ENeRAG Geofluids

The so-called, Green Transition EU strategy motivates oil companies to turn towards a circular economy and the production of green energy. The existing dataset gained through hydrocarbon exploration and the infrastructure of abandoned or barren hydrocarbon wells provides huge potential for geothermal reutilization. The geothermal potential of the Zala region (SW Hungary) is assessed to be good, however, there are only a few sites with ongoing reinjection, which is urgently needed for the sustainability of the systems. However, Neogene (so-called Pannonian) siliciclastic reservoirs in Hungary are the source of various injection-related issues. By predicting the problems, their mitigation becomes possible At the same time the evaluation contributes to a geothermal potential estimation as well. In this research, various scales of problem sources are considered ranging from regional hydraulics, reservoir scale properties and local clogging processes based on methodological results of previous studies (e.g., Markó et al., 2021a) to assess the reinjection potential of abandoned hydrocarbon wells in the region. As a first step, we evaluated the regional hydraulic conditions including pressure analysis as well as the reservoir extension on a regional scale. Hydraulic analysis revealed quasi-hydrostatic conditions in the Pannonian siliciclastic deposits, dominated by the topography driven driving forces. In the deeper regions, few overpressured data points can be found in the Triassic rocks. Significant upward flow was not detected. Accordingly, unlike certain overpressured regions of the Pannonian basin, the hydrostatic conditions are favourable for low-pressure injection in the Zala region. The reservoir conditions are tended to be favourable in the southern and western part of the study area: in these regions the porous reservoir formation is settled deeper and has significant thickness (400-600 m) which foresees sufficient vertical and horizontal extension of the deltaic sandstone bodies.

Lake Velence is a shallow soda lake in Hungary that is located in a tectonic subsidence in the southern foreland of the Velence Hills. Since the lake is semi-astatic (the volume and level of water in the lake fluctuates frequently), climate has a serious effect on its water budget. Until recently, the groundwater inflow into the lake has been neglected and only the recharge from surface water and rainwater have been taken into account. Because increasing climate change threatens the existence of the lake and its unique ecosystem, it is important to properly assess the components of the lake's water budget. To understand the role of groundwater for the lake-water quantity and quality, the groundwater flow patterns were mapped constructing pressure-elevation profiles and tomographic potential maps. During our research, 15 water samples were collected from groundwater wells, springs and from the Lake Velence. Physico-chemical properties of the water (e.g. temperature, pH, redox potential, specific electrical conductivity) were recorded during sampling on the field. The samples were analyzed for major ions (Ca, Mg, Na, K, HCO3 , SO4 , Cl). To verify the results of the groundwater flow mapping, stable isotopes (O, H) and radioactive isotopes (Ra, Rn, U) were applied as natural tracers. δD and δ18O were measured by using PICARRO L2130-i δD/δ18O Ultra High-Precision Isotopic Water Analyzer. 222Rn activity concentration was determined by using TRICARB 1000 TR liquid scintillation detector. The 234U+ 238U and 226Ra activities were measured by a unique method, alpha spectrometry using Nucfilm discs. The p(z) profiles indicated that recharge areas are dominant south from the lake, while groundwater discharges along the lake's shoreline. According to the tomographic potential maps, the regional groundwater flow travels from the Velence Hills toward the regional base level (River Danube). The water chemistry analysis indicated that the majority of the water samples can be classified as Ca-Na-HCO3 and Ca-Na-HCO3-Cl-SO4 type waters. δD measures were between -98.4 and-13.4‰; while δ18O values were between -13.4 and 0.15‰. Most of the samples are characterized by relatively high 234U+ 238U activity concentration (up to 497 mBq L-1). Based on δD and δ18O values, groups of groundwater having different recharge environment, can be distinguished. This is in line with the results of the groundwater mapping: a deep regional flow system with longer residence time and more shallow local flow systems with shorter residence time can be identified. The dominance of recharge areas and the presence of local flow systems can be further supported by the 234U+238U measurements, because uranium can be mobilized by the groundwater primarily under oxiziding conditions. It was revealed that groundwater contribute to the lake's water budget and the lake is fed by local groundwater flow systems known to be more sensible for the climate changes. This topic is part of a project that has received funding from the European Union’s Horizon 2020 research and innovation programme under grant agreement No 810980.

In the Danube-Tisza Interfluve area (Hungary), groundwater levels have declined significantly in the last decades, due to anthropogenic activities and climate change. In the past, several replenishment plans have been prepared, involving large, cross-regional technical investments, but they have not been implemented due to the lack of adequate financial resources and environmental concerns. The aim of this study is to demonstrate a local scale solution by experimental research in a small rural town (Kerekegyháza), which could contribute to easing the water shortage of the area. Rooftop rainwater harvesting coupled with shallow well infiltration was selected as a possible method due to its easy and relatively inexpensive implementation and operation. In addition, rainwater is the only adequate source of recharge water at the study area, where unused dug wells are readily available as well. In the beginning of 2020, a field experiment was set up, leading rainwater from the roof of a family house to the dug well in the yard. The water passes through a filter mesh before it enters the tube system leading it to the well. Water level, temperature and specific electrical conductivity is recorded every half hour in the dug well and in two newly established observation wells. Water samples are taken for laboratory measurements. Precipitation is measured on a daily basis. Long-term water level, hydrochemical and isotopic changes, as well as temperature changes were monitored to determine the physicochemical effects of injected water on the ambient groundwater. Furthermore, water level changes following precipitation events were compared with the amount of precipitation falling to the rooftop to estimate the efficiency of the system. A transient numerical flow model was built to better understand the occurring underground processes and to evaluate the potential and efficiency of rooftop rainwater harvesting with different scenarios. The obtained results can help to determine the potential of this method together with its limitations on settlement level. In addition, they provide background information for further numerical simulations and contribute to the extension of the design to similar settlements in the Danube-Tisza Interfluve. This research is part of a project that has received funding from the European Union's Horizon 2020 research and innovation programme under grant agreement No 810980.

In the Danube-Tisza Interfluve area, groundwater levels have declined significantly in the last decades, due to anthropogenic activities and climate change. The aim of this study is to demonstrate the potential of local, inexpensive solutions, such as rooftop rainwater harvesting that could contribute to easing the water shortage of the study area. In the beginning of 2020, a field experiment was set up, funneling rainwater from the roof of a family house to the dug well in the yard. Changes in water level, as well as thermal, hydrochemical and isotopic footprints were monitored over two years to determine the physicochemical effects of infiltrated water on the ambient groundwater. Water level changes following precipitation events were compared with the amount of precipitation falling to the rooftop to estimate the efficiency of rainwater collection and infiltration. Infiltration curves were analyzed as slug tests to estimate the changes in the hydraulic conductivity of the aquifer. Water chemical measurements were analyzed in order to follow the infiltration process and to delineate possible contaminants. Based on the obtained results, rooftop rainwater harvesting coupled with shallow well infiltration is a suitable local water replenishment technique, both in terms of water quantity and quality. The largest benefit can be reached during summer periods with high rainfall amount, but high evapotranspiration, thus low natural infiltration. Rainwater could improve groundwater quality, however Zn, PO4 3-and NH4 + were identified as possible contaminants which should be monitored. To avoid serious clogging, yearly maintenance of the gutters, filters and well bottom is essential. The results of this research provide background information for further numerical simulations and contribute to the extension of the design to settlement scale and to similar settlements in the Danube-Tisza Interfluve area. In addition, this research can promote the installation of rooftop rainwater harvesting systems with aquifer recharge worldwide which could help reaching sustainability in water management. This research is part of a project that has received funding from the European Union's Horizon 2020 research and innovation programme under grant agreement No 810980.

Springs are sources of freshwater supply. Furthermore, they can also deliver valuable insight into the hydrogeologic processes of a mountainous region, a natural conservation area or a remote study site with no wells. In order to assess the appearance, peculiarities, quality, stability, longevity and resilience of springs and related ecosystems, they need to be regarded in the context of basin-scale groundwater flow systems. The application of spring data evaluation on a basin scale was demonstrated via the carbonate system of Transdanubian Mts., Hungary. The readily measurable physical parameters of springs, the elevation of spring orifice, temperature and volumetric discharge rate provided reasonable classification and characterisation of springs and the related groundwater flow systems. Applying these parameters seemed prospective in a basin-scale understanding of flow systems in data-scarce regions, as monitoring discharge rate and water temperature are cost-effective, requiring no specific tools and analysing procedures. The combined cluster and discriminant analysis (CCDA) can handle uneven data distribution, unequal length and spacing of time series, data gaps, and consider the time-dependent variability of parameters. The optimal number of groups can be determined based on frequently sampled springs (or other entities). The less monitored springs (or other entities) can be classified using a similarity-based approach and linear discriminant analysis (LDA). Diagnosing the relation of springs to groundwater flow systems can advance sustainable water resources management, considering the ecological water needs maintaining various ecosystem services, therefore enhancing the resilience of springs and groundwater-dependent ecosystems.

Pannóniai delta és folyóvízi képződmények hidrosztratigráfiai egységei az Alföldön: szeizmikus geomorfológia és lyukgeofizikai adatok a hidrogeológiai modellezés szolgálatában

The green transition requires adapting the data and methods of the hydrocarbon industry for geothermal purposes and finding new resources in geofluids, like lithium. Moreover, the aligned research and exploration of groundwater, geothermal and hydrocarbon resources are also required for environmental reasons. We could reveal in the last decades that the solid framework of the Earth crust evolves through interactions with geologic fluids. It means that geofluids play an essential role in nearly all geologic processes of sedimentary basins, such as the mobilization, transportation, and accumulation of matter and heat. Different driving forces of regional fluid flow, like topography, tectonic compression, compaction, erosion, buoyancy, can operate together on a geological time scale. The permeability of the rocks may be able to maintain the fluid potential differences, thus enabling the flow systems to work for even up to 10 million years. In addition, the fluid flow systems determine the evolution of the geological resources, such as groundwater, geothermal resources and hydrocarbons. Previously the research of these geological resources has been evolved separately. For today due to environmental reasons, we had to realize the need for coordinated exploitation and utilization of different geofluids. We can see the fundamental differences and similarities regarding the perspective of the specific fields of different geofluids. However, understanding the fluid flow systems can give a scientific basis and a practical approach for all areas of geofluid research. This approach provides background to develop a workflow for the coordinated exploitation and utilization of different geofluids and related geological resources. The research is supported by the ENeRAG project that has received funding from the European Union’s Horizon 2020 research and innovation programme under Grant Agreement No. 810980.

