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The sustainable use of natural renewable resources represents one of the main tasks of the twenty first century. The renewable geothermal resources can be profitably employed for energy production, heating and in several industrial processes allowing the reduction of the greenhouse gases and the human footprint. The knowledge of the main features that favor the development and the renewability of a geothermal system is the subject of detailed studies. In this context, numerical models reproducing the 3D geological setting of a geothermal system represent a tool to evaluate the involved geological and physical processes. The results can be used to perform site specific plans for a sustainable exploitation of the resource preserving it for the future generations. This procedure was adopted for the first time in the case study of the Euganean Geothermal System (EuGS ; Veneto Region, NE Italy). Approximately 15 million cubic meters per year of thermal waters with a temperature ranging from 63 to 87 ℃ are exploited by approximately 200 wells. The Euganean thermal water is of meteoric origin and infiltrates an elevation of about 1500 m a.s.l., as suggested by its stable isotope composition. The recharge area is located on the Veneto Pre-Alps, approximately 100 km to the north of the exploitation area. The high-angle NE-dipping faults that characterize the central part of the Veneto Region allow the groundwater flow from the recharge area to the exploitation area. In the latter, a pattern of local fractures deforming the bedrock favour the rising of the thermal fluids toward the surface. The waters are mainly used for recreational purposes, producing an income of 300 million euros per year. To maintain this natural resource a detailed numerical model based on coupled simulation of fluid flow and heat transport was performed. Being the existence of this geothermal system related to a particular geological and structural setting, a 3D geological reconstruction was achieved by the use of MOVE software. The geological model was implemented into the numerical model through an unstructured mesh with the aim of maintaining a high geological detail. The results achieved by the numerical model allowed both to explain the geological processes that characterize the EuGS and to evaluate its renewability. The unravelling of these processes and of their interplay will allow to perform a management plan for the sustainable exploitation of the Euganean thermal water.

In the twenty-first century the use of natural geothermal resources is significantly increased and their renewability help the reduction of greenhouse gases emissions and the human footprint. A strategy for the sustainable utilization and exploitation of these resources is required in order to preserve them for the future generations. A reliable way to evaluate the future exploitation scenarios is represented by the numerical models in which the geological features of the geothermal system are considered. This approach is used in the case of the Euganean Geothermal System (EuGS) in which approximately 150 wells are active and exploit an amount of 14.9x10⁶ m³ of thermal water per year with a temperature between 63°C to 87°C.

The Euganean Geothermal System (EuGS), located in the central part of the Vento Region (NE Italy), represents one of the most important low-enthalpy geothermal field in the southern Europe (Fabbri et al. 2017). This thermal water is of meteoric origin and infiltrates in the norther part of the system (Veneto Pre-Alps) an elevation of about 1500 m a.s.l. A particular structural setting allows the existence of the EuGS. As a matter of fact, the groundwater flow from the recharge area to the exploitation area is favor by a system of high-angle NE-dipping faults. Moreover, the rising of the deep thermal fluids in the exploitation area is favor by a pattern of local fractures that increase the permeability of the bedrock (Pola et al 2015). Approximately 15x10⁶ m³ per year of thermal waters with a temperature ranging from 63 to 87 °C are exploited from approximately 200 wells. This water is mainly used for balneotherapy and recreational purposes, feeding about 195 SPA, and the related tourism industry produces an income of about 300 million euros per year (Fabbri et al. 2017). These data testify the important role played by this natural resource on the economy of the Veneto Region. As a consequence, a strategy for its sustainable exploitation is required in order to preserve it for the future generations. Numerical simulations can be used as a tool to assess the processes driving the geothermal resource and its renewable component and to define the sustainability of its utilization (Monterrosa and Montalvo Lopez 2010). However, the reliability of the results is strictly related to the dataset that is implemented into the numerical model (Axelsson 2010). Typically, the geological features characterizing a system are reproduced in a very schematic way using some assumptions that reduce the necessary numerical effort. Consequently, the results can be partially useful to perform a reliable utilization strategy. In the EuGS case study, a detailed geological reconstruction of the analyzed geothermal system was carried out through MOVE software. Different type of data (geological and seismic section, wells data, gravimetric and structural maps) were implemented in the geological model to reproduce the main geological features allowing the existence of the geothermal system. This approach was adopted to increase the reliability of the numerical model, reducing the simplification of the conceptual model. To preserve the detail obtained through the geological reconstruction into the numerical model an unstructured grid approach was employed. The unstructured mesh allows to reproduce the high heterogeneity that characterize the geological setting of the analyzed geothermal system (Blӧcher et al. 2010 ; Passadore et al. 2012). As a matter of fact, these meshes can be deformed and distorted in zones characterizing by high variations (i.e. fault and fold zones). This procedure was possible using the open source MeshIt software (Cacace and Blocher 2015). The obtained unstructured mesh was implemented in the FeFlow code to perform coupled simulations of fluid flow and heat transport. The results allowed to define the interplay of geological features ensuring the existence of the geothermal system and its renewability. Starting from this point, particular attention will be paid to analyze the sustainability of the geothermal resource related to the current exploitation of the Euganean geothermal resource.

