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ERE2.4

EDI
Exploration, utilization and monitoring of conventional and unconventional geothermal resources

With an increasing demand for low-carbon energy solutions, the need of geothermal resources utilization is accelerating. Geothermal energy can be extracted from various, often complex geological settings, e.g. fractured crystalline rock, magmatic systems or sedimentary basins. Current advancements also target unconventional systems (e.g., Enhanced Geothermal Systems, super-hot, pressurized and co-produced, super-critical systems) besides conventional hydrothermal systems. Optimizing investments leads to the development of associated resources such as lithium, rare earths and hydrogen. This requires a joint effort for monitoring, understanding and modelling geological systems that are specific to each resource.
A sustainable use of geothermal resources requires advanced understanding of the properties of the entire system during exploration as well as monitoring, including geophysical properties, thermo-/petro-physical conditions, fluid composition; structural and hydrological features; and engineering challenges. Challenges faced are, among others, exploration of blind systems, reservoir stimulation, induced seismicity or related to multiphase fluid and scaling processes.

The integration of analogue field studies with real-life production data, from industrial as well as research sites, and their organization and the combination with numerical models, are a hot topic worldwide. With this session we aim to gather field, laboratory and numerical experts who focus their research on geothermal sites, to stimulate discussion in this multi-disciplinary applied research field. We seek for contributions from all disciplines, ranging from field data acquirements and analysis to laboratory experiments, e.g. geophysical surveys or geochemical experiments, and from the management and organization of information to numerical models as well as from (hydro)geologists, geochemists, (geo)physicists, surface and subsurface engineers.

Convener: Eugenio Trumpy | Co-conveners: Maren Brehme, Anne PluymakersECSECS, Chris Boeije, Martijn Janssen
Presentations
| Wed, 25 May, 13:20–18:13 (CEST)
 
Room 0.96/97

Wed, 25 May, 13:20–14:50

Chairpersons: Eugenio Trumpy, Chris Boeije, Anne Pluymakers

13:20–13:27
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EGU22-10
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On-site presentation
Irina Sidorova

A large scientific project is being implemented in Uzbekistan (2019-2021) to study Heat Flow Density anomalies оn the territory of the Republic. Long-term studies by geophysicists of the Institute of Geology and Geophysics have allowed the creation of a geothermal database and a new Heat Flow distribution map. Comprehensive geophysical work is being carried out, including gravimetric, seismic and magnetotelluric studies in three areas (1) Muruntau, (2) Krasnogorsk, (3) Bayangora. According to the constructed gravimetric maps, zones of decompression and faults were identified. Low and high velocity areas have been identified from seismic sections. Magnetotelluric sounding made it possible to identify conduction zones that correlate with anomalous Heat Flow Density. Based on the complex of geophysical data, a three-dimensional model of the deep structure was built for the promising area ​​Muruntau. The locations of wells for the construction of a geothermal station have been determined.

How to cite: Sidorova, I.: Geothermal research in Uzbekistan, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-10, https://doi.org/10.5194/egusphere-egu22-10, 2022.

13:27–13:34
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EGU22-3378
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ECS
How fluid flow and heat transport models impact predictions of deep geothermal potentials: the "heat in place" method applied to Hesse (Germany)
(withdrawn)
Nora Koltzer et al.
13:34–13:41
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EGU22-3556
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ECS
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Virtual presentation
Federico Rabuffi et al.

Geothermal energy plays a major role in the energy transition context. This presents a constant increasing rate in electricity generation, even if it today represents a smaller part of the renewable energy package. To sustain this natural resource, it is necessary to better understand the geotectonic framework of key places that are historically relevant in terms of innovation, exploration and development of geothermal energy resources. These places represent strategic cases study: i) to better understand the surface manifestation related to a geothermal area; ii) to test new methodologies that can help in the monitoring and identification of new natural resource; iii) to better understand the geodynamic context that characterizes the geothermal area in terms of thermal anomalies, soil alteration, stress field, and fracture distribution inducing secondary permeability.

This work is linked to a PhD project focused on Parco Naturalistico delle Biancane (PNB) area, in southern Tuscany (Italy), the main Italian geothermal region, where geothermal energy production started in 1916.

The aim of the project was to merge original remote sensing techniques and classical structural geology field data to improve the knowledge of the geological setting of PNB geothermal area. Deepening the confidence on this methodological approach, some considerations on its exportability has been carried out. According to the methodology a remote sensed analysis has been performed, leading us to highlights the correlation between the morpho-geological and geothermal features, in terms of thermal anomalies. An automatic lineaments detection has been done by analyzing Digital Elevation Model (DEM) and Land Surface Temperature (LST) maps derived from Landsat8 satellite data. The results obtained by this analysis highlights the NE-SW lineaments domain as the most relevant from both point of view: thermal and structural. The analysis shows a good relationship between the two datasets and allowed to understand how tectonic setting acts on shallow fluid circulation. These data have been compared with the field structural data including faults, joints, fault-synthetic cleavage, shear fractures and beddings. A multi scale spatial analysis has been conducted and includes: the structural data distribution, density of the geo-morphological lineaments derived from the DEM, LST maps, high resolution surface temperature map, and surface classification map (based on ground spectral data acquired in the field). In this spatial analysis each dataset has been considered as a single, independent layer of information, and the spatial distribution of the “anomalies”, recognized in every layers, allowed us to identify and to define the areas that are strategically relevant to understand how a shallow geothermal system works and how to improve it.

How to cite: Rabuffi, F., Cianfarra, P., Musacchio, M., Silvestri, M., Salvini, F., and Buongiorno, M. F.: Geospatial analysis of thermal and structural data for the characterization of shallow geothermal systems: the Parco Naturalistico delle Biancane (Tuscany/Central Italy) study case, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3556, https://doi.org/10.5194/egusphere-egu22-3556, 2022.

13:41–13:48
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EGU22-5160
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Virtual presentation
Steffi Burchardt et al.

Geothermal exploration targets large magmatic intrusions as heat sources because of their size, longevity, and amount of stored energy, but as shallow volcanic plumbing systems comprise numerous smaller intrusions, their geothermal potential warrants consideration. Here, we evaluate the geothermal impact of dykes and sills on caldera-infill rocks. We present geological data and geothermometry on intrusions in the eroded Breiðuvík caldera in Northeast Iceland, which serves as an analogue to the active, and geothermally exploited, Krafla volcano. This data informs 2D finite element models of dyke and sill intrusions that consider heat transfer in porous media. Our results indicate small intrusions create considerable thermal anomalies in their immediate vicinity. These anomalies are larger-magnitude and longer-lasting for individual thick sills and dykes, but networks of smaller sills and dykes emplaced close in time and space can create more widespread thermal anomalies that may be viable economic targets for decades after their emplacement.

How to cite: Burchardt, S., Bazargan, M., Bessi Gestsson, E., Ronchin, E., Tuffen, H., Heap, M. J., Davidson, J., Kennedy, B., Hobé, A., Hieronymus, C., and Saubin, E.: Geothermal potential of small sub-volcanic intrusions in a typical Icelandic caldera setting, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-5160, https://doi.org/10.5194/egusphere-egu22-5160, 2022.

13:48–13:55
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EGU22-5300
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ECS
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On-site presentation
Laureen Benoit et al.

In geothermal exploration, regional 3D geological models, covering the full extent of a sedimentary basin, can be an efficient basis to assess spatial variations in the deep thermal field and related extractable energy. The term “geothermal potential” has been defined in different ways, considering characteristics of an intended geothermal plant and/or the geological reservoir. In this contribution, we concentrate on the latter geological aspects and combine 3D geological with 3D thermal models of the Berlin/Brandenburg region to assess “heat in place” as a quintessential part of the geothermal potential of differently composed geological units.

Our “heat in place” calculations correspond to a volumetric quantification of contained energy distributed across a series of litho-stratigraphic units showing variable thickness, mean temperature, porosity, density, and specific heat capacity. We set special focus on estimating how the calculated heat varies between different thermal models, derived from either purely conductive heat transport or coupled thermal-hydraulic simulations.

