Displays

Decarbonising heating presents a significant societal challenge. Deep geothermal energy is widely recognised as a source of low carbon heat. However, to date there has been no assessment of the carbon intensity of heat from low-enthalpy deep geothermal as previous studies have focussed on geothermal power or higher enthalpy heat. Further, there is currently no established method for assessing the CO₂ emissions reduction from implementing a deep geothermal heating scheme.

To address these gaps, we performed a life cycle assessment of greenhouse gas emissions relating to a typical deep geothermal heat system to (i) calculate the carbon intensity of geothermal heat (ii) identify the factors that most affect these values (iii) consider the carbon abated if geothermal heat substitutes conventional heating sources and (iv) set a benchmark methodology that future projects can adapt and apply to assess and enhance the carbon emissions reduction offered by geothermal heat development in the UK and internationally.

In the absence of an established deep geothermal heat system in the UK, to inform our work we adopted parameters from a feasibility study for a potential geothermal heat system in Banchory, Scotland. The Banchory project aimed to deliver heat to a network sourced from 2-3 km deep in a radiothermal granite where temperatures were predicted to be 70-90 °C. We assumed a 30 year project lifetime and that the heat system operation was powered by the UK electricity grid which was decarbonising over this period.

Our analysis found that the carbon intensity of deep geothermal heat is 9.7 - 14.0 kg(CO₂e)/MWh_th. This is ~5% of the value for natural gas heating. The carbon intensity is sensitive to several factors, and so the carbon intensity of deep geothermal heat could be reduced further by: replacing diesel fuelled drilling apparatus with natural gas or electricity powered hardware; decarbonise the power grid more rapidly than forecast; or substitute mains power with local renewable electricity to power pumps – or decarbonising the electricity grid faster or deeper; source lower carbon steel and cement; design projects to minimise land use change emissions.

Overall, our study provides quantitative evidence that deep geothermal systems can produce long term very low carbon heat that is compatible with net-zero, even for low enthalpy geothermal resources.

How to cite: McCay, A., Roberts, J., and Feliks, M.: Assessing the Carbon Intensity of Low-Enthalpy Deep Geothermal Heat, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-19239, https://doi.org/10.5194/egusphere-egu2020-19239, 2020.

In Geosciences, we face the challenge of characterizing uncertainties to provide reliable predictions of the earth surface to allow, for instance, a sustainable and renewable energy management. In order, to address the uncertainties we need a good understanding of our geological models and their associated subsurface processes.

Therefore, the essential pre-step for uncertainty analyses are sensitivity studies. Sensitivity studies aim at determining the most influencing model parameters. Hence, we require them to significantly reduce the parameter space to avoid unfeasibly large compute times.

We distinguish two types of sensitivity analyses: local and global studies. In contrast, to the local sensitivity study, the global one accounts for parameter correlations. That is the reason, why we employ in this work a global sensitivity study. Unfortunately, global sensitivity studies have the disadvantage that they are computationally extremely demanding. Hence, they are prohibitive even for state-of-the-art finite element simulations.

For this reason, we construct a surrogate model by employing the reduced basis method. The reduced basis method is a model order reduction technique that aims at significantly reducing the spatial and temporal degrees of freedom of, for instance, finite element solves. In contrast to other surrogate models, we obtain a surrogate model that preserves the physics and is not restricted to the observation space. As we will show, the reduced basis method leads to a speed-up of five to six orders of magnitude with respect to our original problem while retaining an accuracy higher than the measurement accuracy.

In this work, we elaborate on the advantages of global sensitivity studies in comparison to local ones. We use several case studies, from large-scale European sedimentary basins to demonstrate how the global sensitivity studies are used to learn about the influence of transient, such as paleoclimate effects, and stationary effects. We also demonstrate how the results can be used in further analyses, such as deterministic and stochastic model calibrations. Furthermore, we show how we can use the analyses to learn about the subsurface processes and to identify model short comes.

How to cite: Degen, D., Veroy, K., Cacace, M., Scheck-Wenderoth, M., and Wellmann, F.: How well do we know our models?, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-10482, https://doi.org/10.5194/egusphere-egu2020-10482, 2020.

An emerging technique for a continuous and low cost geophysical monitoring of deep reservoirs like Enhanced Geothermal Systems (EGS) is based on ambient seismic noise correlation and in particular Coda Wave Interferometry (CWI) from temporal stacks of ambient noise cross-correlation functions (or ANCCFs). We present here a forward numerical model simulating the propagation of scattered waves through a reservoir during its deformation, including non-linear acousto-elastic effects. Our approach is based on the case study of the Rittershoffen geothermal reservoir (France). We validate the numerical model by reproducing seasonal variations of the relative changes in seismic velocity observed from ANCCFs and provide a physical interpretation of this seismic signal. We extend our modelling to the in-situ deformation of the reservoir by considering either a hydraulic pressure increase or an aseismic shear of an embedded fault. The sensitivity of the scattered waves to small strain perturbations enables to detect small travel time changes as dt/t ~ 10^-5, which opens perspectives for the application of ambient noise based techniques to the continuous monitoring of local mechanisms in deep geothermal reservoirs.

How to cite: Azzola, J., Schmittbuhl, J., Zigone, D., Lengliné, O., and Masson, F.: Monitoring deep fractured reservoirs with ambient noise correlation: importance of acousto-elastic effects, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-16260, https://doi.org/10.5194/egusphere-egu2020-16260, 2020.

In recent years several deep geothermal energy projects have been forced to close following the occurrence of large seismic events associated with the stimulation of the surrounding bedrock. In 2018, an enhanced geothermal system (EGS) experiment performed in Helsinki, Finland concluded with no seismicity exceeding the threshold magnitude and thus provides an intriguing showcase for future stimulation experiments in similar environments. During the 49 days of the experiment, the five-stage injection of ~18,000 cubic meters water stimulated many thousands of earthquakes. Like in all previous stimulation cases the earthquake data constitute the primary source for the assessment of the scientific and operational aspects of the reservoir response. Here we apply ambient noise based monitoring and imaging techniques to data collected by 100 short period three-component stations that were organized in three large arrays consisting of nominally 25 stations, in addition to three small four-station arrays, and 10 single stations, during a 100 day period. We compute daily nine-component noise correlations between all stations pairs except for the intra-array pairs in a frequency range between 0.5 and 10 Hz. We measure waveform delays within our correlation functions as a function of frequency and lag time using the Continuous Wavelet Transform. We then invert these observations using a Markov chain Monte Carlo method to obtain the temporal variation in seismic velocity dv/v during the injection. By exploiting the variable spatial sensitivities of the surface- and body-wave components at different coda-wave lapse times and frequencies, we are able to image the medium response to the stimulation in both time and space. We compare the estimated seismic velocity variations to other observations such as H²/V², as well as dv/v observations obtained from collocated borehole data. Importantly, we also compare the observed medium response to seismicity and pumping parameters. Our results suggest that we are able to resolve medium changes that are not solely associated with the induced earthquakes, but also potential signatures of fluid content or pressure changes in the bedrock. The combined observations of seismicity, pumping parameters and dv/v changes collected in this experiment can further advance passive monitoring techniques in the context of enhanced geothermal systems, and facilitate a more comprehensive analysis of fluid-rock interactions that may occur aseismically.

How to cite: Taylor, G. and Hillers, G.: Passive monitoring and 3D imaging of the bedrock response to the 2018 Espoo/Helsinki geothermal stimulation, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-18827, https://doi.org/10.5194/egusphere-egu2020-18827, 2020.

Finland is a part of a low-temperature geothermal regime of Fennoscandian Shield. The need for heating energy is high and ground source heat pumps (GSHP) are common in heating of single houses. Shallow ground source heat can be effectively utilized using a closed collector loop with non-freezing heat carrier fluid operating at the temperature range of about -5 to +5°C. The system is economically feasible, because the average target temperature in heating of well-isolated houses is low. District heating requires high output temperatures (in Finland nowadays up to 110°C), implying that a heat pump must receive the ground temperatures of at least about 20°C. Heat collectors in porous, permeable sedimentary rocks may be based on an open circulation loop between two or more boreholes, whereas in Finland single deep boreholes equipped with a heat collector are mainly considered. A borehole heat exchanger (BHE) in deep and warm bedrock, like in decommissioned underground mines offers great temperature benefits in producing more energy than BHE placed on the ground surface.

The Pyhäsalmi mine in northern Ostrobothnia, Finland, is a 1 440 meter deep underground zinc and copper mine that will be decommissioned in a near future. In the Pyhäsalmi Energy Mine project funded by European Regional Development Fund (ERDF) we examined the heat transfer properties of heat collector types installed in the borehole at the bottom of the mine. The Precambrian crystalline bedrock, consisting of granitoids, migmatites, gneisses and schists typically has low geothermal gradient (10 – 20 K/km), but thermal conductivity is rather high (2.5 – 3.5 Wm^-1K^-1). Thus, the temperature at the depth of 1 440 m is about +20°C. We compared the performance of different collector types in the underground mine environment: coaxial open-loop collector with and without insulation and u-tube collector, as well as different borehole radii to optimize geothermal energy production. Also, we studied the effect of the bedrock temperature (5 – 50°C) on the performance of the BHE.

The heat exchange modelling was carried out with COMSOL Multiphysics®. The modelled physics included conductive heat transfer in bedrock and different collector types, and conductive-convective heat transfer in heat carrier fluid. The models were used to simulate heat transfer from bedrock to the heat circulation loop up to 100 years circulating water (feeding temperature +6°C) in the loop.

The results indicate that a single 300 meter deep energy well placed at the bottom of the mine can be dimensioned to produce water of approximately 12°C with twelve kilowatts power. Further increase in output temperature requires deeper boreholes or serial coupling of two boreholes, allowing heat production at the temperature range of 70 – 90 °C by means of heat pumps. Compared with the conventional shallow geothermal energy solutions, the geothermal potential of the underground mine is several times higher due to higher bedrock temperature. An insulated open-loop coaxial collector is better than a coaxial collector without an insulation or a typical u-tube collector.

How to cite: Martinkauppi, A., Piipponen, K., and Ahonen, L.: Geothermal energy in Pyhäsalmi mine, Finland: performance evaluation of heat collector types, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-8696, https://doi.org/10.5194/egusphere-egu2020-8696, 2020.

The economic and technical efficiency of geothermal plants is often impaired by corrosion, scaling and biological fouling. In Germany, the highly saline fluid of the North German Basin is known to cause severe corrosion. Meanwhile geothermal plants in the southern Molasse Basin, one of the most extensively exploited geothermal regions in Germany, are troubled by carbonate scaling. One possible solution is the employment of a scale inhibitor. A novel scaling inhibitor is evaluated in field- and laboratory tests. This inhibitor consists of a polysaccharide backbone structure and branches of polyacrylic- and maleic acid copolymer.

The laboratory tests with different scaling inhibitor concentrations were designed to observe the biodegradation of the scaling inhibitor in an anaerobic environment similar to the conditions found in heat exchangers of geothermal plants. The concentration of inhibitor was quantified by UV/VIS and liquid chromatography (LC). Molecular biological techniques (PCR, DGGE, Microbiome analysis) were used to characterize the biocenosis on metal surfaces and in fluids of the experiments.

During the experiment the concentration of inhibitor decreased up to  3 % of the initial concentration. The formation of methane and acetate was observed which indicates a biological degradation by acetoclastic methanogenesis. Hydrogen formation was observed in setups containing steel coupons. This implies that hydrogen is primarily formed by corrosion processes and in tests with active microorganisms hydrogen was consumed completely. Various fermentative bacteria classified as Clostridia and Firmicutes as well as methanogenic archaea were identified. In some experiments sulfate reducing bacteria were found. Those are well known to catalyze corrosion processes.

Results of field experiments in a bypass system as well as microbiological monitoring of the inhibitor application in geothermal plant located in the molasse basin will be presented.

How to cite: Otten, C., Schulz, B., Teitz, S., Eichinger, F., Seibt, A., Kuhn, D., and Würdemann, H.: Interactions between a calcium scaling inhibitor, geothermal fluids, and microorganisms – Results of in situ monitoring in the molasse basin and laboratory experiments, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-22434, https://doi.org/10.5194/egusphere-egu2020-22434, 2020.

Finland is located between the 60th and 70th northern parallels and is characterized by continental subarctic climate. Due to climatic conditions, ground surface temperatures are low in Finland. The long-term average annual ground surface temperature ranges from 0.5 to 7.6 °C. Decommissioned mines offer a way to tap into larger geothermal resources by allowing access to deep underground where the temperature regime is more beneficial for heat extraction than in the shallow ground. The Energy Mine project was initiated to investigate how the Pyhäsalmi deep mine could be utilized to tap into the deeper geothermal resources of the Finnish bedrock.

The depth level of the deepest mine tunnel in the Pyhäsalmi mine is 1,440 m. We took this tunnel as the starting point for our study since it offers access to the largest geothermal resources that are accessible from the mine. We modelled the thermal performance of borehole heat exchanger (BHE) fields constructed by drilling the boreholes from a single site in different azimuth and tilt angles so that the resulting BHE fields took the form of a lower hemisphere. The borehole length was 300 m. The collector was coaxial open-loop with an insulated pipe. Bedrock temperatures within the depth range of the BHE fields ranged from 21 to 25 °C. Finite element models were constructed to simulate the operation of various configurations of hemispherical BHE fields. In all simulations, the temperature of the heat carrier fluid fed to the inlets of the BHEs was kept at 6 °C during the 100 simulated years.

