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Albaric J.,NORSAR | Calo M.,EOST | Husen S.,ETH Zurich | Oye V.,NORSAR | And 2 more authors.
Sustainable Earth Sciences, SES 2013: Technologies for Sustainable Use of the Deep Sub-Surface | Year: 2013

We performed a series of tests for passive seismic tomography with data from Paralana, a new Enhanced Geothermal System (EGS) located in South Australia. An injection well was drilled at Paralana in 2009 into a sedimentary basin down to a high heat-producing basement at ~4000 m depth. The first main hydraulic stimulation of the well took place in July 2011 in order to create/enhance a geothermal reservoir. Induced seismicity was monitored by a network of 20 stations (from surface to 1800 m depth) and more than 7000 microearthquakes were detected during the five days of injection. The synthetic tests indicate that small velocity heterogeneities into the reservoir can be resolved at Paralana if high-precision relative arrival times are used, such as provided by waveform-cross correlation. Preliminary results indicate a low P-wave velocity anomaly at the base of the well.

Baujard C.,GEOWATT AG | Schoenball M.,Karlsruhe Institute of Technology | Kohl T.,Karlsruhe Institute of Technology | Dorbath L.,EOST
Geothermics | Year: 2014

The occurrence of induced seismicity during reservoir stimulation requires robust real-time monitoring and forecasting methods for risk mitigation. We propose to derive an estimation of Mmax (here defined as the largest single seismic event occurring during or after reservoir stimulation) using hydraulic energy as a proxy to forecast the total induced seismic moment and to model the transient evolution of the seismic moment distribution (based on the Gutenberg-Richter relation). The study is applied to the vast dataset assembled at the European pilot research project at Soultz-sous-Forêts (Alsace, France), where four major hydraulic stimulations were conducted at 5km depth. Although the model could reproduce the transient evolution trend of Mmax for every dataset, detailed results show different agreement with the observations from well to well. This might reveal the importance of mechanical and geological conditions that may show strong local variations in the same EGS. © 2014 Elsevier Ltd.

Lecomte I.,ICG | Juliussen H.,CSIC - Mediterranean Institute for Advanced Studies | Nagel Storen E.W.,CSIC - Mediterranean Institute for Advanced Studies | Sauvin G.,UiO | And 5 more authors.
Near Surface Geoscience 2012 | Year: 2012

Studying glacial and mountain hazards is necessary as the world seems to face major climate changes, which may increase the frequency of catastrophic events, e.g., debris flows. The latter processes are well understood, but changes in their frequency and relationships to climatic variability are not. In the present study, aiming at imaging an entire debris-flow system from the release area to the depositional area, correlations of lake sediments to specific slope deposits on land are looked for by using a combined approach including geology, sediment-core analysis and geophysical surveys (ERT, GPR and seismic). Our overall goal is to create a chronology of debris-flow events from lake Leirvatnet in order to be able to compare debris-flow records with existing paleo-climatic data and evaluate the climatic impact on debris-flow frequency in a long-term perspective. Following the mapping and thickness estimate of the sediment cover on the lake bottom obtained from GPR, we are evaluating the spatial continuity of reflectors associated with sections of high debris-flow activity to relate them to debris-flow deposits on land (imaged by ERT, GPR and seismic), having a complete Holocene sedimentological history from the lake. Actual results indicate a large temporal variability in debris flows.

Calo M.,EOST | Calo M.,Berkeley Seismolgical Laboratory | Dorbath C.,EOST | Frogneux M.,EOST
Geothermics | Year: 2014