The undulation of topography and the groundwater table serves as a driving force of fluid flow not only in mountainous or volcanic regions but also in sedimentary basins. Since topographical variations existing everywhere in the continental lithosphere, the operation of regional-scale groundwater flow systems and their role in the formation of heat accumulations need to be considered in geothermal intervention planning. A numerical simulation series was performed on a wide range of synthetic groundwater basins with topographical driving forces of groundwater flow to reveal the effects of various geometric and geologic parameters and agents, such as anisotropy of hydraulic conductivity, surface undulation, basin fill and temperature gradient. Our results showed that in identical basin-halves, the same flow pattern develops and there is no flow from one part to the other. However, this ideal situation is not the case in real groundwater basins. Groundwater flows from one basin(−part) to another described as interbasin flow, a general form of basin interplay. This process is a direct consequence of basin geometry since waters enter a territory of another flow system due to the differences in driving forces and/or geographic position. At the convergence of opposing flow systems under a discharge area, quasi-stagnant zones and hydraulic traps may develop and support accumulation of heat, hydrocarbon, and any type of dissolved materials. Furthermore, groundwater flow systems and their carrier fluids provide a continuous natural replenishment of fluid and heat for geothermal systems. The role of basin interplay driven by juxtaposed topographically elevated areas is relevant and important in maintaining groundwater flow systems and related matter accumulation in the basin fill part of a mature basin. Thus, the rejuvenation of a geothermal system is provided by natural topography-driven regional groundwater flow both on a human and a geological time scale. If the production of a geothermal system exceeds the rate of replenishment, reinjection of carrier fluids might be a solution for long-term sustainable operation. Analysis of the basin-scale flow patterns, heat accumulation and natural recharge could also be implemented during the reconnaissance phase of exploration for sustainable energy use. This research is part of the ENeRAG project that has received funding from the European Union's Horizon 2020 research and innovation program under grant agreement No 810980. The research has been supported by the Papp Simon Foundation, Budapest.

The modeling of karst water level fluctuations is a crucial task in the water resource management of vulnerable karstic areas. In the Transdanubian Range (East Central Europe, Hungary), from 1950 to 1990, coal and bauxite mining were carried out, with large amounts of karst water being extracted, thus lowering the water table by amounts ranging between 10 and 100 m. Since the cessation of mining activities in the early 1990s, the volume of natural recharge has exceeded the amount of dewatering, and the system has begun to return to its original undisturbed state. This apparently welcome development does, however, bring economic and technical engineering problems. The estimation and prediction of such water level changes is often tackled via the use of deterministic approaches, however, in the present case, it is also addressed with an alternative approach using trend estimation to monthly water level data from 107 karst water wells over the period 1990-2017. To approximate the change in karst water levels, (i) growth curve models were fitted to the monthly data, allowing the estimation of karst water levels, at least as far as 2030. Similarly, this was also done with (ii) deterministic modelling in order to describe the recovery process up to 2030. Specifically, measured and predicted values for karst water level were used to derive interpolated (kriged) maps to compare the forecasting power of the two approaches. Comparing the results of the trend analysis with those of the traditional deterministic modelling results, it is apparent that the two approaches predict similar spatial distribution of water levels, but slightly different future water level values.

The middle Anisian extensional tectonics of the Neotethyan realm developed a small, isolated carbonate platform in the middle part of the Balaton Highland (western Hungary), resulted in the deposition of uranium-bearing seamount phosphorite on the top of the drowned platform and produced some epigenetic fluorite veins in the Middle Triassic sequence. The stable C-O isotope data of carbonates are shifted from the typical Triassic carbonate ranges, confirming the epigenetic-hydrothermal origin of veining. Primary fluid inclusions in fluorite indicate that these veins were formed from low temperature (85–169 °C) and high salinity NaCl + CaCl2 + H2O type (apparent total salinity: 15.91–22.46 NaCl wt%) hydrothermal fluids, similar to parent fluids of the Alpine-type Pb-Zn deposits. These findings indicate that the Triassic regional fluid circulation systems in the Alpine platform carbonates also affected the area of the Balaton Highland. This is also in agreement with the previously established palinspatic tectonic reconstructions indicating that the Triassic carbonate and basement units in the Balaton Highland area were a part of the Southern Alpine. Similar fluorite veining in phosphorite deposits is also known in the Southern Alpine areas (e.g., Monte San Giorgi, Italy). Raman spectroscopic analyses detected H2 gas in the vapor phase of the fluid inclusions and a defect-rich fluorite structure in violet to black colored growth zones. This unique phenomenon is assumed to be the result of interaction between the uranium-rich phosphorite and the parent fluids of the epigenetic fluorite veins.

Lake Velence is a shallow soda lake whose water level and water quality show a severely deteriorating tendency in recent years. Until recently, the groundwater component in the lake’s water budget has not been taken into consideration. To investigate if the lake has any connection with groundwater and to integrate it into the groundwater flow system, methods of ‘basin hydraulics’ were applied i. e. pressure elevation profiles and tomographic potential maps were compiled. Besides 17 water samples were collected for δ2H and δ18O, and for 234U+238U, 226Ra, and 222Rn activity measurements to use these parameters as environmental tracers of groundwater contribution. Results of on-site measurements (i. e. temperature, pH, specific electronic conductivity, redox-potential) and water chemistry analysis revealed that groundwater samples taken from the concerned Pannonian-Quaternary siliciclastic aquifer system are rather uniform. Neither hierarchically nested groundwater flow systems nor any interconnection between groundwater and Lake Velence could certainly be identified. However, based on the stable isotope measurements, two groundwater groups can be distinguished. The more depleted δ values (δ2H up to -98.4 and δ18O up to -13.27) indicate older groundwater or the proximity of the discharge area. Less negative δ2H and δ18O composition (δ2H up to -86.0 and δ18O up to -11.88) and variability of the δ values among other groundwater samples indicate direct recharge from precipitation in today’s climate. Among the measured radionuclides, uranium was measured in the highest activity concentration (up to 487 mBq L−1) in correspondence with the recharge areas in the Bika Valley south of Lake Velence. The lake itself has also high uranium activity (392 mBq L−1). Groundwater mapping revealed that groundwater recharges in Velence Hills and in the local elevations south of the lake, whereas discharge occurs by the lake’s shoreline and along surface watercourses. The results indicated that Lake Velence is an integrated part of the groundwater flow system and is fed by local flow systems known to be more sensitive for climate changes and anthropogenic activities (e. g. contamination, overexploitation). Groundwater and lake water have similar uranium activity concentrations serving as another sign of groundwater inflow into the lake. Therefore, it is necessary to consider both the groundwater component in the lake’s water management and its vulnerability regarding local and short-term changes in the catchment area. This study was supported by the ÚNKP-17-4-III-ELTE-73 New National Excellence Program of the Ministry of Human Capacities and by the project that has received funding from the European Union’s Horizon 2020 research and innovation programme under grant agreement No 810980.

The ‘Dynamic System Approach for Geofluids and their Resources’ was developed to harmonize research and the sustainable exploration of geofluids (e.g., groundwater, geothermal and hydrothermal fluids) and the related geo-resources (groundwater, geothermal energy and hydrothermal minerals). The conception is based on the basin-scale groundwater flow systems, which behave as a geologic agent, mobilize, transport and deposit matter and heat, whilst it can be evaluated quantitatively and in a distributed manner. Evaluation of these systems combined, for instance, with numerical, stochastic and isotope methods can jointly manage all types of geofluids, the related resources and the environmental consequences of their exploration and utilization. This paper describes the fundamental concepts of the approach and displays the proposed workflow and guidelines for practical applications such as groundwater vulnerability assessment, managed aquifer recharge, geothermal energy utilization, and the evaluation of hydrothermal mineral potential.

This study proposes a concept and presents a workflow to examine potential reasons for low injectivity of sandstone aquifers. Injection related problems are a major challenge for the sustainable utilization of geothermal waters. In order to completely understand and avoid the geothermal reinjection problems, potential problem sources acting on different scales should be taken into consideration. Thus, in the workflow, possible problem sources are considered on regional, reservoir and local scale and categorized into 1) effect of regional hydraulics (potential presence of overpressure and upward flow) 2) inadequate reservoir performance (limited extent, low permeability and performance) and 3) local clogging processes (particle migration, mineral precipitation, microbial activity). Hydraulic conditions are characterized by defining the pressure regime and the direction of vertical driving forces. The reservoir properties are given by determining the grain size and the size of the reservoir layers, as well as the permeability and the transmissivity of the reservoir and the capacity of the injector. Physical, chemical, and biological clogging processes are investigated by specifying the rock properties and determining particle content of the fluid; by analysing the type, probability and amount of the scaling and estimating the potential for corrosion; and by evaluating the possibility of biofilm formation. The concept and the workflow were first tested on a geothermal site (Mezőberény, SE Hungary, installed in 2012) that had to stop operation because of unsuccessful reinjection. The low injectivity of the well is a consequence of several separate problems and their interaction: Reservoir properties are insufficient due to low permeability and transmissivity of the reservoir and the limited vertical and horizontal extension of the sandstone bodies. Precipitation of car-bonates, iron and manganese minerals is predicted in hydrogeochemical models and observed in solid phase analysis. Microbial material is produced from the particularly high organic content of the produced thermal water. Injection problems due to hydraulic effects are not expected since the regional pressure regime is slightly subhydrostatic. In summary, reservoir properties determine a low injectivity, which is further decreased to a critical level by the clogging processes. The proposed generalized concept guides a detailed reservoir and geothermal system analysis which is essential for a sustainable geothermal operation.

Reinjection of thermal waters is a key parameter for sustainability of geothermal systems. However, injection can face difficulties due to several factors, e.g. mineral precipitation, fines migration or biological processes, especially in case of clastic reservoirs. These processes can clog the well screens and the pores of the reservoir, which can result in the decrease of injectivity. Mineral precipitation, which is the focus of this paper, is controlled by hydrochemical and physical changes. In this study, we focus on injection problems at the geothermal site in Mezőberény, SE Hungary. A geochemical model was set up to simulate the geothermal reinjection processes and to model the saturation of the minerals during injection, using changing parameters: fluid composition, rock composition, air contact, injection temperature and injection pressure. For hydrochemical modelling we use PHREEQC Version 3 with the phreeqc.dat database. Based on the results general and site-specific conclusions could be drawn: In general, high concentrations of Fe and Mn content play a role at the injection problems at the Mezőberény site through precipitation of goethite, hematite and Mn-oxides. Furthermore, calcite is also oversaturated, therefore able to form carbonate-scaling. The geochemical model was validated with XRD analysis performed on scale samples from the Mezőberény site: precipitation contains goethite, calcite and magnesioferrite, which confirms our model. Our findings include that air contact radically increases the saturation of Mn minerals, slightly enhance saturation of Fe minerals and decreases the saturation indices of carbonates. Lower injection temperature enhances the saturation of Fe-Mn mineral, in contrast to carbonates. Injection pressure has a negligible effect on the saturation of minerals. The reinjection of heat depleted thermal water into sandstones has a relatively short history in Hungary. With two decades of experience and several successful projects in SE Hungary (Orosháza, Hódmezővásárhely, Szeged), reinjection is successful. Compared with these geothermal systems, saturation indices and the amount of possible precipitation are higher at Mezőberény. By preventing contact with air, iron and manganese minerals would be less saturated and the possibility of precipitation would decrease.