The results indicate that it would require at least 145 BHEs for a hemispherical BHE field to sustain at least 1 MW of heating power from the bedrock for 25 years. Such a field would produce 300 GWh of heating energy during the first 25 years. This amount can be increased by adding boreholes to the field. However, at some point, adding BHEs no longer increases the amount of thermal energy that can be extracted from a hemispherical BHE field. The maximum amount of extractable energy is somewhere around 1.2 TWh which is the estimated heat content of a hemispherical volume of bedrock at the tunnel depth.

The hemispherical design is not the most optimal BHE field design with respect to thermal performance because the distances between BHEs become very small at the drilling site. However, the spatial restrictions imposed by mine tunnels do not allow much leeway in BHE field design. Another possibility is to construct a BHE field along a mine tunnel. But even in this case the BHEs would need to be drilled in a fan-like fashion at several drilling sites along the tunnel length. The hemispherical design is advantageous with respect to drilling and piping compared to a BHE field that is constructed along the length of a mine tunnel.

How to cite: Korhonen, K., Hietava, J., and Ahonen, L.: Hemispherical underground borehole heat exchanger field as a source of geothermal energy, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-9104, https://doi.org/10.5194/egusphere-egu2020-9104, 2020.

The investigation of the deep geothermal systems is a challenging task in active geothermal systems. In order to decrease the mining risk, the study of the analogue exhumed systems sheds light on the relationships between fluid circulation and geological structures through the analyses of faults and ore deposits distributions. In the Las Minas area (Central Mexico), ore deposits are quite diffuse at the boundary between crystalline and sedimentary rocks and in fault zones. This is a consequence of the interaction between cooling of Miocene felsic magmas, hydrothermal fluids and coeval fault activity. We investigated the role of the faults in channeling the hydrothermal fluids by fieldwork and analysis of fractures at outcrops. The field mapping was carried out at 1:10000 scale (60 km2). When possible, kinematic data on recent fault planes influencing the permeability and geothermal fluid paths were collected. This includes information on the main structural trends and the orientation of the intermediate kinematic axis.The evolution and origin of the hydrothermal fluids circulating in the exhumed geothermal system of Las Minas area (Central Mexico) were investigated by i) structural and minero-petrographic studies and, ii) fluid inclusion and isotope analyses carried out on skarn and hydrothermal alteration minerals.Two families of faults have been recognized, NNW-SSE and SW-NE oriented, respectively. The SW-NE trending faults often controlled the emplacement of dykes, indicating that the magmatic fluid was channeled and driven by the faults induced permeability. Their activity is at least encompassed between Miocene and Quaternary. The kinematic relation between these two fault systems could be explained in a extensional framework, assuming that the NNW-SSE fault system acted as transfer faults. Fluid inclusions recorded the circulation of: 1) high-temperature (up to 650°C), high-salinity (up to 60 wt.% NaCl equiv.) fluid of magmatic origin; 2) high-temperature (470-650°C) aqueous-carbonic fluid produced during fluid-rock interaction with carbonate basement rocks and 3) relatively low-salinity (up to 2 wt.% NaCl equiv.) fluid of meteoric origin. A general evolution from high- to low-temperature fluid circulation characterized the geothermal system.

How to cite: Liotta, D., Agostini, A., Bastesen, E., Bianco, C., Boschi, C., Braschi, E., Brogi, A., Caggianelli, A., Garduno, V. H., Gonzalez Partida, E., Morelli, G., Olvera-Garcia, E., Ruggieri, G., Torabi, A., Ventruti, G., Wheeler, W., and Zucchi, M.: Exhumed vs active geothermal systems: faults controlling ore deposits in Las Minas area as a key for the deep exploration in the Los Humeros geothermal field (Mexico), EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-3918, https://doi.org/10.5194/egusphere-egu2020-3918, 2020.

Regional magnetotelluric (MT) survey had been conducted to image resistivity structures beneath Toba Caldera, Indonesia. A crustal-scale 2D inversion model is generated from ten MT stations with extended recording time, deployed along NE-SW regional line to cross perpendicularly both the Caldera and the nearby regional strike-slip fault system, the Sumatran Fault. High resistivity background is likely related to Palaeozoic rocks which is basement of the Tertiary sediments and the Quaternary volcanics. The most noticeable conductive anomaly is located between 10-20 km deep, interpreted as the main magma reservoir beneath the region. An intermediate, less than 10 km-deep, less conductive anomaly beneath the Caldera is interpreted as shallow magma chamber affected by the last major eruption. Shallow, less than 2 km-deep conductive layers are associated either with hydrothermal clay cap beneath the Caldera, or sedimentary formations of the nearby basins. Other conductive anomaly is spatially associated with the Sumatran Fault which located 15 km away from the Caldera. Parameter plots of some stations are consistent with the orientation of basement structures, while the others may be affected by more complex caldera structures. A conceptual model of magma plumbing system beneath the Caldera is then interpreted from the combination of regional resistivity structures, surface geology, and available seismic tomography.

How to cite: Sutrisno, L., Beekman, F., Daud, Y., and Van Wees, J. D.: Revisiting Toba Caldera: an insight from regional magnetotelluric data, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-10764, https://doi.org/10.5194/egusphere-egu2020-10764, 2020.

The Rhine-Ruhr region is one of the largest metropolitan areas in Europe, with more than 10 million inhabitants, located in western Germany. The region is defined by the rich coal-bearing layers from the upper Carboniferous period, extracted as early as the 13^th century and belonging to the sub-Variscan Trough. In 2018, after more than 700 years of exploration, the last black coal mine was closed in the area. One of the most promising re-uses of the abandoned coal mines is the exploitation of geothermal energy sources. Additionally, to the geothermal energy extracted from existing mines, potential deep geothermal reservoirs within the Rhine-Ruhr, may exist at depths between 4.5 and 6 km, where Devonian limestones were found. Based on the available temperature profiles from deep exploration wells in the area, geothermal gradient amounts to 36.8^oC/km and results in reservoir temperatures between 170^oC and 220^oC, which will enable not only heat but even electricity production. This study provides a comprehensive investigation of the full in-situ stress state tensor with its anisotropy and presents crucial physical formation and natural fracture properties. The data for this investigation was acquired from the extensive borehole logging and geomechanical campaigns carried out in deep coal exploration wells throughout the 1980s as well as from the recent shallow geothermal research wells. Acquired data allowed assessing critically-stressed, i.e. hydraulically active, fractures undergoing shear displacement, being primarily responsible for the future geothermal reservoir permeability. Extensive sets of microseismic, subsidence and drilling data were used to confirm the results of the analysis. Additionally, wellbore stability analysis and potential drill paths for the future medium-to-deep geothermal wells in the region were assessed. This study is a part of the 3D-RuhrMarie project, which aims to assess the intrinsic seismic risk within the Rhine-Ruhr region to promote safer and economically more efficient exploration and exploitation of the future geothermal resources.

How to cite: Kruszewski, M., Montegrossi, G., Backers, T., and Saenger, E.: The in-situ stress state of the Rhine-Ruhr region and its implications for the geothermal energy utilization, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-4246, https://doi.org/10.5194/egusphere-egu2020-4246, 2020.

In this case study a method to estimate the geothermal potential is presented for the capital city of Berlin, Germany. Therefore, it is essential to know the temperature distribution in the subsurface which has been studied intensively in the past.
Building on this knowledge, newly available subsurface temperature predictions have been used along with updated geometries and geophysical properties as input data for the application case of hydrothermal doublets and their comparison to earlier realizations. This shows how considering more complex geometries, boundary conditions and processes in numerical 3D thermohydraulic simulations leads to significant changes in the predicted geothermal potential and the associated controlling factors. The model area is part of the Northeast German Basin which consists of a thick sequence (up to 10 km) of differently consolidated sedimentary deposits. This sequence is made up of alternating aquifers and aquitards, wherein several encompass promising targets for different geothermal application scenarios. Namely these include the Jurassic, Middle Buntsandstein and the Sedimentary Rotliegend aquifers. The former two of these reservoirs depict a complex geometry (mainly due to deeper salt movements) leading to a wide range of predicted temperatures, while the latter (situated below the salt) has a more homogenous topography and temperature distribution. This is also connected to the efficacy of different heat transport processes at different depths.
The predicted heating power is therefore also distributed heterogeneously and reaches maxima as large as 1.25 MW_th for the Jurassic, 10 MW_th for the Middle Buntsandstein and 2.2 MW_th for the Sedimentary Rotliegend. The models further show that the geothermal potential (or the heating power) of a hydrothermal doublet is controlled by more than merely the reservoir temperature but also the producible mass flux, which in turn depends highly on the reservoir transmissivity. Due to the high variability of predicted geothermal potentials, different utilization scenarios should be investigated in future studies, such as aquifer thermal energy storage or low enthalpy geothermal utilizations.

How to cite: Bott, J., Frick, M., Koltzer, N., Cacace, M., Lewerenz, B., Schneider, M., and Scheck-Wenderoth, M.: The geothermal potential of sedimentary basins – case study for Berlin, Germany, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-19662, https://doi.org/10.5194/egusphere-egu2020-19662, 2020.

In France, heating networks are largely dependent on fossil fuels (42%), and deep geothermal energy represents less than 5% of the energy mix of heating networks. Deployment of geothermal energy in large cities is limited by a geological risk, difficult to predict. This risk constitutes an obstacle to the future development of geothermal energy in the Ile-de-France region. The aim of this work is to develop a predictive 3D reservoir model in terms of stratigraphic geometries, facies, porosity, permeability and temperature at a given location in Ile-de-France. We focus on the main geothermal reservoirs in the area: the Middle Jurassic limestones. In order to create this 3D model, 80 wells (630 logs), drilled over the last 60 years, were studied over an area of 800 km². The first phase of this study consisted in digitizing the old well data, particularly log data on 80 wells (GR, Sonic, resistivity) and adding all recent wells (with neutron porosity and NMR logs). We also compiled from the drilling reports 694  porosity (phi) – permeability (k) values previously measured on cores from plugs, and we imported them into the geomodeller Petrel®. Two reference wells with cores of the reservoir were studied in detail from a sedimentological and stratigraphic point of view in order to link sedimentary facies, logs and phi-k in a well-defined sedimentological framework. We also digitized temperature in 40 wells. The sequence stratigraphy framework allows to define 11 3rd order stratigraphic sequences from the Bajocian (jason Zone) to the Middle Callovian (zigzag Zone). Twelve surfaces from Bj5 to Ca3 corresponding to 3^rd order Maximum Regressive Surfaces (MRS) allow to correlate all wells and to define stratigraphic geometries. A total of 10 facies are grouped into 4 facies associations (1) marls of lower offshore (facies association FA1), (2) marl-limestone alternations of upper offshore (FA2), (3) oolitic grainstones of the shoreface (FA3) and (4) lagoon micritic limestones (FA4). These facies associations were coded in all wells according to the log depths. The best reservoir is mainly located in the oolitic and bioclastic grainstones (FA3) with average porosity of 12% and permeability of 130 mD. The lagoon micritic facies also presents interesting properties with average porosity of 8.2% and permeability of 46 mD. The model has been meshed into 6.5 million of cells split on 64 vertical cell layers of 150 m x150 m x about 5 m (length ×width ×height) each bearing specific property information (facies, porosity, permeability). The final model shows a high variability of the facies distribution over the 11 depositional sequences. The maximum thickness of the oolitic reservoir is about 50 m in the western part of the study area between surface Bt2 and Bt4. By combining the isopach map of oolitic facies between surface Bt2 and Bt4 with porosity above 10%, permeability of more than 100 mD and temperature larger than 60°C, we locate areas of interest for geothermal development in the Paris Basin.

How to cite: Thomas, H., Brigaud, B., Zeyen, H., Blaise, T., Andrieu, S., Catinat, M., Davaux, M., and Antics, M.: Facies, porosity and permeability prediction and 3-D geological static model in the Middle Jurassic geothermal reservoir of the Paris Basin by integration of well logs and geostatistical modeling, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-20712, https://doi.org/10.5194/egusphere-egu2020-20712, 2020.

CO₂ Capture and Storage (CCS) is regarded as one of the most effective measures for the mitigation of the unfavourable effects of anthropogenic CO₂ emissions on climate change. The implementation of CCS in geothermal fields which are considered as natural analogues for CO₂ storage sites, can contribute to the reduction of CO₂ emissions as well as increasing the energy production within the context of Enhanced Geothermal Systems (EGS). Given that experimental studies of CCS have certain limitations regarding the time span and reservoir conditions, the geochemical modelling studies are highly important. The geochemical modelling studies require the use of “input data” including i) modal mineralogy of the reservoir rocks and ii) hydrogeochemistry of the reservoir fluid, the variations in the former (both type and amount) particularly affecting the modelling results.

