We welcome interdisciplinary contributions from the fields of geology, geophysics, geochemistry, geomechanics, hydrogeology, machine learning, and static and dynamic geomodelling, including case studies from different geological settings such as sedimentary aquifers, volcanic systems, or fractured basements.
Orals: Tue, 5 May, 16:15–18:00 | Room -2.43
Early-stage geothermal exploration depends heavily on geological and numerical modelling to support decision-making under conditions of sparse data, high uncertainty, and significant financial risk. While such models are central to exploration and appraisal workflows, their role, interpretation, and credibility among non-technical stakeholders remain insufficiently understood—particularly during early project phases, when public acceptance, perceived risk, and investment decisions are most sensitive.
This contribution investigates how stakeholders perceive geothermal exploration models and associated uncertainties, with a particular focus on communication challenges at the interface between technical and societal domains. The study accompanies a technically advanced, research-driven modelling framework developed within the GO-Forward project, which can be challenging to interpret even for specialists.
Empirical insights are drawn from two geothermal case areas situated in contrasting national and regulatory contexts: the onshore Gassum Formation (Denmark) and the southern Vienna Basin (Austria). The methodological approach combines expert and stakeholder interviews, a structured stakeholder analysis using a power–interest grid, and two case-specific stakeholder workshops. These workshops address general perceptions of geothermal energy development as well as stakeholder interpretations of modelling outputs, exploration risks, and uncertainties related to assumptions and data limitations.
Preliminary results reveal pronounced procedural differences between the two case areas in terms of stakeholder constellations, institutional roles, and engagement pathways, alongside heterogeneous understandings of modelling and uncertainty. Whereas modelers typically frame uncertainty as an inherent characteristic of subsurface exploration, many stakeholders associate it directly with project risk, credibility, and trust. Practitioners such as energy agencies report relying on geological survey expertise rather than directly using models themselves, for instance when evaluating license applications.
An emerging topic for further investigation is the potential role of advanced modelling approaches in reducing subsurface uncertainty in ways that are relevant for insurance companies, particularly with respect to eligibility and risk assessment criteria. This idea currently stems from discussions with non-insurance stakeholders and will require targeted investigation involving insurance actors.
Despite the limited number of case studies, the findings will provide practical insights into structuring stakeholder interactions during early geothermal exploration and identify uncertainty as a key interface between technical modelling practices and societal expectations. Further results from ongoing stakeholder workshops will be available by May 2026.
How to cite: Seidl, R., Brüstle, A.-K., Stocker, P., van den Brink, J., and Hoyer, S.: Beneath the Surface: Bridging Stakeholder Engagement and Modelling in Geothermal Exploration, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-3840, https://doi.org/10.5194/egusphere-egu26-3840, 2026.
As of the end of 2025, geothermal energy in France is strong of 209 000 shallow geothermal systems (< 200 m) and 73 deep systems that produce heat for a total of 7.1 TWh. In addition, France has two systems that produce electricity using EGS technology in Soultz-sous-Forêt in Alsace and Bouillante on the overseas island of Guadeloupe in the East Caribbean. While shallow geothermal systems can be installed broadly in the whole French territory, deep systems require specific conditions that are mostly found in the two main sedimentary basins, the Paris Basin to the north and the Aquitanian Basin to the west. In these two basins, as well as the basins of the ECRIS system, the development is the most dynamic with 19 permits for the development of heat production. The Rhine Graben, that hosts Soultz-sous-Forêt, sees the development of a combined heat and lithium development with 7 ongoing research permits. In addition, strong developments are happening in French overseas volcanic islands, both in the Caribbean (Guadeloupe and Martinique) and in the Indian Ocean (La Réunion and Mayotte), with 8 research permits delivered.
For its development, the French government has implemented financial support that covers several aspects from risks at the drilling stage to long-term risks. In 2023, the French government has put forward an action plan to accelerate geothermal development with 27 main actions that aim at increasing in 2028 the produced heat and electricity from geothermal. In the French geothermal energy ecosystem, and to contribute to the national action plan, the BRGM is a major contributor for the geothermal energy resources assessment. For deep geothermal, the BRGM is investigating the resources both through existing data at regional scale (GeoScan Hexagone with first application in Paris Basin) and in dedicated geothermal areas with new acquisitions (GeoScan Arc and GeoScan IdF). In addition, favourability maps have been or are being finalised for open and closed loop shallow geothermal systems.
Overall, France is a dynamic territory for a diverse range of geothermal energy, from shallow to deep and high enthalpy systems with a strong aim to develop further in the near future.
How to cite: Bonte, D., Maragna, C., Hamm, V., Maurel, C., Stopin, A., Dezayes, C., and Sanjuan, B.: Geothermal energy in France: a snapshot in 2025, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-22050, https://doi.org/10.5194/egusphere-egu26-22050, 2026.