Fluid injection into overpressured regimes is only possible with an injection pressure higher than the aquifer pressure. The elevated aquifer pressure eventually prevents fluid inflow through reinjection. Elevated pressure (much higher than hydrostatic) in an aquifer under exploitation, however, can also evolve naturally due to overpressure dissipation from underlying units. The suggested basin-scale hydraulic evaluation complements the traditional geothermal potential and risk analysis. A pressure-regime analysis can be also used to estimate the injection capacity and reinjection problems. As a case study, we evaluated the hydraulic conditions surrounding the Mezőberény doublet system (40x50 km in SE Hungary). This site faces reinjection problems since 2012, which resulted in stopping geothermal production. The overpressure was assumed to be among the potential reasons for reinjection problems at that site. The analysis was carried out by 1) analyzing the properties of the underlying aquitard unit, 2) defining the pressure regime and the vertical driving forces, 3) modelling the influence of the overpressure on the hydraulic conditions of the reservoir, 4) evaluating the temperature state, 5) characterizing the water chemistry. Results show that overpressure is present in the underlying units beneath the reservoir with extreme pressure values, dynamic pressure increments (e.g. Δp=11.21 MPa) and superhydrostatic pressure-gradient (indicating ascending flow). Moreover, in the wider study area, the overpressure is likely dissipating into the aquifer indicated by positive dynamic pressure increments (Δp=0.77 MPa and Δp=0.14 MPa) and superhydrostatic pressure gradient (y=11.43 MPa/km). However, at the closer surrounding of the study system, this effect could not be observed: neither the pressure regime nor is the vertical pressure gradient (9.7 MPa/km) superhydrostatic within the reservoir. The reason can be that-based on seismic and well data-the underlying aquitard units are thick and continuous below the study site. Thus, the dissipation of overpressure by vertical leakage through aquitards is likely blocked by them. This is supported by the numerical modelling which suggests hydrostatic conditions at the study site. The numerlical modelling also showed the possible presence of elevated hydraulic heads in the reservoir due to overpressure beneath the aquifer in case of thinned aquitard and/or conduit fault. Consequently, injection problems due to an overpressured regime is not expected close to the well of Mezőberény. However, based on the results, this effect is proposed to be considered in the farther part of the study area as well as in other overpressured regions. We also propose to take hydraulic conditions into consideration and to apply the approaches of this study during geothermal exploration, risk and problem analyses.

This study proposes a concept and presents a workflow to examine potential reasons for low injectivity of sandstone aquifers. Injection related problems are a major challenge for the sustainable utilization of geothermal waters. In order to completely understand and avoid the geothermal reinjection problems, potential problem sources acting on different scales should be taken into consideration. Thus, in the workflow, possible problem sources are considered on regional, reservoir and local scale and categorized into 1) effect of regional hydraulics (potential presence of overpressure and upward flow) 2) inadequate reservoir performance (limited extent, low permeability and performance) and 3) local clogging processes (particle migration, mineral precipitation, microbial activity). Hydraulic conditions are characterized by defining the pressure regime and the direction of vertical driving forces. The reservoir properties are given by determining the grain size and the size of the reservoir layers, as well as the permeability and the transmissivity of the reservoir and the capacity of the injector. Physical, chemical, and biological clogging processes are investigated by specifying the rock properties and determining particle content of the fluid; by analysing the type, probability and amount of the scaling and estimating the potential for corrosion; and by evaluating the possibility of biofilm formation. The concept and the workflow were first tested on a geothermal site (Mezőberény, SE Hungary, installed in 2012) that had to stop operation because of unsuccessful reinjection. The low injectivity of the well is a consequence of several separate problems and their interaction: Reservoir properties are insufficient due to low permeability and transmissivity of the reservoir and the limited vertical and horizontal extension of the sandstone bodies. Precipitation of car-bonates, iron and manganese minerals is predicted in hydrogeochemical models and observed in solid phase analysis. Microbial material is produced from the particularly high organic content of the produced thermal water. Injection problems due to hydraulic effects are not expected since the regional pressure regime is slightly subhydrostatic. In summary, reservoir properties determine a low injectivity, which is further decreased to a critical level by the clogging processes. The proposed generalized concept guides a detailed reservoir and geothermal system analysis which is essential for a sustainable geothermal operation.

Wood Buffalo National Park (WBNP), the largest national park of Canada, has unique and complex ecosystems that depend on specific water quantity and quality. We characterize groundwa�ters and surface waters in WBNP by determining their chemical compositions and water types, the dominant hydrochemical processes affecting their compositions, and their hydrochemical character�istics in relation to interpreted groundwater flow systems. Total Dissolved Solid concentrations in groundwaters and surface waters range from ≤10 mg/L to ≥300,000 mg/L. Four distinct water type groups are found: (1) Ca-SO4 -type waters occur in multiple clusters across the area in outcrop areas of Devonian evaporites; (2) Na-Cl-type waters predominantly occur in the Salt plains region along the central eastern boundary, overlapping evaporite and carbonate-dominated bedrock formations; (3) Ca-HCO3 -type waters dominate the Peace-Athabasca Delta-region in the south and most of the central region; and (4) “mixed” waters. Solutes in the waters originate from three main processes: dissolution of halite, dissolution of sulphate minerals, and dissolution of carbonates. The spatial occurrence of hydrochemical characteristics correlate with hypothesized groundwater flow systems, i.e., Ca-SO4 and Na-Cl-type waters coincide with discharge areas of intermediate to regional ground�water flow paths, and Ca-HCO3 -type waters overlap with recharge areas. The findings of this study contribute to advancing knowledge on the hydrochemical characteristics of this remote and highly protected region of Alberta, Canada, and are important components of any further, comprehensive assessment of the natural water conditions.

Salinization of groundwater has endangered e.g. drinking water supply, agricultural cultivation, groundwater-dependent ecosystems, geothermal energy supply, thermal and hydrocarbon well production to a rising degree. In order to investigate the problem of coupled topography- and salinity-driven groundwater flow on a basin-scale, a systematic simulation set has been carried out in a synthetic numerical model. Detailed sensitivity analysis was completed to reveal the effect of the salinity, permeability, permeability heterogeneity and anisotropy, mechanical dispersivity and water table head on the salt concentration field and the flow pattern. It was established that a saline dome with slow inner convection formed beneath the discharge zone in the base model due to the topography-driven regional fresh groundwater flow. An increase in the salinity or the anisotropy or decrease in the water table variation weakens the role of the forced convection driven by the topography, thus facilitating the formation of a saline, dense, sluggish layer in the deepest zone of the basin. In the studied parameter range, the variation in permeability and dispersivity affects the shape of the saltwater dome to less degree. However, the decrease in permeability and/or the increase in dispersivity advantage the homogenization of the salt concentration within the saline zone and strengthen the coupling between the saltwater and freshwater zone by growing the relative role of diffusion and transverse dispersion, respectively. The interaction of the topography-driven forced and salinity driven free convection was investigated along a real hydrological section in Hungary. Simulation elucidated the fresh, brackish and saline character of the water sampled the different hydrostratigraphic units by revealing the connection between the topography-driven upper siliciclastic aquifer and the lower confined karstic aquifer through faults in high-salinity clayey aquitard. The current study improves the understanding of the interaction between the topography-driven forced and the salinity-driven free convection, i.e. topohaline convection, especially in basin-scale groundwater flow systems.

Groundwater is an important freshwater resource, which can be affected by geogenic radionuclide contamination. To make decisions regarding the use and management of groundwater, understanding the controls of radionuclide mobility is critical. In the southern foreland of a granitic outcrop in Hungary, high gross alpha activity concentration was measured in drinking water wells, related probably to the presence of uranium. It has been suggested that understanding of the groundwater flow system may be a key aspect to understand uranium mobility in groundwater. The goal of the present work was to elucidate the conceptual model of radionuclide mobility in the study area, focusing in particular on the geochemical controls of uranium. For this purpose, water samples were collected and nuclide-specific measurements for ²²⁶Ra and radon isotopes were carried out, in addition to ²³⁴U+²³⁸U measurements, to increase the range of radionuclides and better understand their mobility. A geochemical modeling analysis involving redox-controlling kinetic reactions and a surface complexation model was developed to support the conceptual model. The results from the sampling indicate that excess of ²³⁴U+²³⁸U (3–753 mBq L⁻¹) contribute to the natural radioactivity measured in drinking water to a large degree. ²²⁶Ra was measured in relatively low activity concentrations (<5–63 mBq L⁻¹) with the exception of three specific wells. Notable radon activity concentration was measured in the springwaters from Velence Hills (1.01–3.14 × 10⁵ mBq L⁻¹) and in interrelation with the highest (285–695 mBq L⁻¹) ²²⁶Ra activity concentrations. The geochemical model suggests that uranium distribution is sensitive to redox changes in the aquifer. Its mobility in groundwater depends on the residence time of groundwater compared to the reaction time controlling the consumption of oxidizing species. The longer the flow path from the recharge point to an observation point where U is measured, the more likely it is that reducing conditions will be found in the aquifer and the elemental concentration U will be low.