This study is concerned with a preliminary lithogeochemical characterization of the reservoir levels of two geothermal fields (Akköy-Denizli and Edremit-Balıkesir) from western Anatolia, aiming to establish an input database for a prospective geochemical modelling in EGS. In this regard, drill cuttings belonging to the reservoir levels of the relevant fields are examined both macroscopically and microscopically, followed by the laboratory analyses of the samples using XRF (X-Ray Fluorescence), XRD (X-Ray Diffraction), and confocal Raman Spectroscopy techniques. The results obtained from the analyses are evaluated for the identification and quantification of the present minerals. Since the fields Akköy and Edremit have different reservoir lithologies (schist-calcschist-marble and agglomerate units, respectively), the results provide a means of comparison for the effect of mineralogical changes in possible CO₂ addition to the systems.

How to cite: Elidemir, S. and Güleç, N.: Lithogeochemical Characterization of Akkoy and Edremit Geothermal Fields as Prospective CO2 Storage Sites: A Preliminary Study, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-452, https://doi.org/10.5194/egusphere-egu2020-452, 2020.

In 2015, a legal framework was implemented in the Brussels-Capital Region (BCR) where passive construction has been mandatory with an obliged heat demand not exceeding 15 kW_h/m². Since 2015, the interest in installing shallow geothermal systems has significantly increased. However, limited knowledge of ground conditions, lack of public awareness and the urban nature of the Brussels area restrict the development of shallow geothermal systems despite the high potential of this technique in the RBC. The BRUGEO project aims to facilitate accessibility and the efficient use of shallow geothermal energy in the BCR specifically for commercial and residential sectors. Thanks to Brussels ERDF (European Regional Development Fund) funding a consortium of all major actors in geothermal energy were brought together (ULB, Brussels Environment, BBRI, VUB, and GSB). During the  four years project (2016-2020), specific actions promoting the geothermal potential were addressed: 1- Collect existing data related to the knowledge on Brussels subsurface (geological, hydrogeological, and geothermal data) and consolidate them in a single database; 2- Conduct new laboratory and field tests in order to complete geological analyses and to assess geothermal parameters; 3- Map the geothermal potential for open and closed systems. The Geological Survey of Belgium (GSB) has created, during the last 7 years, a GIS based 2D-3D geological model of the BCR underground. 9266 drillings and geotechnical data collected in and around the BCR have been used to create the Brustrati3D model generating interpolated top and base surfaces for 19 geological layers representing the whole lithostratigraphic sequence from Quaternary to the Paleozoic basement. An important exploration phase was included in the first two years of the BRUGEO project to acquire new data improving the geological and hydrogeological knowledge of BCR. Several in-situ parameters are measured by e.g. new piezometers implementation and monitoring, pumping tests, cores sampling, logging and enhanced thermal response tests (eTRT). These measurements are implemented as far as possible on future private projects by a win-win approach. The idea is to be grafted on existing projects to increase the data acquisition and to avoid purely exploratory drilling that are expensive and not used later for any geothermal exploitation. So far, the BRUGEO consortium has also conducted three exploration drillings to assess the lithology, the structure, the groundwater flows, and geophysical properties of the Cambrian basement (Brabant Massif). In parallel, laboratory measurements are achieved to characterize the determinant thermal parameters of the Brussels underground. From all the subsurface data collected, the BRUGEO consortium aims at mapping the geothermal potential of the BCR. This web-based mapping, accessible to design offices, installers of geothermal systems, citizens, public and private stakeholders or regional and municipalities administrations, will make it easier to foster the use of geothermal energy. The web portal will consist of an interactive decision support and a design tool based on maps built thanks to the geoscientific 3D models and geothermal parameters assessed during BRUGEO. The results are expected to be published online in March 2020.

How to cite: Petitclerc, E., Gerard, P., Devleeschouwer, X., François, B., Huysmans, M., Agniel, M., Gigot, V., Gaudaré, L., Van Lysbetten, G., and Burlet, C.: Shallow Geothermal Resources Assessment of the Brussels Region: Exploration, 3D Geological Model, Geothermal Potential Mapping and Challenges Related, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-9769, https://doi.org/10.5194/egusphere-egu2020-9769, 2020.

In 1986 a well, which was planned as a convetional production well in the Nesjavellir Field in the Hengill Area, SW Iceland, was unexpectedly drilled into a very hot formation at the depth of 2.1 km. The measured temperature in the lowest part of the well was 380°C, which was the upper range of the measuring tool used. Thus, the bottom-hole temperature was most probably higher. No one expected to hit such a hot body in this place and the well design was not appropriate to handle such high temperatures and resulting pressures. Thus, the lower parts of that well were closed off and it has since then been operated as a conventional geothermal well.

This incidence sparked the idea of drilling deeper into volcanic hydrothermal systems in Iceland in order to gain a better understanding of the roots of the geothermal systems and to be able to produce fluids with higher enthalpy. The Iceland Deep Drilling Project (IDDP) is supposed to realize that idea. The IDDP project is a consortium of domestic and international partners, both from industry and academia. The three power companies in Iceland, which operate power-production in volcanic geothermal fields (Landsvirkjun, HS-Orka, OR), committed themselves to drill one deep well each in a field of theirs.

To date two wells have been drilled in the IDDP project. The first one, IDDP-1, was drilled in the Krafla Field, N Iceland, which is operated by Landsvirkjun, and the second well, IDDP-2, was drilled in the Reykjanes Field, which is operated by HS-Orka. The original plan was to drill down to 4-5 km. However, the IDDP-1 in Krafla was drilled into magma of rhyolite composition at the depth of 2.1 km and could therefore not be drilled further. During flow tests, it was flowing superheated steam at high pressure at well head temperature of 450°C. The power capacity was estimated to be 36 MW_e. However, due to hostile chemistry of the fluid and damaged casing, the well had to be abandoned and closed after the well tests. IDDP-2 was drilled down to 4,659 m. The highest temperature measured in the bottom of the well was 426°C at a pressure of 340 bar. It was also possible to obtain core samples from the bottom of the well. However, due to damaged casing it hasn't been possible to do further temperature and pressure measurements in the lower parts of IDDP-2. To date flow tests in IDDP-2 have not started.

The next well in the IDDP project is planned in the Hengill Area. The most promising target is the hot body that started it all in the Nesjavellir Field. According to experience from IDDP-1 and IDDP-2 the main techincal obstacle is the casing. Both wells have serious casing problems. The magma body unexpectedly hit by IDDP-1 illustrated that careful interdisciplinary preperations are needed when drilling into the unknown. Currently, few projects are ongoing to fill the knowledge gaps in order to minimize risk and maximize the probability of successful drilling.

How to cite: Gunnarsson, G., Demusson, V., Gunnarsson, I., Kristjánsson, B. R., Tómasdóttir, S., and Hjörleifsdóttir, V.: Expanding a Geothermal Field Downwards. The Challenge of Drilling a Deep Well in the Hengill Area, SW Iceland., EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-21973, https://doi.org/10.5194/egusphere-egu2020-21973, 2020.

La Palma is one of the eastern islands of the Canary Archipelago located off the West African continental margin. Volcanic activity in the last 123 ka has taken place exclusively at the southern part of the island, where Cumbre Vieja volcano has been formed. Cumbre Vieja, one of the most active basaltic volcano in the Canaries, host seven historical eruptions being Teneguía eruption (1971) the most recent one. Cumbre Vieja volcano, characterized by a main north–south rift zone 20 km long and covering an area of 220 km², does not show any visible degassing that show the existence of active geothermal systems. For that reason, geochemical prospecting of soil gases and volatiles in the soil matrix itself of Cumbre Vieja can provide useful information to investigate the presence of permeable areas and potential upflow areas for the degassing of geothermal systems at depth.

We report herein the results of an intensive soil gas study, focused on non-reactive and/or highly mobile gases such as helium (He) and hydrogen (H₂), in Cumbre Vieja, with geothermal exploration purposes. He has unique characteristics as a geochemical tracer: it is chemically inert and radioactively stable, non-biogenic, highly mobile and relatively insoluble in water. H₂ is one of the most abundant trace species in volcano-hydrothermal systems and is a key participant in many redox reactions occurring in the hydrothermal reservoir gas.

Soil gas samples were collected at 1,201 sites selected from June 2019 to September 2019, with an average distance between sites of ≈ 250 m, at ≈ 40 cm depth using a metallic probe. He content was analyzed by means of a quadrupole mass spectrometer (QMS; Pfeiffer Omnistar 422) and hydrogen concentrations by a micro-gas chromatograph (microGC; VARIAN CP490). Soil He concentration showed values up to 23.9 ppm with an average of 5.73 ppm. Soil H₂ concentrations measured ranged from typical atmospheric values (≈ 0.5 ppm) up to 19.8 ppm. The mean value measured for H₂ was 0.78 ppm. Although He concentration values showed high spatial variability, the highest values can be observed in the north–south rift zone of Cumbre Vieja and around the surface contact with Cumbre Nueva ridge. Spatial distribution of H₂ concentration showed the highest values in the north-west area of Cumbre Vieja volcano. The results showed here are useful to identify the possible existence of permeable portions of deep-seated actively degassing geothermal reservoirs. However, a multidisciplinary approach is essential to obtain additional information about possible geothermal systems underlying at Palma island with the last goal of the selection of appropriate locations for future exploratory wells.

How to cite: Rodríguez, F., Polo Sánchez, A., Dale, K., Codner, C., Martín, A., Pérez, N. M., Amonte, C., Melián, G. V., Alonso, M., and Cordero, M.: Diffuse H2 and He degassing survey to study of hidden potential geothermal systems in La Palma, Canary Islands, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-11218, https://doi.org/10.5194/egusphere-egu2020-11218, 2020.

Key requirement for geothermal power production are temperatures of at least 100°C, while the obtainable flow-rate mainly controls the economic viability. Many geotectonic settings only provide such reservoir temperatures in depths of 3 km or more. Hydrothermal systems reach such temperatures only in specific geotectonically active settings, e.g. the Upper Rhine Graben or the Molasse basin in Germany, and usually are already under exploration and exploitation. Besides these easily accessible hydrothermal systems, which only make up a small share of the overall geothermal potential, petrothermal systems in crystalline or metamorphic basement rocks provide a much larger and ubiquitous resource. Locating and quantifying these petrothermal potentials is still a challenging task.

A newly developed exploration scheme for petrothermal potentials is proposed and applied to the crystalline basement of the Mid-German Crystalline High in the federal state of Hesse, Germany. The exploration is composed by three tiers and subdivided in an outcrop analogue study, a conceptual geological 3D-structural model and the estimation of petrothermal potentials based on the comprehensive geothermal 3D-model composed as result of the first two tiers.

On the example of the Mid-German Crystalline High basement rocks, the assessment scheme is demonstrated. Therefore, the geological 3D-structural model which is based on geophysical, structural geological and well data is presented. Petrophysical rock properties such as porosity, grain and bulk density, compressional wave velocity but also thermal conductivity and thermal diffusivity are measured on outcrop analogue samples and fed into a custom-made weighting matrix as basis for a multi-criteria decision making system. Together with additional criteria such as reservoir geometry, rock mechanical and structural geological features, qualitative potential assessment is performed. Quantification of the petrothermal potentials will be applied by the volumetric method and assumption of recovery factors for petrothermal systems based on operating systems worldwide.

Petrothermal potentials are displayed in the geological model.

How to cite: Weinert, S., Bär, K., Zimmermann, G., and Sass, I.: Assessment of Petrothermal Potentials: An Exploration Scheme for Mid-German Crystalline High Basement Rocks, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-15267, https://doi.org/10.5194/egusphere-egu2020-15267, 2020.

Commonly used host rock reservoirs for Enhanced Geothermal Systems (EGS) are composed of granite, as they display highly conductive and sustainable fracture networks after stimulation. However, considering the large amount of metamorphic rocks in Europe’s underground, these rock types may also show a large potential to extract geothermal energy from the subsurface. Within the framework of the European Union’s Horizon 2020 initiative ‘MEET (Multi-Sites EGS Demonstration)’, we are conducting fracture permeability experiments at elevated confining pressures, p_c, temperatures, T, and differential stresses,

How to cite: Herrmann, J., Rybacki, E., Wang, W., Milsch, H., Wagner, B., and Leiss, B.: Slates: a potential rock type to extract geothermal energy from the underground?, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-8091, https://doi.org/10.5194/egusphere-egu2020-8091, 2020.

Devonian and Carboniferous carbonate rocks are present in the subsurface of the Weisweiler lignite-fired power plant near Aachen, Germany. The utilisation of these rocks for deep geothermal energy extraction is currently being explored within the scope of the transnational EU-INTERREG-funded “Roll-out of Deep Geothermal Energy in North-West Europe (DGE-ROLLOUT)” project, which aims to provide solutions to reduce carbon-dioxide emissions using a variety of geoscientific approaches.

Marine transgressive-regressive cycles during mid-Palaeozoic times enabled the formation of extensive reef complexes on the southerly continental shelf of the Laurussian palaeocontinent. Supported by favourable climatic conditions including warm, clear and shallow waters, the Givetian to Frasnian Massenkalk facies and the Dinantian Kohlenkalk Group, each several hundred meters thick, were deposited in North-West Europe.

