Using highly accurate land gravity and 3D geologic modeling to discriminate potential geothermal areas: Application to the Upper Rhine Graben, France

New land gravity data results acquired in northern Alsace were presented. Compared to the available old Bouguer anomaly, we recovered an accurate Bouguer anomaly field showing data uncertainties [Formula: see text]. A qualitative data analysis using pseudotomographies reveals several negative anomalies suggesting a decrease of the bulk density at the depth of geothermal interest. We have performed a quantitative study on the basis of the existing 3D geologic model derived from a reinterpretation of the vintage seismics. The theoretical gravity response indicates a great mismatch with the observed Bouguer anomaly. The stripping approach was applied, and the stripped Bouguer anomaly indicates that the density values of the Jurassic, but especially for the Triassic, the Buntsandstein, and the upper part of the basement, were overestimated even using the density values measured in the deep geothermal borehole. This suggests that the borehole density values do not reflect the density variations occurring at larger scale. To reduce the Bouguer anomaly during stripping, a negative density contrast should be affected to the Buntsandstein layer overlaying the basement, suggesting that the part located between the Buntsandstein and the upper part of the basement presents a low-density value compared to the reference density, which is not necessarily expected and is not observed in the densities measured in the borehole. Interestingly, a correlation is found between the gravity analyses and the thermal gradient boreholes in the northern part of the study area. For two boreholes, the gravity interpretation suggests a huge density decrease in the Buntsandstein, which may arise from a combination of high-density fracturing and the important quantity of geothermal fluid significantly affecting the bulk density. Analysis of the thermal borehole data suggests that these two boreholes indicate higher geothermal potential compared with the other boreholes.

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Overdeepenings modelled with gravimetry-based data

10.5194/egusphere-egu2020-15807 ◽

2020 ◽

Author(s):

Dimitri Bandou ◽

Patrick Schläfli ◽

Michael Schwenk ◽

Guilhem Douillet ◽

Edi Kissling ◽

...

Keyword(s):

Earth Science ◽

Gravity Data ◽

Bouguer Anomaly ◽

Borehole Data ◽

Regional Trend ◽

Shallow Subsurface ◽

Base Level ◽

Geological Past ◽

Central Switzerland ◽

Density Values

The processes and mechanisms resulting in overdeepenings, valleys carved deeper than today&#8217;s rivers base level during glaciations, are still a matter of debate. Whether or not these valleys formation is due to glacial or fluvio-glacial processes or through fluvial down cutting in the geological past is difficult to affirm, as the depressions are filled with sediment or host lakes (Cook and Swift, 2012). In order to bypass this limitation, we use precise gravimetric data, GNSS data and borehole data, which we combine within a 3D forward modelling code, Gravi3D. We particularly aim at reconstructing the geometry of overdeepened valleys&#8217; walls, which bear information on the erosional mechanism leading to the formation of these troughs. We proceed through the building of models for a given geometry to reproduce the Bouguer gravity that we measured in the field along sections and on a grid of stations. We constrain our models by using precise density values, determined by gravimetry, along with borehole data.We apply this technique to overdeepenings located in the Alpine foreland (Belpberg area, Central Switzerland) because this area hosts multiple overdeepenings from the past glaciations. The region is characterized by three hill ranges made up of Molasse bedrock with c. 300 m-deep and c. 1 km-wide valleys in-between, where overdeepenings with a Quaternary infill are expected. The results of gravity data collection, accomplished over a section with stations spaced between 100 and 300 m and after standard corrections yield a Bouguer anomaly for the Belpberg region that ranges from c. -99 to -106 mgal. We infer this large range to the regional trend (c. 2 mgal over 8 km) and to the effect of the overdeepening infill (2-4 mgal over 1 km), disclosing a sharp anomaly pattern over the inferred overdeeping. The subsequent three steps include: (i) the removal of the regional trend, (ii) the use of the Nettleton method for the quantification of an accurate density contrast between the Molasse bedrock and the Quaternary infill, and (iii) the configuration of Gravi3D for the Belpberg situation, will yield further information on the morphology of the overdeeping. We thus conclude that Gravi3D, within this framework, is a useful tool to determine the geometry of overdeepings in particular, and shallow subsurface bodies and structures in general.Reference:Cook, S.J., Swift, D.A., 2012. Subglacial basins: Their origin and importance in glacial systems and landscapes. Earth-Science Reviews 115, 332&#8211;372.

