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Faults and fractures represent unique features of the solid Earth and are especially pervasive in the shallow crust. Aside from directly relating to crustal dynamics and the systematic assessment of associated risk, fault and fracture networks enable the efficient migration of fluids and therefore have a direct impact on concrete topics relevant to society, including climate-change-mitigating measures like CO2 sequestration or geothermal exploration and production. Due to their small-scale complexity, fault zones and fracture networks are typically poorly resolved, and their presence can often only be inferred indirectly in seismic and ground-penetrating radar (GPR) subsurface reconstructions. We suggest a largely data-driven framework for the direct imaging of these features by making use of the faint and still often underexplored diffracted portion of the wave field. Finding inspiration in the fields of optics and visual perception, we introduce two different conceptual pathways for coherent diffraction imaging and discuss respective advantages and disadvantages in different contexts of application. At the heart of both of these strategies lies the assessment of data coherence, for which a range of quantitative measures is introduced. To illustrate the versatility and effectiveness of the approach for high-resolution geophysical imaging, several seismic and GPR field data examples are presented, in which the diffracted wave field sheds new light on crustal features like fluvial channels, erosional surfaces, and intricate fault and fracture networks on land and in the marine environment.

The purpose of this work is to study the subsoil structure of the Campi Flegrei area using both spectral ratios and array techniques applied to seismic noise. We have estimated the dispersion curves of Rayleigh waves by applying the Frequency–Wavenumber (f–k hereinafter) and Modified Spatial Autocorrelation (MSPAC) techniques to the seismic noise recorded by the underground short period seismic Array “ARF”, by the broadband stations of the UNREST experiment and by the broadband stations of the seismic monitoring network of INGV – Osservatorio Vesuviano. We have performed the inversion of a dispersion curve (obtained averaging the f–k and MSPAC dispersion curves of seismic noise and single phase velocity values of coherent transient signals) jointly with the H∕V spectral ratio of the broadband station CELG, to obtain a shear wave velocity model up to 2000 m depth. The best-fit model obtained is in a good agreement with the stratigraphic information available in the area coming from shallow boreholes and deep wells drilled for geothermal exploration. In active volcanic areas, such as Campi Flegrei, the definition of the velocity model is a crucial issue to characterize the physical parameters of the medium. Generally, a high quality characterization of the medium properties helps to separate the contributions of the volcanic source, path and site in the geophysical observables. Therefore, monitoring possible variations in time of such properties in general can help to recognize anomalies due to the volcano dynamics, i.e. fluid migration connected to the volcanic activity.

The borehole-to-surface electromagnetic (EM) method is a viable imaging and monitoring tool for energy reservoirs, geologic storage, geothermal exploration, fault zones, and other subsurface targets. Data interpretation typically requires considering steel-casing effects, but it is difficult and impractical to directly discretize arbitrarily oriented hollow steel-cased wells in a 3D reservoir-scale earth model because of their extremely high electrical conductivity and long hollow geometry. We have considered a borehole-to-surface EM configuration in which an electric dipole source is placed below the bottom of a steel-cased well. To practically simulate the casing effects on EM measurements, we develop a novel 3D finite-element EM algorithm using an unstructured tetrahedral mesh. To avoid excessive use of fine grids for modeling a steel-cased well, the well is replaced with the combination of a short solid conductive prism and a long linewise perfect electric conductor. We find that this combined structure can approximate casing effects at a small fraction of the computational cost required for modeling a complete hollow casing because the linewise structure is volumeless and does not require an excessive number of small elements. We also find that steel-cased wells distant from sources and receivers can be modeled as simple linewise perfect electric conductors, further improving the computational efficiency. Using this approximation, the 3D EM algorithm presented here is well-suited to modeling many arbitrarily oriented steel-cased wells. After verifying the accuracy and efficiency of this approach using various examples, we performed a 3D borehole-to-surface/surface-to-borehole and surface EM inversion and determine that the inversion can image a deep localized target in the presence of steel infrastructure.

The Geothermal fluid has a very high content of dissolved elements. Geochemical methods are used to determine the potential indication of dissolved economic elements. Geothermal exploration has been carried out throughout Indonesia, mainly by the Geological Agency. The exploration result in the existence of hot spring data by analyzing SiO2, Al, Fe, Ca, Mg, Na, K, Li, As, NH4, B, F, Cl, SO4, HCO3, and CO2. Base on the secondary data of 256 locations of hot spring in Indonesia that were statistically analyzed, an overview of the association of economic elements and impurities elements is obtained. Dieng Geothermal Power Plant with that has recuring problem of silica scale formation, becomes an interesting object as a case study of the potential of dissolved economic elements. The increase in dissolved content in geothermal fluids apart from naturally occurring, is triggered even more strongly by the geothermal power plant operating system, which changes the liquid phase to the vapor phase, hence the remaining liquid phase more concentrated. The potential content of economic chemical elements is determined by discharge measuring of the remaining liquid phase produced and the results of the analysis of the element concentration dissolved. The results of geochemical data clustering of hot springs obtained four elemental association, the association of SiO2-F, Al-Fe-SO4, Ca-Mg-Cl-Na-K, and Li-B-HCO3. Dissolved lithium content is high in several geothermal areas in Indonesia, found in hot springs with chloride type fluids. The brine produced from the reservoir at the Dieng Geothermal Power Plant is from a meteoric type fluid that has intensively reacted with the surrounding rock and a magmatic type fluid. The remaining brine that is from several separators and comes out through the silencer, at the Dieng Geothermal Power Plant has a total discharge of 457.1 m3/hour, contains high levels of several elements, lithium 77.31-99.4 mg/l, silica 1109.25-1220.9 mg/l, boron 404.16-589.4 mg/l, potassium 2532.2-4536.5 mg/l, and manganese 5.49-15.82 mg/l.