In the Weisweiler area, these Palaeozoic carbonate rocks were covered by voluminous paralic sedimentary rocks and deformed to large-scale, generally northeast-southwest-trending, syncline-anticline structures during the Variscan Orogeny. Alpine (post-)orogenic processes further induced faulting, resulting in fault-block tectonics in the Lower Rhine Embayment area of tectonic subsidence. Significant multiphase karstification of the Palaeozoic carbonate rocks, which can be observed in nearby exposed counterparts, supports their enhanced geothermal exploitation potential.

3D-modelling of the depths and dimensions of the Weisweiler subsurface carbonate reservoirs is carried out using the commercial software Move [v2019.1.0; Petroleum Experts Ltd], and is constrained by lithostratigraphic data obtained from drilling operations, geological mapping, and interpretation of seismic profiles. The 3D-model exhibits a complex geotectonic environment, including the development of both parasitic folds and thrust faults prior to the generation of Tertiary fault-block tectonics. The depths of the tops of the reservoirs are estimated to c. 1,200 m for the Carboniferous and to c. 2,000 m for the Devonian carbonate rocks, taking into account typical thicknesses of the overlying and underlying strata. Considering possible tectonic repetition below the thrust faults, the reservoir rocks may also occur significantly deeper in the subsurface. The 3D-model is currently being transformed into a HeatFlow3D [DMT GmbH & Co. KG] / Petrel [v2017; Schlumberger N.V.] model in order to approximate the fluid circulation and pathways within the carbonate reservoirs.

Based on the current model, a target area for 2D-seismic surveys and a c. 1,000 to 1,500 m deep exploration borehole have been selected. These investigations will commence in the summer of 2020, and will then enable geochemical and petrophysical investigations of the Palaeozoic rocks. The possibility of deep geothermal energy extraction from the Weisweiler subsurface and subsequent evaluation of the transition of the conventional lignite-fired power plant towards its utilisation of renewable “green” energy is carried out in close collaboration with DMT GmbH & Co. KG, Fraunhofer Institute for Energy Infrastructures and Geothermal Energy and RWE Power AG, all partners within the DGE-ROLLOUT project. The successful realisation of this project may serve as a pilot for similar projects considering the forthcoming fossil fuel phase-out.

How to cite: Fritschle, T., Salamon, M., Bißmann, S., Arndt, M., and Oswald, T.: Exploring the Deep Geothermal Energy Potential at Weisweiler, Germany: 3D-Modelling of Subsurface Mid-Palaeozoic Carbonate Reservoir Rocks, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-16953, https://doi.org/10.5194/egusphere-egu2020-16953, 2020.

Water pumped from flooded coal mines has been considered as a promising option to extract geothermal energy in many countries situating in sedimentary rock environment, where the ground temperatures are clearly higher than those of the crystalline rocks of the Fennoscandian Shield. Extraction of metals from the 1440 m deep Cu-Zn-S mine in Pyhäsalmi, Finland, will end in the near future. This provides us an optimal environment for studying how much heat energy can be utilized at depths of 500-2500 meters and which method would be the optimal for it. In the Pyhäsalmi Energy Mine project funded by European Regional Development Fund (ERDF) we investigated the geothermal energy potential of the crystalline rock, performance of different borehole heat exchangers and optimized the deep borehole field.

Geothermal potential of the Pyhäsalmi site has the typical constraints of the Finnish crystalline bedrock. Field measurements include temperature measurements of ten different boreholes using Distributed Temperature Sensing (DTS) method. Near-surface annual average temperature is about 4 °C and geothermal gradient is 12-14 K/km. The ore deposit is hosted by metavolcanic rocks (ca. 1.9 Ga). Laboratory measurements show that felsic metavolcanics prevailing in immediate contact with ore have thermal conductivity of 3 – 3.5 W/(m·K), whereas the mafic metavolcanics mainly on the western side of the ore body have thermal conductivity of 2.5 – 3 W/(m·K). Relatively high thermal conductivity of the low-porosity crystalline rock promotes heat extraction from the bedrock temperatures 20 – 25 °C prevailing in the bottom of the mine.

The generated and optimized design concept in this project is based on an underground borehole field and a novel insulated coaxial collector type transferring heat from the bedrock to the fluid circulation system. A technical challenge to be resolved is the heat transfer from the depths of the mine to the ground surface. The borehole field placed at the bottom of the mine can be dimensioned to produce nearly 20 °C water with several megawatts power, allowing annual heat production of up to 10 GWh at the temperature range of 70 – 90 °C by means of heat pumps. This allows the use of geothermal heat in district heating network, something not yet done anywhere in Finland. Moreover, the borehole field can be utilized both for heat extraction and charging, making it possible to use the borehole field as a heat storage in a distributed heating network.

How to cite: Piipponen, K., Hietava, J., Leppäharju, N., Martinkauppi, A., Korhonen, K., and Ahonen, L.: A mine as a source of geothermal energy - case study from Pyhäsalmi, Finland, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-8291, https://doi.org/10.5194/egusphere-egu2020-8291, 2020.

Switzerland supports the energetic transition by promoting the development of geothermal energy among other renewable energies. In particular, the Canton of Geneva is actively prospecting the Geneva Basin, generating a large dataset of geophysical and geological information. This large dataset of the Geneva Basin is used here to constrain geologically complex numerical models of fluid flow. Previous and ongoing projects demonstrated the geothermal potential of the Geneva Basin but a consistent basin-scale fluid flow model of the area has yet to be defined.

We use MRST (Matlab Reservoir Simulation Toolbox) for which we recently developed a geothermal module. The module is available with the last MRST release (2019b) and it is used to build up a 3D basin-scale dynamic model of the Geneva Basin. The goal of our numerical study is to investigate the large-scale control of tectonic structures and lithological hetherogeneities on fluid flow in the basin.

The static model is derived from active seismic and gravity inversion data. Petrophysical data and geo-location of faults are obtained from the existing literature. The resulting heterogeneous model takes into account the main geological facies, observed in the basin. We define a reference simulation with standard initial conditions (geothermal gradient and hydrostatic pressure topographically corrected) and a basal incoming heat flux. We consider a single-phase pure water compressible laminar flow in porous media. The geothermal module solves the mass and energy conservation equations using a fully implicit finite-volume discretisation with two-point flux approximation and single-point upstream mobility weighting.

We design a parametric study along three main axis: tectonic structures (i.e. faults), petrophysical and thermal properties and perform twenty three simulations running for 500 000 years to reach an equilibrium flow (steady-state). Our results show that fluid flow is driven by the hydraulic head of the topographic highs bounding the basin. Hotter fluids are found in the centre of the basin where we propose to focus geothermal exploitation in the future. Our results represent, to our knowledge, the first example of 3D basin-scale fluid flow modelling used as a preliminary prospection method for the assessment of geothermal resources.

How to cite: Alcanie, M., Collignon, M., Møyner, O., and Lupi, M.: 3D basin-scale groundwater flow modeling as a tool for geothermal prospection of the Geneva Basin, Switzerland-France, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-13556, https://doi.org/10.5194/egusphere-egu2020-13556, 2020.

Reasons for injectivity decline were investigated at different geothermal sites in Europe. Due to low injectivities, production rates have to be reduced and the site faces negative commercial implications. In addition to historical operation data, fluid and rock samples were investigated in the laboratory. Analysis and experiments focus on physical, chemical and biological processes and their interaction. Results show different processes being responsible for injection-triggered occlusion of flow pathways, e.g. fines migration, precipitation, micro-biological activity, aquifer properties, corrosion or O₂ inflow.

Lessons learned will be shown, from preparation of large-scale projects, from monitoring programmes towards sustainable operation.

Activities are taking place in the frame of the DESTRESS project. The DESTRESS project has received funding from the European Union's Horizon 2020 research and innovation program under grant agreement No 691728.

How to cite: Brehme, M., Marko, A., Aldaz, S., Blöcher, G., and Huenges, E.: Lessons learned from injection into sedimentary geothermal aquifers, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-21633, https://doi.org/10.5194/egusphere-egu2020-21633, 2020.

Based on a joint analysis of geothermal indicators (e.g. temperature map at different depth, surface heat flux) and practical features (e.g. restricted areas, existing research lease), two promising areas in southern Tuscany were identified to perform a more detailed geothermal resource characterization. An area is located on the north-east of the Larderello-Travale geothermal field, and the other one is located on the west of the Mt. Amiata geothermal field.

A quantitative geothermal resources assessment was performed in the aforementioned areas of Tuscany by solving numerical thermo-fluid dynamic models and by computing the geothermal potential using the ‘ThermoGIS’ software, as further developed for the Italian case (Trumpy et al., 2016).

First of all, geological and geophysical data required for geological and thermo-fluid dynamic modelling were collected and organised. The geological data were used to build a 3D geological model of the two areas of interest suitable for numerical simulations. Static temperature data gathered from the Italian National Geothermal Database together with site-specific heat flow measurements were used to calibrate the simulated steady state temperature distribution.

The geothermal potential computed by integrating geological, thermal and petro-physical information implementing the volume method used in ThermoGIS provided estimates of the heat in place and the geothermal technical potential maps. The resulting technical potential in the area close to Larderello –Travale is 330 MW_e and in the Mt. Amiata sector is 50MW_e.

References

Trumpy E., Botteghi S., Caiozzi F., Donato A., Gola G., Montanari D., Pluymaekers M., Santilano A., Van Wees, J.D., Manzella A. Geothermal potential assessment for a low carbon strategy: a new systematic approach applied in southern Italy. Energy 103, 167-181, 2016.

How to cite: Trumpy, E., Gola, G., Santilano, A., Manzella, A., Brambilla, M., Calabrò, R., Giussani, M., Monti Colombani, R., Palumbo, S., Savoca, V., and Vajda, E.: Geothermal resources characterization of two areas in southern Tuscany, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-21970, https://doi.org/10.5194/egusphere-egu2020-21970, 2020.

The exploration of geothermal resources on the island of La Palma, Canary Islands, was first conducted by the Spanish Geological Survey (IGME) from 1982 to 1984. These studies were focused exclusively on the southern part, where the last historical eruption, Teneguía, took place in 1971. This area still shows some geothermal features such us relatively high ground water temperatures (about 40ºC) and soil CO2 efflux values. Recent studies carried out at Cumbre Vieja volcano, the southern part of the island, on diffuse degassing, 3D gravimetry and Audio-MT probes point to promising results, although more studies are needed. We continue applying a multidisciplinary approach to obtain additional information about the geothermal system underlying at Palma island using novel techniques as well as tools which are appropriate to evaluate this system. For this reason, during summer 2019 a soil diffuse degassing research started at Cumbre Vieja volcano (220 km²) for geothermal exploration purposes. In this first phase of the diffuse degassing study about 1,200 sampling sites, with an average distance between sites of approximately 250 m were selected after taking into consideration the volcano-structural features and accessibility. In each sampling site in-situ soil CO2 efflux measurements were performed, and soil gas samples were collected at 40 cm depth for chemical and isotopic analysis. Spatial distribution of CO₂ efflux, statistical-graphical analysis of CO₂ efflux, and δ¹³C-CO₂ isotopic data to calculate and map the volcano-hydrothermal contribution of CO₂ were combined and used for geothermal exploration. The statistical-graphic analysis of the diffuse CO₂ efflux values confirms the existence of different geochemical populations showing two log-normal geochemical populations, a fact that suggests the addition of deep-seated CO₂. Relatively low CO₂ efflux values were measured ranging from non-detected up to 72.8 g m^-2 d^-1, with an average value of 4.6 g m^-2 d^-1. The highest CO₂ efflux values were measured at the north end of Cumbre Vieja, around the surface contact with Cumbre Nueva ridge. The CO₂ isotopic composition, expressed as δ¹³C- CO₂ showed the contribution of three different end-members: biogenic, atmospheric and deep-seated CO₂. The results indicate that most of the sampling sites exhibited CO₂ composed by different mixtures between atmospheric and biogenic CO₂ with slight inputs of deep-seated CO₂, with a mean value of -15.3‰, being the maximum and the minimum -2.8‰ and -25.4‰ respectively. The results showed here can help to identify the existence of zones where deep-seated actively degassing from geothermal reservoirs occurs, particularly where the interpretation and application of geophysical data might be difficult.

How to cite: Martín Lorenzo, A., Cole, B., Bullock, E., Abassi, S., Pitti-Pimienta, L., Meire, A., Amonte, C., Melián, G. V., Hernández, P. A., and Pérez, N. M.: Soil gas CO2 concentration, isotopic ratio and efflux measurements for geothermal exploration at Cumbre Vieja volcano, La Palma, Canary Islands, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-1164, https://doi.org/10.5194/egusphere-egu2020-1164, 2020.

The UKGEOS Glasgow research field site comprises a network of 12 boreholes into flooded coal mines, and is designed to observe how warm water moves around the abandoned mine workings over time (Monaghan et al., 2018). Minewater geothermal projects involve the redevelopment of abandoned mining areas into large volume, low temperature resources and use heat pumps to drive heating for homes, industry or agriculture. This technique has proven potential as a renewable, decarbonised heat source providing reliable heating, cooling and heat storage with stable pricing to former mining areas.

