/cataclasis textures and precipitation of illite and microquartz; (2) initiation of convective circulation of deep hot brines mixed with descending meteoric waters at the Hercynian basement/sedimentary cover interface during this first stage of Eocene rifting, characterized by dolomite and barite fillings in reactivated Hercynian fractures; (3) N-S tension fractures associated with rift tectonics just prior to uplift of the graben shoulders during Oligocene extension and descending meteoric waters, characterized by cataclastic textures and precipitation of quartz, illite, hematite, and barite; and (4) current convective circulation of deep hot brines mixed with descending meteoric waters at the Hercynian basement/sedimentary cover interface, characterized by calcite and barite fillings within the graben. This convective circulation is today present in deep geothermal wells in the western part of the Rhine graben.

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How Can Deep Geothermal Projects Provide Information on the Temperature Distribution in the Upper Rhine Graben? The Example of the Soultz-Sous-Forêts-Enhanced Geothermal System

Geosciences ◽

10.3390/geosciences10110459 ◽

2020 ◽

Vol 10 (11) ◽

pp. 459

Author(s):

Béatrice A. Ledésert ◽

Ronan L. Hébert

Keyword(s):

Temperature Distribution ◽

Source Rocks ◽

Geothermal System ◽

Upper Rhine Graben ◽

Fluid Temperature ◽

Thermal Anomalies ◽

Rhine Graben ◽

Mature Type ◽

Oil Source ◽

Upper Rhine

The Upper Rhine Graben (URG) hosts thermal anomalies that account for the development of oil fields. Recently, a geothermal power plant has been installed in this area. Data obtained in this framework provide an insight into the temperature distribution in the URG. The present thermal gradient at Soultz-sous-Forêts is not linear: nearly 90 °C/km down to 1400 m depth, then about 12 °C/km from that depth down to 5000 m. The combination of temperature conditions and natural fluid circulation in fracture networks has led to the hydrothermal alteration of the granite into mineral assemblages such as those including illite, quartz and calcite. Illite is locally impregnated with organic matter of two kinds: a mature type derived from oil source rocks and a less mature type derived from surficial sedimentary layers indicating the km-scale of transfer. Newly formed crystals of quartz and calcite from around 2000 m depth record a fluid temperature range of 130 to 170 °C, consistent with modelling and the temperatures measured at present in the drill-holes at this depth. In such hydrothermally altered zones, local variations of temperature are encountered indicating current fluid flows that are being sought for geothermal purposes.

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Upper Rhine Graben: Role of preexisting structures during rift evolution

Tectonics ◽

10.1029/2001tc900022 ◽

2002 ◽

Vol 21 (1) ◽

pp. 6-1-6-17 ◽

Cited By ~ 153

Author(s):

Markus E. Schumacher

Keyword(s):

Upper Rhine Graben ◽

Rhine Graben ◽

Upper Rhine

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

Environmental Earth Sciences ◽

10.1007/s12665-021-10111-z ◽

2022 ◽

Vol 81 (1) ◽

Author(s):

Nora Koltzer ◽

Giulia Kommana ◽

Mauro Cacace ◽

Maximilian Frick ◽

Judith Bott ◽

...

Keyword(s):

Fluid Flow ◽

Boundary Conditions ◽

Groundwater Flow ◽

Flow Dynamics ◽

Upper Rhine Graben ◽

Local Flow ◽

Regional Flow ◽

Rhine Graben ◽

Deep Fluid ◽

Upper Rhine

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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3D Modelling of the Northern Upper Rhine Graben Crystalline Basement by Joint Inversion of Gravity and Magnetic Data

10.5194/egusphere-egu21-477 ◽

2021 ◽

Author(s):

Matthis Frey ◽

Sebastian Weinert ◽

Kristian Bär ◽

Jeroen van der Vaart ◽

Chrystel Dezayes ◽

...

Keyword(s):

High Resolution ◽

Heat Transport ◽

Joint Inversion ◽

Transport Processes ◽

Crystalline Basement ◽

Magnetic Data ◽

Moho Depth ◽

Upper Rhine Graben ◽

Rhine Graben ◽

Upper Rhine

The crystalline basement of the Upper Rhine Graben presents an attractive target for deep geothermal projects due to its favourable temperatures and its high potential as a fractured and faulted reservoir system. It is already exploited at several sites, e.g. Soultz-sous-For&#234;ts or Landau, and further projects are currently planned or under development. The crystalline units are furthermore the main source of radiogenic heat production and thus, together with the shallow Moho depth and convective heat transport along large fault zones, significantly contributing to the crustal temperature field. For these reasons, we developed the most detailed 3D geological model of the basement in the northern Upper Rhine Graben to date within the Interreg NWE DGE-ROLLOUT and Hesse 3D 2.0 projects. Due to the small number of very deep boreholes as well as seismic profiles reaching the basement beneath the locally more than 5 km thick sedimentary cover, we additionally used high-resolution magnetic and gravity datasets. In contrast to common deterministic modelling approaches, we performed a stochastic joint inversion of the geophysical data by applying a Monte Carlo Markov Chain algorithm. This method generates a large set of random but valid models, which enables a statistical evaluation of the results, e.g. concerning the model uncertainties. For a realistic attribution of the model, we used existing petrophysical databases of the region and measured the magnetic susceptibility of more than 430 rock samples. As a result of the inversion, high-resolution voxel models of the density and susceptibility distribution were generated, allowing conclusions about the composition and structure of the crystalline crust, which leads to a reduction of uncertainties and risks associated with deep geothermal drillings in the northern Upper Rhine Graben. Furthermore, our model will serve as a basis for realistic simulations of heat transport processes in the fractured basement and a meaningful assessment of the deep geothermal potential in the future.

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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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Using 3D Seismic Exploration to Reduce the Geological Risk of Developing Geothermal Resources within the Upper Rhine Graben

71st EAGE Conference and Exhibition - Workshops and Fieldtrips ◽

10.3997/2214-4609.201404959 ◽

2009 ◽

Author(s):

M. G. Schreilechner ◽

C. G. Eichkitz ◽

A. Scholz

Keyword(s):

Seismic Exploration ◽

Upper Rhine Graben ◽

3D Seismic ◽

Geothermal Resources ◽

Rhine Graben ◽

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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