The delineation of hydrostratigraphic units depends on the hydraulic conductivity of major rock bodies , which are a complex patchwork of sandstones embedded in muddy lithologies in a fluvio-deltaic system. Hydraulic conductivity primarily depends on the sand/shale ratio,the spatial distribution, both the lateral and vertical connectivity of sandstones. The purpose of this study is to develop a novel method for determination of sand ratios, leading to the hydrostratigraphic classification of the uppermost ca. 1800 m thick Late Neogene Pannonian basin-fill succession. The study area extends over 2000 km 2 in the Pannonian basin, Eastern Hungary. Five combined 3D seismic cubes covering the area, seven master horizons, and 29 well logs were analyzed. First,RMS amplitude maps were elaborated. Their purpose was to investigate the seismic geomorphological features , their associated lithology and depositional architecture. Sand,mud,and heterogeneous muddy-sandy units were determined from the wireline logs (GR and SP) by calculating the shale volume and sand thickness (net-to-gross) for 30 m thick intervals. These values characterize the vertical variations of sand/shale ratios and calibrates the seismic attribute maps. This method allowed the identification of sand bodies, i.e. deltaic lobes, fluvial channels, channel belts,and muddy flood plains. The sequence starts with deltaic lobes characterized by high sand ratios.The overlying fluvial succession is divided into three units. 1)a meandering system of 500-3600 m wide channel belts, with a high sand % and large connectedness, particularly in the NE-SW direction; 2)an anastomosing system, characterized by 100-200 m wide channels, with lower sand% and limited connectedness; 3)a young meandering sytem with high sand ratios. Hydraulic conductivity values were provided for the above large intervals based on the abundance,percentages,and connectivity of sand bodies, determined by the varying paleohydrography. Subsequently, the former single unit was decomposed into 4 hydro-stratigraphical units characterized by hydraulic conductivity values,allowing the modelling of the basinal fluid flow. Acknowledgements O&GD Central kindly provided seismic and well data. Financial support was provided by the EN-eRAG project that has received funding from H2020 under agreement No 810980.

A Duna-Tisza közi Homokhátság területén, számos helyen jelentősen csökkent a felszínalatti vízszint különböző emberi tevékenységek és a klímaváltozás hatására (pl. Major és Neppel 1988, Pálfai 1995, Ladányi et al. 2009, Kovács et al. 2017). A kutatás célja a települési tetővizek sekély kutakon keresztül történő felszín alá juttatási lehetőségének vizsgálata lokális léptékben, amely hozzájárulhat a terület vízhiányának enyhítéséhez. 2020 januárjában, terepi kísérlet keretében, egy családi ház tetőszerkezetéről bevezetésre került a csapadékvíz az udvaron található ásott kútba. A víz egy szűrőn halad keresztül, mielőtt bekerülne a tetőről a csőrendszerbe. Az ásott kútban, valamint az áramlási irányban létesített két új megfigyelőkútban a vízszintet, a hőmérsékletet és a fajlagos elektromos vezetőképességet félóránként automata mérőműszerek rögzítik. A csapadék mennyiségét helyi észlelő méri naponta. Az így kapott idősoradatok, valamint a kutakból származó vízminták laboratóriumi elemzései (főelemek, nyomelemek, izotópok) lehetővé tették a bevezetett csapadékvíz hatásának vizsgálatát a felszínalatti víz szintjére és minőségére. A mérési adatok alapján felépített tranziens vízáramlási modell segíti a felszín alatt lejátszódó folyamatok megértését. A kapott eredmények alapján megismerhetők a tetővíz sekély kútba juttatásának környezeti hatásai, lehetővé téve nagyobb léptékű modellezési tanulmányok elvégzését. Ez hozzájárul hasonló rendszerek települési és regionális szintű kiterjesztéséhez. A kutatás az ENeRAG projekt részét képezi, amelyet az Európai Unió Horizont 2020 kutatási és innovációs programja támogatott, a 810980 azonosító számú támogatási megállapodás alapján. Kovács, A. D., Hoyk, E., Farkas, J. Z. (2017). Homokhátság–A semi-arid region facing with complex problems in the Carpathian Basin. European Countryside, 9(1), 29-50. Ladányi, Z., Rakonczai, J., Kovács, F., Geiger, J., Deák, J. Á. (2009). The Effect of Recent Climatic Change on the Great Hungarian Plain. Cereal Research Communications, 37, 477-480. Major, P., Neppel, F. (1988). A Duna-Tisza közi talajvízszint-süllyedések. Vízügyi Közlemények, 70(4), 605-623. Pálfai, I. (1995). A Duna-Tisza közi hátság vízgazdálkodási problémái és megoldásuk lehetséges útjai. Vízügyi Közlemények, 77(2), 144-165.

Climate change, along with the rapid increase in population and mismanagement of water resources, resulted in a decline in the quality and quantity of groundwater worldwide. Balochistan, the largest and driest province of Pakistan, is located in the south western part of the country. This region is suffering from the declining water table, land subsidence, and intense soil erosion. Rapidly increasing population, sea level rise, increasing temperature, declining average annual precipitation, and short-duration intense rainfalls with reduced percolation rates are further aggravating the situation. Managed Aquifer Recharge (MAR) is considered as a solution to reduce the stress on groundwater resources and achieve resilience to climate change. Creating a MAR suitability map may be one of the steps to be taken to reach sustainable groundwater management. This study produced the first MAR suitability map of the Quetta Valley, the most densely populated city of Balochistan, and Poralai and Hingol coastal basins suffering from seawater intrusion. To construct the MAR suitability map, the online INOWAS platform was first used to narrow down the suitable MAR options. Then, the six influencing factors including geology, slope, land-cover, precipitation, drainage density, and soil were identified, and the raster map of each factor was scored and weighted using GIS tools and the Multi Influencing Factor (MIF) method. All the factors were integrated according to their weight by using the ‘Weighted Overlay Analysis’ tool and the Multi-Criteria Decision Analysis (GIS-MCDA) in ArcGIS to produce the final MAR suitability map. The suitability map divided the study area into high, moderate, low, and very low suitability classes. The results depict that 80% of Poralai Basin, 10% of Hingol Basin and less than 5% of Quetta Valley falls in the high MAR suitability zone especially for trenches, ditches, furrows, and leaky dams. The first MAR suitability map for the basins of Balochistan can serve as the guidance and screening tool to focus site specific studies for highly suitable areas for MAR implementation. In the following phase of the study, an analysis of source, quality, and final use of water can serve to design and develop the specific MAR structures according to local conditions and needs. The displayed method is applicable to further MAR suitability studies for other arid-semiarid regions.

The Danube-Tisza Interfluve is one of the largest areas covered by wind-blown sand in Hungary characterized by sand plains, dunes and deflationary depressions. Two major morphologic region types are the flat-bottomed valleys of the Danube and Tisza rivers and a central elevated ridge region. The ridge area is poor in surface waters. Previously many lakes were present here, but most of them dried out due to climate change, water abstraction, forestation and canalization related water level reduction. In the past, several replenishment plans have been made, involving large, cross-regional technical investments, but have not been implemented due to the lack of adequate financial resources and environmental concerns. The main aim of this research was to compare the possibilities of different Managed Aquifer Recharge methods, in the context of the local topographical, geological and hydrogeological conditions of the Danube-Tisza Interfluve, studying a characteristic area, to increase the resilience of water reserves of this ecologically important area. Firstly, a MAR surface infiltration suitability map was constructed, that shows areas with favourable hydraulic conductivity in the upper 10 m and characterized by deeper water levels, which means that there is a reservoir in the unsaturated zone to store infiltrated water. Based on suitability mapping, a local research area was selected which showed promising potential. Geophysical measurements (ERT – Electrical Resistivity Tomography, RMT – Radio-magnetotellurics) were performed, existing shallow wells were surveyed and additional boreholes were drilled to characterize shallow hydrogeological conditions. Finally, a saturated-unsaturated flow model and different scenario models were built up in 2D, in order to analyse different Managed Aquifer Recharge possibilities (infiltration basin, shallow and deeper wells) and their effectivity considering the topographical conditions and geological-hydrogeological built-up. The results of the different model scenarios can provide a good basis for planning further water replenishment plans and selecting appropriate MAR methods for the area. This research is part of a project that has received funding from the European Union's Horizon 2020 research and innovation programme under grant agreement No 810980.

The undulation of topography and the groundwater table serves as a driving force of fluid flow not only in mountainous or volcanic regions but also in sedimentary basins. Since topographical variations do exist at any part of the continental lithosphere, the existence of regional-scale groundwater flow systems and their role in the formation of heat accumulations need to be considered. A numerical simulation series was performed on a wide range of synthetic groundwater basins with topographical driving forces of groundwater flow to reveal the effects of various geometric and geologic parameters and agents, such as anisotropy of hydraulic conductivity, surface undulation, sedimentary basin fill and temperature gradient. Our results showed that in identical basin-halves, exactly the same flow pattern develops and there is no flow from one part to the other. However, this ideal situation is not the case in real groundwater basins. Groundwater flows from one basin(−part) to another described as interbasin flow, a general form of basin interplay. This process is a direct consequence of basin geometry since waters enter a territory of another flow system due to the differences in driving forces and/or geographic position. At the convergence of opposing flow systems under a discharge area, quasi-stagnant zones and hydraulic traps may develop and support heat accumulation. Furthermore, groundwater flow systems and their carrier fluids provide a continuous natural replenishment of geothermal systems. Mountain-block recharge (a form of basin interplay) is essentially the subsurface groundwater contribution from a topographically elevated area to the adjoining lowland sedimentary aquifers. The role of mountain-block recharge is relevant and important in maintaining groundwater flow systems and related heat accumulation in the basin fill part of an area. Thus, the rejuvenation of a geothermal system is provided by natural topography-driven regional groundwater flow both on a human and a

Almost 100% of worldwide geothermal development is related to convection dominated geothermal plays, such as volcanic, plutonic, and extensional domain types. In these geothermal systems, heat transport mechanisms are strongly controlled by subsurface fluid flow, which transfers heat and modifies the temperature distribution. On the other hand, concerning sustainability and longevity of geothermal systems, reinjection can provide a solution for prolonging their operation, however, natural groundwater flow systems are an integral part of geothermal systems as they sustain groundwater replenishment and convective heat transport. Consequently, investigation of a geothermal play and its extended surrounding area must involve an analysis of its basin-scale groundwater flow systems. A numerical simulation series was performed on a wide range of synthetic groundwater basins, which can be considered as simplified representations of a selection of real systems. The aim was to reveal the effects of various geometric and geologic parameters and agents, such as anisotropy of hydraulic conductivity, surface undulation, sedimentary basin fill and temperature gradient on heat accumulation, location of thermal spring discharge and prevailing mechanisms of heat transfer. Our simulation results showed that in the absence of thermal springs, the extent of the thermal water reservoir might be larger, and the temperatures might be higher. Sedimentary basin fill fosters the formation of heat accumulation under and within this unit, but its extent, i.e. half or full, had an insignificant influence on the temperature pattern. We introduced as a new "parameter" in basin-scale groundwater and geothermal studies, basin asymmetry, which plays a critical role in discharge and accumulation patterns, thereby controlling the location of parts of the basin that have the highest geothermal potential. So, if thermal water can reach the ground surface, the discharge might not take place exactly above the thermal water reservoir due to the asymmetric driving forces of groundwater flow. Furthermore, the extent and temperature of thermal water reservoirs are also influenced by local-scale anisotropy, heterogeneities, as faults, fault zones and fractures, and, of course, basal heat flux. Therefore, the application of basin-scale models in a preliminary geothermal potential assessment would be beneficial for understanding heat distribution. The results also have further implications on the interplay between basin-parts and the rejuvenation of geothermal resources. A conceptual, generalized and simplified model of groundwater flow and heat transport can support the identification of prospective areas. The preliminary numerical interpretation of the influencing factors also provides a good starting point for realistic 3D models for planning of shallow and deep geothermal energy utilization, concerning reinjection possibilities as well.