Flow through minewater systems is partitioned between flow through the mine voids, through fractured media, and through porous media. This heterogeneity in flow is crucial to the development of models to predict the efficacy of minewater geothermal systems, as water flowing through the fractured material should absorb more heat than that flowing directly through the mine voids. This heat exchange then goes on to control the rate at which heat can be sustainably extracted from the minewater system.

The majority of fluid flow has generally been assumed to be through the mine voids. However, the proportion of fluid flow through the porous wallrocks is very sensitive to the fracture populations that they contain, due to the shallow nature of these mine workings leaving them under low stress.  Geothermal tests at the Gaspé mines in Québec demonstrate this clearly, with high wallrock conductivities (10^-6-10^-4 m.s^-1) attributed to mine-blasting (Raymond & Therrien, 2008). Coal mining in the Glasgow area was predominantly carried out using the Pillar & Stoop or Longwall methods, which lead to very different damage states in the wallrocks, and so the effect of these fracture populations is expected to have a large effect on flow partitioning.

Here, relationships between in-situ stress, fracture population and permeability were determined from well-core samples of the Glasgow Main Coal and underlying mudstone and sandstone strata, in order to characterise how flow may be partitioned within different regions of these mine-workings.

Stress-dependent permeability and storativity were measured using the osciallting pore-pressure method, and elastic tensors were determined using an array of ultrasonic transducers. Axial fractures were then generated within these samples under low triaxial stress states, and the change in permeability with induced fractures then measured at a single stress state, with the newly developed fracture population characterised through the changes in the elastic tensor.

Monaghan, A. A., Starcher, V., Dochartaigh, B. É. Ó., Shorter, K., & Burkin, J. (2018). UK Geoenergy Observatories : Glasgow Geothermal Energy Research Field Site - Science infrastructure. http://nora.nerc.ac.uk/id/eprint/521444/%0A

Raymond, J., & Therrien, R. (2008). Low-temperature geothermal potential of the flooded Gaspé Mines, Québec, Canada. Geothermics. https://doi.org/10.1016/j.geothermics.2007.10.001

How to cite: Chandler, M., Mecklneburgh, J., and Rutter, E.: The role of fractures in flow partitioning during minewater geothermal energy extraction, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-1225, https://doi.org/10.5194/egusphere-egu2020-1225, 2020.

At the real-world site underlying the scoping simulation example, adding a fourth well (second producer) is being endeavored in order to maximize the benefit from an unexpectedly high injectivity at the already existing two injectors, whereas the modest productivity of the existing producer is acting as the turnover-limiting factor in the currently operating triplet. Up-sizing to a quadruplet configuration (two producers instead of one) might thus also, by virtue of competing pressure diffusion and poroelastic effects, improve the productivity of the first producer, so to say as an ‘added bonus’ for up-sizing. In the currently operating triplet regime, injectivity also appears to increase with operation time i. e. with the cumulative volume of fluid turnover, this being attributed to (thermo-)hydrogeochemical rather than hydraulic-poroelastic effects. Scoping poroelastic simulations are complemented by a comparison of fluid residence time distributions and thermal lifetime expectations between the two (quadruplet versus triplet) configurations.

How to cite: Adu Ntow, D., Ghergut, J., Sauter, M., Wagner, B., Wiegand, B., and Yamah, M.: Poroelasticity and self-stimulation around geothermal producers in quadruplet versus triplet configurations, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-3911, https://doi.org/10.5194/egusphere-egu2020-3911, 2020.

The Moil valley geothermal field is located in the northwest of Sabalan volcano in the northwest of Iran. The geothermal activities attributed to the Sabalan volcano was intensified during Plio-Quaternary time and the manifestations of these activities are observable around the volcano especially in the northwestern corner. The hot springs, surficial manifestations, and extracted fluids from drilled wells represent the whole composition of underground reservoir fluids. The thermal measurement of fluids show wide ranges of temperature of fluids where the hottest spring show 89˚C and the fluids obtained from well samplings show maximum temperature of 202˚C.  

The reservoir temperature estimations based on different geothermometers show 250˚C for the reservoir. The interpretation of carried out chemical analyses represent Na-K-Cl dominant composition for the studies samples taken from hot springs and drilled wells. All of sampling stations show pH ranges of 4.2-7.6 which reveal acidic to neutral pH range. The variation of TDS for the studied samples ranges between 209 to 320 mg/L. The evaluation of correlation coefficients between main parameters gives notable results. The positive and good correlation coefficient between temperature and Cl is obvious in most of samples and consequently the Cl content of samples increases in high temperature samples.        

Boron as a key constituent in geothermal fluids show variable concentrations in Moil Valley geothermal fluids and shows 0.28-35 mg/L Boron content in the studied samples. The correlation between Boron and pH for the studied samples is positive. This correlation displays the highest concentrations in pH=7. The main Boron species in this pH value is B(OH)₃ which is more stable comparing to the other Boron phases.  

The stable isotope analyses of the studied samples show -12 to -9.1‰ for δ¹⁸O and -71.3 to -77.6‰ for δD. The interpretation of obtained δ¹⁸O and δD values represents the main role of meteoric waters in reservoir fluids of Moil Valley geothermal field. Magmatic waters show negligible share of the reservoir fluids.      

The Tritium analyses for the studied samples show 0.1 to 41.7 TU amounts. The evaluation of obtained Tritium contents reveals the circulation of young waters inside the reservoir and considering to the δD/δ¹⁸O ratios, it is most likely that the recharge zones of the reservoir are situated in close distance and there are evidences of mixing with meteoric waters.

How to cite: Masoumi, R., Bakhshandeh GharehTapeh, F., and Bakhshandeh GharehTapeh, B.: Geochemistry of geothermal fluids in Moil Valley geothermal field, NW Iran, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-4125, https://doi.org/10.5194/egusphere-egu2020-4125, 2020.

For the sustainable utilization of deep geothermal resources it is essential to predict the exploitable potential thermal energy from the subsurface. One main parameter influencing the geothermal potential is the reservoir temperature that may vary locally or regionally in response to fluid flow and heat transport processes.

This study aims at combining highly complex 3D thermo-hydraulic numerical simulations of heat transport and fluid flow with predictions of the geothermal potential for the application case of a hydrothermal doublet. Quantifying the influences of conductive, advective and convective heat transport mechanisms on the thermal field and moreover on the predicted heating power requires fundamental numerical investigations. We use the Federal State of Hesse in Germany as study area where heat transport processes have been quantified in recently published studies. There, the heterogeneous geology consists of outcropping Variscan Crust and up to 3.8 km and 1.8 km thick sedimentary deposits of the Upper Rhine Graben and the Hessian Depression, respectively. This geological complexity is expressed by areas of different hydraulic and thermal configurations: in the flat, but tectonically active Upper Rhine Graben high heat flow from below the graben sediments is in contrast to the variable topography of the Hessian Depression with low heat input from the Rhenohercynian Basement.

The heating power in the three reservoir units (I) Cenozoic, (II) Buntsandstein and (III) Rotliegend is only predicted to be high in the Upper Rhine Graben. There the reservoir temperature is high enough and varies between 50 °C in the convective thermal model of the Cenozoic reservoir and 170 °C in the conductive thermal model of the Buntsandstein reservoir. Predicted low temperatures in the Hessian Depression lead to negligible low heating power, but as production mass flux is above ~6 kg s^-1 investigations should continue to assess the geothermal potential for other applications like seasonal energy storage or low enthalpy geothermal utilization.

How to cite: Koltzer, N., Frick, M., Scheck-Wenderoth, M., Lewerenz, B., Bär, K., and Bott, J.: Influence of fluid flow and heat transport on predictions of geothermal potentials in sedimentary layers of Hesse (Germany), EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-4685, https://doi.org/10.5194/egusphere-egu2020-4685, 2020.

Super-hot geothermal systems are promising targets for near future geothermal exploration either for direct fluid exploitation or as potential reservoirs of Enhanced Geothermal Systems. Although reservoir conditions assessment is crucial for the evaluation of the geothermal resources, temperature measurement is still a major challenge in super-hot systems since their extreme conditions (i.e. very-high temperature, possible presence of aggressive fluids) preclude the use of conventional logging methods. During two EU projects (i.e. IMAGE (FP7) and the DESCRAMBLE (H2020)) two methods based on fluid inclusions synthesis were developed for in-situ measurements of very high-temperature (i.e. ≥400°C). Synthetic fluid inclusions are produced by trapping fluid within pre-fractured minerals, free of natural fluid inclusions, placed in a gold capsule together with an aqueous solution. Laboratory tests showed that fluid inclusions in quartz form in a relatively short time (down to 48 hours) if an alkaline-saline solution (0.4 M of NaOH + 10 to 20 wt.% NaCl) is used. In the first method synthetic fluid inclusions in quartz chips are produced within gold capsules placed inside a micro-reactor containing a volume of de-ionised water in such amount that the density of water in the micro-reactor has the critical value. Under these conditions, the trapping temperature of synthetic inclusions can be computed by the intersections between inclusion isochores, determined through microthermometry, and the critical isochore of water. Thus, if the micro-reactor is kept for at least 48 hours at the depth of measurement in a geothermal well, the trapping temperature of fluid inclusions formed in capsules would correspond to the well temperature at that depth. The second method consists in the production of fluid inclusions in gold capsules in direct contact with the environment of the geothermal well. Under the conditions of the super-hot systems characterized by relatively low pressure (such as the deepest part of the Larderello-Travale geothermal system in Italy), pressure-temperature conditions would cause fluid immiscibility in the gold capsule (i.e. the saline-alkaline fluid splits in a high-salinity liquid and a low-salinity vapor). In this case, the trapping temperature of both high-salinity and low-salinity inclusions is equal to their homogenization temperature. Laboratory tests demonstrated that the trapping temperatures of fluid inclusions produced by both methods can provide a good estimate of the experimental temperatures. Two field tests following the first method were performed in geothermal wells of Krafla (Iceland) and Larderello-Travale (Italy) characterized by measured temperature at the test depth of 336°C and 249°C, respectively. These tests showed that synthetic fluid inclusions trapping temperatures closely approach the temperature measured using conventional methods. Finally, a field test was also attempted in the Venelle 2 (Larderello-Travale) geothermal well characterized by super-hot conditions. Trapping temperatures of fluid inclusions formed at 2900 below ground level (b.g.l.) by both methods resulted compatible with independent measurement by an electronic device which gave 444°C at 2810 m b.g.l..

The research leading to these results has received funding from the EC Seventh Framework Programme under grant agreement No. 608553 (Project IMAGE) and from the Horizon 2020 Programme under grant agreement 640573 (Project DESCRAMBLE).

How to cite: Ruggieri, G., Orlando, A., Borrini, D., Caporali, S., and Weisenberger, T. B.: Two methods for temperature measurement in super-hot geothermal systems based on synthetic fluid inclusions, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-4979, https://doi.org/10.5194/egusphere-egu2020-4979, 2020.

This study investigates the seismic activity occurring at the Larderello-Travale geothermal field (LTGF), central Italy, from June 2017 to January 2018. We deployed a network composed of 9 broadband stations around the Venelle 2 well drilling for supercritical fluids. During the experiment, we recognise a group of events that usually occur in swarms and that show a periodic pattern, a narrow frequency band, and almost identical waveforms. Their source is estimated to be located near the well, and their occurrence ceases after about 3 weeks from the conclusion of the drilling. We propose a causal link with the drilling operations where pressure fronts inside the well may promote phase changes and fluid flow across the drilled formations.

Our study sheds light on the anthropogenic seismic activity at the LTGF. More generally, we show that microseismic activity occurring during drilling in high-pressure and high-temperature conditions can remain at low magnitudes and that geothermal wells targeting geothermal fluids in such systems may be handled safely despite the critical conditions encountered at depth. The drilling of the Venelle 2 well is an encouraging example for the development of geothermal energy in critical conditions.

How to cite: Montanari, D., Minetto, R., Plànes, T., Bonini, M., Del Ventisette, C., Antunes, V., and Lupi, M.: Fluid-driven anthropogenic micro-seismic activity while drilling towards supercritical conditions in the Larderello-Travale geothermal field , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-5612, https://doi.org/10.5194/egusphere-egu2020-5612, 2020.

The utilization of geothermal reservoirs as alternative energy source is becoming increasingly important worldwide. Details of rock properties, structures, heat transfer and resulting interactions are the basis for the implementation of a sustainable reservoir management, but are often not well enough understood. The investigated warm water reservoir in Waiwera, New Zealand, has been known for many centuries. Triggered by overproduction in the third quarter of the 20th century, the reservoir pressure dropped significantly and in the 1970s the natural seeps on the beach dried up [1]. However, the shutdown of the main user's pumps (Waiwera Thermal Pools) in 2018 led to renewed temporary and location-specific artesian activity. The question now is whether the seeps on the beach will also reappear?

Hydrogeological models are the basis for a sustainable management of groundwater resources. The key point for the Waiwera reservoir is the amount of geothermal water which is permanently available. However, models are also used to describe the current hydraulic and thermal situation of the study area [2].