The Euganean Geothermal System (EuGS), located in the Veneto region (NE Italy), is one of the most important, economically profitable, low-enthalpy geothermal resource in southern Europe. From the Euganean Geothermal Field (EuGF) approximately 15 Mm³/y of thermal water are exploited with a temperature ranging from 63 to 87 C. The water is mainly used for balneotherapy and recreational purposes and the related tourism industry produce an income of approximately 300 million € per year. A conceptual hydrogeological model, describing the heating of groundwater during their flow from the recharge area to the exploitation field, was recently developed. In order to validate this conceptual model, a regional 3D numerical model was carried out. The model results, in agreement with the temperature measured by thermal logs, confirm the suggested conceptual model. However, several geological and hydrogeological features that characterize the geothermal system was not taken into account in its implementation (i.e. the real extension of the regional fault system and the hydrostratigraphic units geometries). Since the existingmodeling was essentially focused on the simulation of the processes producing the EuGS, this work aims to refine the existing 3D regional numerical model improving the geological and hydrogeological settings. For this reason, a detailed geological reconstruction by Move code is performed. In order to achieve the geological reconstruction geological and seismic section and stratigraphic logs of wells located in the Veneto plain are used. Furthermore, in the EuGF area approximately 500 stratigraphic logs are available that allow to define in detail the geological setting of the exploitation field. Subsequently, the geological reconstruction will be implemented in GOLEM code carrying out coupled simulations of fluid flow and heat transport.

The Laguna Blanca basin is a rhomb-shaped basin located at the SE margin of the Puna plateau in the southern Central Andes (Catamarca, Argentina). An interactive analysis using remote sensing and field mapping enabled us to produce a geo-structural map at a 1:350,000 scale. Satellite images from multispectral sensors (ASTER and Landsat 7 ETM+) and medium resolution Digital Elevation Models (SRTM and ASTER GDEM) were used in order to recognize the structures and main lithologies, which were validated in the field and through laboratory tests (e.g. spectral analysis). The final result is a geo-structural map of the Laguna Blanca basin with a new geological unit subdivision, highlighting its tectonic origin, which appears to be related to a releasing stepover along N-S sinistral strike-slip master faults.