As part of the Northeast German Basin, the Berlin/Brandenburg region is known to be potentially suitable for deep geothermal energy exploitation. As this source of energy is not well-established yet, while energy demand from renewables is increasing in the metropolitan area of Berlin, this study aims at contributing to a more efficient decision making on promising sites for geothermal energy production by means of a series of new geothermal potential maps.

How to cite: Benoit, L., Bott, J., and Scheck-Wenderoth, M.: Insights into the deep geothermal potential from heat in place calculations of the Berlin/Brandenburg region (Germany), EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-5300, https://doi.org/10.5194/egusphere-egu22-5300, 2022.

13:55–14:02
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EGU22-10526
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ECS
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Virtual presentation
Duygu Kiyan et al.

One aim of the DIG Project (De-risking Ireland’s Geothermal Potential: Chambers et al., this conference) is to evaluate the geothermal energy potential of the Upper Devonian Munster Basin within the Variscides of southern Ireland. One of our primary targets is the Mallow Warm Springs Area (MWSA) which is sited along the Killarney-Mallow Fault Zone (KMFZ). The fault zone represents the major basin-bounding normal fault system to the basin and regionally controls sediment facies and thickness distribution. The KMFZ was re-activated as a compressional reverse fault in late Carboniferous-early Permian time, during the Variscan Orogeny. Tectonic strain variation is well understood from structural/geological analysis and increases towards Killarney, where the highest strain is associated with a large Bouguer gravity low in the (Avalonian) Caledonian basement. The basin-fill sediments are dominated by siliciclastic sediments, deposited in thick alluvial fan systems, that are succeeded by lower Carboniferous carbonate-prone marine limestones.

Primary porosity in sediments is obliterated by sub-green-schist metamorphism and Variscan deformation fabrics. Fluid flow within the crust around the KMFZ is likely related to the Cenozoic tectonic reactivation of faults and thermally driven uplift as revealed by recent thermo-chronological results in the vicinity of the fault. There was also significant fluid flow during the Munster basin extension and Variscan basin inversion. The focussed part of the DIG study uses potential field (gravity/magnetic) and legacy wide-angle seismic data from the Munster Basin to develop a “new” geological model for crustal structure, with direct application to geothermal research. Critical properties such as thermal conductivity and heat production measurements will also encompass the island-wide aspect of the DIG Project. 

The constraints gathered by the magnetotelluric and passive seismic data within the KMFZ will be integrated with rock physics and geochemical data. This substantial body of work will also include a fluid chemistry program to understand the fluid rock interactions within the KMFZ and their impact on physical properties (electrical conductivity and velocity). Collectively, using this expertise, the study evaluates the geothermal and economic potential of the region and more specifically the MWSA. This local focus on the MWSA aims to directly image fault conduits and fluid aquifer sources at depth, within a convective/conductive region associated with the known occurrence of warm thermal springs. This will determine the scale of the geothermal anomaly, its correlation with our gathered data and will so evaluate the potential for both local and industrial-scale space heating in the survey locality.

The project is funded by the Sustainable Energy Authority of Ireland under the SEAI Research, Development & Demonstration Funding Programme 2019 (grant number 19/RDD/ 522) and by the Geological Survey Ireland.

How to cite: Kiyan, D., Chambers, E. L., O'Reilly, B. M., Rezaeifar, M., Tomar, G., Ye, T., Fullea, J., Lebedev, S., Bean, C. J., and Meere, P. and the DIG team: Geothermal Study of Southern Ireland: DIG Project , EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-10526, https://doi.org/10.5194/egusphere-egu22-10526, 2022.

14:02–14:09
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EGU22-12492
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ECS
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Virtual presentation
Olga Knaub et al.

Issues of sustainability and climate change are among the driving forces of current research aiming to remedy the grave consequences of greenhouse gas emissions. The consequent system change into the usage of regenerative energy sources through the replacing of fossil fuels represents the most promising solution. This structural change poses large challenges not only for metropolitan areas, but also for smaller towns, which intend to increasingly utilize renewable energies. One such example is the city of Minden in the northernmost part of the state of North Rhine-Westphalia, which serves as case study for this project. The city is geologically situated in the inverted part of the Lower Saxony Basin. This represents a sub-basin in the western part of the North German Basin, which is one of three economically viable regions for geothermal energy production in Germany. The investigation of the feasibility of generating electricity and heat through the exploitation of the deep geothermal reservoirs was driven based on the requirements of a company situated in Minden, which exclusively uses fossil fuels for their industrial processes. In order to generate steam, the production requires high temperatures from the subsurface (> 140°C).

The evaluation of geothermal projects conducted in the North German Basin, regional studies and interpretation of 2D seismic data confirmed the existence of the so-called Wiehengebirge Syncline with outcropping Jurassic rocks in the mountain range to the south of Minden. The compilation of all available data and models highlighted Mesozoic layers of the middle Bunter sandstone (Volpriehausen-Solling formations, 4.0-4.5 km), the Keuper (Stuttgart formation, 3.0-3.3 km) and the Dogger (Bathonium-Callovium formations, 1.8-2.4 km) as potential target horizons within the syncline. Moderate to good hydraulic properties are anticipated for the siliciclastic targets. Furthermore, the hydraulic productiveness of a fault mapped in the immediate vicinity of the investigation site was determined through dynamic reservoir simulations.

Moreover, drilling data provided by the hydrocarbon industry from the gas fields to the north of the city (e.g. Uchte) were used to set up a thermo-hydraulic model in order to determine temperatures and flow rates. These should ultimately specify the most promising formations within the afore mentioned Mesozoic units for further geothermal exploration and developments.

Summarizing, first results of this study have confirmed the deep geothermal energy potential of the western part of the North German Basin and the city area of Minden.

How to cite: Knaub, O., Jüstel, A., Bussmann, G., Wellmann, F., and Kukla, P.: Geothermal exploitation in the inverted part of the Lower Saxony Basin: A case study from the Minden area, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-12492, https://doi.org/10.5194/egusphere-egu22-12492, 2022.

14:09–14:19
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EGU22-6919
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ECS
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solicited
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On-site presentation
Denise Degen et al.

For geothermal applications, we aim to obtain an understanding of the physical processes in the subsurface, to predict the geothermal potential reliable. Naturally, the reliability of the prediction of the physical processes directly relates to the reliability of the evaluation of the geothermal potential. Unfortunately, predicting the physical processes reliable is a non-trivial task because of high uncertainties related to these processes. These uncertainties may arise, for instance, from uncertainties of the rock properties (e.g. thermal conductivity, permeability), structural uncertainties, and not considered physical processes.

Considering the various sources of uncertainties yields a high-dimensional and therefore computationally extremely demanding problem that is not solvable even with state-of-the-art high-performance software packages. To address this curse of dimensionality, we employ a methodology, namely the non-intrusive RB method, combining advanced mathematical algorithms and machine learning methods. This method aims to significantly reduce the dimensionality of the problem while maintaining the physical principles. In contrast to other machine learning methods, the method produces interpretable and scalable models, which are crucial to obtain reliable and robust predictions.

In this work, we show how the method constructs surrogate models for coupled geothermal applications, which allow, in turn, the performance of global sensitivity analysis and uncertainty quantifications. Both methods are essential for improving our model understanding. Furthermore, we demonstrate how the method in combination with developments from the field of computer graphics (e.g. NURBS, and subdivision surfaces) can be used to quantify the influence of structural uncertainties on the temperature distribution.

How to cite: Degen, D., Cacace, M., Moulaeifard, s. M., and Wellmann, F.: The Value of Scientific Machine Learning for Geothermal Applications, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6919, https://doi.org/10.5194/egusphere-egu22-6919, 2022.

14:19–14:26
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EGU22-3608
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ECS
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On-site presentation
Eszter Békési et al.