The current study deals with an estimate of the Curie point depth, heat flow and geothermal gradient from spectral analysis of aeromagnetic data covering an area located approximately between latitude 7.5o N to 11.5o N and longitude 7.5o E to 10.5o E, which corresponds to parts of the Benue trough (lower part of the Upper Benue trough, the entire middle Benue trough, and upper part of the Lower Benue trough), lower part of the Gongola and Yola Basins, the Precambrian Basement, the Jurassic Younger Granites and two prominent hot Springs, Wiki hot spring in Bauchi state (in the north-eastern part) and Akiri hot spring in Nasarawa state (in the south-western part) of central and north-eastern Nigeria. Radially power spectrum was applied to the aeromagnetic data of the study area divided into 48 square blocks and each block analysed using the spectral centroid method to obtain depth to the top, centroid and bottom of magnetic sources. The depth values were subsequently used to evaluate the Curie-point depth (CPD), geothermal gradient and near-surface heat flow in the study area. The values of the curie point depths (Zb), range from 7.6341 km to 34.5158 km, with a mean value of 14.7928km, geothermal gradient, range from 16.8039 0C km-1 to 75.97490C km-1, with mean value of 45.7021 0C km-1 and heat flow (q), range from 42.0097 mWm-2 to 189.9372mWm-2, with a mean value of 114.2554mWm-2. Which reveals that, there might probably be good sources for geothermal and thereby further recommended for detailed geothermal exploration.

Multiple geophysical techniques have been applied to geothermal exploration within the Teshikaga area. The three-dimensional inversion of HeliFalcon® airborne gravity gradiometry (AGG) data has enabled a detailed interpretation of subsurface features. The vertically elongated high-density anomalies beneath lava domes located near Wakoto Peninsula and Mt. Atosanupuri are interpreted as subsurface intrusive bodies, while low-density anomalous feature to the depth represents the Kutcharo caldera structure, which was filled with large scale of low-density pyroclastic materials. Helitem® electromagnetic data acquired in combination with the AGG data revealed a widespread conductive anomaly west of Mt. Atosanupuri, which may represent the cap rocks to a geothermal reservoir. The distribution of a low magnetic intensity zone matches that of a low-resistivity zone, suggesting that magnetite degradation and demagnetization possibly occur, most likely caused by hydrothermal activities. Integrated interpretation of airborne gravity gradiometer, electromagnetic and magnetic data helps with identification of prospective areas and planning of a drilling program for the development of geothermal energy with greater precision.

espanolPara el desarrollo de un campo geotermico, el conocimiento de la distribucion de fracturas, la hidrologia y la evolucion tectonica del sitio a traves de la caracterizacion estructural del sistema natural es un requisito previo a la perforacion de pozos exploratorios. Fallas y fracturas representan vias preferenciales por el flujo de fluidos en el subsuelo y pueden ser detectadas mediante investigaciones geologicas en la superficie y geofisicas en el subsuelo. Una anomalia magnetica positiva y de forma sub-circular en planta se encuentra en el medio del lago Cuitzeo, Mexico. A traves de un levantamiento geomagnetico dentro y alrededor del area que comprende la anomalia tratamos caracterizar el reservorio geotermico que, al sur del lago, esta notificado por manifestaciones hidrotermales. Utilizando filtros computacionales basados sobre el uso de operaciones con las derivadas de valores de campo a los datos magneticos grabados, hemos puesto en luz algunas de las estructuras que influencian la circulacion de los fluidos en el sistema geotermal. Nuestra atencion se focalizo sobre fallas ~N-S and E-W, pertenecientes respectivamente a la tectonica Basin & Range (B&R) y a la del Cinturon Volcanico Mexicano (CVM). Segun nuestra interpretacion, la interaccion de dos o mas estructuras de diferentes origenes (B&R y CVM), ademas del entorno geodinamico especifico (subduccion de zona de fracturas), facilito el surgimiento de cuerpos magmaticos basicos del profundo que, bloqueados por la capa argilosa de sedimentacion lacustre del Cuitzeo, dieron lugar, enfriandose lentamente, al sistema geotermal y contribuyeron a la formacion de la anomalia magnetica. EnglishFor the development of a geothermal field, the understanding of fracture distribution, hydrology and tectonic evolution of the site through structural characterization of the natural system is a prerequisite to the drilling of exploratory wells. In order to image the underground shape of approximately planar, relatively permeable, geologic features (fractured rock-volumes around fault planes) and to detect hot rock volumes, geologic and geophysical surveying is carried out. A strong positive magnetic anomaly, nearly circular in 2D, characterizes the middle of Cuitzeo lake, Michoacan, Mexico, apparently not related with a volcanic structure on the surface. It may instead be associated to the geothermal system in the area which yields at present hot springs at the southern shore of the lake, at boiling temperatures. In this study, we conducted a ground magnetic survey within and around Lake Cuitzeo with the aim of characterizing this anomaly, following one-kilometer-spaced survey-lines and covering an area of approximately 100 km2. To enhance interpretability, we applied computational filters based on directional derivatives (vertical and horizontal) to our reduced-to-pole magnetic-field raw data – illuminating underground faults and other permeable pathways for fluids and delineating contacts between differently magnetized rocks, through maxima and minima on maps. While most filters used were able to define the basic configuration of the system, we found that computational filters working with ratios of derivatives (vertical and horizontal) were able to better account for the depth of a magnetic source. Also, faults were more clearly imaged on maps. We could mainly highlight ~E-W and ~N-S striking fault-systems, respectively belonging to the ~N-S TransMexican Volcanic Belt extensional tectonics and to the ~E-W Basin & Range, both with lateral movements and still active today. We interpret the magnetic source as a magma body (related to the volcanism of Michoacan-Guanajuato Volcanic Field) that remained trapped during its ascent under Cuitzeo lacustrine sedimentation, during the last 500 ka, forming the once stronger geothermal system.

