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Spichak V.,Russian Academy of Sciences | Geiermann J.,Institute for Geothermic Resources Management Bingen | Zakharova O.,Russian Academy of Sciences | Calcagno P.,Bureau de Recherches Geologiques et Minieres | And 2 more authors.
Near Surface Geophysics | Year: 2015

An indirect electromagnetic geothermometer is used for deep temperature estimations in the Soultz-sous-Forêts geothermal area (France) using magnetotelluric sounding data. Validation of temperature assessment carried out by comparison of the forecast temperature profile with temperature log from the deepest borehole has resulted in the relative extrapolation accuracy of less than 2%. It is found that the resistivity's uncertainty caused by magnetotelluric inversion errors and by possible effects of external factors very weakly affects the resulting temperature, with the latter being influenced mainly by the ratio between the borehole length and the extrapolation depth. The temperature cross-section constructed up to the depth 5000 m manifests local temperature maxima at large depths beneath the wells GPK2 and RT1/RT3. The analysis of the temperature profile in GPK2 location beneath 5000 m indicates that its behaviour continues to be of the conductive type (as in the depth range of 3700 m-5000 m) up to the depth 6000 m, while manifesting convective type below this depth. Finally, application of the indirect electromagnetic geothermometer for the deep temperature forecasting in the Rittershoffen site enabled us to constrain the location for future drilling. © 2015 European Association of Geoscientists & Engineers. Source

Baillieux P.,University of Neuchatel | Schill E.,GEIE Exploitation Miniere de la Chaleur | Edel J.-B.,Ecole et Observatoire des science de la Terre | Mauri G.,University of Neuchatel
International Geology Review | Year: 2013

The European Cenozoic Rift System hosts major temperature anomalies in Central Europe. In its central segment, the Upper Rhine Graben (URG), temperatures range from 75°C to nearly 150°C at a depth of 2000 m. Different hypotheses have been suggested to explain the localization of these anomalies. Our review and comprehensive interpretation of gravimetric and magnetic data, as well as neotectonic activity patterns, suggests that low-density, mostly magnetic and fractured granitic basement is systematically associated with major temperature anomalies. Further analyses provide insight into different heat transport processes contributing to the localization of these anomalies. Magnetic and gravity anomalies are known to represent lithological variations associated with the pre-Permian.We show their spatial relationship with positive temperature anomalies in the URG. Correlation between magnetics and temperature reveal a mean contribution of heat production to the temperature anomaly of about 10-15°C. A slightly higher mean value is obtained from correlation between gravity and temperature, which may be attributed to effects resulting from fracture porosity. The spatial relationship between temperature anomalies and neotectonic patterns indicates compressional shear and uplift regime for the major anomalies of the central segment of the URG. This is in agreement with different numerical models indicating free convection on fracture zones linked to faults. Our findings show that about 15-25% of the temperature anomaly can be attributed to variation in heat production. Hydrothermal circulation convection along faults, activated by the tectonic context, may explain the remaining 75-85% of the temperature anomalies. © 2013 Taylor & Francis. Source

Held S.,Karlsruhe Institute of Technology | Genter A.,GEIE Exploitation Miniere de la Chaleur | Kohl T.,Karlsruhe Institute of Technology | Kolbel T.,EnBW | And 2 more authors.
Geothermics | Year: 2014

The EGS pilot project in Soultz-sous-Forêts, is now operated by an industry consortium, heading for optimal reservoir management.A 3D thermo-hydraulic numerical model, based on a complex geological model of the reservoir is presented with the goal to determine input parameter for an economic analysis, comparing reservoir management based on levelized cost of energy.Over the projected life time of 30 years no major thermal breakthrough is predicted, small temperature decline affects net energy output only negligibly. The results highlight the benefits of multi-well systems, offering a larger heat exchanger surface and higher flexibility for reservoir management. © 2014 Elsevier Ltd. Source

Dorbath L.,University of Strasbourg | Evans K.,ETH Zurich | Cuenot N.,GEIE Exploitation Miniere de la Chaleur | Valley B.,ETH Zurich | And 3 more authors.
Comptes Rendus - Geoscience | Year: 2010

The stress field at the EGS geothermal site of Soultz-sous-Forêts has been the subject of many studies, because it largely controls the response of the reservoir to fluid injection. The analysis of borehole logging data, especially breakouts and drilling-induced tension fractures, in the four geothermal wells define an average SHmax orientation ranging between 170° and 180° down to 5 km depth. It also reveals strong heterogeneities in several depth intervals. In this paper, the inversion of double-couple source mechanisms of seismic events induced during GPK2 and GPK3 stimulation tests is performed to retrieve the orientation and shape factor of the stress tensor, using the Slickenside Analysis Package of Michael (1984, 1987a, 1987b). The results indicate a well-determined orientation of Shmin in GPK2 and in GPK3; in GPK3 Shmin is clockwise rotated by about 10°. The stress tensor defines an uniaxial extension. The results from both methods, analysis of borehole logging data and inversion of focal mechanisms, are only slightly different; the discrepancy may be due to the larger reservoir volume covered by the focal mechanisms, which can include strong stress heterogeneities. © 2010 Académie des sciences. Source

Nitschke F.,Karlsruhe Institute of Technology | Scheiber J.,GEIE Exploitation Miniere de la Chaleur | Kramar U.,Karlsruhe Institute of Technology | Neumann T.,Karlsruhe Institute of Technology
Neues Jahrbuch fur Mineralogie, Abhandlungen | Year: 2014

Scaling formation in surface installations of geothermal power plants can substantially affect power production by impairing heat transfer and reducing pipe diameters. In addition, the mineral deposits can incorporate naturally occurring radioactive nuclides into the crystal lattice during precipitation and have to be regarded as a potential hazard to health and environment. A profound understanding of formation mechanisms should facilitate the prevention of scaling in the future. Therefore fluid samples and scalings from the geothermal power plant at Soultz-sous-Forêts were investigated in detail. The fluid shows a total salinity (TDS) of 92 g/l and can be classified as Na-(Ca)-Cl-type. Considerations of the saturation state reveal a slight oversaturation with respect to barite (BaSO4) and celestine (SrSO4). X-Ray diffraction measurements together with scanning electron microscopic observation reveal that the scalings consist of barite-celestine solid solution ((Ba,Sr) SO4) interlayered with very fine layers of galena (PbS). The mineralogical composition was confirmed by X-ray fluorescence analysis showing a bulk composition of Ba (31.7-34.6 %), Sr (10.8-12.1 %), Pb (6.2-12.4 %) and S (13.1-14.5 %) for the sulfates, and Pb (66.6 %) and S (11.7 %) for the sulfidic part of the scalings. Other metals/metalloids like Sb (5.6 %), Cu (4.2 %), As (2.3 %) and Fe (2.0 %) were found to be present in minor amounts in the sulfides. Sulfur isotope studies show strong fractionation between the sulfate (δ34S =+15 ‰) and sulfide (δ34S = -12 ‰) phases. This indicates that bacterial sulfate reduction occurs, initiating sulfide precipitation from sulfate-rich fluids. The layered structure of the scalings can be correlated well with the operation state of the plant. Accordingly, sulfate layers precipitate under regular operation conditions, whereas sulfides were formed during start and shut-off phases of the plant. © 2014 E. Schweizerbart'sche Verlagsbuchhandlung, Stuttgart, Germany. Source

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