Hydrostratigraphic divisions are based on the hydraulic conductivity of the rock bodies, which depends primarily on their extent, i.e. the thickness, the spatial distribution, and both the lateral and vertical connectivity of sand-rock bodies are embedded in various muddy lithologies. The purpose of this study is to determine the hydrostratigraphic classification within the Late Neogene Pannonian basin-fill succession in Hungary. To proceed, we are going to build the 3D lithological model for the upper-most part of succession, that will be transformed later into hydrostratigraphic units and hydraulic conductivity values. The stratigraphic architecture of deltaic and fluvial sand lithologies can be identified from seismic and well data. The depositional environments have shown a change from deltaic to fluvial and within the fluvial system itself. It alternates between meandering and anastomosing river channels. In the Pannonian basin, Eastern Hungary, 2000 km2 of merged 3D seismic cubes covering the study area, 7 master horizons, and 237 well logging suites were analyzed, and several attribute maps were generated (e.g. dominant frequency, Root Mean Square amplitude, coherency, similarity variance). The purpose of the maps is the investigation of seismic geomorphological features and their associated depositional environments. The wireline logs (gamma, spontaneous potential, and resistivity) were interpreted simply in terms of sand, mud, and heterolithic muddy-sand, and finally were tied to the seismic cube. The lithology of rock bodies could be determined from the interpretation of well data; an average lithology for 200 m intervals in the late Neogene-Quaternary succession was generated from the Volume of shale calculated. With this method, we could identify sandy deltaic lobes, sandy fluvial channel belts, and muddy flood plains. Based on the abundance of the sand bodies, percentages of sand vs clay (net-to-gross; N/G), as well as connectivity percentages of sand, were determined. The fluvial depositional setting, situated above the deltaic succession, can be divided into three units. These units start with a meandering fluvial system, characterized by 500-3600 m wide channel belts and a high N/G. Further above, in the 350 m thick Pliocene sequence, a transition into an anastomosing river system is identified. This unit is characterized by channels about 100-200 m wide, with relatively lower N/G ratios and less connectedness. In the uppermost part of the succession, large meandering channel belts reappear to the area. All these changes in river style and paleo-hydrography affect the sand and clay ratio and their connectivity; accordingly, a new hydrostratigraphic units’ decomposition of the succession is under process. The diffusion of these results is supported by the ENeRAG project funded by the European Union’s Horizon 2020 research and innovation program under grant agreement No 810980.

In the Duna-Tisza Interfluve area, groundwater levels have declined significantly in the last decades, due to anthropogenic activities and climate change. The aim of this study is to demonstrate a local scale solution by experimental research in Kerekegyháza, which could contribute to easing the water shortage of the area. Rooftop rainwater harvesting coupled with shallow well infiltration was selected as a method due to its easy and relatively inexpensive implementation and operation. In addition, rainwater is the only adequate source of recharge water at the study area and unused dug wells are readily available. In the beginning of 2020, a field experiment was set up leading rainwater from the roof of a family house to the dug well in the yard. The water passes through a filter mesh before it enters the tube system leading it to the well. Water level, temperature and specific electrical conductivity is recorded every half hour in the dug well and in two newly established observation wells. Water samples are taken for laboratory measurements. Precipitation is measured on a daily basis. Efficiency was estimated by comparing water level changes after precipitation events with the amount of precipitation falling to the rooftop. Furthermore, long-term water level, hydrochemical and isotopic changes, as well as temperature changes were analyzed to determine the physicochemical effects of injected water on the ambient groundwater. Moreover, a transient numerical flow model was built to understand the occurring underground processes and assess the potential of rooftop rainwater harvesting with different scenarios. The obtained results can help to understand the effects of rainwater harvesting through shallow well infiltration to follow its effect below the surface, provide background information for further numerical simulations and contribute to expanding the design of similar systems on settlement and regional level in the Duna-Tisza Interfluve.

In the Duna-Tisza Interfluve area, groundwater levels have declined significantly in the last decades, due to anthropogenic activities (e.g. water abstraction, canalization, and forestation) and climate change. In the past, several replenishment plans have been prepared, involving large, cross-regional technical investments, but have not been implemented due to the lack of adequate financial resources and environmental concerns. The aim of this study is to demonstrate a local scale solution by experimental research, which has several environmental and economic benefits and could contribute to ease the water shortage of the area. Three approaches were used during the experimental research: (i) on-site field observations and measurements, (ii) time series analyses of the monitored data and (iii) transient numerical simulations to understand on-site processes. A field experiment was set up to lead rainwater from the roof of a family house to the dug well in the yard. Furthermore, two observation wells were established where the water level, temperature and electrical conductivity were recorded every half hour. Water samples were taken from the dug well and the monitoring wells for laboratory measurements. Precipitation was measured on a daily basis. The effects of shallow water injection on water level and water quality have been monitored for a year and the project is planned to be continued for at least one more year. In the second step, geomathematical methods have been applied to analyze time-series data and assess the effects of injected water on water levels and water quality. Moreover, a transient MODFLOW model was built (i) to evaluate the impact of the injected roof water on the groundwater level, (ii) to separate the influence of natural infiltration from the injected water, and (iii) to better understand the seasonal differences related to artificial and natural infiltration processes. The obtained results can help to understand the effects of rainwater harvesting through shallow well infiltration, provide background information for further numerical simulations and contribute to expand the design of similar systems on settlement and regional level. In the Duna-Tisza Interfluve, rooftop rainwater harvesting and Managed Aquifer Recharge can be effective tools for climate change adaptation and increasing groundwater resilience.

In the Duna-Tisza Interfluve area, groundwater levels have declined significantly in the last decades, due to anthropogenic activities and climate change. The aim of this study is to demonstrate a local scale solution by experimental research, which could contribute to ease the water shortage of the area. A field experiment was set up leading rainwater from the roof of a family house to the dug well in the yard. Water level, temperature and specific electrical conductivity was recorded every half hour in the dug well and in two newly established observation wells. Water samples were taken for laboratory measurements. Precipitation was measured on a daily basis. The obtained data was analyized to assess the effects of injected water on water levels and water quality. Moreover, a transient MODFLOW model was built to understand the occurring underground processes. The obtained results can help to understand the effects of rainwater harvesting through shallow well infiltration, provide background information for further numerical simulations and contribute to expand the design of similar systems on settlement and regional level.

Groundwater flow can be generated by several driving forces including gravity. While gravity is the most common force, overpressure due to tectonic compaction or compression, underpressure, or variable density can also have an important effect. In large sedimentary basins, numerous driving forces can often influence groundwater movement, resulting in a complex system. Understanding the effects behind groundwater flow, and knowledge of the distribution of different flow regimes are necessary in any groundwater-related scientific or practical problem. Numerical modelling is a useful tool to recognize and distinguish between the different driving forces. In addition, the geological history of the area is a key factor in determining the pressure, temperature and chemical conditions, which have influenced the formation and distribution of flow systems. The Danube-Tisza Interfluve area, Hungary, was chosen as a study area to investigate the complex effects of various possible driving forces in a porous basin. The area has been very well studied over the past thirty years based on hydraulic data analysis. The presence of a shallow, hydrostatic system and a deep overpressured regime have already been identified. In addition, under favorable geothermal conditions, the effect of temperature cannot be excluded, but its role has not been studied in detail yet. Based on the geological history of the area and applying the groundwater flow system concept, a detailed numerical modelling study was carried out to identify the role of the main driving forces on the groundwater flow regimes. The detailed modelling study suggested that not only gravity, but compression/compaction and density also influence the current flow paths.

Two-dimensional numerical simulations were carried out in order to elucidate the mechanism of the coupled fluid flow and heat transfer in synthetic and real groundwater flow (GWF) basins. Based on a theoretical concept, effects of geothermal gradient, regional relief, model depth and anisotropy of hydraulic conductivity were investigated on groundwater flow pattern and temperature field. Using the thermal Rayleigh and the modified Péclet number, the role of heat advection and thermal buoyancy was separated in GWF system. The thermally driven free convection is facilitated by higher geothermal gradient and greater model depth, while increasing regional relief and anisotropy intensify the effect of forced, water table-controlled convection. Such a theoretical approach has been applied in hydrogeology modelling; therefore, it was demonstrated for the Buda Thermal Karst (BTK), Hungary. Three main types of heat transport phenomena (heat conduction, advection, thermal buoyancy) were examined to highlight the role of different driving forces of GWF. The Nusselt number and the recharge rate were used to confirm the numerical method, and to reveal the dominant driving force. Although the radiogenic heat production and the hydraulically conductive faults have only a minor influence on basin-scale GWF system, boundary conditions applied for fluid flow and heat transfer significantly affect the numerical results. The results from numerical simulations were compared with the available temperature data. In each scenario, time-dependent mixed thermal convection evolved in the thick, karstified Triassic carbonates of the BTK.

In the last decades, geologists recognized that the solid framework of the crust evolves through interactions with geologic fluids. Geofluids play an essential role in all geologic processes, such as the mobilization, transportation, and accumulation of matter and heat. Driving forces of regional fluid flow, like topography, tectonic compression, compaction, erosion, buoyancy, can operate together on a geological time scale. The permeability of the rocks may be able to maintain the fluid potential differences, thus enabling the flow systems to operate for even up to 10 million years. In addition, the fluid flow systems determine the evolution of the geological resources, such as groundwater, hydrothermal mineral and geothermal resources, and hydrocarbons. Moreover, they influence the consequences of human impacts on the environment, and their mitigation. In this presentation, we focus on some fundamental questions for example: i) How can the term "geofluids" be defined? ii) What are the basic differences regarding the perspective of the specific fields of groundwater, hydrothermal fluids, and hydrocarbon? iii) Why should geologists be encouraged to incorporate flow systems in their research on geofluids? iv) What is the significance of not only acknowledging the existence but also exploring the role of the flow systems in geofluid research? In this interactive presentation, we will attempt to find answers to these questions collectively. We demonstrate that understanding flow systems provides the scientific basis and a practical approach for all areas of geofluid research, from regional to local scale. This approach is used to develop the workflow guideline applied in the ENeRAG focusing on the coordinated exploitation and utilization of different geofluids and geological resources.