SUMMARY The Greater Geneva Basin (GGB), located in southwestern Switzerland and neighboring France, is enclosed by the rotating northwestern edge of the Alpine front and the Jura mountains chain. Recently, this basin has received increasing attention as a target for geothermal exploration. Historical and instrumental seismicity suggest that faults affecting the basin may still be active. Moderate-magnitude earthquakes have been located along the Vuache fault, a major strike-slip structure crossing the basin. Before geothermal exploration starts, it is key to evaluate the seismic rate in the region and identify possible seismogenic areas. In this context, we deployed a temporary seismic network of 20 broad-band stations (from September 2016 to January 2018) to investigate the ongoing seismic activity, its relationship with local tectonic structures, and the large-scale kinematics of the area. Our network lowered the magnitude of completeness of the permanent Swiss and French networks from 2.0 to a theoretical value of 0.5. Using a new coherence-based detector (LASSIE - particularly effective to detect microseismicity in noisy environments), we recorded scarce seismicity in the basin with local magnitudes ranging from 0.7 to 2.1 ML. No earthquakes were found in the Canton of Geneva where geothermal activities will take place. We constructed a local ’minimum 1-D P-wave velocity model’ adapted to the GGB using earthquakes from surrounding regions. We relocated the events of our catalogue obtaining deeper hypocentres compared to the locations obtained using the available regional velocity models. We also retrieved eight new focal mechanisms using a combination of polarities and waveform inversion techniques (CSPS). The stress inversion shows a pure strike-slip stress regime, which is in agreement with structural and geological data. Combining the background seismicity with our catalogue, we identified seismogenic areas offsetting the basin.

There is considerable interest in optimizing geothermal exploration techniques via the mapping of alteration and evaporate mineralisation, as well as of thermal emissions associated with geothermally active areas on the Earth’s surface. Optical and thermal satellite sensor technologies, improvements in processing algorithms and the means for large scale (e.g. 1:250,000) spatial data distribution are required for detecting both these attributes. The extensive visible, -near, -shortwave and thermal infrared (VNIR-SWIR-TIR) data archive acquired by the multi-spectral Advanced Spaceborne Thermal Emission Reflectance Radiometer (ASTER) provides a rich source of geoscience related imagery for geothermal exploration. Examples of generating large scale mosaicked ASTER imagery to provide province to continental mineral mapping have been undertaken in areas including such as Australia, western USA, Namibia and Zagros Mountains Iran. In addition, ASTER’s thermal infrared imagery also provides night time land surface temperature (LST) estimates relevant for detecting possible geothermal related anomalies. This study outlines existing methods for the application of ASTER data for geothermal exploration in East Africa. The study area encompasses a section of the East African Rift System across the Tanzanian and Kenyan border. The area includes rugged volcanic terrain which has had geological mapping of limited coverage at detailed scales, from various heritages and mapping agencies. This study summarizes the technology, the processing methodology and initial results in applying ASTER imagery for such compositional and thermal anomaly mapping related to geothermal activity. Fields observations have been used from the geothermal springs of Lake Natron, Tanzania, and compared with ASTER derived spectral composition and land surface temperature results. Published geothermal fields within the Kenyan portion of the study area have also been incorporated into this study.