As one of the largest and most extensive utilized geothermal system in northern Italy, the Euganean Geothermal System (EGS, Veneto region, NE Italy) has long been the subject of still ongoing studies. Hydrothermal waters feeding the system are of meteoric origin and infiltrate in the Veneto Prealps, to the north of the main geothermal area. The waters circulate for approximately 100 km in the subsurface of the central Veneto, outflowing with temperatures from 65◦C to 86◦C to the southwest near the cities of Abano Terme and Montegrotto Terme. The naturally emerging waters are mainly used for bal-neotherapeutic purposes, forming the famous Euganean spa district. This preferential outflow is thought to have a relevant structural component producing a high secondary permeability localized within an area of limited extent (approx. 25 km2). This peculiar structure is associated with a local network of fractures resulting from transtentional tectonics of the regional Schio-Vicenza fault system (SVFS) bounding the Euganean Geothermal Field (EGF). In the present study, a revised conceptual hydrothermal model for the EGS based on the regional hydrogeology and structural geology is proposed. Particularly, this work aims to quantify: (1) the role of the regional SVFS, and (2) the impact of the high density local fractures mesh beneath the EGF on the regional-to-local groundwater flow circulation at depths and its thermal configuration. 3D coupled flow and heat transport numerical simulations inspired by the newly developed conceptual model are carried out to properly quantify the results from these interactions. Consistently with the observations, the obtained results provide indication for temperatures in the EGF reservoir being higher than in the surrounding areas, despite a uniform basal regional crustal heat inflow. In addition, they point to the presence of a structural causative process for the localized outflow, in which deep-seated groundwater is preferentially conducted to the surface, warming up on its way, by the high level of connected fractures beneath the EGF, thus corroborating the proposed conceptual model.

The construction of a reliable conceptual model is a crucial aspect in modern hydrogeology. A detailed conceptual model can be used as a starting point for a subsequent numerical model aimed to plan a sustainable utilization of the hydrogeological resource. Usually, conceptual modelling of a regional, deep hydrothermal system is puzzling due to its geological complexity or the lack of exhaustive data over a wide area. In this peculiar case, numerical modelling can be used to validate the conceptual model evaluating some aspects of the flow. The Euganean Geothermal System in Veneto Region (NE Italy) is the subject of still ongoing studies because the naturally emerging thermal water (temperature from 65°C to 86°C) represents a profitable resource for the touristic industry, impacting the regional economy. The thermal water is of meteoric origin, and infiltrates in Veneto Prealps to the north of the main geothermal area (i.e., Euganean Geothermal Field, EGF). The water flows for 100 km in the subsurface of the central Veneto heating up to 100°C by the crustal heat flux. The conduits hosting the fluid flow are identified in the damage zones of the Schio-Vicenza fault system (SVFS), while the outflow in the EGF is associated to an interaction zone between the SVFS faults. The stress concentration produces a localized high secondary permeability, maintaining the aperture of the fractures. This work aims to validate this conceptual model through 3D coupled flow and heat transport numerical simulations unravelling the impact of fracture networks on the regional-to-local groundwater circulation. A reconstruction of the geological setting, including the high permeable zones, is performed. The distribution of the hydraulic and thermal properties is reproduced using the equivalent porous medium approach and discrete elements. The modelled temperature in the EGF reservoir results higher than in the surrounding areas, according to the measured temperature distribution. This local increase is produced by the rising of deep-seated groundwater driven by the local fractures. The results validate the proposed conceptual model. In addition, they suggest that the temperature in the deeper part of the reservoir could be higher than the expected value, opening a new scenario for the utilization of the thermal resource.

Euganean Geothermal System, fault system, 3D coupled flow and heat transport numerical model., Flowpath 2017, National meeting on hydrogeology 2017