Primarily due to the lack of production of geothermal fluids from subsurface aquifers, closed-loop geothermal systems are promising solutions for sustainable and cost-effective exploitation of geothermal energy. Compared to conventional or unconventional open-hole geothermal systems, the performance of deep borehole heat exchangers (DBHE) are relatively low. However, DBHEs may become favorable choices in certain areas due to the significantly lower exploration risks and their potential to be constructed in abandoned deep boreholes. We investigate the thermal performance of DBHEs in the Pannonian basin, exhibiting one of the hottest regions within Europe, with an average geothermal gradient of ~45 °C/km. We analyze the effect of various geological and technical parameters on the resulting outflow temperatures and output thermal powers in order to find the optimal sets of parameters for the long-term sustainable operation of DBHEs in the Pannonian basin. We approximate the performance of coaxial DBHEs through finite-element numerical modelling using the FEFLOW software. We construct the reference model in a geological environment representative for the Great Hungarian Plain based on information from well logs and literature data. The most important geological parameters we consider in the parameter tests include the geothermal gradient, lithologies, and the presence and significance of natural groundwater flows in the surroundings of the DBHE. Furthermore, we test the influence of various technical and operational parameters such as the type of working fluids, the depth of the DBHE, the thermal conductivity of the tubes, and the temperature and flow rate of the injected fluids. We predict the thermal output for the period of 10 years in order to find realistic parameter combinations that can facilitate sustainable production and reveal the most critical parameters that influence system performance in Pannonian basin settings. These results can help estimating system performance in case of actual geothermal projects and can be used as input parameters for economic calculations.

How to cite: Békési, E., Szekszárdi, A., Porkoláb, K., Tóth, K., and Gáti, M.: Performance analysis of deep borehole heat exchangers in the Pannonian Basin, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3608, https://doi.org/10.5194/egusphere-egu22-3608, 2022.

14:26–14:33
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EGU22-7690
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ECS
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On-site presentation
Muhammad Anees et al.

The western Himalaya-Karakoram region in northern Pakistan has such hydrothermal features as hot springs and alteration zones. The heat source for these features remains unclear, with suggested mechanisms including radiogenic heat production from minerals, frictional heating caused by shearing along faults, residual heat from Miocene plutonic intrusions, metamorphic heat caused by tectonic collision, and heat advection related to rapid exhumation. In this study, we provide a quantitative estimation of the radiogenic heat production of 158 locations from different crystalline lithologies exposed in the three distinct tectonic domains of the western Himalayan-Karakoram region, i.e., Nanga Parbat-Haramosh Massif, Kohistan-Ladakh Batholith, and Karakoram Batholith. The radiogenic heat production values are calculated from the concentrations of the uranium (ppm), thorium (ppm), and potassium (wt%), which are determined directly in the field using a portable gamma spectrometer on exposures of Proterozoic to Tertiary crystalline rocks. The radiogenic heat production in the Nanga Parbat-Haramosh Massif ranges between 0.72 and 18.46 µWm-3, with mean and median values of 7.12 and 6.74 µWm-3, respectively. Furthermore, Proterozoic gneisses, Tertiary granites, and pegmatites within the Nanga Parbat-Haramosh Massif have mean radiogenic heat production values of 7.86, 10.67, and 6.47 µWm-3, respectively. The radiogenic heat production in the Kohistan-Ladakh Batholith ranges between 0.42 and 5.16 µWm-3, averaging at 2.49 µWm-3 with the highest mean of 3.68 µWm-3 in granites and lowest 0.74 µWm-3 in tonalites. The radiogenic heat production of the Karakoram Batholith ranges between 1.04 and 23.54 µWm-3 with a mean of 5.84 µWm-3 and a median of 4.45 µWm-3. Within the Karakoram Batholith, the Tertiary granites have the highest mean radiogenic heat production of 11.17 µWm-3,  while the lowest mean radiogenic heat production of 2.86 µWm-3 is found in the Cretaceous diorites. Our results suggest that the Nanga Parbat-Haramosh Massif, which is composed of Proterozoic Indian plate basement rocks, has high concentrations of uranium, thorium, and potassium, and consequently a higher radiogenic heat production. This also correlates with similar high radiogenic heat-producing basement rocks exposed in southern India. The presence of high radiogenic heat production in Tertiary granites and pegmatites indicates mobilization and enrichment of incompatible uranium and thorium due to crustal evolution processes related to the Himalayan Orogeny. We suggest that high radiogenic heat production in Proterozoic rocks may have contributed significantly to the enhanced heat flux in the active Himalayan Orogen.

How to cite: Anees, M., Kley, J., Leiss, B., Wagner, B., and Shah, M. M.: Spatial variation of radiogenic heat production related to the crystalline rock types in the western Himalaya-Karakoram region of Pakistan , EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7690, https://doi.org/10.5194/egusphere-egu22-7690, 2022.

Wed, 25 May, 15:10–16:40

Chairpersons: Martijn Janssen, Eugenio Trumpy, Maren Brehme

15:10–15:17
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EGU22-1578
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ECS
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Virtual presentation
Chanmaly Chhun et al.

To reveal the seismic velocity structure and anisotropy in potential geothermal fields, Kenya, we analyzed ambient noise data from nine vertical components of broadband seismometer stations. Our analysis is based on the cross-correlation of ambient noise data by extracting phase velocity dispersion curves via the zero-crossing method and then applying surface-wave inversion to estimate S-wave velocity structures. The results for both phase velocity and S-wave velocity structures show a clear velocity contrast in volcanic systems (i.e., Korosi-Paka-Silali) in the Kenyan Great Rift (KGR). The phase velocity structure (i.e., 1400 - 2200 km/s) significantly drops in the Silali trachytic shield volcano and the Pleistocene Paka shield volcano. Such velocity contrasts are also observed where they are parallel and perpendicular to the geological structure of the KGR. Most decreasing seismic velocities are normal to abundant faults and fractures in the inner trough of the KGR. This direction is aligned with local extension direction, linked to divergent plate boundaries. The resulting S-wave velocity structures further disclose the anomaly features that can indicate permeable or non-permeable layers. Permeable layers are extensively existing that can provide potential geothermal fluid accumulations. Most potential areas are below the rift floor between the Paka and Silali volcanoes, involved in intense faulting/fractures and young porous rocks (i.e., intercalated pyroclastic, trachyte, and basalt lavas). The lithocap zones are mostly less than 1 km. The magma heat sources are most likely deeper than 3 km at Paka and 4 km at Silali. Therefore, geothermal reservoirs can be relatively interconnected due to shallow magma-volcanic systems, existing groundwater, porous volcanic rocks (i.e., pumice) and intensive fractures controlled by main graben faults in the KGR, regardless of impermeable volcanic rocks or (ore) mineralization in this study area. This work was supported by Leading Enhanced Notable Geothermal Optimization (LENGO) of SATREPS (JICA-JST), Japan.

Keywords: ambient noise, S-wave velocity, seismic anisotropy, shallow magma-reservoir systems, rifting and volcanism

How to cite: Chhun, C., Tsuji, T., and Ikeda, T.: S-wave velocity structure in Kenyan potential geothermal fields inferred from ambient seismic noise data analysis, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-1578, https://doi.org/10.5194/egusphere-egu22-1578, 2022.

15:17–15:24
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EGU22-2634
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ECS
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On-site presentation
Annette Dietmaier and Thomas Baumann

Multiple operators use geothermal wells in Lower Bavaria and Upper Austria for balneological (medical and wellness) applications and for energy and/or heat mining purposes. These applications depend heavily on the well‘s hydrochemical and geophysical stability (mineralization, pressure, temperature).

At the moment, wells are submitted to inspection once a year, which includes the analysis of ions, pH, pressure, temperature etc. These „offline“ analyses, while covering a large set of parameters, obviously fail to show intra-annual variability within the measured parameters. On the other hand, some geothermal wells are being monitored quasi-continually. These „online“ sensors, however, only cover a small set of selected parameters, such as electric conductivity, temperature and pressure.

This study aims at forecasting hydrochemical and physical stability based on annual measurements by assessing the degree of intra-annual variability covered or neglected by the yearly measurements. The results are required for a sound assessment of possible adverse effects of other exploration activities and short term variations of the withdrawal rates reflecting the demand for heat, energy and/or spa water. To do this, we followed the concept of virtual sensors and their correlation to detailed yearly measurements.

We found that, while annual measurements, when taken approximately in the same season of the year, do match the data sampled online quite well, intra-annual variability at the examined wells was quite strong for some parameters and not represented by the offline data. Thus, annual data can be used to make predictions regarding long-term variability. In order to forecast intra-annual variability, higher temporal resolution is necessary. While not a replacement for the detailed analyses, the virtual sensors presented here provide a robust method to trigger further actions.