Deep geothermal energy is essential for a sustainable European energy future, yet its growth is hindered by high exploration costs associated with the technical risk of finding suitable sites with water-bearing structures while avoiding seismically susceptible faults in the context of hydrothermal systems, or avoiding seismically susceptible faults entirely in the case of enhanced geothermal systems. We present a novel geothermal exploration approach that integrates innovations at three spatial scales, developed under the GeoHEAT project funded by Horizon Europe and the Swiss State Secretariat for Education, Research and Innovation (SERI). At the regional scale (~100 km), we create Levelized Cost of Electricity (LCOE) heat maps using a techno-economic and metamodel analysis to identify optimal sites while considering social and environmental factors. This allows us to select several potential sites to perform a reservoir scale (~10 km) assessment using low-cost passive seismics and gravity. By integrating these geophysical data with probabilistic geological and geomechanical modeling, we quantify structural uncertainties and propose optimal locations to drill exploration boreholes. Then follows a high-resolution borehole characterization incorporating various analyses, the central one being a novel geothermal-grade georadar probe - currently being designed and built within the project - that allows the illumination of permeable structures up to 100 m away from the borehole wall. This characterization is further enhanced by digital rock physics (DRP) analysis of drill cuttings to link rock properties to geomechanical and hydraulic parameters, alongside the denoising and real-time monitoring of drilling-induced micro-seismicity to integrate seismic risk into high-resolution 3D fracture models. Ultimately, data from all scales are integrated into a coupled Thermo-Hydro-Mechanical (THM) model to optimize reservoir productivity and enhance public acceptance through improved risk communication. We present initial results from these multi-scale efforts.
How to cite: Villiger, L., Shakas, A., Pezzulli, E., Bobe, C., Wellmann, F., and Saenger, E. and the GeoHEAT team: The GeoHEAT project: Georadar-Aided High-Resolution Exploration for Advancing Geothermal Energy Usage, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-11686, https://doi.org/10.5194/egusphere-egu26-11686, 2026.
Traditionally, in faulted/sedimentary systems, geothermal injection wells are drilled away from known faults to reduce the risk of induced seismicity, e.g., in the VITO geothermal project in Mol, Belgium. Unless there is high layer/matrix permeability in the area, this can limit the well capacity and result in prohibitively high injection pressures that can induce high stress changes on smaller potentially unknown faults in the area. Further, in geothermal applications, temperature changes in the subsurface may induce large stress changes that can also result in fault reactivation. As part of the HEU-URGENT project, a risk management toolbox has been developed to allow for more effective placement of geothermal wells in doublet systems to maximize heat production while minimizing the risk of induced seismicity.
An essential part of the risk management toolbox is the geomechanical solution to evaluate effective stress changes on known faults and structures in or near the reservoir. In this work, we evaluate three techniques for stress calculation. The first is a simple, but fast, 1D semi-analytical calculation based on Hooke’s law for elasticity. This approach allows for direct pore pressure and thermal stress effects to be considered but ignores elastic stress transfer and Poisson effects. The second semi-analytical approach utilizes the nucleus of strain concept to account for the elastic stress transfer and Poisson effects but comes at a higher computational cost. The third approach is a numerical finite element approximation of linear elastic material behavior. The pros and cons of each approach will be discussed, and the comparison of the results will be presented.
How to cite: Kurgyis, K., pogacnik, J., Janiga, D., Wojnarowski, P., Harcouët-Menou, V., Saifullin, I., and Hernandez, E.: A Risk Management Toolbox for Minimizing Induced Seismicity and Maximizing Production – HEU URGENT Update, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-22980, https://doi.org/10.5194/egusphere-egu26-22980, 2026.
Reducing exploration risk in geothermal projects requires workflows that can robustly connect subsurface characterization to subsequent decisions on well siting and heat/energy extraction. Here, we present an island-scale, multi-physics imaging workflow that integrates magnetotelluric (MT) and gravity data to constrain the geometry of a volcanic magmatic system and its associated hydrothermal system. We invert MT in 3-D on a locally refined, topography-conforming mesh, and jointly invert gravity using a cross-gradient structural coupling to the resistivity model. The resulting coupled resistivity-density models image a dense, resistive intrusive complex beneath the Palawai Basin interpreted as the remnant upper crust magma reservoir, and radially oriented lineaments consistent with rift-zone dike complexes that terminate around 5 km depth. Above the intrusive core, we resolve a moderately conductive layer that may signify hydrothermal alteration products and/or groundwater, while low resistivities near the coastline delineate extensive seawater/brackish intrusion within the basal aquifer system.
Our models identify a region where the intrusive body -- interpreted as a potential heat source -- is shallow, suggesting an elevated thermal gradient. More broadly, this case study shows how multi-parameter geophysical observations and 3-D imaging can inform conceptual models that support geothermal exploration.