Understanding the anatomy of magma plumbing systems of active volcanoes is essential not only for unraveling magma dynamics and eruptive behaviors but also to define the geometry, depth, and temperature of the heat sources for geothermal exploration. The Pleistocene–Holocene Los Humeros volcanic complex is part of the eastern Trans-Mexican Volcanic Belt (central Mexico), and it constitutes one of the most important exploited geothermal fields in Mexico with ca. 90 MW of produced electricity. With the aim to decipher the anatomy (geometry and structure) of the magmatic plumbing system feeding the geothermal field at Los Humeros, we carried out a field-based petrological and thermobarometric study of the exposed Holocene lavas. Textural analysis, whole-rock major-element data, and mineral chemistry are integrated with a suite of mineral-liquid thermobarometric models. Our results support a scenario characterized by a heterogeneous multilayered system, comprising a deep (depth of ca. 30 km) basaltic reservoir feeding progressively shallower and smaller discrete magma stagnation layers and batches, up to shallow-crust conditions (depth of ca. 3 km). The evolution of melts in the feeding system is mainly controlled by differentiation processes through fractional crystallization (plagioclase + clinopyroxene + olivine + spinel). We demonstrate the inadequacy of the existing conceptual models, where a single voluminous melt-controlled magma chamber (or “Standard Model”) at shallow depths was proposed for the magmatic plumbing system at Los Humeros. We instead propose a magmatic plumbing system made of multiple, more or less interconnected, magma transport and storage layers within the crust, feeding small (ephemeral) magma chambers at shallow-crustal conditions. This revised scenario provides a new configuration of the heat source feeding the geothermal reservoir at Los Humeros, and it should be taken into account to drive future exploration and exploitation strategies.