How to cite: Dietmaier, A. and Baumann, T.: Forecasting high resolution variations in deep geothermal wells based on low resolution measurements utilizing virtual sensors, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2634, https://doi.org/10.5194/egusphere-egu22-2634, 2022.

15:24–15:31
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EGU22-5775
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ECS
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Virtual presentation
Loris Piolat et al.

   With the development of geothermal energy in response to the 21st century environmental challenges, it appears that developing geothermal energy in off-grid regions can be a durable investment, providing electricity production and various direct thermal use, and bypassing the usual development of fossil energy in remote areas. In this context, the European Union funded project “Geothermal Village”, within the Horizon 2020 LEAP-RE program, aims to set up the geothermal exploration process for isolated areas in the East African Rift Valley. A field mission at Lake Abhé (Djibouti) was set up in late 2021, with geophysical, geochemical and geological researchers, in order to investigate the hydrothermal features of the area and to assess the feasibility of setting up a small-scale geothermal plant for local communities. 

    The area analysed with electrical resistivity tomographies (ERT) on the lake’s eastern shore is characterized by the presence of linear chains of active travertine chimneys built up on top of fluvio-lacustrine deposits. Chimney alignment orientations match those of the major structural lineaments observed through the basaltic units surrounding the lake. The ERT survey was set up with the aim of describing the main accessible fault structures, getting the resistivity information of the local lithologies to calibrate the magneto-tellurics (MT) survey, and getting the chargeability information to describe alteration processes over the geothermally active zones. Profiles of spontaneous polarization have also been done over the majority of ERT profiles.

    The method used was technically challenging, because of field conditions (especially because of the very low resistivity top layers) and incompatibilities between the data logger and the cable set. To process the data, pre-processing has been implemented with Python scripts, which allows poor quality data to improve, essentially thanks to geometrical reallocation of electrodes. The injection protocol is a randomized Wenner, in order to minimize noise due to near-electrode polarisation with steel electrodes.

    The main results show fault structures, and allow to determine fault offsets for some basalt blocs. It also provides resistivity values for the sedimentary top layer, allowing with the basalt resistivity for a low depth calibration of the MT survey, and a preliminary assessment of the distribution of pore water salinity across the area. The chargeability values are less accurate, showing in the best cases good signatures of the chimney’s structure, and demonstrating in the worst cases the artefact effects of the very conductive values of this salty area. 

    In conclusion, this survey has faced a lot of technical issues, but the results are defining more precisely the previous surveys done on this area. The results can be used for geothermal modelling (describing the fluid path within the reservoir and along the chimney’s structures), water exploration (with the salinity assessment), and geotechnical safety (depth of hardened rock for drilling).

How to cite: Piolat, L., Géraud, Y., Diraison, M., Walter, B., Chibati, N., Favier, A., Ibrahim-Ahmed, N.-A., and Magareh, H.-M.: Electrical geophysical exploration of Lac Abhé’s geothermal system, Djibouti, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-5775, https://doi.org/10.5194/egusphere-egu22-5775, 2022.

15:31–15:38
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EGU22-9238
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ECS
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Virtual presentation
Serhat Tonkul et al.

Scale problems in geothermal power plants are one of the reasons that reduce power plant efficiency. Silica scaling, calcite scaling, and sulfide scaling are the most common scale types in geothermal power plants. These scale problems in geothermal power plants can be seen in geothermal wells and surface equipment systems. In this context, various measures should be taken to control the scale problems in geothermal power plants. In this study, the stibnite scaling observed in the preheater system of the Germencik geothermal power plant in the west of Turkey is discussed in full detail. Possible types of scale that may occur in the geothermal wells in the power plant were revealed, and the optimum reinjection temperature was determined for stibnite scaling, which reduces the efficiency of the power plant. Within the 3D modeling of the geothermal power plant and different geochemical models, the precautions to be taken at the power plant are examined in all details.

Keywords: Stibnite, Scaling, Binary power plants, Germencik, power plant efficiency

Acknowledgments: This study has received funding from the European Union’s Horizon 2020 research and innovation programme under agreement, REFLECT Project,  No: 850626.

How to cite: Tonkul, S., Baba, A., Demir, M. M., and Regenspurg, S.: Investigation of Stibnite (Antimony) Scale in Germencik Geothermal Site, Büyük Menderes Graben, Western Turkey, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9238, https://doi.org/10.5194/egusphere-egu22-9238, 2022.

15:38–15:45
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EGU22-9276
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ECS
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Virtual presentation
Alexander Jüstel et al.

Vintage seismic lines from the area of the city of Aachen from the early 1980s were reprocessed and interpreted in order to characterize the deeper subsurface for its geothermal energy potential. In focus are Lower Carboniferous and Middle to Upper Devonian carbonates as possible karstification is assumed due to the occurrence of thermal springs in the region. Further, extensional NW-SE striking faults of the Tertiary Lower Rhine Graben Rift may provide opportunities for geothermal field development.

The Paleozoic units northwest of the Variscan Rhenish Massif range from Lower Devonian to Upper Carboniferous. Upper Devonian to Upper Carboniferous strata was thrusted onto folded Upper Carboniferous rocks of the foreland molasse basin (e.g. Wurm Syncline) during the Variscan orogeny. As a result, a complex tectonized belt with (at least) three major NE-SW striking thrusts developed, which are cropping out in the region of the city of Aachen. Later, during Upper Cretaceous and Cenozoic times, the region experienced SW-directed rifting and block faulting orthogonal to the Variscan strike as well as inversion movements. Along two of these Paleozoic thrusts, the Aachen Thermal Springs are arising from the subsurface with a temperature of up to 72°C assuming pathways for thermal water from karstified rocks in the deeper subsurface of the Inde Synclinorium. In addition, the strata is exposed along the margins of the Inde Synclinorium or was encountered in wells such as the RWTH-1 well located in the Wurm Syncline or Frenzer Staffel 1 in the Inde Syncline. While the stratigraphy of the geological units is well known from outcrops, their facies distribution and related lithology in the subsurface and within the different fault blocks of the thrust system remains fairly unknown. This was shown from the drilling of the well RWTH-1 in 2004 where the Kohlenkalk (platform carbonates) and the Massenkalk (reef carbonates) were expected but not encountered despite cropping out 10 kilometers to the southwest.

For this investigation, two roughly NW-SE trending seismic lines (~70 km long) were interpreted. The lines were acquired perpendicular to the strike of the Variscan structural elements. The seismic data imaging is challenging due to highly consolidated rocks and very high impedances, partly steep inclination of bedding planes due to thrusting and back-thrusting, low angle faulting (thrust planes), and possible 3D effects where migration is difficult. However, based on the new processing, surface geology correlation, integration of well data, and back-stripping check-ups, we were able to map the key thrust outlines at depths and lithology targets based on their characteristic reflectivity pattern. The most prominent feature on the seismic data is a sharp reflection, which dips approx. south from a very shallow level (~1.000 m) below 6.000 m. The feature was also evident on vintage DEKORP-data and is interpreted as the seismic expression of the Aachen Thrust. Current models can thus be validated or adapted based on our sweet spot maps including the deeper tectonic fabric of the region and regional distribution of carbonate sequences with possible insights on karstification to de-risk future geothermal developments in the area.

How to cite: Jüstel, A., Ritzmann, O., Strozyk, F., and Kukla, P.: Interpretation of seismic reflection vintage lines from the Variscan Fold and Thrust Belt in the Aachen region, Germany: Implications for geothermal exploration, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9276, https://doi.org/10.5194/egusphere-egu22-9276, 2022.

15:45–15:52
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EGU22-11499
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ECS
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On-site presentation
Aurélia Crinière and Andrea Moscariello

As part of the energy transition effort in Switzerland, the ‘GEothermies’: exploration program carried out in the Geneva Basin and its neighbouring areas (Fig. 1) for direct geothermal heat production and storage is ongoing in the Molasse sedimentary basin. Results from previous hydrocarbon exploration and subsequent geothermal drilling campaigns confirmed the presence of five possible stratigraphic targets for geothermal projects.