Fluid, as an elemental component of a geothermal system, transports and distributes underground heat according to the topographic driving force within a groundwater basin. As the water table configuration has diverse and distinct forms in real-life basins, asymmetric hydraulic head variation may occur from basin to basin in accordance with real physiographic characteristics. Therefore, the effects of an asymmetric water table distribution in groundwater basins were investigated in several model sets with special emphasis on the temperature field and with the help of five response parameters: maximum temperature of outflowing water, average temperature, the portion of the thermal water reservoir, Péclet number and location and extent of thermal water discharge. Our simulation results showed that in the absence of thermal springs, the extent of the thermal water reservoir might be larger and the temperatures might be higher. Sedimentary basin fill fosters the formation of heat accumulation under and within this unit. As a new "parameter" in the basin-scale groundwater and geothermal studies, basin asymmetry was introduced which has a critical role in discharge and accumulation patterns, thus it controls the location of basin parts bearing the highest geothermal potential. So if thermal water can reach the ground surface, the discharge might not take place exactly above the thermal water reservoir due to the asymmetric driving forces of groundwater flow. Furthermore, the extent and temperature of thermal water reservoirs are also influenced by local-scale anisotropy, heterogeneities, i.e. faults, fault zones and fractures, and, of course, basal heat flux. Therefore, the application of asymmetric basin-scale models in preliminary geothermal potential assessment would be beneficial for understanding heat distribution. The results also have further implications on the identification of prospective areas and planning of shallow and deep geothermal energy utilization, the interplay between basin-parts and rejuvenation of geothermal resources.

This study focuses on the stratigraphic architecture of deltaic and fluvial sand lithologies within the Late Neogene Pannonian basin-fill succession in Hungary, identified from seismic and well data, in order to develop a quantitative hydrostratigraphic classification of the sequence. Hydrostratigraphic divisions are based on the hydraulic conductivity of the rock bodies, which depends on their extent, i.e. the thickness and the spatial distribution, as well as the lateral and vertical connectivity of sand bodies embedded in various muddy lithologies. Thus, we are going to build a simplified 3D lithological model for the uppermost 1500 m of the basin fill succession, that can later be transformed into hydrostratigraphic units and hydraulic conductivity values applied in a numerical flow model. The depositional environments change from deltaic to fluvial and within the fluvial system, the environment alternates between meandering and anastomosing. These intervals will appear as different hydrostratigraphic units in the model. In our work-flow, a merged three-dimensional seismic cube covering an area of approximately 50 x 40 km2 was analyzed: 7 master horizons and several proportional slices were delineated in different attribute maps (e.g. amplitude, Root Mean Square amplitude, symmetry, similarity). These maps were generated to investigate the seismic geomorphological features and their associated depositional environments. Rock bodies were defined on the planform geometry of seismic attributes. Basic wireline logs (gamma, spontaneous potential, and resistivity) from 237 wells were interpreted simply in terms of sand, mud, and heterolithic muddy-sand, and finally were tied to the seismic cube. Lithology of rock bodies was determined with the help of well data. With this method, sandy deltaic lobes, sandy fluvial channel belts, and the muddy flood plains were identified. Based on the extension and density of sand bodies, percentages of sand vs clay (net-to-gross; N/G) as well as sand connectivity percentages were determined. Above the deltaic succession, the fluvial depositional setting can be divided into three minor units. These units start with a meandering system, with 500-3600 m wide channel belts and a relatively high N/G. For an interval in the Pliocene about 350 m thick, a transition into an anastomosing river system is observed. This unit is characterized by channels about 100-200 m wide, with significantly lower N/G ratios and less connectedness. In the uppermost part of the succession, large meandering channel belts returned to the area. These changes in river style and paleo-hydrography affect the sand and clay ratio and their connectivity; therefore, definition of previous hydrostratigraphic units must be reconsidered. This research is part of a project that has received funding from the European Union's Horizon 2020 research and innovation program under grant agreement No 810980.

The theoretical examination of the combined effect of heat and mass transfer in porous media is relevant to improve understanding thermohaline natural convection in both local- and basin-scale groundwater flow systems. Numerical model calculations were carried out to investigate the interaction of the temperature- (∆T) and salinity-driven (∆c) natural convection in a synthetic model, as in a two dimensional homogeneous porous medium. Effects of the non-dimensional thermal expansion (α'=α∆T=1E-3–1) and the non-dimensional relative density contrast (β'=β∆c=1E-7–0.1) were systematically studied in order to examine their influence on the temperature, the concentration and the Darcy flux field. Thus, the thermal (Rat) and the haline (Rah) Rayleigh number, and the Buoyancy ratio (BR) were varied within the following ranges: 1.4≤Rat≤1400, 0.1≤Rah≤105, 1E-7≤BR≤100, while the Lewis number was fixed, Le=714. As the results of simulations, the Darcy flux (U), the Nusselt (Nu) and Sherwood numbers (Sh) were computed. In the examined cases, both effects facilitated the onset of natural convection. Depending on the studied parameters (α' and β'), six types of flow systems were separated in the numerical model including: 1) no convection, 2) steady-state haline convection, 3) time-dependent haline convection, 4) forced thermohaline convection, 5) steady-state thermohaline convection, 6) time-dependent thermohaline convection. However, the effect of haline term was strongly influenced by the heat transport mechanism due to the relation between the thermal and the molecular diffusivity (κ>>D0). These simulations draw attention to the importance of understanding the physical background of thermohaline convection, for instance, in aquifers separated by salt domes, in the deep (hypogene) karstified carbonates (e.g. the Buda Thermal Karst), in the case of groundwater flow induced by water pumping/injection of deep geothermal power plants, or in contaminated groundwater transport process.

Quartz from the stockwork zone of various Cyprus type volcanogenic massive sulfide deposits (Boccassuolo, Reppia, Campegli, Bargone and Vigonzano) from the unmetamorphosed, Jurassic Northern Apennine ophiolites was studied in order to provide details on the submarine hydrothermal conditions and the characteristics for ore formation. Our detailed SEM-CL investigation of quartz contributed to a robust characterization and interpretation of primary fluid inclusions and microthermometry data. SEM-CL imaging was also useful for reconstructing the consecutive steps of quartz precipitation. The determination of trace element contents according to growth zon-ing in quartz by LA-ICP-MS constrained the compositional variations of parent fluids during the hydrothermal activity. A continuously cooling fluid regime characterized each studied volcano-genic massive sulfide (VMS) occurrence although the minimum formation temperatures were different (Bargone: 110-270 °C; Boccassuolo: 60-360 °C; Campegli: 110-225 °C; Reppia: 50-205 °C; Vigonzano: 260-330 °C), the range of temperature most probably depends on the original position of sampling in relation to the centers of the hydrothermal systems. Compositional changes are reflected by variations in the methane content (0.13-0.33 mol/kg) and salinity (2.6-9.3 NaCl equiv. wt. %) in the fluid inclusions of quartz and calcite as well as a changeable Al content (11-1526 ppm) in quartz. This study demonstrates that the combined use of SEM-CL imaging and LA-ICP-MS analyses , coupled with fluid inclusion microthermometry, can constrain the different fluid conditions of ore forming and the barren stages of evolving submarine hydrothermal systems.

Study region Buda Thermal Karst system, Hungary. Study focus The pilot area has high geothermal potential characterized by prominent thermal anomalies, such as thermal springs and spas which tap the Triassic carbonate aquifers. Therefore, numerical simulations were carried out to examine the temperature field and flow pattern considering three successive heat transport mechanisms: thermal conduction, forced and mixed thermal convection in order to highlight the role of different driving forces of groundwater flow in the Buda Thermal Karst. New hydrological insights for the region Compared to thermal conduction, topography-driven heat advection increases the surface heat flux. The superimposed effect of free thermal convection facilitates the formation of time-dependent mixed thermal convection from the deep carbonate layers. The Nusselt number varied between Nu = 1.56 and 5.25, while the recharge rate (R) ranged from R = 178 mm/yr to 250 mm/yr. Radiogenic heat production and hydraulically conductive faults have only a minor influence on the basin-scale temperature field and flow pattern. Boundary conditions prescribed on the temperature and pressure can considerably affect the numerical results. In each scenario, independently of the model parameters, time-dependent mixed thermal convection evolved both in the deep and the confined parts of the karstified carbonates of the Buda Thermal Karst system.

The aim of our research is to offer a simple and cost-effective solution to the water management problems of the Danube-Tisza Interfluve, Hungary. In this area, groundwater levels have declined significantly in the last decades, due to climate change and anthropogenic activities. In the past, several replenishment plans have been made, involving large, cross-regional technical investments, but have not been implemented due to the lack of adequate financial resources and environmental concerns. The aim of our research is to prove that local scale solutions, which have several environmental and economic benefits, could contribute to ease the water shortage of the area. A field experiment was set up to lead rainwater from the roof of a family house to the dug well in the yard, and the effects of infiltration on water level and quality are planned to be monitored for a one-year period. The implementation started with cleaning the dug well and the gutters, which were connected by PVC hoses. Furthermore two observation wells were established, where water level, temperature and electrical conductivity were recorded every half hour. Precipitation was measured on a daily basis. Water samples were taken from the dug well for laboratory measurements. Geomathematical methods have been applied to analyze time-series data and assess the effects of recharged water. Moreover, a transient MODFLOW model was built, to evaluate the impact of the infiltrated roof water on the groundwater level, and to separate the influence of the infiltrating rainwater from the surface and the infiltrated roof water to the dug well. The preliminary results are very encouraging. In the first two month the water level increased by 9 cm in the dug well, 20 and 17 cm in the observation wells. The water quality has improved significantly, the TDS, Cl-, SO42- and NO3- content decreased remarkably. Groundwater temperature decreased due to lower winter/spring air temperature. As a result of the modelling, the effect of natural infiltration was found to be higher, however it is overestimated by neglecting the unsaturated zone and the processes therein, and thus further research is needed in this aspect. The results can help to understand shallow subsurface processes, provide background for numerical simulations and contribute to the design of settlement and regional level recharge systems. Rooftop Rainwater Harvesting and Managed Aquifer Recharge can be effective tools for climate change adaptation and increasing groundwater resilience. This research is part of a project that has received funding from the European Union's Horizon 2020 research and innovation programme under grant agreement No 810980.