How to cite: Grayver, A., Hill, G., Haroon, A., Roots, E., Wallin, E., and Lautze, N.: Imaging of an extinct magmatic system to de-risk geothermal exploration: 3-D joint Magnetotelluric and Gravity inversion on Lānaʻi (Hawaiʻi), EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-17070, https://doi.org/10.5194/egusphere-egu26-17070, 2026.
Sketch-based geological modelling with flow diagnostics provides an interactive and intuitive prototyping approach to quickly build geomodels and generate quantitative results to evaluate volumetrics and flow behaviour. This approach allows users to rapidly test the sensitivity of model outputs to different geological concepts and uncertain parameters, and informs selection of geological concepts, scales and resolutions to be investigated in more detailed models. Existing applications focussed on production, connectivity and storage of fluids and ignored or oversimplified thermal aspects. Furthermore, geothermal exploration relies on different types of constraining data. As part of the FindHeat project (findheat.eu), we investigate how the sketching and prototyping approaches can be applied to geothermal exploration and integrated with other tools.
Rapid Reservoir Modelling (RRM) is a free open-source sketch-based geological modelling tool with an intuitive interface that allows users to rapidly sketch geological models in 3D (bitbucket.org/rapidreservoirmodelling/rrm). Geological models that capture the essence of the geothermal target and related uncertainty can be created within minutes. Geological operators ensure correct truncation relationships between 3D surfaces by the modelling engine. Flow diagnostics then computes key indicators of predicted flow and storage behaviour within seconds.
Two aspects of sketch-based modelling with flow diagnostics can be adapted for use in geothermal exploration:
(1) Scenario screening to capture uncertainty in geological concepts cannot be achieved by changing a numerical variable but can be varied easily by sketching the different concepts, such as lateral connectivity, continuity and geometry of geological heterogeneities that act as flow barriers and pathways. Capturing multiple different concepts is time-consuming in conventional modelling approaches, and in practice is rarely carried out in geothermal projects.
(2) Mini-models and hierarchical models can be used to derive effective properties and thereby capture the effects of multiscale geological heterogeneity. This approach has been successfully applied to date to upscale single-phase permeability, relative permeability curves and capillary pressure curves, but can similarly be applied to upscale thermal conductivity and heat capacity. Models with varying complexity of heterogeneity are sketched at the smallest relevant scale, and effective properties are calculated. Calculated effective properties can then be used to populate models sketched at larger scale. Similarly electrical resistivity and seismic velocity can be upscaled to support inversion of seismic and magnetotelluric surveys.
How to cite: Jacquemyn, C., Petrovskyy, D., Al Sa'd, M., Hampson, G. J., Jackson, M. D., Nogales Herrera, V., Claridge, H. L., Daniilidis, A., Bruna, P.-O., Geiger, S., and Grayver, A.: Sketch-based modelling and flow diagnostics for geothermal exploration, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-19405, https://doi.org/10.5194/egusphere-egu26-19405, 2026.
This study presents a strategic assessment of geothermal energy development in the Canary Islands through the application of a SWOT (Strengths, Weaknesses, Opportunities, and Threats) analysis. Rather than focusing exclusively on geothermal resource characterization, the work aims to evaluate the broader set of conditions that influence the feasibility and sustainability of geothermal deployment in the context of these volcanic islands
The SWOT framework integrates geological, technical, regulatory, socio-economic, and environmental factors relevant to the Canary Islands. Identified strengths include the volcanic nature of the archipelago, evidence of relatively high geothermal gradients, and the inherent advantages of geothermal energy as a stable, low-carbon, and dispatchable renewable source. These characteristics are particularly valuable for isolated island energy systems with limited interconnections and high shares of intermittent renewables. Key weaknesses are associated with high exploration risk, limited subsurface data availability, substantial upfront investment costs, and the lack of a consolidated regulatory and institutional framework specifically designed for geothermal development.
Opportunities are identified within the broader context of the ongoing energy transition. Geothermal energy could contribute to diversifying the renewable energy mix, enhancing energy security, and reducing dependence on imported fossil fuels. Additional opportunities stem from the potential for direct-use applications, sector coupling, and integration with desalination and industrial processes. Moreover, the Canary Islands’ status as a European outermost region provides access to specific funding mechanisms and research programs, which could facilitate pilot projects and demonstration initiatives. Successful development could also position the archipelago as a reference case for geothermal exploitation in other volcanic island regions. Conversely, the analysis highlights several threats that may hinder progress, including public concerns related to geological risk, environmental restrictions in protected areas, competition from rapidly expanding solar and wind technologies, and uncertainty in long-term energy planning. Institutional fragmentation and lengthy permitting procedures are also identified as significant external constraints.