This study focuses on the shallowest: the Cretaceous-Cenozoic Transition (CCT), a poorly known stratigraphic interval marked by a sedimentary hiatus related to the tectonic phase and the climate that dominated the area at this period. It displays good geothermal potential for its flow rate due to the occurrence of karstification and open fracture systems in the Lower Cretaceous characterized by low-porosity carbonates. The Alpine orogenesis has subaerially exposed and faulted the Lower Cretaceous generating karsts that were infilled with Eocene and Oligocene coarse sediments: the ‘Sidérolithique’, a quartz-rich sandstone facies, and the ‘Gompholite’, a polygenic conglomerate facies.

A better understanding of this stratigraphic interval is provided by tackling the following aspects:

  • Sedimentological framework and diagenetic history of the Cenozoic sediments based on outcrop data and description of cores, further refined by geochemical and mineralogical analyses aimed at reconstructing their depositional processes and environment,
  • Petrophysics, reservoir properties and evaluation of their geothermal reservoirs potential,
  • Regional 2D geological model based on outcrops, wells record, 2D and 3D seismic data in order to predict their lateral and vertical distribution.

The CCT is identified in a few outcrops in the Salève, the Vuache and the Jura, in 35 wells (Fig. 1) and in seismic data, with a depth ranging between 31.20 m (well SPM-3) and 1376 m (well Thônex; Fig. 1). The most significant ‘Sidérolithique’ deposit of 130 m thickness was recorded at 630 m depth in the geothermal exploration well GEo-02 drilled in 2019. According to cores and outcrops observations, the ‘Sidérolithique’ facies have a variable clay content of kaolinite and chlorite as well as a variable abundance of siderite. In the Geo-02 well, a kaolinite-rich content at the bottom of the 'Sidérolithique' shows a mixed signature of the doline palaeosol with the sandstone fill. Despite the presence of clay and siderite, in the Gex wells, porosity values in the CCT deposits ranges from 0 to 20 % while permeability values can reach up several hundreds of mD (Fig. 2) indicating overall good reservoir potential.

Ultimately, this study aims at improving the predictive capability of the geological model of the Canton of Geneva and neighbouring France and provides new insights on the potential of the CCT deposits as geothermal reservoirs.

Figure 1. Location of the study area with the 35 wells that recorded the CCT. Two NW-SE major faults are showed in red: the Vuache Fault and the Arve Fault.

Figure 2. Summary of porosity and permeability values from 86 plugs sorted by facies from the Gex wells including different units in the CCT interval from younger Molasse (left) to older Lower Cretaceous units (right).

How to cite: Crinière, A. and Moscariello, A.: Reservoir geology of the Cretaceous-Cenozoic Transition in the context of geothermal exploration in the Geneva Basin and neighbouring France (Switzerland & France), EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-11499, https://doi.org/10.5194/egusphere-egu22-11499, 2022.

15:52–16:02
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EGU22-10870
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ECS
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solicited
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On-site presentation
Genevieve Savard et al.

Affordable geophysical survey methods to image in detail the upper crust are critically needed to encourage the growth of the geothermal sector and ensure safe operation conditions. Recent ambient noise imaging studies using surface or body waves retrieved from dense nodal networks have shown that it is a promising technique for reliable, low-cost geothermal prospection and monitoring. The northern canton of Aargau is one of a few regions in Switzerland being investigated for its high geothermal potential. The local positive heat flow anomaly is thought to be linked to hydrothermal circulation along faults bounding the Permo-Carboniferous trough crossing the area. In the Winter of 2020-2021, we deployed a temporary dense network of 210 nodal stations that recorded for about 30 days The goal was to assess the performance of ambient noise tomography by comparing the derived images against existing 2D seismic reflection profiles and geological data. In this study, we invert for the 3D S-wave velocity structure using surface wave dispersion. We discuss the challenges and solutions we encountered in processing the large-N data such as the automatic picking of the large number (~43k) of dispersion curves and a few solutions we applied, including machine-learning-derived techniques

How to cite: Savard, G., Planès, T., and Lupi, M.: Ambient Noise Tomography applied to a large-N nodal network in Aargau, Switzerland. , EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-10870, https://doi.org/10.5194/egusphere-egu22-10870, 2022.

16:02–16:09
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EGU22-12768
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Virtual presentation
Maria Ask and Simona Pierdominici

There is an increased interest in Scandinavia for development of deep geothermal energy as fossil-free heat-source of district heating system. As part of exploration for Enhanced Geothermal System (EGS) to 5-7 km depth where the groundwater temperature is 120°C can potentially be extracted at 5-7 km depth, Göteborg Energi AB has cored a 1 km deep borehole in Högsbo, southwest Sweden. The objectives of testing was to (1) measure in situ temperatures and derive the geothermal gradient, (2) measure thermal properties of the bedrock, and (3) constrain hydrogeological and mechanical properties of the fracture zone.

The target for drilling and a subsequent EGS facility, is a heat-producing granite that is overlain by a regional fracture zone with inferred elevated permeability. The in-situ temperature of this type granite is boosted by radioactive gamma-ray decay from heat producing elements (K, U, Th).

Knowledge of the state of stress is central to understand bedrock stability, induced seismicity and fluid flow patterns. Acoustic borehole televiewer logging was conducted to map fracture occurrence and their geometry, as well as to investigate of stress-induced failure has occurred in the wellbore. For vertical boreholes, drilled parallel with a principal (vertical) stress, borehole breakouts and drilling induced tensile fractures reveal the orientation of minimum- and maximum horizontal stress, respectively, if the tangential stress concentration generated by the borehole overcomes the compressional and tensile strength of the rock mass, respectively.

An unexpected large number of stress indicators has been observed, both borehole breakouts and drilling induced tensile fractures. We observed two types of borehole breakouts: (1) Well-developed borehole breakouts that are clearly visible on both travel-time and amplitude logs; and (2) Poorly-developed borehole breakout that are best visible on the Amplitude log. The shallowest stress indicators are observed from 172-174 m depth, where both types of indicators show NNW-SSE orientation of maximum horizontal stress. This orientation is confirmed from deeper observation, regardless of type of stress indicator. It appears that the regional fracture zone is not influencing the orientation of the stress field in the borehole.

The observations of overlapping drilling induced tensile fractures and borehole breakouts, from such a shallow depth is interesting. It raises questions regarding the magnitudes of stress and the strength of the rock mass. We note that elevated temperature during drilling may induce thermal stresses that favors the formation of drilling induced tensile fractures. On the other hand, the heat producing granites also are known to be probe to weathering. Further studies are required to understand the observed stress indicators, but it appears that the stress orientation is uniform.

How to cite: Ask, M. and Pierdominici, S.: Constraining horizontal stress orientations from acoustic borehole televiewer logs in Högsbo, Southwest Sweden: geothermal exploration, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-12768, https://doi.org/10.5194/egusphere-egu22-12768, 2022.

16:09–16:16
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EGU22-6705
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ECS
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On-site presentation
Mohamed Ezzat et al.

Geothermal energy can be a limitless and CO2-free energy resource. However, moderate geothermal temperature gradients of ∼30 oC/km in most regions typically require employing so-called "Advanced" or "Enhanced" geothermal systems, called AGS and EGS, respectively, which require reservoirs with temperatures >150 oC. To access such high temperatures, we need to drill deeper than 5 km, i.e., in hard rock. The costs of drilling to such depths, using traditional rotary drilling, increase exponentially with depth and can be up to 80% of the total geothermal project investment. These high drilling costs can be reduced significantly with contactless drilling technologies (e.g., thermal spallation drilling, laser drilling, microwave drilling, and Plasma Pulse Geo-Drilling), as they avoid the lengthy tripping times associated with drill-bit damage.