The European Enhanced Geothermal System (EGS) program of Soultz-sous-Forêts is organized around three wells (GPK2, GPK3, and GPK4) drilled to a depth of about 5000. m. Hydraulic stimulations were performed in order to increase the injectivity of the reservoir and the connectivity among the wells. The stimulation of GPK4 was carried out in two stages, in September 2004 and in February 2005, followed by an acidification test performed in March 2005. The stimulations produced fewer induced events than those of the other wells, with interpretation remaining difficult. In this work we present some new observations on the seismicity of the GPK4 stimulations after a complete review of the seismic bulletins collected in 2004 and 2005. Furthermore, the events were relocated using the double difference method. The new images of the seismicity are presented in temporal sequences according to the main variations of the injection parameters. The seismic events that occurred during the 2004 stimulation are grouped in a dense cloud and centered on the well open-hole section, while in 2005 seismicity depicts a specific pattern suggesting that the "natural" stress field in the reservoir was not completely restored. Finally, the events recorded during the acidified test show that the reservoir behaved differently from the previous injections, which suggests that a different mechanism has controlled the induced seismicity. © 2013 Elsevier Ltd.

Sausse J.,University of Lorraine | Dezayes C.,Bureau de Recherches Géologiques et Minières | Dorbath L.,EOST | Genter A.,British Petroleum | Place J.,EOST
Comptes Rendus - Geoscience | Year: 2010

This study presents a new deterministic 3D model of the fracture zones observed in the granitic reservoir of the Soultz European geothermal project. The major fracture zones encountered around 6 wells (4550, EPS1, GPK1, GPK2, GPK3 and GPK4) consist in 53 main structures that are located and characterized in terms of size and orientation: 39 fracture zones, 8 microseismic structures and 6 structures derived from vertical seismic profiles are represented in the 3D model using Discrete Fracture Network tools of the gOcad modelling platform (Paradigm™, Earth Decision™). This work illustrates the complexity of 3D fracture zone correlation and interpretation in crystalline rock masses characterized at meter scale (borehole) and at the reservoir scale (kilometer) thanks to geophysical imaging techniques. © 2010 Académie des sciences.

Agard P.,University Pierre and Marie Curie | Omrani J.,Geological Survey of Iran | Jolivet L.,University of Orléans | Whitechurch H.,EOST | And 5 more authors.
Geological Magazine | Year: 2011

This paper presents a synthetic view of the geodynamic evolution of the Zagros orogen within the frame of the Arabia-Eurasia collision. The Zagros orogen and the Iranian plateau preserve a record of the long-standing convergence history between Eurasia and Arabia across the Neo-Tethys, from subduction/obduction processes to present-day collision (from ∼ 150 to 0 Ma). We herein combine the results obtained on several geodynamic issues, namely the location of the oceanic suture zone, the age of oceanic closure and collision, the magmatic and geochemical evolution of the Eurasian upper plate during convergence (as testified by the successive Sanandaj-Sirjan, Kermanshah and Urumieh-Dokhtar magmatic arcs), the P-T-t history of the few Zagros blueschists, the convergence characteristics across the Neo-Tethys (kinematic velocities, tomographic constraints, subduction zones and obduction processes), together with a survey of recent results gathered by others. We provide lithospheric-scale reconstructions of the Zagros orogen from ∼ 150 to 0 Ma across two SW-NE transects. The evolution of the Zagros orogen is also compared to those of the nearby Turkish and Himalayan orogens. In our geotectonic scenario for the Zagros convergence, we outline three main periods/regimes: (1) the Mid to Late Cretaceous (115-85 Ma) corresponds to a distinctive period of perturbation of subduction processes and interplate mechanical coupling marked by blueschist exhumation and upper-plate fragmentation, (2) the Paleocene-Eocene (60-40 Ma) witnesses slab break-off, major shifts in arc magmatism and distributed extension within the upper plate, and (3) from the Oligocene onwards (∼ 30-0 Ma), collision develops with a progressive SW migration of deformation and topographic build-up (Sanandaj-Sirjan Zone: 20-15 Ma, High Zagros: ∼12-8 Ma; Simply Folded Belt: 5-0 Ma) and with partial slab tear at depths (∼10 Ma to present). Our reconstructions underline the key role played by subduction throughout the whole convergence history. We finally stress that such a long-lasting subduction system with changing boundary conditions also makes the Zagros orogen an ideal natural laboratory for subduction processes. © 2011 Cambridge University Press.