By systematically organizing internal and external factors, the SWOT analysis offers a structured overview of the challenges and prospects for geothermal energy development in the Canary Islands. The results underline the importance of strategic planning, risk mitigation instruments, stakeholder engagement, and targeted policy support to translate geothermal potential into viable and sustainable projects. This study demonstrates the value of SWOT analysis as a decision-support tool for guiding geothermal development in the Canary Islands.
How to cite: Pérez, N. M., D'Auria, L., Rodríguez Díaz, G., Domínguez Hernández, N., Torres, L., Rodríguez, F., Morales González-Moro, Á., and Santiago Aguiar, B.: Geothermal energy in the Canary Islands: a SWOT analysis for sustainable development, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-11148, https://doi.org/10.5194/egusphere-egu26-11148, 2026.
The economic viability of deep hydrothermal heat production strongly depends on achievable production rates. For economic operation, flow rates on the order of 60-100 l/s are required. Such rates exceed those of producing hydrocarbon wells by up to two orders of magnitude setting high demands on the hydraulic conductivity. Geothermal exploration of unproven reservoirs from which no production data is available consequently bears a high reservoir risk. Therefore, the overarching goal of this project is the reduction of the discovery risk through a cost-effective characterization of the reservoir properties.
Reservoir properties were investigated in (1) two shallow boreholes and (2) surface outcrops. Well data bridge the mesoscale between lab measurements on small rock volumes and deep-borehole data, and after upscaling serve as representative reservoir parameters for subsequent reservoir modeling. Wells and outcrops are located in geological units that extend beneath the Vienna Basin and are regarded as analogues for the subsurface targets with respect to lithostratigraphy, tectonic position, and deformation history.
(1) The boreholes EVN RO-1 (64.5 m) and EVN RO-2 (25.0 m) penetrate fractured dolomites and dolomite breccias. Geophysical logging (DFEL, Full Wave Sonic, Spectral Gamma, Acoustic Image Log) and permeability measurements (packer-, slug- and pumping tests) were carried out in both boreholes. Logs indicate porosities of ~8 %, while packer tests reveal highly variable permeabilities spanning more than two orders of magnitude (0.13-385 mD), mainly due to variable fracture density and clay content.
(2) Outcrops were investigated through geological profiles, sampling, and petrophysical analyses of parameters relevant to geothermal reservoirs, including porosity (0.9-9.8 % with an average of 4.02 %; measured at 400 psi confining pressure), permeability (plug-derived values 0.002-130 mD with an average of 6.23 mD at 400 psi), thermal conductivity (mean values 4.21 and 5.45 W/mK for dry/water-saturated dolomite), heat capacity (average 2.38 and 2.98 J/m³K dry/water-saturated), and fracture density. Power-law porosity-permeability relationships (K = a·ϕ^b) were derived for datasets representing different sample volumes (plugs, slug tests, and packer tests). All correlations exhibit high scatter, low exponents (b = 0.28-1.36), and weak correlation coefficients (<0.1), likely reflecting a substantial proportion of closed or isolated pores that contribute little to permeability. Porosity/permeability measurements at confining pressures corresponding to those at ca. 3000-3500 m depth show that porosity/permeability in this depth is about 90 % (permeability) and 50 % (porosity) lower than the data measured under atmospheric conditions or low confining pressure. Thermal conductivity and heat capacity are expected to increase at higher confining pressures at depth due to the sensitivity of porosity to pressure.
In sum, borehole and lab data characterize the investigated dolomite formation as a highly inhomogeneous fractured reservoir. Results also show that lab and well data are required to account for the scale dependence of permeability and predict petrophysical reservoir properties that are adequately extrapolated to pressures at reservoir depth. Future work will use the data in conceptual reservoir models for predicting the most likely reservoir performance.
How to cite: Binder, S., Decker, K., Scheidl, A., Götzl, G., and Scholey, R.: Reducing geothermal exploration risks by predicting the properties of potential deep geothermal reservoirs from surface and shallow borehole data, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-13640, https://doi.org/10.5194/egusphere-egu26-13640, 2026.
The Aguas de Vichy hot spring is located in the Eastern Cordillera of northeastern Colombia, on the eastern flank of the Santander Massif, a crystalline basement complex. This hydrothermal manifestation, together with a few others in the region, occurs in an atypical geological setting for geothermal systems, away from active volcanic arcs or extensional basins. At Aguas de Vichy, the heat source and the spatial variation of the local geothermal gradient remain unknown.
To address this knowledge gap, we present an integrated workflow for early-stage geothermal assessment. Our methodology combines (1) the construction of a detailed two-dimensional geological cross-section, (2) laboratory measurements of key thermophysical properties, including thermal conductivity, density, porosity, and radiogenic heat production from K-U-Th, on representative outcrop samples, and (3) cationic geothermometry applied to the thermal waters to estimate reservoir temperature.