PPGD uses high-voltage pulses of a few microseconds duration to fracture the rock, thereby drilling without any mechanical abrasion. Future PPGD costs may be as low as 10% of mechanical rotary drilling costs (Schiegg et al., 2015). Our PPGD research addresses two outstanding questions: (1) Understand the fundamental physics of the electric breakdown inside the rock and associated rock fracturing processes, which we investigate numerically (Ezzat et al., 2022, 2021; Vogler et al., 2020; Walsh and Vogler, 2020). (2) Evaluate the PPGD performance under deep-wellbore conditions of  ~5 km (i.e., high pore and lithostatic pressures, and high temperatures). Our ongoing numerical and experimental studies are expected to provide further insights into the applicability of PPGD for geothermal energy utilization.

First, we numerically model the formation of a plasma in rock pores, which constitutes the onset of rock failure during the PPGD process. These numerical models show the significant effect of the pore characteristics on the PPGD process and give insight into how future PPGD operations should be designed. Second, we conduct PPGD physical experiments, where we employ lithostatic pressures of up to 1500 bar, pore pressures of up to 500 bar, temperatures of up to 80 oC, and voltages of up to 300 kV. Concluding these experiments with the associated challenges shall demonstrate whether PPGD is efficient at great depths of up to 5 km. Combining our numerical and experimental results allows optimizing future PPGD operations.

 

References

Ezzat, M., Adams, B. M., Saar, M. O., and Vogler, D. (2022). Numerical modeling of the effects of pore characteristics on the electric breakdown of rock for plasma pulse geo drilling. Energies, 15(1).

Ezzat, M., Vogler, D., Saar, M. O., and Adams, B. M. (2021). Simulating plasma formation in pores under short electric pulses for plasma pulse geo drilling (ppgd). Energies, 14(16).

Schiegg, H. O., Rødland, A., Zhu, G., and Yuen, D. A. (2015). Electro-pulse-boring (epb): Novel super-deep drilling technology for low cost electricity. Journal of Earth Science, 26(1):37–46.

Vogler, D., Walsh, S. D., and Saar, M. O. (2020). A numerical investigation into key factors controlling hard rock excavation via electropulse stimulation. Journal of Rock Mechanics and Geotechnical Engineering, 12(4):793–801.

Walsh, S. D. and Vogler, D. (2020). Simulating electropulse fracture of granitic rock. International Journal of Rock Mechanics and Mining Sciences, 128:104238.

How to cite: Ezzat, M., Börner, J., Vogler, D., Wittig, V., and Saar, M. O.: Plasma Pulse Geo-Drilling as a Low-cost Drilling Technology for Deep-geothermal Energy Utilization: Status and Challenges, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6705, https://doi.org/10.5194/egusphere-egu22-6705, 2022.

16:16–16:23
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EGU22-11017
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ECS
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Virtual presentation
Berker Polat et al.

Geothermal energy out of deep and thus, hot reservoirs do pose viable means to supply and well support the changeover to renewables and still increasing energy demand worldwide as it is virtually available everywhere 24/7, having a carbon neutral footprint and being so-called baseload capable. Therefore, application of enhanced geothermal and petrothermal systems do require the exploitation of such deep geothermal resources to provide more and better geothermal energy. The EU ZoDrEx project and consortium recently demonstrated that installation and exploitation of such geothermal resources can be done safely and economically. Fraunhofer IEG and project partners proved superb hydraulic improvement between wellbore and surrounding reservoir, via Fraunhofer´s high pressure jetting and milling operation, leading to subsequent, much improved reservoir flow by further micro well enhancing measures of Partner GES and others. A variety of high-pressure based water jet technologies for general mineral and rock weakening, erosion and destruction via ultra-short radius deviation were field tested in downhole operation to better connect main wellbore with surrounding reservoir through micro sidetracking and notching. The incorporation of these rock penetration type measures into a functional, downhole EGS system constituted the field work being done in ETH’s Bedretto Underground Laboratory with partners from the ZODREX consortium.

How to cite: Polat, B., Wittig, V., Boerner, J., Geissler, N., Krusenbaum, S., and Bunk, M.: Exploration, utilization and monitoring of conventional and unconventional geothermal resources, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-11017, https://doi.org/10.5194/egusphere-egu22-11017, 2022.

Wed, 25 May, 17:00–18:30

Chairpersons: Martijn Janssen, Chris Boeije, Maren Brehme

17:00–17:07
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EGU22-8257
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ECS
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On-site presentation
Taylan Akın et al.

Emissions of greenhouse gases such as CO2 emitted at Turkish geothermal power plants are an obstacle to accepting geothermal energy as green power. However, recent advances in carbon capture and storage technologies have enabled low emissions by re-injecting produced CO2. Carbfix is one of the recent projects where geothermal gases are re-injected into the reservoir. In the Carbfix project, waste gases from Hellisheidi Power Plant are dissolved in effluent water and gas-charged fluid is injected into the basaltic subsurface where some portion of the gases precipitate as minerals. To understand whether the Carbfix methodology can be a standard application for the geothermal industry worldwide, an international research project called Geothermal Emission Control (GECO) was started in 2018. GECO is funded by the EU through the H2020, and the project consortium is consisting of 18 partners from 9 countries across Europe.

GECO aims to develop near-zero-emission geothermal power plants in four sites by providing clean geothermal energy at a lower cost. Kızıldere (Turkey) geothermal field (KGF) is one of the demonstration sites in the project where emission gases are injected into Menderes Metamorphic units. Zorlu Energy and METU are partners of the project from Turkey, and they operate the demonstration and monitoring of CO2 injection in KGF. We present here a geological overview of the Kızıldere injection site, baseline monitoring studies, fluid chemistry of the reservoir, and the predicted chemistry of the gas-charged fluid at the site. Moreover, geochemical simulation conducted for predicting fluid-rock interaction taking place in the geological formation is being assessed.

This work was done in the framework of the GECO Project, funded by the European Union’s Horizon 2020 research and innovation program under grant agreement No. 818169.

How to cite: Akın, T., Erol, S., Akın, S., Şentürk, E., and Şengün Çetin, R.: Injection of geothermal gases at the Kızıldere field: A pre-injection overview, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-8257, https://doi.org/10.5194/egusphere-egu22-8257, 2022.

17:07–17:14
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EGU22-9083
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ECS
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Virtual presentation
Francesco Parisio and Victor Vilarrasa

Technological advances have allowed to target geothermal systems at greater depth and higher temperature in the supercritical regime. Supercritical geothermal systems (SCGS) could potentially provide a drastic increase in power generation, with estimates up to 50 MW per well. A handful of wellbores worldwide have either (or have shown potential to) reached supercritical resources in magmatic provinces. As a common occurrence in volcanic area, the resident fluid is not pure and mixtures of water and CO2 are the norm. In this contribution, we will explore the flow conditions of H2O-CO2 mixtures at temperature and pressure conditions above the critical point of water. The multi-phase and multi-component problem of H2O-CO2 mixture flow is a non-trivial problem and few studies have been done in the past. We present finite element simulations with the open-source multi-physics framework MOOSE that explore the flow conditions of H2O-CO2 mixtures at high temperature and pressure. As a benchmark problem, we assume an injection of cold CO2 into a water filled reservoir. We analyse the pressure and temperature changes and the evolution of the injected CO2 in time. We show how gravity forces play a role in the long term and at relatively large distance from the injection. We discuss the potential of employing CO2 as a working fluid in SCGS.

How to cite: Parisio, F. and Vilarrasa, V.: CO2 flow in supercritical geothermal systems, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9083, https://doi.org/10.5194/egusphere-egu22-9083, 2022.

17:14–17:21
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EGU22-9905
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ECS
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On-site presentation
Barnaby Fryer et al.