Magnenet V.,CNRS Computer Science and Engineering Laboratory | Fond C.,CNRS Computer Science and Engineering Laboratory | Genter A.,British Petroleum | Schmittbuhl J.,EOST
Geothermal Energy | Year: 2014

Background: A two-dimensional numerical model is developed for the Soultz-sous-Forêts reservoir from an idealized cross-section containing six homogeneous horizontal layers. The considered constitutive equations are those of homogenized saturated porous media involving Thermo-Hydro-Mechanical (THM) couplings, and most of materials properties (for brine and rocks) are taken dependent on temperature and pressure. Methods: The constitutive equations are solved in transient regime with the finite element software Code_Aster to reach a stationary state of the reservoir. Results: We show that a large scale natural convection is compatible with present boundary conditions if the permeability of the reservoir is of the order of 1.0×10−14m2. Convection cells are of the order of 1.3 km in width and we analyze several vertical profiles and maps of physical properties. Conclusions: A stationary convective solution at large scale is highlighted. © 2014, Magnenet et al.; licensee Springer.

Ordonez A.,EOST | Sollner W.,PGS
75th European Association of Geoscientists and Engineers Conference and Exhibition 2013 Incorporating SPE EUROPEC 2013: Changing Frontiers | Year: 2013

The imaging condition needs special attention in imaging of separated wavefields because of the increased complexity of the source wavefield. Starting from reciprocity relations and using pressure-normalized wavefield decomposition, we introduce a new deconvolution imaging condition in which the subsurface image is determined from the upgoing pressure and the downgoing vertical particle velocity wavefields. In a recent work, Lameloise et al. (2012) elaborated on migration of separated wavefields using dual-sensor towed streamer data of a simultaneous source system. This work was the starting point to set up a feasibility study and test the new imaging condition. Synthetic and real data examples showed that this approach leads to a better match between the depth images of multiples and primaries. Copyright © (2012) by the European Association of Geoscientists & Engineers All rights reserved.

Beaumont S.,EOST | Sollner W.,EOST
75th European Association of Geoscientists and Engineers Conference and Exhibition 2013 Incorporating SPE EUROPEC 2013: Changing Frontiers | Year: 2013

Multi-azimuth data acquisition has shown benefits in noise reduction and structure illumination, which leads generally to improved seismic images. However the current time processing, which is based on independent processing of the data from the different predominant azimuths, may lead to destructive interferences and deterioration of the final stacked image when the earth model is anisotropic or laterally heterogeneous. In order to solve this problem a prestack time migration for anisotropic, weakly heterogeneous media has been recently introduced and tested on synthetic data. In this work, we ran a first field data application on a multi-azimuth data set. From data in three different acquisition azimuths we performed migration velocity analysis to build azimuth-dependent migration operators. We processed the data in parallel also with conventional narrow azimuth prestack time migration in order to assess the performance of the new approach. Copyright © (2012) by the European Association of Geoscientists & Engineers All rights reserved.

Tatevossian R.E.,Russian Academy of Sciences | Aptekman Z.Y.,Russian Academy of Sciences | Dorbath C.,EOST | Vakarchuk R.N.,Russian Academy of Sciences | Tatevossian T.N.,Russian Academy of Sciences
Izvestiya, Physics of the Solid Earth | Year: 2011

Relationship between the intensity of seismic shaking on the surface and the velocity structure of the medium at large depth is studied. The Spitak earthquake of December 7, 1988 is chosen as an object of study. A method to correlate the intensity of shaking in the localities to the geophysical parameters specified in the nodes of regular spatial grid is proposed. Formalized definition of anomalous intensity is suggested; it takes into account the distribution of distances from the localities with given intensity degrees to the hypocenter or to the nearest segment of the surface fault. It is found that the seismic wave velocities at a depth of 1 km are higher (up to 0.2-0.6 km/s) under the localities with anomalously high intensity. No any certain regularity is found in deeper layers. © 2011 Pleiades Publishing, Ltd.

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