These inputs are incorporated into a steady-state two-dimensional conductive heat-flow model solved using the finite-element method. Model outputs include subsurface temperature fields, heat flow, and derived geothermal gradients, allowing the identification of anomalies related to lithological heterogeneity or potential deep-seated heat sources. This conductive model establishes a thermal baseline for the area. By comparing this baseline with reservoir temperatures inferred from geothermometry, we assess whether the observed heat transfer is dominantly conductive or if additional processes need to be considered.
This study provides the first quantitative estimate of the geothermal gradient for the Aguas de Vichy system. More broadly, the proposed workflow offers a cost-effective and replicable approach to reduce uncertainty in geothermal prospects located in underexplored regions lacking borehole data. As such, it constitutes a transferable methodological framework for early-stage geothermal project development where direct subsurface temperature measurements are unavailable.
How to cite: Salcedo-Rodríguez, M., Schonwalder-Angel, D., and Bernal-Olaya, R.: Geothermal Gradient Characterization at Aguas de Vichy Hot Spring via Thermophysical Analysis and 2D Conductive Modeling (Santander, Colombia), EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-15747, https://doi.org/10.5194/egusphere-egu26-15747, 2026.
Taiwan, situated along the Pacific Ring of Fire, possesses substantial high-enthalpy geothermal resources, particularly within its subduction zone regions. Consequently, the deployment of geothermal energy has become a pivotal component of the national energy-transition policy. Focusing on a tectonically active field in eastern Taiwan, this study evaluates geothermal development potential by integrating advanced well-logging analysis with numerical reservoir simulation. To characterize stratigraphy, structural layers, and fracture networks, we utilize natural gamma ray, resistivity, sonic, and Formation Micro-Resistivity Imager (FMI) logs, integrated with High-resolution Sonic Scanner data. The inclusion of the Far Field Sonic Scanner specifically allows for imaging fracture systems and formation heterogeneities beyond the detection range of conventional acoustic tools. These geophysical datasets support the construction of a three-dimensional geomechanical model that captures in-situ lithological variations and geothermal reservoir properties. Subsequently, thermal–hydraulic behavior is simulated using the TOUGH3 code via the PetraSim interface, allowing for efficient model calibration and post-processing. Model parameters are constrained by in-situ logging measurements to refine estimates of temperature distribution, fracture pathways, and structural orientation. Ultimately, this study aims to deliver a robust conceptual model and a 3D numerical representation of the geothermal system, providing quantitative estimates of recoverable thermal reserves and power generation potential. The proposed workflow enhances the accuracy of geothermal resource evaluation in Taiwan and offers a transferable methodological framework for similar metamorphic tectonic environments.
How to cite: Wang, C., Wu, H.-Y., Lee, C.-A., and Tseng, S.-Y.: Integrated Well-Logging and Numerical Simulation for Geothermal Resource Assessment in Eastern Taiwan, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-2196, https://doi.org/10.5194/egusphere-egu26-2196, 2026.
Industry standards for geothermal exploration commonly rely on electromagnetic geophysical techniques. Subsurface and high temperature fluids are responsible for alteration of clays which are observed in locations with geothermal potential. These geological conditions exhibit elevated conductivity values, making EM methods viable for geothermal prospecting. This study presents the results of a magnetotelluric (MT) survey conducted in the Kaplanlı region in Afyon, Western Anatolia, aimed at identifying geothermal potential within a structurally complex tectonic setting. A total of five MT profiles with 51 stations were acquired and subjected to two-dimensional inversion to resolve the subsurface resistivity structure. The results reveal a prominent medium-resistivity zone with a thickness of 2.5 km and at 3 km’s floor depth, interpreted as a potential geothermal reservoir. Geophysical interpretations, supported by regional tectonic analysis, suggest the presence of deep-seated magmatic intrusions acting as a heat source. The findings indicate that the Kaplanlı area within Afyon holds significant promise for geothermal exploration, and demonstrate the effectiveness of MT methods in delineating favorable reservoir conditions in extensional tectonic settings.
How to cite: Mahmutyazıcıoğlu, E., Çavdar, E. N., and Avşar, Ü.: Geothermal potential assessment of the Kaplanlı region (Afyon) using the magnetotelluric method, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-834, https://doi.org/10.5194/egusphere-egu26-834, 2026.
Known for its world class hydrocarbon plays, the Middle East also offers the opportunity to explore lower carbon emissions energy sources; geothermal.
Understanding the geologic evolution of our basins was key to capitalize and focus the lessons learned from hydrocarbon exploration to the investigation and growth of geothermal resources within the kingdom.
Oil and gas exploration is based on the statistical study of six different elements: trap, reservoir, seal, source, migration, and timing. Whereas the factors that mostly define the success of a geothermal project are flow volume and temperature. Our strategy involved understanding the main elements that define success in geothermal exploration, and follow four main steps to characterize areas of interest: Research, screening, risk, and exploration.