A detailed understanding of the geological structural elements is vital for geothermal reservoir exploration. Among existing geophysical methods, seismic methods are most commonly used for subsurface imaging due to the relatively high resolution at significant depths. However, seismic campaigns are rather expensive. The high upfront investment cost represent a substantial barrier for heat/electricity production from geothermal resources. Thus, developing new techniques is vital for further reduction in exploration and drilling costs, which is necessary for geothermal project advancements. Within the framework of the joint research project RissDom-A, the subsurface exploration of the Groß Schönebeck in-situ geothermal laboratory, situated 40 km north of Berlin, a seismic survey was carried out using 3D surface seismic and 3D vertical seismic profiling methods. VSP was acquired with wireline distributed acoustic sensing (DAS), which allows converting a freely suspended fibre optic cable inside a borehole into a dense array of seismic sensors to record strain or strain rate. In this thesis, the applicability of this method is evaluated for seismic imaging of an enhanced geothermal reservoir. The survey design consisted of 61 vibrator source positions organised in a spiral pattern around the boreholes E GrSk 3/90 and Gt GrSk 4/05 in such a way to optimise the illumination of the reservoir. The DAS recordings have an excellent signal-to-noise ratio (40-50 dB around 1000 m, 4-10 dB at around 4200 m). This data quality was reached with 16 vertical stacking rates on average. In addition, a comparison with a conventional accelerometer measurement showed excellent waveforms agreement. The acquisition campaign was conducted within four days, illustrating that wireline DAS is very attractive both from a data quality point of view and economically. A 3D VSP processing workflow was adapted to the Groß Schönebeck specifics and applied to the data. Particular depth ranges of the recorded data are subjected to strong coherent noise, which has a distinct pattern both in the time and the frequency domain. This type of noise is related to the poor coupling conditions of the cable in the borehole. For signal-to-noise ratio improvement, several existing denoising methods have been analysed. After coupling noise filter function assessment, a new noise elimination method was proposed based on the matching pursuit decomposition technique with Gabor atoms. The developed processing routine was uniformly applied to the whole dataset, which significantly improved the data quality, and as a result, migration images created using the Kirchhoff depth migration algorithm with restricted aperture. After data processing, a detailed subsurface analysis in the vicinity of the boreholes at the Groß Schönebeck was carried out using the 3D DAS VSP image. The resulting borehole cube data resolve new features that could not be imaged with the 3D surface seismic cube due to the lower resolution of the 3D surface seismic cube, with respect to the 3D VSP cube. Complex thin interlaying of the Upper Rotliegend horizons has been revealed in the geothermal reservoir section, allowing for the first time to access and characterise so-called “phantom horizons” which are typical for the Brandenburg area, Germany. Furthermore, the borehole cube provided new insights on two main targets for future exploration. The 3D DAS VSP cube revealed an intra-reservoir structure inside the Elbe reservoir sandstone layer, which could represent porous parts of a stacked fluvial sandstone body. The estimated thickness of this structure varies between 25 to 40 m, which is thinner than previous estimations. Additionally, a lower Rotliegend unconformity (at around 4.2 km depth) was mapped in the study area. This allowed to estimate the possible thickness of the vulcanite sections below this boundary. VSP data thus helped to reduce the uncertainty and exploration risks by providing valuable information for the geological characterisation of the Groß Schönebeck site. With this successful case study I demonstrated that fibre optic data could significantly contribute to the characterisation of deep geothermal reservoirs. Consequently, presented results contribute to the wireline distributed acoustic sensing method promotion to develop modern, reliable and economically affordable exploration methods for geothermal energy assessments., Ein detailliertes Verständnis der geologischen Strukturelemente ist für die Erkundung geothermischer Reservoire unerlässlich. Unter den bekannten geophysikalischen Methoden werden vor allem seismische Untersuchungen zur Abbildung des Untergrunds aufgrund der vergleichsweise hohen Auflösung bis in große Tiefen genutzt. Seismikkampagnen sind jedoch verhältnismäßig teuer. Die hohen Anfangsinvestitionskosten bilden eine erhebliche Hürde für die Wärme- und Stromproduktion aus geothermischen Ressourcen. Daher ist die Entwicklung neuer Techniken zur Reduktion von Exploarations- und Bohrkosten für die notwendige Förderung geothermischer Projekte essenziell. Im Rahmen des Verbundforschungsprojekts RissDom-A, der Untergrunderkundung des 40 km nördlich von Berlin gelegenen Groß Schönebeck in-situ Geothermielabors, wurden seismische Messungen durchgeführt, bestehend aus einer 3D-Oberflächen- und einer 3D-Bohrlochseismik. Die VSP-Daten (Vertical Seismic Profiling) wurden mittels kabelgebundenem DAS (Wireline Distributed Acoustic Sensing) aufgezeichnet, was die Umwandlung eines frei im Bohrloch hängenden faseroptischen Kabels in ein dichtes Array seismischer Sensoren zur Registrierung von Strain oder Strain-Rate erlaubt. In dieser Doktorarbeit wird die Anwendbarkeit dieser Methodik für die seismische Abbildung von EGS-Reservoiren (Enhanced Geothermal System) eingehend ausgewertet. Die Messkonfiguration bestand aus 61 Vibrator-Quellpositionen, die in einem spiralförmigen Pattern um die beiden Bohrlöcher E GrSk 3/90 und Gt GrSk 4/05 derart verteilt wurden, dass eine optimale Durchschallung des Reservoirs gegeben war. Die DAS-Aufzeichnungen zeigen ein exzellentes Signal/Rausch-Verhältnis (40-50 dB bei ca. 1000 m, 4-10 dB bei ca. 4200 m). Diese Datenqualität konnte aufgrund der durchschnittlich 16-fachen vertikalen Stapelrate erzielt werden. Zu Vergleichswecken zusätzlich vorgenommene konventionelle BeschleunigungsaufnehmerMessungen zeigen eine sehr gute Übereinstimmung der Wellenformen. Die Messkampagne umfasste vier Tage, was die Attraktivität von Wireline-DAS unter sowohl qualitativen als auch ökonomischen Aspekten überzeugend demonstriert. Eine 3D-VSP Bearbeitungssequenz wurde an die Besonderheiten der Groß Schönebeck Messungen angepasst und auf die Daten angewendet. Einzelne Tiefenbereiche der Aufzeichnungen enthalten starke kohärente Störsignale, die ein ausgeprägtes Muster sowohl im Zeitals auch im Frequenzbereich aufweisen. Diese Art Noise ist auf eine ungenügende Ankopplung des Kabels im Bohrloch zurückzuführen. Zur Verbesserung des Signal/Rausch-Verhältnisses wurden verschiedene gebräuchliche Unterdrückungsmethoden untersucht. Nach Analyse der Kopplungsnoise-Filterfunktion konnte eine neuartige Methode zur Rauschunterdrückung etabliert werden, welche auf einer Matching-Pursuit Dekompositionstechnik mit Gabor-Atomen basiert. Der auf diese Weise entwickelte Prozessierungsansatz wurde gleichmäßig auf den gesamten Datensatz angewendet, was die Datenqualität signifikant erhöhte, so dass in der Folge Migrationsabbilder unter Verwendung eines Kirchhoff-Tiefenmigrationsverfahrens mit beschränkter Apertur erzeugt werden konnten. Nach erfolgter Datenbearbeitung wurde anhand der DAS/VSP 3D-Daten eine detaillierte Untergrundanalyse im Bereich der Groß Schönebeck Bohrlöcher durchgeführt. Das resultierende Bohrlochaten-Volumen löst viele neue Details auf, die mit dem 3D-Volumen der Oberflächenseismik aufgrund des vergleichsweise geringeren Auflösungsvermögens nicht abgebildet wurden. So konnten in der geothermischen Reservoirsektion komplexe dünnschichtige Einlagerungen im Oberen Rotliegend nachgewiesen werden, die erstmalig die Ansprache und Charakterisierung sogenannter „Phantom-Horizonte“ ermöglichen, wie sie typisch für das Gebiet Brandenburg, Deutschland sind. Weiterhin liefert der Bohrlochdaten-Kubus neue Einblicke auf zwei Hauptziele zukünftiger Explorationen. Das DAS/VSP 3D-Datenvolumen zeigt eine Intra-Reservoir Strukur innerhalb der Elbe-Sandstein Schicht, die poröse Anteile eines gestapelten fluvialen Sandsteinkörpers repräsentieren könnte. Die geschätzte Mächtigkeit dieser Struktur variiert zwischen 25 und 40 m, was dünner ist, als zuvor angenommen. Des weiteren konnte im Untersuchungsgebiet eine Diskordanz im Unteren Rotliegend (in einer Tiefe von ca 4.2 km) kartiert werden. Dies erlaubt es, die mögliche Mächtigkeit der Vulkanite darunter abzuschätzen. Somit helfen die VSP-Daten dabei, die Unklarheiten und das Explorationsrisiko zu reduzieren, indem sie wertvolle Informationen zur geologischen Charakterisierung des Groß Schönebeck Standorts liefern. Mit dieser Fallstudie konnte ich erfolgreich demonstrieren, dass mithilfe faseroptischen Kabels gewonnene Messdaten zur Charakterisierung geothermischer Reservoire maßgeblich beitragen können. In der Konsequenz fördern die präsentierten Ergebnisse die Bedeutung von Wireline Distributed Acoustic Sensing im Hinblick auf eine moderne, verlässliche und ökonomische Explorationsmethode für geothermische Energiekonzepte.