An expedition was carried out in 2019 to investigate the artesian activity of the reservoir, which has been observed again since 2018, and to build a new geological model. For the first time, thermal cameras carried by unmanned aerial systems (UAS) show the emergence of warm water at the beach and photogrammetric analyses carried out allow structural and lithological mapping on exposed cliffs where localized thermal anomalies were identified for the first time. The Waitemata formation found there is considered as analogue of the reservoir rock and thus serves for an improved understanding of the subsurface reservoir properties. The analyses show individual water and heat conducting lithologies and thus provide details about geological units that also constitute the geothermal reservoir at depth.

Based on the field exploration and the associated structural interpretations, a geological and thermal 3D model is now available for the first time, which will be employed to improve calibration of the hydraulic conditions of the warm water reservoir. Further, the model will be applied in the context of a sustainable reservoir management to clarify the question about the natural seeps on the beach. The reappearance of artesian activity in the Waiwera area due to significant adaptation of production rates is unique but the improved understanding of the interaction between rock properties, existing structures and heat transfer will also enable other reservoirs to be better understood.

[1] Kühn M., Stöfen H. (2005) A reactive flow model of the geothermal reservoir Waiwera, New Zealand. Hydrogeology Journal 13, 606-626

[2] Kühn M., Altmannsberger C., Hens C. (2016) Waiwera’s warm water reservoir – What is the significance of models? Grundwasser 21, 107-117

How to cite: Präg, M., Becker, I., Walter, T. R., and Kühn, M.: Unmanned arial system imaging and refined geologic modelling of the Waiwera geothermal Reservoir, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-6051, https://doi.org/10.5194/egusphere-egu2020-6051, 2020.

The Vallès geothermal system is located in the Catalan Coastal Ranges (CCR) (NE Spain). The CCR are formed by horst and graben structures limited by NE-SW and ENE-WSW striking normal faults, developed during the opening of the Valencia Trough (northwestern Mediterranean) (Gaspar-Escribano et al., 2004). In the Vallès Basin area, the thermal anomaly is located in the northeastern horst-graben limit, where a highly fractured Hercynian granodiorite is in contact with Miocene rocks by a major normal fault. This main structure seems to control the heat and the hot-water flow, nevertheless, the geological structure of this area, as well as the role of the Vallès normal fault, is poorly understood.

Magnetotellurics and gravity methods together with a detailed geological map have been applied in this area to understand the main structure. Although the geophysical part makes up most of the study, we are also elaborating a detailed geological map of the area, making a fractures study at different scales. We are working with DEM alignments analysis, and fractures study from outcrops and thin sections.

Our preliminary results in gravity show a strong gravity gradient in the NE-SW Vallès half-graben system and the recent MT profiles image the main fault of that system (Vallès normal fault). These results show a basin geometry with the major thickness of the basin towards the depocenter, disagreeing with the roll-over geometry assumed in previous works.

Interpretations of the fractures study, together with geophysical data and models, have allowed a preliminary characterization of damage zones associated with the fault system, which are directly related to the fluid flow and the hot springs. The nature of this damage zones could be related to relay ramps, commonly regarded as efficient conduits for fluid flow (Fossen and Rotevatn, 2016).

How to cite: Mitjanas, G., Ledo, J., Queralt, P., Alías, G., Piña, P., Marcuello, A., and Martí, A.: Integration of geophysical methods and fractures study for the Vallès geothermal system characterization (NE Spain), EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-6769, https://doi.org/10.5194/egusphere-egu2020-6769, 2020.

The Federal Institute for Geosciences and Natural Resources (BGR) has drilled the approx. 3,900m deep geothermal well Groß Buchholz Gt1 as part of the GeneSys geothermal project. The Bunter sandstone (Lower Triassic) was initially recovered as the target formation for the borehole. Due to the difficult geological conditions found, it was decided to abandon the Bunter sandstones. It is now intended to heat the properties of the GEOZENTRUM Hannover (GZH) using a geothermal doublet. In addition to the direct benefit for the GZH from the utilization of this regenerative energy source and the associated relief for the environment, the demonstration of the use of multiple, low thickness sandstone layers is of particular importance in this project. It should be proven that the sandstones of the Wealden formation (Lower Cretaceous / Berriasian) at a depth of approximately 1200m are suitable for geothermal usage. Moreover, a reference site for locations with similar geological conditions will be created.

As a requirement for further technical work in the borehole, a bottom cementation will be carried out at the final depth of the wellbore. This seals the perforation at a depth of approx. 3,700m and the access to the Bunter sandstones. A sidetrack is then drilled out of the existing hole into the Wealden sandstones. For this, a window is milled at a depth of approx. 750m and the sidetrack is drilled down to a depth of approx. 1300m. The determination of the landing point of the sidetrack is the subject of current investigations, as the Wealden sandstones are spatially heterogeneous. The reinterpretation of existing seismic profiles is of great importance for this. After successful completion of the sidetrack and evaluating the production tests and after a successful production test a second well is drilled from the same drilling site to a target depth of approx. 1300 m. The calculated distance of the two holes at the target depth is approx. 500 m.

In the previous project, the sandstone layers of the Lower Cretaceous were examined for their suitability for geothermal use. A maximum expected transmissibility can be estimated from the sum of six suitable sandstone units (total 46m), as well as the average permeability of these units of approx. 75mD. This results in a maximum transmissibility to be expected of approx. 3.5Dm. The measured temperature at a depth of 1200m is exceptionally high with 69°C.

In order to further increase the productivity of the drilling, it is planned to open up or stimulate the target horizons with different drilling techniques: for example, radial jet drilling and / or acid stimulation.

How to cite: Stechern, A., Torsten, T., and Prevedel, B.: GeneSys Doublet: setup and test of a geothermal well doublet in Lower Cretaceous sandstones of northern Germany – an outlook., EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-9266, https://doi.org/10.5194/egusphere-egu2020-9266, 2020.

The GEMex^* project is a recently finalized European-Mexican collaboration that aimed to improve the understanding of two geothermal fields: Acoculco and Los Humeros Volcanic Complex . These sites are located in the Trans-Mexican Volcanic Belt, a region that hosts numerous active volcanoes and is favorable for geothermal exploitation. Currently, the  Los Humeros Volcanic Complex is one of Mexico’s main geothermal systems with an installed capacity of ~95MW. Many studies have been performed at this site since the 70s highlighting several features and characteristics of the shallow subsurface. However a thorough knowledge of structures and behavior of the system at greater depths is still quite sparse. Hence one main objective of the GEMex project was to conduct several geological, geochemical, and geophysical experiments to investigate deeper structures for future development of local and regional geothermal resources.

In this framework, for the period of one year (September 2017 to September 2018), a seismic array consisting of 45 seismic stations was set to record continuously at the Los Humeros Volcanic Complex. In this study we analyzed the continuous seismic records to detect the micro-seismicity mainly related to exploitation activities. After applying a recursive STA/LTA detection algorithm, we assembled and manually picked P- and S- phases of a catalog of about 500 local events. The detected events were mostly clustered around injection wells, with fewer events located close to known structures. We use the retrieved catalog to derive a new minimum 1D velocity model for the Los Humeros site. We then performed a joint inversion to obtain the 3D Vp and Vp/Vs structures of the geothermal field. A post-processing averaging of several inversions was also computed to increase resolution of the investigated region. In this study we will show the derived Vp and Vp/Vs models for the  Los Humeros Volcanic Complex to emphasize various underground structures and potentially identify possible variations due to changes in temperature, fluid content, and rock porosity.

*This project has received funding from the European Union’s Horizon 2020 research and innovation programme under grant agreement No. 727550 and the Mexican Energy Sustainability Fund CONACYT-SENER, project 2015-04-68074. We thank the Comisión Federal de Electricidad (CFE) for kindly granting the access to the geothermal field for installation and maintenance of seismic stations.

How to cite: Toledo, T., Jousset, P., Gaucher, E., Maurer, H., Krawzcyzk, C., Calò, M., and Figueroa, A.: Local earthquake tomography at the Los Humeros geothermal field, Mexico, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-9865, https://doi.org/10.5194/egusphere-egu2020-9865, 2020.

During geothermal exploration, the geochemical methods play a major role in both exploration and exploitation phases. Discovery of new geothermal systems requires exploration of areas where the resources are either hidden or lie at great depths. A good example of young volcanic territory with high geothermal potential where geothermal resources are either hidden or lie at great depths is La Palma island (Canary Islands). La Palma is one of the youngest and westernmost island of the Canarian archipelago, located at the West African continental margin. Cumbre Vieja volcano (220 km²) is the last stage in the geological evolution of the island and has suffered 8 volcanic eruptions in the last 500 years, the last one in 1971. Among geochemical methods for geothermal exploration, soil gas surveys are useful for delineating main upflow regions and areas of increased subsurface permeability related to high temperature hydrothermal activity at depth. Soil gas Rn surveys are particularly useful since it is a naturally occurring radioactive gas present in geofluids that may serve as a subsurface tracer of geothermal reservoirs. An intensive soil gas was carried out from June to September 2019 in order to study the potential geothermal resource in Cumbre Vieja and the presence of vertical permeability structures related to high temperature hydrothermal reservoirs. A total of 1200 samples were taken with an average distance between sites of ≈250 m. Soil gas Rn-222 activity were measured by means of a portable SARAD RTM 2010-2 radon monitor; the instrument pumped gas through a stainless steel probe inserted at 40 cm depth and measured the Rn activity by electrostatic detection of the positively charged daughter isotopes. The soil gas Rn values ranged from atmospheric levels to 8.7 kBq m-3, with an average of 1.5 kBq m-3. The spatial distribution of soil Rn displays enrichments along the three main volcanic-rift zones: N-S, N-W and N-E, and confirms a strong structural control in the degassing processes of the volcano. The three volcanic-rift areas are zones of enhanced permeability for deep gas migration and preferential routes for degassing. It is worth noting the presence of an important soil gar Rn anomaly located at the eastern part of Cumbre Vieja, out of the three volcanic-rift areas. The data presented here are important to  identify  main  upflow  regions  and  areas  of  increased  and  deep  permeability at Cumbre Vieja.

How to cite: Pitti-Pimienta, L., Weidner, A., Shah, R., McClintock, R. L., Martín-Lorenzo, A., Rodríguez-Pérez, C., Padrón, E., Asensio-Ramos, M., Hernández, P. A., Rodríguez, F., and Pérez, N. M.: Geothermal prospecting at Cumbre Vieja volcano (La Palma, Canary Islands) by ground radon and thoron measurements , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-11305, https://doi.org/10.5194/egusphere-egu2020-11305, 2020.

Terceira Island is located in the Azores Archipelago and it lies at the intersection of four submarine volcanic ridges. Due to its characteristics the geothermal potential of Terceira Island has begun to receive some interest from researchers and decision makers from the 70s of last century, but only in 2000 an exploration license was granted in favour of GEOTERCEIRA (now EDA RENOVÁVEIS S.A.). The area of this license is located in the central part of the island in the Pico Alto Volcanic Complex, and includes the fumarolic field of Furnas do Enxofre.

The main aim of this study is to provide additional information about the presence of fluids upflow regions and areas of increased subsurface permeability related to high temperature hydrothermal activity at depth, as part of an study to expand the current geothermal plant of Terceira. To achieve this objective, a soil gas and diffuse CO₂ and H₂S degassing survey, which included in situ CO₂ emission measurements and soil temperature at 15 and 40 cm deep and the collection of soil gas samples, was performed during September 2019. 122 sampling sites were selected spaced at ~100 meters at Pico Alto Volcanic Complex. Diffuse CO₂ and H₂S measurements were performed according to the accumulation chamber method, using a non-dispersive infrared (NDIR) LICOR-830 CO₂ analyser and ALPHASENSE H₂S-BH detectors, respectively. In addition, soil gas samples were collected to analyse the He, H₂, O₂, N₂, CO₂, CH₄ and CO contents and the isotopic composition of the CO₂. Soil CO₂ efflux values ranged between non-detectable values and 56.2 g m² d^-1, with an average of 21.7 g m² d^-1. Soil H₂S efflux values ranged between non-detectable values and 0.245 g m² d^-1, with an average of 0.027 g m² d^-1. The probability plot technique applied to the soil CO₂ efflux data allowed to distinguish three different geochemical populations: background, intermediate and peak represented by 36.9 %, 59.8 % and 3.3 % respectively, with geometric means of 10.8, 25.4 and 50.0 g m² d^-1 respectively. The spatial distribution of soil CO₂ efflux data, constructed by means of Sequential Gaussian simulations algorithm, depicted the most important emission anomalies at the western section of the study area. These results can help to identify the possible existence of additional actively degassing geothermal reservoirs to reduce the uncertainty inherent to the selection of the area with the highest potential success in the selection of new exploratory wells at Terceira.

How to cite: Rodríguez-Pérez, C., Martín-Lorenzo, A., Rodríguez, F., Melián, G. V., Asensio-Ramos, M., Nunes, J. C., Martins, R. A. S., Carvalho, M. D. R., and Pérez, N. M.: Soil gas physical-chemistry survey for geothermal exploration at Terceira Island, Azores., EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-11845, https://doi.org/10.5194/egusphere-egu2020-11845, 2020.