1. Introduction The Euganean Geothermal Field (EGF) is the most important thermal field in the northern Italy. The EGF extends on a plain band of approximately 25 km² to the southwest of Padova (Veneto ; Italy), and comprises the towns of Abano and Montegrotto Terme (Fig. 1). Currently about 170 wells are active, and the total average flow rate of exploited thermal fluids is 14*10⁶ m³/year. The surface temperature of thermal waters ranges from 65°C to 86°C, and their TDS is up to 6 g/L (primary Cl- and Na+). ³H and ¹⁴C measurements suggest a fluid residence time greater than 60 years, probably in the order of thousand years. The EGF is located within the NW-trending Schio-Vicenza fault system (SVFS), a group of high-angle faults partly buried under Quaternary alluvial sediments and bordering to the West the foreland of the eastern Southern Alps (Pola et al., 2014). These faults, originated partly in the Mesozoic as normal faults, were reactivated in an extensional regime during the Paleogene. The EGF is located within an inferred subsurface relay zone between the Schio-Vicenza (SV) and the Conselve-Pomposa (CP) fault segments (Pola et al., 2015). Given the present sinistral transtensional regime of the western foreland margin, this structure is submitted to a local tensional regime that opens an ESE-WNW set of fractures maintaining the local conduits for the rising of the thermal fluids. The results of approximately 50 years long studies on the EGF and its thermal waters were used to propose a regional, tectonically-controlled conceptual model of the Euganean Geothermal System (EGS ; Pola et al., 2015). The aim of this research is to evaluate if and how a regional numerical model can improve the proposed EGS conceptual model. 2. EGS conceptual model The Euganean waters are of meteoric origin, as depicted by stable isotope analysis, and infiltrate about 80-100 km to the north of the EGF in the carbonate Sette Comuni-Tonezza plateau and the reliefs facing the area (Fig. 1A). The hydrological mass balance of the area shows that 23% of the infiltration (260 mm/y) is not balanced by the discharge of the springs located at the base of the reliefs representing the possible recharge of the system. The waters infiltrate in depth thanks to the high secondary permeability of the outcropping rocks and flow to the South in a Mesozoic carbonate reservoir (Fig. 1B). The SVFS defines the flowpath of the hot waters. In particular, the associated fracture mesh of the faults damage zones greatly enhance the fluid flow thanks to the high permeability (Faulkner et al., 2010). In the middle part of the EGS, the waters reach a depth of about 3000 m and warm up by the regional normal density heat flux (70-80mW/m²). Near the EGF area, the thermal fluids intercept the transtensional relay zone linked to the SVFS. This structure increases the rock fracturing and permeability, enhancing the migration to the surface of the thermal waters. 3. Methodology The conceptual model was reproduced in a 3D numerical model, simulating the regional fluid flow for the first time. The aim was to physically test, and improve, the EGS conceptual model by the results of the numerical simulations taking into account the regional geological constrains. The simulations are performed using the hybrid approach with the finite element code FEFLOW (Diersch, 2014). The model domain is 80 km long, 26 km width and 5 km deep, and it is discretized in 1.5 M nodes on 24 layers (Fig. 2). The geological setting is implemented by grouping the 24 layers into 5 horizons with different hydro-thermal properties obtained from a literature research. The main regional geological structures driving the fluid flow (i.e., the Schio-Vicenza and the Conselve-Pomposa damage zones, and the relay zone) are reproduced increasing the porosity and permeability of the nodes corresponding to these structures (Fig. 2). In addition, the fluid flow in the EGF is concentred by a network of planar discrete elements comparable with the one deforming the subsurface of the EGF. The simulations were conducted on a plausible geologic time of 2.5 My, and their execution time by a 24-core Intel Xeon CPU at 2.1 GHz was approximately 12 hrs. A calibration was also performed, with the aim to evaluate how different parameters could affect the temperature and the flow in the subsurface of the EGF. Finally, the temperature results of the numerical model were compared with the experimental well thermal logs carried out in the EGF. 3. Results & Conclusion Initially, the conceptual model expected a reservoir temperature of 90°-100 °C in EGF as depicted by SiO2 geothermometer results, and few degree lower than the exploited water temperatures. Conversely, the simulated temperatures are higher in the EGF reservoir. The increase of permeability, and consequently of the fluid circulation, within the relay zone enhances the EGF reservoir temperature despite a normal density heat flux (70-80 mW/m²) in the central Veneto plain. These results are also endorsed by Na-K-Ca geothermometers, suggesting a reservoir temperature of up to 170°C. Such a temperature is modelled into the accommodation zone at a depth of 2 km, while 100°C is simulated at 1 km as experimentally measured by well thermal logs.