Quantification of the subsurface geothermal potential primarily relies on the assessment of the thermal and mechanical configuration of the lithosphere. Such investigations require a detailed knowledge of the geological and tectonic forcing on the regional thermal, stress and hydraulic regimes and their counter feedback mechanisms. This approach becomes even more relevant in complex and active tectonic settings. In this regard, the Sicily region, which is located in the Central-Western Mediterranean, is an exceptional case study due to its almost unexplored geothermal potential hosted in a complex geodynamic setting. The present-day geological configuration resulted from the collision between the African and European plates, which led to the coexistence of compressional phases, beginning with the Oligocene-Miocene clockwise rotation of Corsica-Sardinia and alternated extensional phases in the Tyrrhenian basin due to the southward progression of the Sicilian-Maghrebian chain towards areas of the internal foreland (Hyblean domain). In this study, we attempt a reconstruction of the present-day lithospheric state of Sicily to quantify its thermal regime at shallow and intermediate depths. We have carried out a 3D lithospheric-scale gravity modelling in order to define the main geological units and their lithology-dependent rock properties, then integrated into a 3D geological model consistent with available borehole and seismic datasets. We have used the constructed geological model with its lithology-dependent density, thermal conductivity, and radiogenic heat production to derive the present-day conductive thermal field as a whole and for individual tectonic or geological units, thereby considering different boundary conditions. We have finally validated results of the modelling against a shallow temperature dataset derived from hydrocarbon explorations. Our results indicate that the thermal field at depths shallower than 10 km is largely controlled by variability in sedimentary thickness in the foreland and the orogen, while deeper temperatures are primarily controlled by the distribution of the heat transferred from the mantle together with the radiogenic contribution of the shallow crystalline basement rocks and deeper crustal layers. The thermal modelling portrays a rather heterogenous Moho heat flow, locally higher than 80 mW/m2, revealing a particular geodynamic setting with specific areas characterized by high-to-medium enthalpy geothermal potential. As such, our modelling provides new perspectives for the exploration of geothermal resources in Sicily and helps to better constrain the thermal structure of the complex Sicilian collisional setting.

Geothermal exploration will help move towards a low-carbon economy and provide a basis for green and sustainable growth. The development of new practical, reliable methods for geophysical characterization of a reservoir has the potential to facilitate a broader application of deep geothermal energy. At the Groß Schönebeck in situ laboratory, a unique vertical seismic profiling (VSP) dataset was recorded in two 4.3 km deep geothermal boreholes using fibre-optic cables in early 2017. The experiment set-up consisted of 61 vibrator points organized in a spiral pattern around the well site to ensure a proper offset and azimuth distribution in the target reservoir section. Data were processed using a standard workflow for VSP. As a result, a detailed three-dimensional 0.75km×1km×4.5 km image around the existing boreholes was created using the Kirchhoff migration algorithm with restricted aperture. The imaging resolved small-scale features in the reservoir essential for the future exploration of the geothermal research site. Borehole data with vertical resolution up to 16 m revealed the existing depth variations of the Elbe reservoir sandstone horizon at 4.08–4.10 km depth and indications of an unconformity in the area where we expect volcanic rocks. In addition, in the borehole data a complex interlaying with numerous pinch-outs in the Upper Rotliegend reservoir section (3.8 to 4 km depth) was discovered. Thereby, we demonstrate that wireline fibre-optic data can significantly contribute to exploration by providing an efficient and reliable method for deep geothermal reservoir imaging.

In autumn 2017 a network of 14 broadband seismic stations was deployed at the Theistareykir high temperature geothermal field (NE Iceland). This experiment was conducted as part of the current efforts to characterize the field's main structures, and possible short and long term stress variations due to the ongoing fluid injection and extraction operations which started in autumn 2017. In this work, we use two years of continuous seismic records (October 2017–October 2019) to compute a 3D shear wave velocity model of the geothermal field and to detect possible crustal stress changes related to the injection and production activities. From phase cross-correlations of the vertical component recordings, we measure the Rayleigh wave group velocity dispersion curves to obtain 2D group velocity maps between 1 and 5 s. Subsequently, we use a neighborhood algorithm to retrieve the 3D shear wave velocity model of Theistareykir. Mainly, two sets of elongated high and low velocity anomalies can be observed oriented in a NW/WNW direction, parallel to the lineaments of the active Tjörnes fracture zone. Velocity reductions west of Ketilfjall and at Baerjafjall could indicate the location of upflow zones of the magmatic reservoir or hydrothermal system. We analyzed the temporal evolution of phase and amplitude of phase auto-correlations using the stretching technique and discuss their behavior in relation to the geothermal field operations. We notice a slightly stronger long-term velocity decrease in the reservoir region compared to outer regions. This could be related to the mass depletion in that area (higher fluid extraction compared to the water reinjection). In summary, our findings show how a monitoring network can be set up to enable a detailed imaging and monitoring of reservoir behavior in general., Journal of Volcanology and Geothermal Research, 429, ISSN:0377-0273