The stress state in the subsurface has been shown to be a hugely important parameter for a wide variety of considerations related to seismicity, both natural and anthropogenic. Industrial operations have been shown to be capable of influencing this subsurface state of stress, as most notably evidenced by instances of induced seismicity related to mining, reservoir impoundment, and reservoir-engineering applications such as production- and injection-induced seismicity related to pore pressure increase. The recognized significance of the stress state for many industrial operations as well as operators' proven ability to influence it, has led to the notion that the stress state can be intentionally preconditioned prior to an operation to that operation’s eventual benefit. The idea of preconditioning was first introduced by the mining industry in the late 1950's as a way to improve rockburst conditions in mines, by blasting to relieve stress in near-face regions. This idea of stress preconditioning has since been extended to the petroleum industry, beginning in the 1970’s and typically focused around hydraulic fracturing. Enhanced Geothermal Systems (EGSs) have been plagued by a number of instances of high-profile induced seismicity, most notably in Basel, Switzerland. This has led to the realization that the development of new reservoir stimulation techniques is crucial for the development of EGS. Here, we propose that the effective stress along a fault intersected by an EGS well be preconditioned prior to stimulation through an extended period of fluid production. Following this production phase, the fault is stimulated through high-pressure injection. Through analytical models related to pressure diffusion, earthquake nucleation, and earthquake rupture, it is suggested that this methodology would result in the halting of near-well nucleated events as they rupture towards the zone of reduced pore pressure. These models assume a constant permeability, linear slip weakening, and a near-critically stressed fault. The investigation is supported by a scaling analysis, shedding light on the suggested required magnitude of the preconditioning phase.

Figure: A schematic illustrating the proposed strategy. On the left, a well (A) is drilled into a fault, shown in plane-view. Fluid is produced from this well, reducing the pore pressure. This production is continued for a significant amount of time, allowing the reduction of pore pressure to be significant and far reaching (D). The well is then stimulated with a short high pressure burst of injection (B). The stimulated zone shears near the well in this high-pressure zone, but is halted by the low-pressure zone (C). The corresponding pore pressure as a function of the radial distance is plotted on the right.

How to cite: Fryer, B., Lebihain, M., and Violay, M.: Single well pore pressure preconditioning for EGS, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9905, https://doi.org/10.5194/egusphere-egu22-9905, 2022.

17:21–17:28
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EGU22-12358
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Virtual presentation
Pablo Salinas et al.

Numerical modelling of fluid flow and heat transport in geothermal reservoirs can be very challenging. One reason is the broad range of length-scales that control the flow behaviour, spanning several orders of magnitude from fractures (millimetre-scale) and wells (metre-scale) to facies architecture and faults (kilometre-scale). The usual approach for modelling geothermal reservoirs is to discretise the equations using the finite-volume method and variants thereof to ensure mass conservation, subdividing space onto a fixed, structured mesh. However, using a fixed mesh resolution across the entire model domain can be very computationally expensive, and prohibitive if the model must resolve many length-scales.

Here we report an efficient method to apply dynamic mesh optimisation (DMO) to model geothermal reservoirs. DMO is widely used in other areas of computational fluid dynamics because it offers significant advantages in providing higher resolution, multi-scale solutions at much lower computational cost. However, application of DMO to geothermal reservoir modelling has so far been very limited.

The method reported here uses a surface-based representation of all geological heterogeneity that should be captured in the model. The numerous surfaces in the model represent geologic features such as faults, fractures, and boundaries between rock types with different material properties. The surfaces bound rock volumes, termed geologic domains, within which material properties are constant. When simulating flow and heat transport, the mesh dynamically adapts to optimize the representation of key solutions metrics of interest such as temperature, pressure, flow velocity or fluid saturation, but the surface architecture is preserved. The advantage of this approach is that up-, cross- or down-scaling of material properties during DMO is not required, as the properties are uniform within each geologic domain.

We demonstrate the method using a number of example problems, including complex wells. Another advantage of our approach is that well trajectories are accurately represented as the mesh conforms to the wells. The well trajectory is also preserved during DMO. We show that more accurate results are obtained at lower computational cost as compared to conventional, fixed mesh approaches.

How to cite: Salinas, P., Regnier, G., Jacquemyn, C., Pain, C. C., and Jackson, M. D.: Geothermal reservoir modelling by using dynamic unstructured meshes for improved heat recovery in highly heterogeneous reservoirs, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-12358, https://doi.org/10.5194/egusphere-egu22-12358, 2022.

17:28–17:35
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EGU22-2751
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ECS
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On-site presentation
Lilly Zacherl and Thomas Baumann

Successful development of the geothermal energy sector requires an understanding of the geological systems and processes that occur within. In the North Alpine Foreland Basin, a hydrogeothermal play type, most sites are affected by inorganic precipitates which reduce the efficiency and safety of plants. Although the gas concentrations in the geothermal waters are generally low, any formation of an independent gas phase induces carbonate precipitation. A quantitative prediction of the precipitates, however, is not yet possible because kinetic data for gas phase induced precipitates is not available.

To address this issue laboratory experiments were run where a gas (CO2, air) was induced into a column containing an aqueous solution (tap water, water with high salinity). The scalings produced were analyzed by Raman spectroscopy, a mass balance of the process including the dissolving of scaling by inducing CO2 into the scaled column was based on ion chromatography data. The experiments show that by injecting air into tap water a full stripping of CO2 occurs which is the experimental proof of the disruption of the lime carbonic acid equilibrium by gas bubbles. The salinity of the initial solution influences - in agreement to previous investigations - the polymorph: only aragonite crystals were detected in tap water (ionic strength: 8.5e-03 mol/L), whereas only calcite crystals showed up in tap water with additional 0.2 g/L NaCl (ionic strength: 1.2e-02 mol/L).  Precipitation was inhibited when 120 g/L NaCl were added to the tap water before stripping (ionic strength: 2.1 mol/L).

The data were evaluated using a combination of hydrogeochemical calculation and precipitation kinetics (PhreeqC) with gas bubble kinetics (Python) and PEST++ for the final parameter adjustment. We successfully modelled the process of stripping, CO2-injection and the experiments with higher salinity with one model.  This experimental proof of the gas phase induced carbonate precipitation and the new adequate description of the scaling process is a further step to predictive maintenance for geothermal sites and a more reliable holistic site assessment during the planning stage. Together, this improves the sustainability and the attractiveness of the geothermal energy sector to investors.

How to cite: Zacherl, L. and Baumann, T.: Gas phase induced carbonate precipitation - experimental proof and model verification, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2751, https://doi.org/10.5194/egusphere-egu22-2751, 2022.

17:35–17:42
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EGU22-4982
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ECS
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On-site presentation
Lin Jia et al.

Geothermal energy is considered as one of the renewable energy resources to meet the world's growing low-carbon energy demand. There are increasing number of oil wells to be abandoned and these wells could be potentially retrofitted to geothermal wells for sustainable purpose. There have been some studies and practices on retrofitting oil wells, but most of the existing retrofitting methods suffer from either low efficiency or high cost. In this study, we designed and modelled a novel retrofitting pattern to a single well featured with enhanced reservoir system (ERS). We established numerical models of ERS in abandoned oil reservoirs configured with a vertical well. We simulated the effects of reservoir initial oil saturation, thickness, permeability and different ERS designs on the production temperature and output power after 50 years. We found these effects have positive feedback on the production temperature and output power. In addition, we also modeled the temperature effect on oil-gas-water relative permeability as it would highly affect the oil viscosity and mobility in the oil reservoir. Moreover, through sensitive analyses of this retrofitted single well and the traditional doublet geothermal well, we found the retrofitted single well in our study could be as high as that from doublet geothermal well, implying that one single abandoned oil well could work either for direct use or power generation with economic yield but little retrofitting investment. Lessons learned in this study might also be applied to other geothermal scenarios, such as enhanced geothermal system.

How to cite: Jia, L., Li, K., and Zhang, C.: Modelling of a retrofitting methodology to revive abandoned oil reservoirs for geothermal exploitation, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4982, https://doi.org/10.5194/egusphere-egu22-4982, 2022.

17:42–17:49
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EGU22-7285
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ECS
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On-site presentation
Felix Schölderle et al.

Interpretation and monitoring of hydraulically active zones in hydro-geothermal wells is critical for assessing the hydraulics of a reservoir and for understanding sustainable reservoir management. For this purpose, flowmeter runs are often performed during injection at the end of short-term pumping tests after the well is completed. Because conventional well designs do not allow direct monitoring in the reservoir once the well is in operation, it is often not clear whether the flowmeter's interpreted injection zones reflect subsequent production zones.