Research of worldwide successful geothermal developments, with similar geological settings of those found within the kingdom. Screening our geological basin to find analog settings where we could apply the same principles. Risking each factor through a scrutinized statistical analysis similar to the process used in hydrocarbon exploration. Finally, choosing two areas to further investigate their geothermal potential with exploration wells.
The following work further illustrates each step of our exploration process and highlights our lessons learned and future areas of investigation.
How to cite: Asuaje, R.: Geothermal exploration in the Middle East, a case study, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-1369, https://doi.org/10.5194/egusphere-egu26-1369, 2026.
While the sampling of waters and gases from natural thermal discharges remains the standard approach for geochemical characterization, its application is limited in areas where surface geothermal manifestations are scarce or the reservoir's boundaries are poorly defined. In such cases, soil geochemistry and soil-gas surveys emerge as useful tools for delineating the hidden extent of hydrothermal systems. This type of surveys relies heavily on the identification of surface geochemical anomalies that reflect the presence and characteristics of underlying hydrothermal systems. Among the various chemical species utilized in soil geochemistry, Boron (B), Ammonium (NH4+) and Mercury (Hg) are regarded as "pathfinder" elements of primary importance due to their high volatility and mobility in geothermal fluids. Integrating the analysis of these three species allows exploration teams to differentiate between deep-seated geothermal signals and shallow environmental noise.
This study presents the results of soil B, NH4+ and Hg surveys conducted across two specific areas at Tenerife: (1) Madre del Agua (0.7 km2) located within the Tenerife South Rift Zone (TFSRZ) and (2) Abeque (0.8 km2) situated within the Tenerife Northwest Rift Zone (TFNWRZ). A high-density sampling strategy was implemented, with a spatial resolution of 450–550 sites/km2, to ensure the detection of small-scale anomalies. The investigation aims to characterize the spatial distribution of these key pathfinder elements to delineate potential upflow zones and identify the structural controls governing the underlying hydrothermal activity. Statistical-graphical analysis was performed to identify distinct geochemical populations within the dataset. To assess the spatial distribution of soil B, NH4+ and Hg concentrations, sequential Gaussian simulations (sGs) were implemented.
Statistical analysis identified two distinct geochemical populations (background and peak) within both study areas. The geometric means for the background populations were estimated as: (1) Madre del Agua (176.4 μg/kg for B, 61.9 mg/kg for NH4+, and 25.4 μg/kg for Hg) and (2) Abeque (109.0 μg/kg for B, 36.5 mg/kg for NH4+ and 9.7 μg/kg for Hg). In both areas, the background levels of B and NH4+ for Madre del Agua are relatively higher than those observed in Abeque, suggesting a different baseline for hydrothermal influence or lithological variations between the TFSRZ and the TFNWRZ. Furthermore, the geometric means values for the peak populations were estimated as: (1) Madre del Agua (723.2 μg/kg for B, 229.9 mg/kg for NH4+, and 122.5 μg/kg for Hg) and (2) Abeque (1,358.1 μg/kg for B, 182.4 mg/kg for NH4+, and 105.5 μg/kg for Hg). These relatively high geometric mean peak values, particularly for B at Abeque, indicate localized zones of enhanced permeability and volatile transport, reinforcing the potential for active hydrothermal upflow in this study area, where the highest absolute soil concentrations of B (1,798.0 μg/kg) and Hg (1,474.9 μg/kg) were also detected. Conversely, soil NH4+ surveys showed relatively higher geometric mean peak values at Madre del Agua. This enrichment may suggest distinct boiling conditions within the hydrothermal reservoir or, alternatively, a more pronounced interaction with organic-rich soil horizons during geothermal steam ascent.
How to cite: Melián, G. V., Pérez, N. M., Martín-Lorenzo, A., Cartaya-Arteaga, S., Perdomo-Sosa, O., Lodoso, E., Padrón, E., Asensio-Ramos, M., Hernández, P. A., and Padilla, G. D.: Assessment of soil boron, ammonia and elemental mercury for geothermal exploration in the Canary Islands, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-8258, https://doi.org/10.5194/egusphere-egu26-8258, 2026.
Geothermal conditions in the Pannonian Basin are among the most favorable in continental Europe, thus increasingly more geothermal projects are being launched in Hungary. However, reinjection is often burdened with practical problems, which can seriously decrease its efficiency, and endanger the entire geothermal project.
While most research tends to concentrate on local scale biological-mechanical-chemical problems (e.g. pore-scale clogging), we argue that reservoir (regional) scale heterogeneity of siliciclastic aquifers can pose an equally important risk to reinjection well efficiency. Significant reservoir heterogeneity affects (i) the size of the effective reservoir volume, (ii) the degree of connectivity between zones of high permeability, and (iii) the communication between production and reinjection wells, as a consequence, it can influence the success of reinjection.