The investigation of permeable hydrothermally altered and fractured zones and their distribution is a key issue for the understanding of fluid circulation in granitic rocks, on which the success of geothermal projects relies. Based on the use of short-wave infrared (SWIR) spectroscopy applied to rock cuttings coupled with interpretation of geophysical logs, we propose an investigation of the clay signature of fault and fracture zones (FZ) inside the granitic basement. This methodology was applied to two geothermal wells: GRT-2 from the Rittershoffen and GPK-1 from the Soultz-sous-Forêts (Soultz) geothermal sites, both located in the Upper Rhine Graben (URG). A total of 1430 SWIR spectra were acquired and analysed. Variations in the 2200 nm absorption band area are correlated with hydrothermal alteration grades. The 2200 nm absorption band area is found to reflect the illite quantity and its variations in the granitic basement. Low, stable values are observed in the unaltered granite facies, showing good reproducibility of the method, whereas scattered high values are associated with high hydrothermal alteration and FZs. Variations in the 2200 nm absorption band area were correlated with the gamma ray and electrical resistivity logs. This procedure allowed us to confirm that illite mainly controls the resistivity response except inside the permeable FZs, where the resistivity response is controlled by the geothermal brine. Thus, the architecture of these permeable FZs was described precisely by using a combination of the 2200 nm absorption band area data and the electrical resistivity log. Moreover, by correlation with other geophysical logs (temperature (T), porosity, and density), paleo-permeable and currently permeable FZs inside the reservoir were distinguished. The correlation of SWIR spectroscopy with electrical resistivity logs appears to be a robust tool for geothermal exploration in granitic reservoirs in the URG.

In the Bavarian Molasse Basin, especially in the greater Munich, geothermal exploration of the hydrothermal Upper Jurassic reservoir is rapidly expanding. Until now, little seismic reservoir response is observed, only at two out of 16 sites seismic events with M L > 2.0 were detected: at Unterhaching, in 2008, six events with M L > 2 occurred soon after the onset of circulation; at Poing, in 2016, 5 years after circulation started, two events with ML∼2.1 occurred, both located near the injection well. The analysis of the reactivation potential allows to connect seismicity to fault structures. In the Bavarian Molasse Basin, fault structures generally exhibit low seismic reactivation potential, as long as they trend ENE-WSW. By Monte-Carlo simulation, the geological uncertainty and the sensitivity of the individual parameters are quantified. They show that critically pre-stressed fault segments, e.g. at Unterhaching, combined with minimum change of the hydraulic reservoir conditions can lead to a dramatic increase of the reactivation potential of seismicity. For uncritical fault segments, e.g. at the Poing site, two self-enforcing effects are discussed which increase the reactivation potential over time: first, stress field modification by thermo-hydraulic effects and, second, fault alteration by carbonate dissolution can reduce the fault friction and cohesion. Both effects increase the sensitivity of the reactivation potential to the fault friction and can bring previously uncritical fault segments to critical state. Finally, the possible impact of coupled thermo-hydro-mechanical and chemical processes at hydrothermal systems on the reactivation potential is highlighted: at fault segments with high reactivation potential hydro-mechanical effects may dominate whereas at low reactivation potential thermo-mechanical processes can potentially yield to a slow rotation of the stress field.

Geothermal exploration will help moving towards a low-carbon economy and provide a basis for green and sustainable growth. The development of new practical, reliable methods for geophysical characterisation of a reservoir has the potential to facilitate a broader application of deep geothermal energy. At the Groß Schönebeck in-situ laboratory, a unique vertical seismic profiling (VSP) dataset was recorded in two 4.3 km deep geothermal boreholes using fibre optic cables in early 2017. The experiment set-up consisted of 61 vibrator points organised in a spiral pattern around the well site to ensure a proper azimuth distribution in the target reservoir section. Data were processed using a standard workflow for VSP. As a result, a detailed 3-dimensional 0.75 × 1 × 4.5 km size image around the existing boreholes was created using the Kirchhoff migration algorithm with restricted aperture. The imaging resolved small-scale features in the reservoir essential for the future exploration of the geothermal research site. Borehole data with vertical resolution up to 16 m revealed the existing depth variations of the Elbe basis sandstone horizon at 4.08–4.10 km depth and indications of an unconformity in the area where we expect volcanic rocks. In addition, in the borehole data a complex interlaying with numerous pinch outs in the Upper Rotliegend reservoir section (3.8 to 4 km depth) was discovered. Thereby, we demonstrate that wireline fibre optic data can significantly contribute to exploration by providing an efficient and reliable method for deep geothermal reservoir imaging.