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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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Geothermal Reservoir Identification based on Gravity Data Analysis in Rajabasa Area- Lampung

RISET Geologi dan Pertambangan ◽

10.14203/risetgeotam2021.v31.1164 ◽

2021 ◽

Vol 31 (2) ◽

pp. 77

Author(s):

Muh Sarkowi ◽

Rahmat Catur Wibowo

Keyword(s):

Gradient Analysis ◽

Hot Spring ◽

Gravity Data ◽

Bouguer Anomaly ◽

Ground Level ◽

Geothermal System ◽

Mountain Area ◽

Density Values ◽

Fault Structures ◽

Reservoir Identification

Gravity research in the Rajabasa geothermal prospect area was conducted to determine geothermalreservoirs and faults as reservoir boundaries. The research includes spectrum analysis and separation of the Bouguer anomaly to obtain a residual Bouguer anomaly, gradient analysis using the second vertical derivative (SVD) technique to identify fault structures or lithological contact, and 3D inversion modeling of the residual Bouguer anomaly to obtain a 3D density distribution subsurface model. Analysis was performed based on all results with supplementary data from geology, geochemistry, micro-earthquake (MEQ) epicenter distribution map, and magnetotelluric (MT) inversion profiles. The study found 3 (three) geothermal reservoirs in Mount Balirang, west of Mount Rajabasa, and south of Pangkul Hot Spring, with a depth of around 1,000-1,500 m from the ground level. Fault structures and lithologies separate the three reservoirs. The location of the reservoir in the Balirang mountain area corresponds to the model data from MEQ, temperature, and magnetotelluric resistivity data. The heat source of the geothermal system is under Mount Rajabasa, which is indicated by the presence of high-density values (might be frozen residual magma), high-temperature values, and the high number of micro-earthquakes epicenters below the peak of Mount Rajabasa.

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Geometry of alpine overdeepenings assessed with gravimetry and 3-D modelling

10.5194/egusphere-egu21-2756 ◽

2021 ◽

Author(s):

Dimitri Bandou ◽

Patrick Schläfli ◽

Michael Schwenk ◽

Guilhem A. Douillet ◽

Edi Kissling ◽

...

Keyword(s):

Gravity Data ◽

Bouguer Anomaly ◽

Satellite System ◽

Gravity Gradient ◽

Gravitational Attraction ◽

Borehole Data ◽

Regional Trend ◽

Study Region ◽

The North ◽

Modelling Framework

Interpretations of the processes leading to the formation of overdeepened valleys, where the bedrock lies well below sea level today, are contested as the overdeepenings have been filled by sediments or host lakes making observations difficult. Here, we combine gravimetric, GNSS (Global Navigation Satellite System) and borehole data within a 3D forward modelling framework (Gravi3D) to assess the 3-D subsurface geometry of such overdeepenings in the Swiss plateau, to the North of the Alps. Gravi3D has two components (PRISMA and BGPoly), which allow to obtain analytically the gravity effect of prisms and polygons (Nagy (1966) and Talwani & Ewing (1960)). PRISMA allows first to estimate the spatial extent of an overdeepening and the density contrast between the overdeepening fill and the bedrock. In contrast, BGPoly is designed to disclose the details of a complex 3-D geometry of an overdeepening fill through an approximation of its shape with polygons. Gravi3D will be open access and is designed for a larger scientific community.&#160; Here, we focus on overdeepenings beneath two valleys, the Aare valley and the G&#252;rbe valley to the South of Bern. In this region, the occurrence of overdeepenings has already been disclosed through drilling, but the details about the geometry have not been elaborated yet. The study region is characterized by three mountain ranges oriented North-South and comprises Burdigalian Upper Marine Molasse bedrock. The G&#252;rbe and Aare valleys in-between are c. 300 m-deep and c. 1 km-wide, where overdeepenings with a >100 m-thick Quaternary fill have already been identified by drilling. The gravity data collected along an 8 km-long profile with stations spaced between 100 and 300 m yield a Bouguer anomaly that ranges from c. -99 to -106 mGal. We relate this anomaly to the regional trend (c. 2 mGal over 8 km) and to the effect of the overdeepenings&#8217; sedimentary fillings (2 &#8211; 4 mGal/km), disclosing a sharp anomaly pattern over the inferred tunnel valleys. The removal of the signal related to the regional trend results in a residual anomaly of c. 1 mGal for the bedrock ridge in-between the valleys (Belpberg mountain), and of -2.65 and -3.56 mGal for the G&#252;rbe and Aare valley overdeepenings, respectively. We observe a steeper gravity gradient for the Eastern flank of both overdeepenings. The use of Nettleton method to model the residual gravity anomaly across Belpberg yields a density of 2.5 g/cm3 for the Molasse bedrock. In addition, the estimation of the largest gravity response through the overdeepening fill, calculated with Prisma yields a density value of c. 2.0 &#8211; 2.2 g/cm3 for the Quaternary sediments. As a further information, Prisma predicts a maximum thickness of 140 m for the Quaternary suite beneath the G&#252;rbe valley and at least 200 m beneath the Aare valley. This yields a minimum slope of approximately 18&#176; for the G&#252;rbe overdeepening.&#160;REFERENCESNagy, D.: The gravitational attraction of a right rectangular prism. Geophysics 31, 362&#8211;371, 1966.Talwani, M., Ewing, M.: Rapid computation of gravitational attraction of three&#8208;dimensional bodies of arbitrary shape. Geophysics 25, 203&#8211;225, 1960.