Geochemistry is a fundamental tool in surface geothermal exploration. In particular, the analysis of the composition of the soil atmosphere, the measurement of diffuse CO₂ flux and of the gas ²²²Rn activity are important parameters to detect and characterize the contribution of volcanic/hydrothermal sources in the diffuse soil degassing.

The analysis of the soil atmosphere usually consists of determining the chemical and isotopic composition of the gases, including concentrations and molar ratios of multiple chemical species (e.g. He, H₂, N₂, Ar, Ne, O₂, CH₄, CO₂), as well as the C isotopic ratios (¹³C/¹²C). In practice a single geochemical survey provides tens of different parameters for each sampling point. Taking into account that a typical survey is composed of hundreds of sampling points, the huge amount of collected data requires effective data mining tools to perform analyses going beyond the simple mapping of concentrations and/or ratios and to detect hidden patterns in the dataset.

Among the most effective multivariate statistical tools is clustering analysis. This technique allows determining the presence of groups of points showing a given degree of similarity. In this work we used and compared two different clustering techniques: the K-means and the DBSCAN algorithms, applying them to a geochemical dataset related to surveys realized in 2010 in the southern part of the island of Tenerife (Canary Islands Spain) with the aim of geothermal exploration. We show how the clustering analysis allows determining the presence of areas characterized by a similar chemical and isotopic composition. The use of standard geochemical tools allows interpreting the nature of these areal groups in terms of their relevance for the purposes of surface geothermal exploration.

How to cite: González-Moro, Á. M., D'Auria, L., and Pérez, N. M.: Clustering analysis of soil gas chemical ratios as a potential geochemical tool for surface geothermal exploration, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-11962, https://doi.org/10.5194/egusphere-egu2020-11962, 2020.

For the future development of deep geothermal energy exploitation in Europe, large magnitude induced seismic events are an obstacle. On the other hand, the analysis of induced microseismicity allows to obtain the spatial distribution of fractures within the reservoir, which can help, not only to identify active faults that may trigger large induced seismic events, but also to optimize hydraulic stimulation operations and to locate the regions with higher permeability, enhancing energy production. The project COSEISMIQ (COntrol SEISmicity and Manage Induced) integrates seismic monitoring and imaging techniques, geomechanical models and risk analysis methods with the ultimate goal of implementing innovative tools for the management of the risks posed by induced seismicity and demonstrate their usefulness in a commercial scale application in Iceland.

Our demonstration site is the Hengill region in Iceland. The Hengill volcanic complex is located in SW Iceland on the plate boundary between the North American and Eurasian plates. In this region, the two largest geothermal power plants of Iceland are currently in operation, the Nesjavellir (120MW electricity) and the Hellisheidi (300MW electricity) power stations. In October 2018, we densified the permanent seismic network run by ISOR and IMO in this area (14 stations) with 23 broadband seismic stations.

We present the project and show first results from high resolution imaging of the shallow crust with ambient seismic noise, as well as first results from the relocated seismic events. The ambient noise imaging highlights an area of low seismic velocity close to the Þingvallavatn Lake, characteristic for the presence of supercritical fluids. The main geothermal production area is located as well in a low velocity zone that reaches 200 meters depth below Hellisheidi and around 700 meters below Nesjavellir.

How to cite: Obermann, A., Sánchez-Pastor, P., Duran, A., Diehl, T., Hjörleifsdóttir, V., and Wiemer, S.: COSEISMIQ: First results of high resolution imaging of the shallow crust and relocation of induced seismicity in the Hengill area, Iceland, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-12923, https://doi.org/10.5194/egusphere-egu2020-12923, 2020.

Subsurface formation temperature in the upper Yangtze area, southwest China, is significant for assessment of hydrocarbon generation and preservation, especially that of shale gas. The upper Yangtze area, with well-developed marine carbonate rocks, is one of the important preferred areas of shale gas exploration and development in China. Previous studies have analyzed the accumulation mechanism, development characteristics, hydrocarbon generation potential and occurrence modes of shale gas. However, the analysis of subsurface formation temperature is rare due to a lack of highly accurate temperature data. Here we combined new steady-state temperature logging data, drill-stem test temperature data and measured rock thermal properties, to investigate the geothermal regime and to estimate the formation temperature at specific depths in the range 1000~6000 m in this area.

Our results show that the present-day geothermal gradient for this area ranges from 10 to 74℃/km, with a mean of 24℃/km; While the heat flow varies from 27 to 118mW/m², with a mean of 64mW/m², indicating a moderate-high geothermal regime. Formation temperature at the depth of 1000 m is estimated to be between 26 °C and 71°C, with a mean of 40°C; the temperature at 2000 m ranges from 36~125°C with an average of 64°C; 45~180°C is for that at the depth of 3000 m, and the mean is 88°C; the temperature at 4000 m varies from 88 to 235°C, with a mean of 112°C; 65~290°C is for that at 5000 m depth, with a mean of 136°C; 75~344°C is for that at the depth of 6000 and the mean is 160°C. Generally, the pattern of the estimated subsurface temperatures in different depths is similar and has an obvious sub-area characterization, showing a trend of gradually increasing of temperature from northeast to southwest area. Most areas in the south and southeast of Sichuan Basin are with moderate temperature area, which maybe is the “sweet spot area” for shale gas exploration.

How to cite: Li, X., Liu, S., and Xu, M.: Estimation of subsurface formation temperature in the Upper Yangtze Area, Southwest China, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-13276, https://doi.org/10.5194/egusphere-egu2020-13276, 2020.

High temperature aquifer thermal energy storage (HT-ATES) can play a key role for a sustainable interplay between different energy sources and in the overall reduction of CO₂emission. In this study, we numerically investigate the thermo-hydraulic processes of an HT-ATES in the Greater Geneva Basin (Switzerland). The main objective is to investigate how to handle the yearly excess of heat produced by a nearby waste-to-energy plant. We consider potential aquifers located in different stratigraphic units and design the model from available geological and geophysical data. Aquifer properties, flow conditions and well strategies are successively tested to evaluate their influence on the HT-ATES economic performance and environmental impact. This was achieved using a new open-access, user-friendly and efficient code that we also introduce here as a possible tool for geothermal applications.

The results highlight the importance of thorough numerical simulations based on more realistic exploitation when designing HT-ATES systems. We show that relations between thermal performance and the shape of the injected thermal volume are generally hard to derive when complex well schedules are imposed because the injected/produced volumes may not be equal. Despite more complex storage strategies to comply with legal regulations, the shallower group of investigated aquifers in this study remains economically more suitable for storage up to 90ºC. In average four well doublets will be required to store the yearly excess of energy. The deeper group of investigated aquifers, however, become interesting for storage at higher temperatures.

How to cite: Collignon, M., Klemetsdal, Ø., Møyner, O., Alcanié, M., Rinaldi, A., Nilsen, H., and Lupi, M.: Evaluating thermal losses and storage capacity in high-temperature aquifer thermal energy storage (HT-ATES) systems with well operating limits: insights from a study-case in the Greater Geneva Basin, Switzerland, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-13510, https://doi.org/10.5194/egusphere-egu2020-13510, 2020.

During June and July of 2018 St1 Deep Heat Oy (ST1DH) performed a hydraulic stimulation between 6 km and 7 km depth beneath the Aalto University campus in Otaniemi, Espoo, Finland to establish an Enhanced Geothermal System (EGS) for district heating. The area surrounding the EGS is among the most densely populated areas in Finland with downtown Helsinki located only ~6 kilometers away.

The Institute of Seismology, University of Helsinki (ISUH) monitored the stimulation using a network of surface seismic stations and geophones. ISUH operates a temporary network of 5 broadband stations recording at 250 Hz in the Helsinki and Espoo region within ~10 km of the EGS well. During the stimulation and the immediate post-stimulation stage, ISUH also operated a temporary ~100 geophone network. This network consisted of three-component 4.5 Hz PE-6/B-geophones connected to DATA-CUBE3 digitizers recording at 400 Hz. The geophones were organized in 3 large arrays consisting of ~25 stations, 3 small 4-station arrays, and 8 single stations. ISUH was also granted access to data from borehole stations installed by ST1DH. These 12 semi-permanent borehole seismometers were installed at depths between 238 m and 1620 m and registered at 500 Hz. 

Our goal is to explore the performances of the simultaneously operating surface and borehole networks in monitoring induced seismicity in an urban hard rock environment with comparatively low attenuation of seismic signals. The results can be used in planning and designing future acquisition and monitoring systems around natural laboratories in similar envrionments.

For this we analyze the induced event detection capability based on data from the surface broadband and geophone stations and compare it to the data collected by the borehole sensors. First, the regular tools used in ISUH routine automatic analysis are applied to borehole station data to form the baseline for detection capability. We then apply the same procedures to the surface data where we take advantage of the geophone arrays by utilizing beamformed stacks in order to enhance the quality of automatic detection by improving the signal-to-noise ratio (SNR) of induced events. Second, we compile statistics of the residuals of a dataset of manually refined picks and the automatic detections to evaluate systematic effects or biases.  Third, we apply a detection and picking routine from the literature to ~500 event traces recorded at a borehole station and a colocated 25 sensor array to form a consistent data base for comparison with the routine ISUH picker. We explore the detection capability of beamformed surface record stacks by evaluating the SNR and detection statistics compared to the single borehole station. We focus on the effect of the number of traces per stack and on the frequency dependent diurnal and weekly noise variations associated with the urban environment.

How to cite: Vuorinen, T., Hillers, G., and Kortström, J.: Comparison of surface and borehole seismic network performances in observing induced seismicity from a deep EGS stimulation, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-13814, https://doi.org/10.5194/egusphere-egu2020-13814, 2020.

In the framework of the Geothermie2020 project, the canton of Geneva and the Industrial Services of Geneva (SIG) are currently developing geothermal exploration in the Greater Geneva Basin (GGB), located in south-western Switzerland and neighbouring France. Before geothermal exploration begins, it is important to investigate the ongoing seismic activity, its relationship with local tectonic features, and the large-scale kinematics of the area. Background seismicity suggest that the local tectonic structures affecting the basin may still be active. Moderate-magnitude earthquakes have been identified along the Vuache fault, a major strike-slip structure crossing the basin. In this context we deployed a dense temporary network of 20 broadband stations around and within the GGB, during ~1.5 years, and reaching a detection threshold 0.5M_L. 

Using a new coherence-based detector (LASSIE), we detected and located 158 events in our area of interest. However, only 20 events were located in the GGB, with local magnitudes ranging from 0.7 to 2.2M_L. We found no earthquakes in the Canton of Geneva where geothermal activities are taking place. We constructed a local minimum 1D velocity model with VELEST, using the recorded seismicity together with earthquakes from adjacent regions, in a total of 1263 P- and S-picks. The new velocity model allowed to relocate micro-seismic activity up to 11km depth along the main fault systems (i.e. Vuache, Cruseilles, Le Coin, and Arve) offsetting the GGB. We retrieved 8 new focal mechanisms for the area, using a combination of polarities and waveform inversion techniques (CSPS method). A stress inversion shows a tectonic deformation dominated by a quasi-pure strike-slip regime in the GGB, consistent with structural and geological data.

The study of microseismicity in a quiet sedimentary basin is challenging due to the scarce occurrence of seismic events combined with low signal-to-noise ratios and the often strong attenuation. However, the investigation of the sporadic (yet present) natural seismicity with dedicated dense networks could provide useful information about the GGB, even with a short-term experiment. We propose a newly-computed 1D velocity model that can be used in the GGB for seismic monitoring purposes throughout the geothermal project. This model can be easily improved later on, whenever more data is available. Monitoring the evolution and dispersion of the seismic-activity through the identified seismogenic areas during the geothermal project is essential. Quantifying the seismic rate in the basin before geothermal operations start will help to quantify the impact that geothermal energy extraction might have on the GGB. 

How to cite: Antunes, V., Planès, T., Zahradník, J., Obermann, A., Alvizuri, C., and Lupi, M.: A seismotectonic study and minimum 1D velocity model for the Greater Geneva Basin, Western Switzerland, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-16519, https://doi.org/10.5194/egusphere-egu2020-16519, 2020.

Interferometric Synthetic Aperture Radar has been used worldwide for investigating ground deformation due to subsurface extraction processes. However, in the Central and Eastern European region, no such studies are available so far. We present a case study for the Buda Thermal Karst demonstrating the effectiveness of satellite-based monitoring of the region. Budapest (and the whole territory of Hungary) is well-known from balneology for centuries. Thermal bathes in Budapest mainly utilize water discharging from carbonate reservoirs. Hot springs in the area are commonly located along fault zones controlling the groundwater flow systems. We investigate ground deformation in the vicinity of the Buda Thermal Karst by Persistent Scatterer time series analysis based on Sentinel-1 data for the period of 2014-2018. Results show that surface movements associated with the extraction of thermal water and groundwater recharge and discharge exist. Inverse geodetic modeling based on various deformation sources embedded in an elastic half-space is applied to infer for reservoir processes and properties and fault structures controlling fluid pathways. The modeling results are jointly interpreted with geological and hydrogeological models of the area. The satellite-based monitoring together with the modeling results allow a better understanding of the characteristics of fluid flow systems in the area and the dynamics of geothermal reservoirs under production. Such information can be of high importance for the sustainable production of thermal water in the future.