Extensional domain type geothermal plays, as fertile targets for future resource development, consist of an orogen and an adjoining sedimentary basin of asymmetric physiographic and geologic setting. Preliminary geothermal potential, i.e. prospective geothermal regions, basin-scale flow patterns, heat transfer processes, temperature distribution and appearance of thermal springs were analyzed systematically by numerical simulations in groundwater basins with special emphasis on the effects of basin asymmetry. The importance of basin-scale regional groundwater flow studies in preliminary geothermal potential assessment was demonstrated for synthetic and real-life cases. A simulated series of simplified real systems revealed the effects of anisotropy, asymmetry of the topographical driving force for groundwater flow, basin heterogeneity and basal heat flow on heat accumulation, locations of thermal spring discharge and prevailing mechanisms of heat transfer. As a new aspect in basin-scale groundwater and geothermal studies, basin asymmetry was introduced which has a critical role in discharge and accumulation patterns, thus controlling the location of basin parts bearing the highest geothermal potential. During the reconnaissance phase of geothermal exploration, these conceptual, generalized and simplified groundwater flow and heat transport models can support the identification of prospective areas and planning of shallow and deep geothermal energy utilization, also with respect to reinjection possibilities. Finally, the scope of “geothermal hydrogeology” is defined in a scientific manner for the first time.

Karst aquifers are indispensable, yet vulnerable, resources; therefore, they require a comprehensive protection strategy. Since springs are the terminal points of the karst flow systems, knowledge of their distribution is a key element for the better understanding of groundwater flow, availability and vulnerability. The present study aims to introduce a data-driven analysis by the application of a spatial statistical technique (Weights of Evidence (WofE)) for the evaluation of factors influencing spring distribution in karst areas. A workflow was developed for investigating two questions: where will the springs locate, and where will the permanent springs evolve? This workflow has the potential for application to unconfined karst areas. This enhanced approach was applied to an unconfined transboundary aquifer, the Gömör-Torna Karst (HU and SK). The roles of five factors was statistically investigated: terrain elevation, distance to faults, distance of the carbonate-non-carbonate rock contact, distance to sinkholes, and precipitation distribution. The validation procedures confirmed the effectiveness of the approach. The resulting predictive maps are useful for decision-makers to delineate areas holding potential karst springs and to address water availability problems and protection measures. In addition, the WofE technique improved the comprehension of the geological conditions favourable for the formation of the springs.

Magyarország ivóvízellátásának nagy része felszínalatti vízből származik, melyben előfordulhatnak természetes radionuklidok. Mivel ezek mobilitása erősen függ a geokémiai környezettől, a felszínalatti víz geokémiai paramétereinek ismerete fontos tényező, melyek erősen függnek a felszínalatti víz áramlási rendszereitől. Ezért a hidrogeológiai háttér ismerete elengedhetetlen ezeknek a radionuklidoknak a vizsgálatakor, különösképpen, ha megemelkedett koncentrációban fordulnak elő a felszínalatti vizekben. Kutatásunk során egy partiszűrésű- és karsztos kutakat egyaránt használó vízbázis megemelkedett természetes radioaktivitásának okát vizsgáltuk. Az esetek többségében a területen található felszínalatti vizek összes alfa aktivitása meghaladja a 0,1 Bq/l határértéket. A kutatás célja meghatározni melyik radionuklid felelős a megemelkedett aktivitásért és jelenlétére hidrogeológiai szempontú magyarázatot adni. A kutatás során vett vízminták mindegyikének (U-238+U-234), Ra-226, Rn-222 koncentrációja került meghatározásra. A területen jelen levő megemelkedett urán aktivitás mértéke összefüggésbe hozható a folyó vízszint ingadozásaival, ezáltal a kutatás rávilágít ezen partiszűrésű rendszerek tranziens viselkedésére, melynek figyelembevétele nem elhanyagolható a mintázások és a biztonságos ivóvízellátás kapcsán. A kutatás az Innovációs és Technológiai Minisztérium ÚNKP-19-3 kódszámú Új Nemzeti Kiválóság Programjának szakmai támogatásával készült. In Hungary the drinking water supply is mainly based on groundwater, in which radionuclides are common components. Since the mobility of the most common radionuclides, uranium and radium, is strongly influenced by the geochemical conditions, knowledge on the geochemical parameters of water is required. This depends on the flow system and the flow regime. Therefore, hydrogeology has a crucial role in revealing the origin of elevated activity concentrations. This research presents a case study in Hungary where the drinking water supply is provided by bank filtered and karst wells. In most of the wells of the research area the gross alpha values are above the limit, 0.1 Bq L-1. The aim of this study is to determine which radionuclides may cause the elevated radioactivity and explain their occurrence using the hydrogeological approach. All samples of the study were analysed for (U-238+U-234), Ra-226, Rn-222. The study revealed the correlation between the river water level fluctuation and the uranium content of the wells. The results of this study highlighted the transient nature of river bank filtered systems, which should be taken into account in the monitoring and water supply strategy. Supported by the ÚNKP-19-3 New National Excellence Program of the Ministry for Innovation and Technology.

n Hungary the drinking water supply is mainly based on groundwater from aquifers characterized by different lithology. Riverbank filtered systems represent 40 % of drinking water supply. According to the EURATOM drinking water directive, there are recent regulations in Hungary regarding the natural radioactivity of drinking waters. Based on this, if gross alpha or gross beta radiation exceeds the limit, nuclide-specific measurements are required to be performed by the relevant waterworks. Since the mobility of uranium and radium is strongly influenced by the geochemical conditions, knowledge on the geochemical parameters of water is required. Therefore hydrogeology has a crucial role in revealing the origin of elevated activity concentrations. This research presents a case study in Hungary where the drinking water supply is provided by bank filtered and karst wells. The main aim of this study is to determine which radionuclides may cause the elevated radioactivity and explain their occurrence using hydrogeological approach, considering also the temporal variation of groundwater/surface water ratio. In most of the wells of the research area the gross alpha values are above the screening level, 0.1 Bq L-1. The study revealed the correlation between the river water level fluctuation and the uranium content of the wells. Among the investigated radionuclides, the uranium activity concentrations responded the most to the water level changes of the river and showed systematically higher values during low water conditions. In addition the karst wells showed low activity concentrations. This suggests, that uranium is transported by the groundwater component, and possibly sourced from the fluviatile sediments. The results of this study highlighted the transient nature of river bank filtered systems, which should be taken into account in the monitoring and water supply strategy. Nevertheless, the study emphasizes the importance of considering the dynamics of groundwater and associated geochemical environment in addition to geological factors, when investigating the radioactivity of groundwater or other potential contaminants. This study was supported by the ÚNKP-19-3 New National Excellence Program of the Ministry of Human Capacities. This study is part of a project that has received funding from the European Union’s Horizon 2020 research and innovation programme under grant agreement No 810980.

On geological time scale, different processes take place during the formation of the sedimentary basins in interaction with fluids. Regional groundwater flow has the ability to carry organic matter and several chemical substances on a basin scale, it is also responsible for their areas of accumulation. Thus, the groundwater flow has a direct effect on quality of the groundwater as well as surface water in discharge areas. Therefore, the understanding of the regional groundwater flow systems the driving forces, and adjoining processes may have big support in the knowledge of the locations of hydrocarbon and thermal water accumulations. In this framework, a study of the path of groundwater flow in Ebes-Hajdúszoboszló area, Eastern Hungary (Pannonian basin) was elaborated, where signs for the coexistence of thermal water and hydrocarbon accumulations in the specific area appears. A hydrogeological evaluation of the area was executed based on field measurements and supported by numerical simulation of the regional groundwater flow. Two different methods are used in this study. In the beginning, a basin-scale hydrogeological evaluation of the recent fluid flow condition including archive hydraulic, chemical, borehole temperature data interpretation, and regional pressure field evaluation was carried out. The interpretation of all these data could confirm the superposition of two regimes, an over-pressured flow regime driven by tectonic compression and compaction and in the upper part, the regime where fluids have the tendency of upwelling in the gravity driven-flow system (Szabó et al., 2018). Both results of data analysis and the interpretation of the 2D simulations could show the potential for the existent relationship between the hydrocarbon accumulations and the presence of thermal water due to the upwelling of groundwater flow. The regional data analysis and subsequent 2D simulation could confirm the favorable conditions for hydraulic trapping of hydrocarbons and the heat accumulation in groundwater due to advective heat transport.

Groundwater is depleting across the globe. According to NASA, 33% of the world’s major basins are overexploited. This water shortage could be alleviated by using Managed aquifer recharge (MAR) techniques. MAR is defined by Gale, 2005 as “Intentional storage and treatment of water in aquifers”. The three most common methods of MAR are a) direct infiltration into the aquifer through wells, b) interception in the river bed, c) indirect infiltration from the land surface (Dillon et al., 2009a). Baluchistan, the largest province of Pakistan by area (44 % of the total area of Pakistan) has hyper-arid to dry climate and is comprised of 18 river basins, 11 of which are suffering from groundwater depletion (2-3 m cumulative decline in watertable) . To solve the issue, 300 delay action dams were constructed but due to high-intensity rainfalls, steep slopes, and lack of vegetative cover, the sediment erosion rate was very high which converted the delay action dams into evaporation ponds and this scheme failed. After the failure of delay action dams, the leaky dam technique along with effective watershed management was applied, this enhanced the percolation and reduced the sedimentation in the reservoir (Asharaf and Sheikh 2017). Leaky dams reduce the energy of flood, initiate the sedimentation of suspended load and release the water downstream through leakage to infiltrate in the riverbed (Gale, 2005). The integrated approach of watershed management, leaky dams, ditches, and furrows positively affected the watertable in the area (Asharaf and Sheikh, 2017). The goals of this research are to revise the development of MAR in Baluchistan (Pakistan), to display a MAR suitability map using INOWAS platform and update of MAR sites in Baluchistan at Global MAR portal. To delineate potential MAR sites, thematic layers such as slope, rainfall, drainage, land cover, and soil characteristics are integrated using GIS multi-criteria decision analysis (based on weighted linear combination method) (Senanayake et al, 2016). MAR suitability maps are used as a preliminary step to field investigation to decide whether an area is suitable for a particular MAR type and hold the potential to be integrated into sustainable groundwater management plans . This study helps design a suitable groundwater management plan for Baluchistan.