International audience; Due to its geodynamic location in the Lesser Antilles arc, Basse-Terre of Guadeloupe displays an active volcanism which is favourable to the development of high-enthalpy geothermal energy. An exhumed analogue of the Bouillante geothermal reservoir has been recently characterized in Terre-de-Haut island (Les Saintes archipelago), giving an opportunity to study the cooling of a natural geothermal system and the related alterations.By coupling chlorite geothermometry and primary fluid inclusions in associated zoned quartz crystals located in N70 trending fractures, new insights on the Terre-de-Haut paleo-geothermal evolution can be inferred by distinguishing three new different episodes during functioning and cooling of this system: (i) a temperature of at least 240–270 °C in fluid inclusions trapped in the quartz core, (ii) chlorite formation at about 120 °C, and (iii) temperatures of ~50 °C - or less - in fluid inclusions of the quartz outer growth zones. Fluid inclusions also reveal that the hydrothermal fluid is of low salinity (2 wt% NaCl), probably of meteoric and sea water origin. Additionally, a second type of fluid inclusions observed in a banded quartz vein indicates at least an episode of a CO2-(H2O) fluid, with traces of H2S. Hence, some similarities can be highlighted between Terre-de-Haut and the Bouillante active geothermal systems in term of the highest temperatures of circulation events and gas composition, despite a difference in fluid origin. This study shows that some alteration episodes also occur at low temperature during the cooling of the geothermal system. Moreover, the N70 trending fractures, that have been identified as drains for the hot temperature fluids, have to be considered for future geothermal exploration.

Accurate imaging of subsurface complex structures with faults is crucial for geothermal exploration because faults are generally the primary conduit of hydrothermal flow. It is very challenging to image geothermal exploration areas because of complex geologic structures with various faults and noisy surface seismic data with strong and coherent ground-roll noise. In addition, fracture zones and most geologic formations behave as anisotropic media for seismic-wave propagation. Properly suppressing ground-roll noise and accounting for subsurface anisotropic properties are essential for high-resolution imaging of subsurface structures and faults for geothermal exploration. We develop a novel wavenumber-adaptive bandpass filter to suppress the ground-roll noise without affecting useful seismic signals. This filter adaptively exploits both characteristics of the lower frequency and the smaller velocity of the ground-roll noise than those of the signals. Consequently, this filter can effectively differentiate the ground-roll noise from the signal. We use our novel filter to attenuate the ground-roll noise in seismic data along five survey lines acquired by the U.S. Navy Geothermal Program Office at Pirouette Mountain and Eleven-Mile Canyon in Nevada, United States. We then apply our novel anisotropic least-squares reverse-time migration algorithm to the resulting data for imaging subsurface structures at the Pirouette Mountain and Eleven-Mile Canyon geothermal exploration areas. The migration method employs an efficient implicit wavefield-separation scheme to reduce image artifacts and improve the image quality. Our results demonstrate that our wavenumber-adaptive bandpass filtering method successfully suppresses the strong and coherent ground-roll noise in the land seismic data, and our anisotropic least-squares reverse-time migration produces high-resolution subsurface images of Pirouette Mountain and Eleven-Mile Canyon, facilitating accurate fault interpretation for geothermal exploration.

The 3.1- and 3.7-km-deep FFC-1 and DGE-1 geothermal explorations wells drilled into the Precambrian crystalline basement on the southern margin of the Fennoscandian Shield are evaluated regarding experiences from drilling, geological conditions, and thermal properties. Both wells penetrate an approximately 2-km-thick succession of sedimentary strata before entering the crystalline basement, dominated by orthogneiss, metabasite and amphibolite of the (1.1–0.9 Ga) Eastern Interior Sveconorwegian Province. The upper c. 400 m of the basement is in FFC-1 severely fractured and water-bearing which disqualified the use of percussion air drilling and conventional rotary drilling was, therefore, performed for the rest of the borehole. The evaluation of the rotary drillings in FFC-1 and DGE-1 showed that the average bit life was very similar, 62 m and 68 m, respectively. Similarly, the average ROP varied between 2 and 4 m/h without any preferences regarding bit-type (PDC or TCI) or geology. A bottomhole temperature of 84.1 °C was measured in FFC-1 borehole with gradients varying between 17.4 and 23.5 °C/km for the main part of the borehole. The calculated heat flow varies between 51 and 66 mW/m2and the average heat production is 3.0 µW/m3. The basement in FFC-1 is, overall, depleted in uranium and thorium in comparison to DGE-1 where the heat productivity is overall higher with an average of 5.8 µW/m3. The spatial distribution of fractures was successfully mapped using borehole imaging logs in FFC-1 and shows a dominance of N–S oriented open fractures, a fracture frequency varying between 0.85 and 2.49 frac/m and a fracture volumetric density between 1.68 and 3.39 m2/m3. The evaluation of the two boreholes provides insight and new empirical data on the thermal properties and fracturing of the concealed crystalline basement in the Fennoscandian Shield Border Zone that, previously, had only been assessed by assumptions and modelling. The outcome of the drilling operation has also provided insight regarding the drilling performance in the basement and statistical data on various drill bits used. The knowledge gained is important in feasibility studies of deep geothermal projects in the crystalline basement in south Sweden.