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Stratigraphie und Morphogenese von frühpleistozänen Ablagerungen zwischen Bodensee und Klettgau

E&G Quaternary Science Journal ◽

10.3285/eg.58.1.02 ◽

2009 ◽

Vol 58 (1) ◽

pp. 12-54 ◽

Cited By ~ 4

Author(s):

Hans Rudolf Graf

Keyword(s):

Climatic Conditions ◽

Early Pleistocene ◽

Tectonic Activity ◽

Lake Constance ◽

Systematic Evaluation ◽

Upper Rhine Graben ◽

Borehole Data ◽

Rhine Graben ◽

Lithostratigraphic Units ◽

Upper Rhine

Abstract. The stratigraphy and paleogeography of the Deckenschotter (“cover gravels”) of the Rhine glacier system between Lake Constance, the city of Schaffhausen and the Klettgau area (Switzerland, Germany) was revised. This was achieved by means of new surveying and mapping, petrographical analysis und a systematic evaluation of available literature and borehole data. Within the Deckenschotter three morphostratigraphic units can be discerned: (a) Höhere (higher) Deckenschotter, (b) Tiefere (lower) Deckenschotter and (c) Tiefere Deckenschotter, unteres Niveau (lower level). The topographically highest unit, the Höhere Deckenschotter, cannot be subdivided into lithostratigrafic units. The gravels classified as Tiefere Deckenschotter are grouped into two morphostratigraphical units; the altitude difference of the bases of both units is minor. They are, however, separated by an erosional discontinuity caused by a signifi cant rearrangement of the hydrographic network.The older one of the two units (Tiefere Deckenschotter) comprises sediments of at least two depositional phases, separated from each other by a hiatus. There are signs of temperate climatic conditions during the period of non-deposition. The tectonic analysis of the study area showed that in general the altitude of the Deckenschotter was not affected by post-depositional tectonic activity. A tectonic displacement of the Deckenschotter occurrences in the Hegau cannot be ruled out as their topographic position is unusually high compared to equivalent deposits further paleo-downstream. However, this does not affect the proposed morphostratigraphic subdivision. The Upper Rhine Graben system (tectonic lowering) controlled the hydraulic base level and the morphogenesis for both the Deckenschotter occurrences discussed here and those in central northern Switzerland. Therefore, the morphostratigraphic units of both regions can be correlated, even though the number of lithostratigraphic units does not match. In the Höhere Deckenschotter this could be ascribed to an incomplete sedimentary record or a lack of data; on the other hand, this might indicate that the connection Lake Constance – Upper Rhine Graben was established later than the connection Lake Walen – Upper Rhine Graben. In contrast, there is no simple morpho- or lithostratigrafic correlation with the early pleistocene deposits of the German Alpine Foreland, since they are oriented towards and controlled by the Donau river system.