How to cite: Békési, E., Grenérczy, G., Frey, S., Farkas, P., van Wees, J.-D., and Fokker, P.: Ground movements associated with thermal water production from the Buda Thermal Karst (Hungary) by PS-InSAR, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-18126, https://doi.org/10.5194/egusphere-egu2020-18126, 2020.

Both energy applications, such as assessing one of the controlling factors of conductive geothermal plays, and geodynamics modelling, are influenced by the large uncertainties arising from uneven sampling of the direct observable of the Earth's thermal state, surface heat flow. Heterogeneity in structure and composition of the continental lithosphere complicate the temperature field even in stable provinces in thermal equilibrium. The measurements deviate from what simple relationships with geological and geophysical data predict, requiring more sophisticated schemes such as those based on multivariate inversion (e.g. Mather et al. 2018) and geostatistics (e.g. the similarity method employed by Lucazeau, 2019).

Recently, we aimed at assessing the performance of satellite-gravity-constrained modelling of surface heat flow [1], with the aim of employing the unparalleled spatial uniformity of global gravity models in the fill-in of sparsely sampled surface heat flow data. The model we obtained, in a test area in Central Europe, provided additional information on the lithospheric structure and revealed a satisfactory coherence with the geological features in the area and their controlling effect on the conductive heat transport. That test was based on a fit of radioactive heat production to available heat flow data, based on a misfit linearization and substitution strategy, which we have shown to be independently consistent with available heat production relationships (e.g. Hasterok and Webb, 2017). Furthermore, model validation techniques provide additional metrics on the predictability in areas devoid of heat flow measurements.

To reach those objectives, we developed a finite-difference based solver for the heat equation in conductive, stable lithosphere, relying on the assumption of steady state, 3-D heat conduction from the thermal base of the lithosphere to surface. It allows for non-homogeneous heat production and thermal conductivity, and non-flat upper and bottom boundaries. Concurrent joint forward modelling of the gravity field is also possible.
Through compromise between complexity and approximation, it was designed favouring easy and fast forward modelling, such as in assessing parameter sensitivity and performing grid searches or parameter fitting. Geological models and parameters can be defined using an user-friendly plain text layer-wise definition, which is then turned into a volume, on a rectangular mesh.
Computational requirements are lean: a 75 × 75 × 104 node model such as the one employed in [1] can be forward-modelled on an ordinary workstation in 135 seconds. A direct solver is employed to solve the FD system of linear equations: the Matlab built-in Cholesky decomposition for sparse arrays (Davis, 2006).

Albeit initially developed as an ad-hoc tool for a proof of concept, its ease of use and versatility suggest its potential in other applications. We therefore present the solver and the accompanying tool set, both openly available, along with a set of promising examples.

[1] Pastorutti, A., Braitenberg, C. (2019) "A geothermal application for GOCE satellite gravity data: modelling the crustal heat production and lithospheric temperature field in Central Europe." Geophysical Journal International, doi:10.1093/gji/ggz344

How to cite: Pastorutti, A. and Braitenberg, C.: A lightweight thermal modelling tool for physics-based continental heat flow interpolation, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-18306, https://doi.org/10.5194/egusphere-egu2020-18306, 2020.

Switzerland is strongly promoting the development of geothermal energy extraction from low- to high-enthalpy resources. However, the broad development of geothermal energy exploitation is hindered by the lack of subsurface knowledge and the high cost of traditional subsurface exploration methods. Affordable passive seismic methods may provide valuable information about the geological structures targeted for geothermal energy extraction. In this context, we are investigating the potential of the Ambient-Noise Tomography (ANT) technique. We present past results obtained from surface-wave ANT in the Geneva basin with a sparse seismic network, and we share preliminary insights from the starting PSIGE project aiming to try refracted P-wave ANT on dense nodal networks (~500 nodes) at several Swiss geothermal exploration sites. From synthetic examples based on prior subsurface models, we discuss the expected depth of investigation and potential resolution of the method with various network configurations. 

How to cite: Planès, T., Obermann, A., Antunes, V., and Lupi, M.: Testing Ambient-Noise Tomography as a Geothermal Exploration Method in Switzerland, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-18395, https://doi.org/10.5194/egusphere-egu2020-18395, 2020.

While coal energy is phased out to decarbonise our energy supply, the water within flooded abandoned mines provide a huge source (2.2 million GWh) of geothermal heat for the future, enough to meet the UK’s heating demand for more than a century. The mine water is only lukewarm (12-20^oC), but by using a heat pump, temperatures can be increased to a more comfortable 40-50^oC. Heat pumps need electricity, but for every kW of electrical input, the heat output is 3-4 kW, making this an efficient energy source. Research has shown that our abandoned mines could meet our heat demands for a century or more, and will deliver economic opportunities to former mining areas.

After abstraction of water from the mine and subsequent heat extraction , the mine water is returned to the subsurface to avoid surface water contamination. Understanding the subsurface to ensure the right location(s) for re-injection of the water is crucial for the thermal evolution of the mine system. In addition, mine water could interact with nearby (potable) aquifers, so a proper understanding of the hydrogeological behaviour of the mined system is required. Therefore, numerical modelling of mine water and surrounding groundwater flow and associated heat exchange is an essential first stage for the successful deployment of these geothermal mine energy systems.

Here, we present numerical modelling results of the thermal evolution of mine water circulation systems. A parameter sensitivity study gives insight in the rate of heat depletion of the mines, and the importance of several model parameters, such as mine tunnel connectivity, mine water flow speed, and water re-injection location.

This project involves collaboration with the Coal Authority and Durham county council in the UK. Available mine plan data offer opportunities to apply the modelling to proposed mine energy sites across coalfields in the UK and further afield. Results will be applied for planned geothermal energy sites at Stanley (county Durham), South Tyneside and Blyth Port in north-east England.

How to cite: van Hunen, J., Adams, C., Gluyas, J., de la Harpe, J., Hastie, K., and Norman, T.: The Heat beneath Our Feet, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-19190, https://doi.org/10.5194/egusphere-egu2020-19190, 2020.

Social consensus is a condition precedent for any intervention having an impact on the territory, such as geothermal power plants. Therefore, private investors studied and proposed innovative solution for the exploitation of the medium enthalpy geothermal resource, with “zero emissions” in atmosphere, with the target of minimizing its environmental impact. “Montenero” project, developed by GESTO Italia, complies with this precondition.

The area covered by the exploration and exploitation permit is located on the northern edge of the great geothermal anomaly of Mt. Amiata (Tuscany), about 10 km north of the geothermal field of Bagnore, included in the homonymous Concession of Enel Green Power.

The geological - structural setting of the area around the inactive volcano of Mt. Amiata has been characterized by researches for the geothermal field of Bagnore, carried out by Enel Green Power over the years. The geothermal reservoir is present in the limestone and evaporitic rocks of the “Falda Toscana”, below which stands the Metamorphic Basement, as testified by the wells of geothermal field of Bagnore. The foreseen reservoir temperature at the target depth of 1.800 m is 140 °C, with an incondensable gas content of 1,8% by weight.

The project was presented to the authorities in 2013 and it is now undergoing exploitation authorization and features the construction of a 5 MW ORC (Organic Ranking Circle) binary power plant. The plant is fed by three production wells for a total mass flow rate of 700 t/h. The geothermal fluid is pumped by three ESPs (Electrical Submersible Pump) keeping the geothermal fluid in liquid state from the extraction through the heat exchangers to its final reinjection three wells.

The reinjection temperature is 70 °C and the circuit pressure is maintained above the incondensable gas bubble pressure, i.e. 40 bar, condition which prevents also the formation of calcium carbonate scaling. The confinement of the geothermal fluid in a “closed loop system” is an important advantage from the environmental point of view: possible pollutants presented inside the geothermal fluid are not released into the environment and are directly reinjected in geothermal reservoir.

The environmental authorization procedure (obtained) has taken into account all the environmental aspects concerning the natural matrices (air, water, ground, ...) potentially affected by the activities needed for the development, construction and operation of “Montenero” ORC geothermal power plant. A numerical modeling was designed and applied in order to estimate the effect of the cultivation activity and to assess the reinjection overpressure (seismic effect evaluation). The project also follows the “best practices” implemented in Italy by the “Guidelines for the usage of medium and high enthalpy geothermal resources” prepared in cooperation between the Ministry of Economic Development and the Ministry of the Environment.

How to cite: Basile, P., Brogi, R., Lorenzo, F., and Mazzoni, T.: Feasibility, Design and authorization of a zero-emission Geothermal Power Plant in Italy; Case Study: “Montenero” Project, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-20541, https://doi.org/10.5194/egusphere-egu2020-20541, 2020.

The GeoTief EXPLORE project aims to explore the geothermal potential and quantify the geothermal resources of the Vienna Basin (Austria) and the underlying Northern Calcareous Alpine basement. The main target of geothermal interest is the massive and tectonically remolded Hauptdolomite facies that has been identified as potential geothermal reservoir in previous studies. Now, this formation is studied using outcrop analogues for the investigation of their petrophysical characterization and specific thermal properties (thermal conductivity and thermal diffusivity).

Here, we report new measurements on a total of 60 samples from 6 outcrops in and around the area of Vienna applying different methods for the laboratory measurement of thermal and hydraulic rock properties. The petrophysical analysis considers the impact of deformation along and across fault zones, which introduces heterogeneity of storage properties and consequently in the thermophysical properties. Using the standard fault core and damage zone model, outcrop samples were grouped into unfractured and fractured protoliths, as well as in fault rocks, like breccias and cataclasites. Rock samples are then classified by their fracture density (m² fracture surface per m³ rock) and by their matrix content and differences in grain sizes, respectively.

The measured thermal rock properties vary significantly between the selected rock groups. The total range [90 % of values] is between 3.2 and 5.0 W/(mK) for thermal conductivity and between 1.3 and 2.7 mm²/s for thermal diffusivity. The results generally met the expected trend for fractured rocks as conductivity and diffusivity decreases with increasing porosity under unsaturated and saturated conditions. The total porosities are less than 5%. The variability of thermal conductivity under saturated conditions shows complex trends depending on the different rock classifications where fault rocks and highly fractured rocks of the damage zone show lower increase in thermal conductivities.

The new petrophysical characterization will be the base for further numerical investigations of the hydraulic and thermal regime as well as for the analysis of the geothermal resources of the Hauptdolomite.

How to cite: Rupprecht, D., Fuchs, S., Förster, A., and Penz-Wolfmayr, M.: Thermophysical reservoir properties of the Hauptdolomit-facies underneath the Viennese basin across fault zones analogues – a reservoir study for the GeoTief EXPLORE project , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-21332, https://doi.org/10.5194/egusphere-egu2020-21332, 2020.

The Triassic–Jurassic sandstone reservoirs in the Danish subsurface at c. 1–3 km depth contain an enormous geothermal resource that is currently utilized in only three geothermal plants due to a number of geological, technical and commercial barriers. These barriers have been addressed in the GEOTHERM project funded by Innovation Fund Denmark and recommendations for overcoming the obstacles have been made. Some of the methods that are used in the oil and gas sector have successfully been introduced in the geothermal reservoir evaluations to reduce the risk associated with new exploration wells. Quantitative seismic interpretation proved capable of giving a reliable reservoir characterization with regards to estimation of porosity and sand/clay distribution. Diagenesis modelling gave good estimates of reservoir quality by utilizing the knowledge obtained about depositional environments, petrography, reservoir properties and burial history. Relationships between fluid and gas permeability have been established such that the regularly measured gas permeability can be recalculated to fluid permeability giving a better representation of the reservoir. The composition of the formation water in the three geothermal plants has been measured and used for geochemical modelling to evaluate the risk of scaling, where especially barite showed a tendency to precipitate upon cooling of the brine. Simulations of the thermal development of the reservoirs during long-term geothermal exploitation demonstrate significant heat extraction from the layers present above and below each reservoir, which ensures that only a small decrease in production temperature occurs over several decades. The regional geothermal resource estimation has been updated based on a new comprehensive 3D temperature model of the subsurface, confirming the presence of a huge geothermal resource with wide geographical extend covering most of the country. The causes of injection problems have been investigated including corrosion and scaling processes, showing that careful choice of well-lining and tubing materials besides cautious operation of plants are of utmost importance to prevent problems. A geothermal business case has been developed to give a lifetime assessment of geothermal plants including feasibility, design, drilling, construction, production and abandonment, showing that the operational costs are closely linked to the existing infrastructure and to the choices made when designing the geothermal plant. In conclusion, the new scientific results and best-practice manuals provide a significantly higher chance of success of new geothermal projects when including the recommended measures to minimize the geological uncertainties and prevent problems during drilling and production.

How to cite: Olivarius, M., Balling, N., Baunsgaard, J. P. M., Dalgaard, E., Holmslykke, H. D., Mathiesen, A., Mathiesen, T., Vosgerau, H., Weibel, R., and Nielsen, L. H.: Investigation of the geological, technical and economical obstacles for large-scale utilization of geothermal energy from Danish sandstone reservoirs, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-21618, https://doi.org/10.5194/egusphere-egu2020-21618, 2020.