Stochastic permeability distributions were generated using Sequential Gaussian (SGS) and Sequential Indicator Simulations (SIS) to represent the heterogeneity of a siliciclastic porous reservoir. The effect of lateral permeability heterogeneity was quantified on head increase in the injection well screened within the reservoir. The propagation of the front of the pressure increase is also monitored in the numerical simulations to make a comparison between the pressure evolution in homogeneous and heterogeneous reservoirs. The effect of the mean, variance and correlation length (i.e. heterogeneity scale) of the permeability distribution was investigated on the pressure increase and calculated using 2D transient numerical flow modelling with COMSOL Multiphysics finite element software package.
Model results show a pressure increase of several bars over the lifetime of the injection well, depending on all three statistical parameters characterizing the permeability heterogeneity. When the well is placed into a high-permeability zone (common operational practice), anomalous pressure rise occurs when the pressure front reaches low-permeability rock. Therefore, the success of the reinjection could also depend on the permeability distribution of areas farther away from the well. The onset time of the head increase observed in the well depends on the actual permeability realization, but, in general, greatly exceeds the time period of a typical pumping test. Insufficient preliminary data and/or disregarding the macroscale hydrogeological variations can lead to relevant overestimations of the injection well capacity. On the other hand, understanding the influence of aquifer heterogeneity on reinjection efficiency can contribute to more proper positioning of reinjection wells and to more successful injection projects.
How to cite: Nagy, B., Markó, Á., Galsa, A., and Molnár, B.: Numerical analysis of pressure increase in injection wells within stochastically heterogeneous reservoirs, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-8325, https://doi.org/10.5194/egusphere-egu26-8325, 2026.
Geothermal energy is becoming an attractive green energy since it is baseload-capable, and highly suitable for the supply of district heating in Europe. Identifying optimal locations for deep geothermal wells is essential, but such exploration typically depends on conventional active seismic surveys, which are logistically complex and costly. Recent development of nodal technology has pushed the method to higher frequencies, enabling high-resolution imaging of local and shallow velocity structure for more applied applications. In eastern Austria, the Vienna Basin is the primary target for deep geothermal production serving the city of Vienna. Meanwhile, the southern Vienna Basin also shows potential for geothermal production for smaller cities like Wiener Neustadt in lower Austria. During summer 2025, we deployed 139 5-Hz geophones along a profile running from the foothills of the eastern Alps to the Vienna basin. Using ambient noise interferometry, we extract Rayleigh- and Love-wave dispersion curves at short periods (0.8-5 s) and develop a high-resolution radially anisotropic shear wave velocity model of the southern Vienna basin. The isotropic shear-wave velocity model reveals the Neogene and Pre-Neogene sedimentary layers as well as the top of the crystalline basement. We also map a normal listric fault controlling the shape of the western edge of the basin. Moreover, we find that the anisotropic structure of the southern Vienna basin is bi-layered, with a slightly negative anisotropy in the upper 1-1.5 km depth and a strong and positive anisotropy at greater depths. We interpret the shallow negative anisotropy to reflect the influence of vertically oriented cracks, while the deeper positive anisotropy corresponds to the horizontal layering of sedimentary rocks. Combined, these findings hold significant implications for early-stage geothermal exploration in the southern Vienna Basin.
How to cite: Estève, C., Kramer, R., Gosselin, J., Muzellec, T., and Bokelmann, G.: 2-D S-velocity and radial anisotropy across the Vienna Basin (Austria) from nodal probabilistic ambient noise tomography, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-9457, https://doi.org/10.5194/egusphere-egu26-9457, 2026.
Pantelleria Island represents one of the most promising yet poorly constrained geothermal targets in the Mediterranean volcanic domain, characterized by high geothermal gradients, widespread hydrothermal manifestations, and a complex volcano-tectonic setting. The Pantelleria islAnd geotheRmal ExploratIon (PANTA REI) project, in the framework of the INGV–MUR project Pianeta Dinamico, aimed to provide a comprehensive reassessment of the geothermal system of Pantelleria through an integrated, multidisciplinary approach combining geophysical imaging, structural and seismic analyses, geochemical investigations, and numerical modelling.
The integrated interpretation of magnetotelluric, gravity and magnetic data provided a coherent geophysical model of the shallow crust of Pantelleria, resolving key contrasts in electrical resistivity and density, as well as thermal constraints, and highlighting the main volcano-tectonic structures of the island. Geophysical modelling enabled the identification of two shallow geothermal reservoirs in the central–southern sector of the island, structurally controlled by caldera-related faults and resurgent blocks.
To further constrain this geophysical model, seismic, geodetic and structural investigations were strengthened through the deployment of temporary seismic stations and GNSS receivers. Seismic noise analysis allowed the definition of the first 1D shear-wave velocity model of Pantelleria Island, enabling an improved relocation of the recorded seismicity. The resulting earthquake distribution is characterized by low background activity and shows spatial consistency with the main volcano-tectonic structures, while GNSS measurements confirm a long-term subsidence trend affecting the central sector of the island.