The Euganean Geothermal Field (EGF) represents one of the biggest thermal areas of Europe extending on a plain band of 25 km² in Veneto region (NE Italy). Approximately 14x10⁶ m³ of water with temperature from 65 to 86°C were exploited in 2014 from fractured layers located in Mesozoic to Oligocene formations. The hydrogeological setting of the 300-600 m deep aquifer is elucidated through transmissivity and temperature maps, while the 800-1000 m deep aquifer is less exploited and investigated. The exploitation influences the natural regime of the aquifers causing seasonal fluctuations of the level related to the variation of the extraction. In 2014-15, five surveys were conducted to measure the potentiometric level and the water temperature in approximately 130 wells (depth up to 1064 m) during periods of high and low exploitation. The data are used to perform temperature maps of both aquifers outlining the spatial and temporal variations of the temperature. The maps of the shallow aquifer evidence two areas with temperature higher than 84°C and an outward decrease. The higher temperature is comparable with the 100°C reservoir temperature calculated with geothermometers suggesting a quick ascent of deep fluids through open fractures with a small loss of heat, while a longer path causes the decrease. The maps of the deep aquifer show higher temperature than the shallow one, but the few available data do not allow a detail ed analysis. Small variations of temperature among the surveys are depicted, but the distributions are slightly comparable. In addition, the temperature collected during 30 vertical thermal logs are examined evidencing a correspondence with the maps, although the logs are performed in inactive wells. Therefore, the correlation of the areal variations depicted with different methods suggests that the geological setting controls the temperature distribution in the EGF. In conclusion, the performed spatial and temporal reconstruction improves the knowledge of the hydrogeological setting of the thermal area providing useful data for the management of such resource.

The Euganean Geothermal Field (EGF) extends on a plain band to the south-west of Padua (NE Italy). Approximately 14*10⁶ m³/y of thermal water with temperature from 65°C to 86°C are exploited from different, 300-1000 m deep, fractured rock aquifers located within Mesozoic carbonate formations. The EGF represents the outflow area of a regional, 100 km-long, hydrothermal system. Oxygen isotopic analysis evidences the meteoric origin of the water that infiltrates at approximately 1500 m a.s.l. in the Veneto Prealps. The water flows towards the South in the Mesozoic carbonate formations and reaches a depth of approximately 3000 m warming to 100°C due to the normal geothermal gradient. The regional Schio-Vicenza fault systems and its highly permeable damage zone increase the water flow. In the EGF area, an interaction zone between the segments of the fault system and the related extensional tectonic regime produce a local fracture network that enhances the permeability and the quick rising of the thermal water. The conceptual model of the thermal system is reproduced in a 3D numerical model using FEFLOW code with the aim of understanding the influence of the fault system and its damage zone on the thermal water flow. The numerical simulation is based on the Equivalent Porous Medium Approach (EPM), while the geological setting is implemented using a simplified, planar stratigraphic sequence made by 3, 1400 m thick, layers (isotropic permeability: k1 = 1*10ˉ⁹ m/s, k2 = 1*10ˉ⁶ m/s, k3 = 1*10 ˉ¹¹ m/s ; thermal conductivity: c1 = 2.1 W/m*K ; c2 = 3.1 W/m*K ; c3 = 3.25 W/m*K ) and increasing the permeability of both the damage zone and the interaction zone by 2 orders of magnitude. The result evidences the development of convective cells along the damage zone of the faults and the local increase of the temperature in the subsurface of the EGF up to 110°C, comparable with the temperature of the Euganean thermal water. Further simulations will be carried out refining the geological model up to 8 layers, which represent the complete stratigraphic sequence involved in the thermal system. In addition, the influence of fault system on the development of the convective cells will be unraveled testing different width of the damage zone and different permeability ratios between the protolith and the damage zone.

