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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.

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.

Lengline O.,University of Strasbourg | Lamourette L.,University of Strasbourg | Vivin L.,University of Strasbourg | Cuenot N.,GEIE Exploitation Miniere de la Chaleur | Schmittbuhl J.,University of Strasbourg
Journal of Geophysical Research B: Solid Earth | Year: 2015

The static stress drop of an earthquake, which quantifies the ratio of seismic slip to the size of the rupture, is almost constant over several orders of magnitudes. Although variations are often observed, it is difficult, however, to attribute these variations either to a well-defined phenomenon or simply to measurement uncertainty. In this study we analyze the static stress drop of earthquakes that occurred during a water circulation test in the Soultz-sous-Forêts, France, geothermal reservoir in 2010. During this circulation test, 411 earthquakes were recorded, the largest event having a magnitude MD2.3. We show that several earthquakes in the reservoir can be combined into groups of closely located similar repeating waveforms. We infer that the amplitudes, and hence magnitudes, vary between the repeaters although the waveforms and spectra are both similar in shape. We measure similar corner frequencies for these events despite their different magnitudes, suggesting a similar rupture size. Our results imply that events at the same location may exhibit stress drop variations by as much as a factor of 300. We interpret that this variation in stress drop is caused by fluid pressure at the interface reducing the normal stress. We also hypothesize that the observed variations reflect a transition from stable to unstable slip on the imaged asperities. ©2014. American Geophysical Union. All Rights Reserved.

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 Géologiques et Minières | 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.

Mundhenk N.,Karlsruhe Institute of Technology | Huttenloch P.,Institute for Energy Research of Germany | Scheiber J.,GEIE Exploitation Miniere de la Chaleur | Genter A.,GEIE Exploitation Miniere de la Chaleur | And 2 more authors.
NACE - International Corrosion Conference Series | Year: 2014

Scaling and corrosion are both issues that account for serious problems in geothermal operation. Their occurrence is related to the hydrochemical characteristics of the geothermal water. In this work we report experiences from geothermal operation in Soultz-sous-Forêts (France) and provide preliminary results from a material testing campaign. The produced brines contain high amounts of dissolved solids (approx. 100 g/l) and challenge many materials. Conventional mild steels suffer uniform corrosion rates < 0.2 mm/year. Standard CrNiMo stainless steel S31600 and duplex S31803 undergo pitting in such environments. To be on the safe side higher alloyed materials or highly resistant organic coatings have to be chosen. Scaling is another serious concern and describes the formation of precipitates from the brine or from the interaction of the brine with metallic materials. These scales include barite-celestine solid solutions, galena, and siderite. Due to their toxicity the removal and disposal is necessary and accounts for extensive and frequent downtime periods. © 2014 by NACE International.

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.

Meller C.,Karlsruhe Institute of Technology | Genter A.,GEIE Exploitation Miniere de la Chaleur | Kohl T.,Karlsruhe Institute of Technology
Geophysical Journal International | Year: 2013

The appearance of clay in fractures is an important issue of applied geoscience as it not only affects the stability but also the flow paths through rocks. Forming a link between hydraulic, geochemical and mechanical processes, clay structures need to be thoroughly investigated. The growing importance of clay for waste disposal, petroleum research, geothermal exploration and geotechnical engineering necessitates tools to find and to characterize clay structures and clay minerals indirectly from geophysical measuring methods. Particularly, there is need for a technique enabling to map clay-rich zones from geophysical well logs acquired on-site in order to assess the mechanical and hydraulic properties of rocks. In this study, we present a neural network based method to map clay bearing fracture zones in crystalline facies. The study has been performed on the basis of geophysical and geological data acquired at the geothermal site of Soultz-sous-Forêts (France), in the granitic reservoir. A neural network was trained on geophysical logs from the fully cored exploration well EPS1. Calibration of the network was done on reference logs derived from the drill core. The effective calibration enabled the creation of synthetic clay content logs, which predict the clay amount in fractures along the well with >74 per cent accordance with a reference log. High clay contents could be located in faults, on which aseismic movements have been identified. The validation of this relationship destines the synthetic logs to help identifying potentially weak zones from geophysical logging methods.With application on non-cored wells, this tool can become a powerful means for assessing the probability of aseismic movements on faults caused by the presence of clay and estimating the hydraulic properties of fractures. © The Authors 2013. Published by Oxford University Press on behalf of The Royal Astronomical Society.

Guglielmetti L.,University of Neuchatel | Guglielmetti L.,University of Turin | Guglielmetti L.,Magma Energy Italia S.r.l. | Comina C.,University of Turin | And 3 more authors.
Tectonophysics | Year: 2013

Thermal sources are common manifestations of geothermal energy resources in Alpine regions. The up-flow of the fluid is well-known to be often linked to cross-cutting fault zones providing a significant volume of fractures. Since conventional exploration methods are challenging in such areas of high topography and complicated logistics, 3D geological modeling based on structural investigation becomes a useful tool for assessing the overall geology of the investigated sites. Geological modeling alone is, however, less effective if not integrated with deep subsurface investigations that could provide a first order information on geological boundaries and an imaging of geological structures. With this aim, in the present paper the combined use of 3D geological modeling and gravity surveys for geothermal prospection of a hydrothermal area in the western Alps was carried out on two sites located in the Argentera Massif (NW Italy). The geothermal activity of the area is revealed by thermal anomalies with surface evidences, such as hot springs, at temperatures up to 70. °C. Integration of gravity measurements and 3D modeling investigates the potential of this approach in the context of geothermal exploration in Alpine regions where a very complex geological and structural setting is expected. The approach used in the present work is based on the comparison between the observed gravity and the gravity effect of the 3D geological models, in order to enhance local effects related to the geothermal system. It is shown that a correct integration of 3D modeling and detailed geophysical survey could allow a better characterization of geological structures involved in geothermal fluids circulation. Particularly, gravity inversions have successfully delineated the continuity in depth of low density structures, such as faults and fractured bands observed at the surface, and have been of great help in improving the overall geological model. © 2013 Elsevier B.V.

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.

Scheiber J.,GEIE Exploitation Miniere de la Chaleur
NACE - International Corrosion Conference Series | Year: 2016

At the Soultz-sous-Forêts Enhanced Geothermal System (EGS) site, impairment of cast iron and mild steel surfaces was observed on downhole equipment like production pump, production pipes and some parts of the inner casing. The impairment went always along with arsenic enrichment in the related corrosion layer with increasing arsenic concentration close to severe corrosion damages. The related level of enrichment, which could reach several tenth of weight percent, rose the question whether or not arsenic is a trigger or a result of corrosion phenomena at the Soultz-sous-Forêts EGS site. This question is of importance for the Soultz location and other locations in the Upper Rhine Graben region as cast iron and mild steels are frequently used for downhole equipment like casing, production pipes and in some components of the production pump. An intense re-evaluation of downhole equipment showed that at the Soultz location arsenic is very probably enriched by adsorption on iron oxide surfaces and is therefore a result but not a trigger of electrochemical corrosion. The surface impairment is caused by transformation of the metal surface into iron oxide with high concentrations of adsorbed arsenic and, in some cases, antimony. Severe arsenic and antimony enrichment was found in combination with galvanic corrosion caused by connection of mild steel to ferritic-austenitic stainless steel. In this specific case, the deposition of pure arsenic and antimony cannot be excluded but it is considered to be a result and not the original trigger of the corrosion process. © 2016 by NACE International.

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