High-resolution geochemical datasets, together with surface temperature measurements, were integrated within a GIS environment to support the spatial interpretation of hydrothermal manifestations and fluid circulation patterns. The distribution of fumarolic and hydrothermal emission areas coupled with the defined structural pattern show as fluids circulating mainly along faults and fracture systems of the caldera.
The resulting multidisciplinary dataset was integrated into an updated conceptual model of the Pantelleria geothermal system, which provided the basis for steady-state numerical simulations of fluid circulation and heat transport. Numerical modelling, performed using TOUGH2 and constrained by a petrophysical model derived from geophysical results, provides robust quantitative constraints on the geothermal potential of the island and supports the evaluation of small- to medium-scale exploitation scenarios consistent with the natural state of the system.
How to cite: Di Giuseppe, M. G., Nardone, L., Bellomo, S., and Carlino, S. and the PANTA REI project team: Integrated geophysical, geochemical and modelling constraints on the geothermal system of Pantelleria Island (Italy): results from the PANTA REI project, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-15151, https://doi.org/10.5194/egusphere-egu26-15151, 2026.
Geothermal systems emerge from the interplay of available heat and sufficient permeability that allows for heat and mass transfer in the Earth’s upper crust. While temperature increases with depth according to the geothermal gradient and may be locally elevated by magmatic intrusions, fluid flow pathways are often structurally controlled. Structures such as faults and fracture networks can locally increase permeability, leading to focused upflow of hot fluids and downflow of cold meteoric fluids. In volcanic provinces as well as amagmatic geothermal systems, complex structural settings including fault relay zones and fault intersections are commonly described as potential favourable locations to form economic geothermal resources. Here, we conduct 3D numerical fluid flow simulations to test the controls of high-permeability structures on intermediate- and high-temperature geothermal system formation in both magmatic and amagmatic settings.
The model domain extends over 40x40x8 km, includes four normal faults, and a relay zone between two overlapping fault terminations. We systematically vary the permeability of the fault zones and the relay zone to explore their effect on geothermal system formation, while the background permeability is depth- and temperature-dependent. In magmatic settings, a magma body with an initial temperature of 900 °C provides additional energy during magma crystallisation and cooling; its location relative to the fault planes is varied to test effects on geothermal resource formation.
Preliminary results suggest that amagmatic settings with a uniform heat source at the bottom boundary rely on high-permeability structures, as they can locally enhance heat and mass transfer, potentially leading to the formation of intermediate-temperature geothermal systems. Structurally complex settings with larger rock volumes of increased permeability (e.g., relay zones) are of particular interest due to the increased potential of enabling and hosting upflow of geothermal fluids. Additional heat from magmatic intrusions, however, can override the structural controls on geothermal reservoir formation. In such magmatic settings, faults may temporarily enhance the upflow of hot fluids if flow pathways from the intrusion are naturally directed into the fault plane, which requires the intrusion to be located underneath the fault. Overall, however, heat and heat source location are the key controlling parameters governing both the formation and spatial location of geothermal reservoirs in magmatic settings.
How to cite: Köpping, J., Lamy-Chappuis, B., and Driesner, T.: How important are faults to form geothermal systems?, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-16388, https://doi.org/10.5194/egusphere-egu26-16388, 2026.
Several potential hazards are linked to geothermal operations, including hazards arising when reservoir integrity is compromised. This contribution provides a framework for assessing the potential risk of loss of integrity of a geothermal reservoir. Focus is on low enthalpy, matrix permeable sedimentary systems at depths of approximately 1500-3000 m, typical for the Netherlands, but the framework can also be applied to other geothermal plays. Loss of reservoir integrity via a number of leakage pathways is considered, such as newly formed fractures in the caprock induced by thermal cooling or increased fluid pressures, abandoned wells through the caprock, pre-existing faults in the caprock and through the matrix of the caprock. Possible effects of loss of reservoir integrity that are taken into account include groundwater contamination, subsidence/uplift and interference of operations with those in other neighbouring permit areas. With the proposed framework, a qualitative assessment can be made of the risk related to each of these effects, leading to a general evaluation of the risk of loss of reservoir integrity. This framework can be used by geothermal operators in their exploration for suitable locations for geothermal systems and for underpinning the safety of their application for permits for these operations. It can also be used by regulators in their evaluation of geothermal permit applications.
How to cite: den Hartog, S., Hardebol, N., Janssen, F., Morales-Rua, T., Muntendam-Bos, A., and Veeningen, R.: Risk-based assessment of geothermal reservoir integrity, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-1810, https://doi.org/10.5194/egusphere-egu26-1810, 2026.