To gain insight into the long-term hydraulic and thermal behavior of geothermal wells in operation, a fiber-optic monitoring system was installed down to 3683 m MD of a geothermal production well in 2019 and below the electric submersible pump into the reservoir in 2021. The well is part of the Schäftlarnstraße geothermal site in Munich, Southern Germany, where six doublets develop the deep hydrothermal Upper Jurassic “Malm” reservoir of the Northern Alpine Foreland Basin. The fiber-optic monitoring system is the first of its kind installed permanently in a geothermal production well. It allows monitoring of temperature (distributed temperature sensing, DTS) and acoustic/strain (distributed acoustic sensing, DAS) continuously in space and time and of pressure and temperature at a fiber-optic gauge located at top of the reservoir at 2748 m MD.

Using DTS technology, the temperature inside the borehole was monitored when the wells at the geothermal site started production. The recorded data were used to analyze the temperature signature at the hydraulically active zones known from previous hydraulically injection tests (flowmeter and temperature monitoring during cold-water injection).

The results show that both hydraulics and production temperature are dominated by an active, karstified zone in the uppermost part of the reservoir of the monitored well. The production of another well of the three doublets geothermal site also strongly affects the temperature distribution in the monitored well. We highlight the importance of continuous monitoring and show the benefit of the permanent fiber-optic monitoring system for sustainable reservoir management.

How to cite: Schölderle, F., Pfrang, D., Meinecke, M., Dirner, S., and Zosseder, K.: Characterization and permanent monitoring of the hydraulically active zones of a deep geothermal reservoir using a fiber-optic monitoring system in a production well in the Bavarian Molasse Basin, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7285, https://doi.org/10.5194/egusphere-egu22-7285, 2022.

17:49–17:59
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EGU22-9572
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solicited
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On-site presentation
Iwona Galeczka et al.

The global framework of the Paris Agreement aims for rapid reduction of GHG emissions to keep the global average temperature below 2 °C above pre-industrial levels. Renewables including geothermal are crucial in transition from a current carbon intensive to carbon neutral or carbon negative energy sources. Although considered as green and sustainable, the subsurface pressure changes caused by thermal fluid extraction might affect the spatial distribution and content of surface manifestations, e.g., fumaroles and may disturb the groundwaters system in the area. As such monitoring of natural features and groundwaters during the geothermal utilization is crucial in the sustainable management of the power plant and it contributes to the understanding of the hydrothermal system through its production lifetime. The aim of this study is to assess the possible effect of the Theistareykir power plant operation on the fumaroles and groundwater chemical composition.

The deep exploration wells in Theistareykir drilled in 2002-2012 confirmed predicted downhole temperatures of >300 °C and high energy generation capacity of the field. The production drilling in 2016-2017 and construction of the power plant carried out in 2015-2017 resulted in a 45 MWe production unit that started commercial operation in 2017. In 2018 a second 45 MWe unit was added increasing the total power output to 90 MWe. Today 12 production and 2 reinjection wells are in use. The results of the continuous fumarole monitoring within the geothermal field since 2012, show no substantial differences in the gases’ concentrations. The current temperature of the reservoir based on the gas geothermometers is similar to the one obtained during the exploration stage (270-315 °C). The fumaroles located in the center and eastern parts of the production field show a continuous decrease in H2S and H2 since 2015, before commencement of the power plant. The concentrations of the elements of concern such as As, Al, Cu, Zn, Cd, Pb, Cr, Ni in groundwaters show no major variations since monitoring first began in 2011. Furthermore, they have not exceeded limits established by the Icelandic directive for surface waters to protect sensitive biota. Even though the absence of noticeable changes in the compositions of the fumaroles and groundwater indicate that the production that started in 2017/18 has currently not posed an environmental threat, observations made in the other production fields suggest that this can be expected in the future. 

How to cite: Galeczka, I., Óskarsson, F., Clark, D., Kristinsson, S. G., Ólafsson, M., Óladóttir, A. A., Ingimarsson, H., Nielsen, S., and Sigurðardóttir, Á. K.: The effect of utilization of the Theistareykir (N-Iceland) high temperature field on the natural geothermal surface manifestations and groundwater composition, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9572, https://doi.org/10.5194/egusphere-egu22-9572, 2022.

17:59–18:06
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EGU22-9858
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ECS
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Virtual presentation
Benedikt Ahrens et al.

Medium-depth and deep geothermal systems hosted in carbonate rocks are amongst the most promising geothermal resources in the world due to their favorable geological and stress- and temperature-sensitive petrophysical heterogeneity. In general, structural heterogeneities such as natural fractures, karstifications, cavities or entire fracture networks mainly dominate geothermal fluid flows and storages and, thus, dictate the reservoir quality. However, especially for carbonate reservoirs, it is even more complex, as a profound understanding of the links between diagenetic processes, facies, deformations, porosities, and fluid flow properties is essential to estimate the distribution of reservoir quality. This assessment is further complicated by the spatially and temporally varying pressure and temperature conditions (e.g., recharge and discharge of geothermal systems).

In the wake of Bavaria’s (southern Germany) success story in exploiting the geothermal systems hosted in deep carbonates, there are extensive investigations to determine the geothermal potential of Devonian carbonates in North Rhine-Westphalia (western Germany). The geothermal potential of these Devonian carbonates strongly depends upon how and to what extent the tectonically influenced burial history and diagenetic processes have modified the pore network and promoted heterogeneities such as fractures and karstifications. In our triaxial experiments, we examined the influence of in-situ stress and temperature and their histories as well as the influence of brittle faulting on porosities and hydraulic properties of different Devonian carbonate rocks. From analogue outcrops limestone, dolomitic limestone, dolostone, and fractured carbonates were sampled and petrophysically investigated. The stresses simulated covered both hydrostatic and triaxial states. Furthermore, the influence of elevated temperature and stress on the hydraulic properties of samples triaxially compressed at effective confining pressures was also studied systematically. Our results show that the interplay of temperature and stress state, and their histories, are fundamental for the evolution of hydraulic properties in the reservoir. Depending on the rock’s mineralogy, the mineral expansion caused by the increased temperature can surpass the effect of microcracking due to heating, resulting in a significant decrease in hydraulic properties. Our results were supplemented by micro-CT images of the microstructure of the samples before and after triaxial testing. It is shown that the interaction of temperature and stress is fundamental for the assessment of the geothermal potential of both intact and fractured carbonate reservoirs.

How to cite: Ahrens, B., Lippert, K., and Nehler, M.: Fluid flow properties of carbonate rocks under simulated in-situ conditions: Implications for geothermal reservoir quality, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9858, https://doi.org/10.5194/egusphere-egu22-9858, 2022.

18:06–18:13
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EGU22-12849
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ECS
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On-site presentation
Deirdre Clark et al.

The monitoring of a geothermal reservoir during its development and production stage is crucial for sustainable and long-lasting utilization. Production wells can cut through several feeding aquifers resulting in discharging of a mixture of fluids originating from these different zones. As such, a sample obtained from a well head during conventional sampling represents an average chemical composition of the subsurface fluids. In contrast, a downhole sampler can collect fluids at precise depths and therefore providing an information about fluid properties at individual feed zones. As it has been observed in high temperature geothermal fields, lack of such a knowledge can lead to a decreased production efficiency and high cost of utilization. For example, extreme corrosion rates of perforated liners have been observed at specific depths due to localized mixing of fluids characterized by distinct compositions. Such damages could be avoided by identifying of such mixing depths before well flow test and by casing off these mis-matching feed zones through cement plugs or tiebacks. Similarly, scaling induced by fluid mixing, could be reduced by assessing appropriate casing depth, and therefore preventing the inflow of problematic fluids into the well.

The aim of this study is to design the downhole sampler that is capable of collecting fluids from high temperature wells at up to 300-400 °C during every stage of the geothermal utilization. The chemical data obtained from fluids at different depths will not only help to select the most energy efficient discharge fluids for improved productivity of the well. It will also contribute to the conceptual models of the reservoirs, hence, to better understanding of hydrothermal reservoirs through their production lifetime.

How to cite: Clark, D., Kaldal, G. S., Gunnarsson, B. S., Galeczka, I., Þorbjörnsson, I. Ö., Nielsen, S., and Sigurðardóttir, Á. K.: Geochemical monitoring of the geothermal reservoirs using a high-temperature downhole sampler, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-12849, https://doi.org/10.5194/egusphere-egu22-12849, 2022.