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Influence of the Main Border Faults on the 3D Hydraulic Field of the Central Upper Rhine Graben

Geofluids ◽

10.1155/2019/7520714 ◽

2019 ◽

Vol 2019 ◽

pp. 1-21 ◽

Cited By ~ 7

Author(s):

Jessica Freymark ◽

Judith Bott ◽

Mauro Cacace ◽

Moritz Ziegler ◽

Magdalena Scheck-Wenderoth

Keyword(s):

Heat Transport ◽

Structural Model ◽

Fluid Velocity ◽

Three Dimensional ◽

Upper Rhine Graben ◽

Rhine Graben ◽

Dimensional Interaction ◽

Geothermal Potential ◽

Hydraulic Regime ◽

Upper Rhine

The Upper Rhine Graben (URG) is an active rift with a high geothermal potential. Despite being a well-studied area, the three-dimensional interaction of the main controlling factors of the thermal and hydraulic regime is still not fully understood. Therefore, we have used a data-based 3D structural model of the lithological configuration of the central URG for some conceptual numerical experiments of 3D coupled simulations of fluid and heat transport. To assess the influence of the main faults bordering the graben on the hydraulic and the deep thermal field, we carried out a sensitivity analysis on fault width and permeability. Depending on the assigned width and permeability of the main border faults, fluid velocity and temperatures are affected only in the direct proximity of the respective border faults. Hence, the hydraulic characteristics of these major faults do not significantly influence the graben-wide groundwater flow patterns. Instead, the different scenarios tested provide a consistent image of the main characteristics of fluid and heat transport as they have in common: (1) a topography-driven basin-wide fluid flow perpendicular to the rift axis from the graben shoulders to the rift center, (2) a N/NE-directed flow parallel to the rift axis in the center of the rift and, (3) a pronounced upflow of hot fluids along the rift central axis, where the streams from both sides of the rift merge. This upflow axis is predicted to occur predominantly in the center of the URG (northern and southern model area) and shifted towards the eastern boundary fault (central model area).

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Bouguer density determination by fractal analysis

Geophysics ◽

10.1190/1.1442909 ◽

1990 ◽

Vol 55 (7) ◽

pp. 932-935 ◽

Cited By ~ 12

Author(s):

Freyr Thorarinsson ◽

Stefan G. Magnusson

Keyword(s):

Fractal Dimension ◽

Fractal Analysis ◽

Gravity Data ◽

Bouguer Anomaly ◽

New Method ◽

Data Sets ◽

Isostatic Compensation ◽

Topographic Features ◽

Density Determination ◽

Density Values

Density values for the Bouguer reduction of two gravity data sets from Iceland are determined using a new method based on minimization of the roughness of the Bouguer anomaly surface. The fractal dimension of the surface is used as a gauge of the roughness. The analysis shows the size of topographic features supported by crust without isostatic compensation to be 25 to 30 km in southwest Iceland and 9 to 10 km inside the active rifting zone. The densities selected for these areas are 2490 and [Formula: see text], respectively.

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Scaling in a Geothermal Heat Exchanger at Soultz-Sous-Forêts (Upper Rhine Graben, France): A XRD and SEM-EDS Characterization of Sulfide Precipitates

Geosciences ◽

10.3390/geosciences11070271 ◽

2021 ◽

Vol 11 (7) ◽

pp. 271

Author(s):

Béatrice A. Ledésert ◽

Ronan L. Hébert ◽

Justine Mouchot ◽

Clio Bosia ◽

Guillaume Ravier ◽

...

Keyword(s):

Heat Exchanger ◽

Energy Production ◽

Electricity Production ◽

Normal Operation ◽

Upper Rhine Graben ◽

Geothermal Heat ◽

Deep Wells ◽

Upper Rhine ◽

Management Issues

The Soultz-Sous-Forêts geothermal site (France) operates three deep wells for electricity production. During operation, scales precipitate within the surface installation as (Ba, Sr) sulfate and (Pb, As, Sb) sulfide types. Scales have an impact on lowering energy production and inducing specific waste management issues. Thus scaling needs to be reduced for which a thorough characterization of the scales has to be performed. The geothermal brine is produced at 160 °C and reinjected at 70 °C during normal operation. In the frame of the H2020 MEET project, a small heat exchanger was tested in order to allow higher energy production, by reinjecting the geothermal fluid at 40 °C. Samples of scales were analyzed by XRD and SEM-EDS, highlighting that mostly galena precipitates and shows various crystal shapes. These shapes can be related to the turbulence of the flow and the speed of crystal growth. Where the flow is turbulent (entrance, water box, exit), crystals grow quickly and mainly show dendritic shape. In the tubes, where the flow is laminar, crystals grow more slowly and some of them are characterized by well-developed faces leading to cubes and derived shapes. The major consequence of the temperature decrease is the increased scaling phenomenon.

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