The Euganean Geothermal Field (EGF) extends on a plain band to the south of Padova in the central part of Veneto Region (NE Italy). Approximately 400 wells up to 1 km deep have been drilled since 1950s, and 170 wells are currently active exploiting 14*106 m3/y of thermal water. The water has a temperature from 65°C to 86°C, and it is used for balneotherapy feeding 240 pools. Therefore, the EGF represents an important thermal field of Italy, and its recreational tourism is a significant economic resource for the Veneto region. The EGF is the outflow area of a regional hydrothermal system (Pola et al., 2015). The water is of meteoric origin infiltrating 100 km to the north of the EGF in the Veneto Prealps. The water flows towards the South in a Mesozoic carbonate aquifer reaching a depth of 3 km and warming to 100°C due to a normal geothermal gradient. The flow is enhanced by the highly permeable damage zone of the regional Schio-Vicenza fault systems (SVFS). In the EGF area, the water intercepts a local network of fractures associated to an interaction zone between the SVFS. The water rises quickly through the open fractures, and subsequently it spreads horizontally within fractured layers located at depth from 300 m to 1 km. The aim of this research is to understand the role of SVFS on the regional fluid flow, as well as the influence of the local fractures mesh on the upwelling of the hot water. The FEFLOW code is employed to reproduce the conceptual model of the thermal system in a 3D numerical model using the Equivalent Porous Medium Approach. The regional geological setting is simplified by 3 planar hydrostratigraphic units with a thickness from 1.4 km to 2 km. The units are simulated using 26 layers of constant thickness, and the values of their hydro-thermal properties are estimated using literature values. In addition, the damage zones of the faults are modelled increasing the local permeability by 1 order of magnitude compared with the protolith, while the permeability in the central part of the domain is increased by 2 order of magnitude representing the fracture mesh. Preliminary results show the development of convective cells along the damage zones and the increase of the temperature in the EGF subsurface. However, the modelled temperature is lower than that estimated into the reservoir. Therefore, a sensitivity analysis will be performed to evaluate the impact of the permeability (i.e., permeability of the units, ratios between the permeability of the protolith and the fractured rock and between horizontal and vertical permeability) on the modelled temperature in the EGF. This impact will be evaluated comparing the results with the subsurface temperature measured with thermal logs in the wells.

The Euganean Geothermal Field (EGF) extends on a plain band of 36 km² in the north eastern Italy nearVenice. Thermal waters (65°C to 86°C) are exploited from about 250 wells for a total flow rate of 17 Mm³/y.The Euganean thermal waters are of meteoric origin and infiltrate 80 km to the north of the EGF in the Venetopre-Alps. The geothermal reservoir is situated at a depth of 3 km in Mesozoic carbonate formations, whilethe regional Schio-Vicenza fault system and its permeable damage zone enhance the thermal fluid flow in thesubsurface. In the EGF area, the hot waters intercept an interaction zone between faults of the fault systemand rise quickly to the surface through the local fracture mesh. In order to constraint the upwelling timeof this thermal water from the deep reservoir, an isotopic study on stable (oxygen, hydrogen, carbon) andradioactive isotopes (radium, radon, actinium) has been carried out. In this paper we will report on the resultsof the radioactive isotopes.

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The Euganean thermal waters (65-86°C) constituting the homonymous thermal field (Euganean Geothermal Field ; Veneto region ; NE Italy) are investigated in this work to constraint the time scales of their upwelling based on Ra and Rn isotopes. Two groups of samples can be distinguished on the base of the 223Ra/226Ra and goethite saturation index. The thermal waters in the northern part of the thermal field are characterized are characterized by goethite S.I. 1.6) and in general characterized by 223Ra/226Ragreater than equilibrium value (0.046). This result was interpreted as connected to a slower rising path through a finely fractured aquifer yielding an enhanced water/rock interactions.

This work presents the geological reconstruction and the evolution of the western margin of the Veneto-Friuli foredeep that is marked by the Schio-Vicenza fault. Approximately 1, 000 km of 2D seismic sections and more than 10 deep wells acquired by ENI for hydrocarbon exploration were interpreted. The results show a complex system of NW-SE trending, NE dipping, high angle faults synthetic to the more known Schio-Vicenza fault. This system of faults (called Schio-Vicenza fault system, SVFS) extends for approximately 150 km from the foot of the pre-Alps to the Po delta and accommodated the polyphasic deformation affecting the foredeep. The results of the throw analysis show that the SVFS developed during the Mesozoic regional extension. Subsequently, it was reactivated during the Pliocene-Pleistocene flexuring, accommodating with a scissor movement the differential bending between the Lessini-Berici-Euganei block to the W and the Veneto-Friuli foredeep to the E.