During the evolutionary stages of sedimentary basins, different processes are active. Secondary migration means the movement from the source area to the trap and it has most likely the tendency to move along with water. Thus, the secondary migration of petroleum is directly affected by the different driving forces which also influence the ambient groundwater (Tóth 1988). In other words, understanding the regional groundwater flow systems and driving forces may support petroleum exploration. In this theoretical framework, a hydrogeological evaluation of the broader environment of Ebes-Hajdúszoboszló area(Eastern Hungary, Pannonian basin) was executed on the interpretation of the coexistence of thermal water and hydrocarbon accumulations in the specific area. The study is based on the application of two different methods. At first, a basin-scale hydrogeological evaluation of the recent fluid flow condition including archive hydraulic, chemical, borehole temperature data interpretation, and regional pressure field evaluation was carried out. These data confirmed the superposition of an over-pressured flow regime driven by tectonic compression and compaction and the upwelling of fluids in the gravity driven-flow system in the upper part (Zentai-Czauner et al., 2018). The data analysis could provide the initial understanding and conceptual framework for 2D numerical evaluation of superposition of the topography differences and overpressure as driving forces It was carried out using the Heat Flow Smoker software version 7.0 developed by (Molson, 2014) which can simulate density-dependent flow and advective-dispersive transport of thermal energy, mass or residence time in three-dimensional porous or fractured media. The interpretation of the 2D simulation of the cross-section was compared with the results of the data analysis and it can show the relationship between the hydrocarbon accumulations and the existence of thermal water is due to groundwater flow. The regional data analysis and subsequent 2D simulation could confirm the favorable conditions for hydraulic trapping of hydrocarbons and the heat accumulation in groundwater due to advective heat transport.

The Danube-Tisza Interfluve is one of the largest areas covered by wind-blown sand in Hungary. Two major morphologic region types are the flat-bottomed valleys of the Danube and Tisza rivers and a central elevated ridge region, characterized by sand plains, dunes and deflationary depressions. The area is poor in surface waters, mainly artificial channels can be found. Previously many lakes were present, but most of them dried out due to water abstraction, climate change, forestation and canalization related water level reduction. Water management problems in the broader area have been known for decades, many plans have been made to address water scarcity, but none have materialized (Kovács et al. 2017). These plans usually tried to solve water shortage with large scale engineering solutions, e.g. to pump water up from the Danube River Valley through surface channels to the ridge region (Nagy et al. 2016). This is very expensive, influences the ecological pattern, moreover water can easily infiltrate from the channels and would not reach the higher regions in the required amount (Silva Cisneros, 2019). The aim of the research was to examine the suitability of Managed Aquifer Recharge methods, then a local scale field research was carried out in order to find local scale solutions. Finally the results were checked by numerical simulation to contribute to the solution of water shortage of this ecologically important area. Firstly, a MAR surface infiltration suitability map was constructed, that shows areas with favorable hydraulic conductivity at the upper 10 m and low water levels, which means that there is a reservoir in the unsaturated zone to store infiltrated water. Based on suitability mapping, a local research area was selected which showed promising potential. Geophysical measurements (ERT-Electrical Resistivity Tomography, RMT-Radio-magnetotellurics) were performed, shallow wells were surveyed, and additional wells were drilled by hand driller. The results obtained during the field sampling contributed to the preliminary characterization of the area from a geological and hydrogeological point of view. In order to understand the effects of artificial channels and the possible water recharge methods a saturated-unsaturated flow model and different scenario models were built up in 2D. This local scale case study was a first step towards the further aim of this research, which is to understand the effects of man-made changes on groundwater flow systems in the broader area and suggest appropriate local scale MAR solutions accordingly. This research is part of a project that has received funding from the European Union's Horizon 2020 research and innovation programme under grant agreement No 810980.

This study offers a reinterpretation of archive aquifer tests, predominantly on the basis of recovery data, from an original datasheet of thermal water wells located in carbonate and sandstone aquifer units in the vicinity of Budapest, Hungary. The study compares the hydraulic conductivity (K) and specific storage (Ss) values derived in the first instance from an aquifer test evaluation. This included an initial application of the classical analytical Cooper and Jacob method. Subsequently, the visual two-zone (VTZ) numerical method was applied, then third, a more complex model, namely, WT software. It was found that the simple analytical solution is not able to represent the field conditions accurately, while in the course of the application of the VTZ model, it proved possible to alter the various hydraulic parameters within reasonable limits to fit the field data. In the case of the VTZ model, the researcher is required to calculate the accuracy of the fitted model separately, while with the WT model, this is automatic, the software seeks out the best fit. In addition to VTZ parameters, the WT model can efficiently incorporate data on up to 500 model layers, water level, and pressure. The optimization of the parameters may be achieved by automatic calibration, improving the accuracy of the numerical results. Recovery tests for 12 wells were numerically simulated to obtain values for vertical and horizontal hydraulic conductivity and specific storage for Triassic and Eocene fractured carbonate and the Upper-Miocene-Pliocene granular sandstone aquifer units. When an analytical solution is applied, only average values could be obtained. The conclusion reached was that the results of the analytical solution can be improved by the use of numerical methods. These methods are able to incorporate basic information on well design, aquifer material and the hydrogeological environment in the course of the evaluation. The revision of the archive recovery data using numerical methods may assist in the quest for better data for numerical flow and transport simulations without the need to perform new tests. In addition, the methods employed here can explain cases in which the original analytical interpretations proved unable to yield reliable data and predictions.

Groundwater flow mobilises, transports and accumulates hydrocarbons, thus the evaluation of recent fluid flow systems contributes to the mapping of hydraulically favourable places for hydrocarbon trapping and preservation. The aim of our research was (i) to understand the recent fluid flow systems and regional pressure field in the broader area of Hajdúszoboszló and Ebes, Hungary, (ii) to find potential areas for hydraulic trapping in the study area and (iii) to explore the hydraulic connection between Hajdúszoboszló and Ebes gas fields and their surroundings. First the hydrostratigraphic build-up was determined based on borehole sequences, seismic horizons and sections. Then mapping of the fluid-potential field was carried out from measured hydraulic (pressure and hydraulic head) data by pressure vs. elevation profiles, tomographic fluid-potential maps, and hydraulic cross sections. This evaluation was complemented by water chemical and temperature data analyses by TDS (total dissolved solids content) and temperature vs. elevation profiles, tomographic isoconcentration and isotherm maps, as well as cross sections. As a result of the data processing, two distinct flow systems were identified and characterized, namely the nearly hydrostatic, gravitational, and the overpressured flow systems, which are well known in the Pannonian Basin. The connection between the flow systems and the areas of Hajdúszoboszló and Ebes gas fields were analysed in detail. The favorable hydraulic conditions of entrapment and accumulation right here are provided by coincidences of different factors. Namely, in the area of the Hajdúszoboszló gas field upward gravity-driven flow dominates from the elevated Pre-Neogene basement, which may focus flows of the underpinning overpressured system from the South, up to the land surface. This upward flow zone could force the dominantly horizontal SW-directed gravitational flows to turn upward, whilst pressure and temperature drop, as well as salinity increase and these together decrease the solubility of hydrocarbons in groundwater. Furthermore the differences related to the topography of the Pre-Neogene basement between the Hajdúszoboszló–Ebes High and the Derecske Trough were described, as they determine the pressure and heat dissipation and secondary migration pathways for hydrocarbon as well. These conclusions demonstrate the significance of hydraulic studies in the understanding of secondary hydrocarbon migration and accumulation. Combining these methods with the commonly used practice in industry as a hand-in-hand experience, can help to reach better scores in hydrocarbon exploration. These results are contributing to a project that has received funding from the European Union’s Horizon 2020 research and innovation programme under grant agreement No 810980 and was supported by Vermilion Hungary Ltd. as well.

A vízpótlás régóta használt eljárás a vízgazdálkodásban itthon és nemzetközileg egyaránt. Ugyanakkor, a célzott felszínalatti vízutánpótlás (Managed Aquifer Recharge – MAR) mint fogalom, viszonylag fiatal (Dillon et al. 2018). Definíció szerint a víztartók tudatos utánpótlását jelenti, későbbi vízkivétel vagy környezeti haszon elérése céljából (NRMMC, EPHC és NHMRC 2009). Ezek között tartják számon a parti szűrésű rendszereket, melyek tekintetében hazánk élen jár a 150 éves üzemeltetési tapasztalatoknak köszönhetően. A témakör fokozódó nemzetközi jelentősége, a technológiai megoldások bővülése következtében, mára elkészült egy globális, több, mint 1200 MAR helyszínt összefogó adatbázis, mely az ott alkalmazott módszerek alapvető információit tartalmazza, ezzel segítve az újonnan létrejövő projekteket (Stefan és Ansems 2017). Az adatbázis 6 magyarországi helyszínt tartalmaz, köztük 5 parti szűrésű rendszert (Nagybajcs-Szőgye, Koppánymonostor, Esztergom, Szentendrei-sziget és Csepel-sziget), valamint egy talajvízdúsító/beszivárogtató medencét (Borsodszirák), de ezek adatai is hiányosak. Az ENeRAG (Excellency Network Building for Comprehensive Research and Assessment of Geofluids) ELTE projekt keretein belül, az Országos Vízügyi Főigazgatóság (OVF) közreműködésével elkészült egy hazai MAR adatbázis, mely a helyszínek alapadatain túl hidrogeológiai információkat, valamint kialakítási és fenntartási költségeket is tartalmaz. Ez az adatbázis nem csak a globális adatbázis bővítésére szolgálhat, hanem elősegítheti a MAR rendszerek széles spektrumának hazai alkalmazását is. A MAR rendszerek elterjedése hozzájárul a felülvizsgált Vízgyűjtő-gazdálkodási Terv (2015) intézkedési program kapcsolódó intézkedéseinek végrehajtásához. Az előadás bemutatja a MAR technológiai lehetőséget, a nemzetközi adatbázishoz készült hazai felmérés eredményeit és röviden kitekint a jövőbeni lehetőségekre. A szerzők ezúton is megköszönik a vízművek szakembereinek az adatszolgáltatást. A kutatás az Európai Unió H2020 kutatási és innovációs programja által támogatott ENeRAG (810980 sz.) projekthez kapcsolódik.

Groundwater flow mobilises, transports and accumulates matter and heat, thus the evaluation of recent fluid flow systems can contribute to hydrocarbon and geothermal exploration, among others (Tóth, 1999). The main focus of our research was the mapping of hydraulically favourable places for hydrocarbon trapping and preservation in an Eastern Hungarian study area and comparing the results with the already known hydrocarbon fields. The aims were the following: (i) to understand the recent fluid flow systems and regional pressure field in the broader area of Debrecen, Eastern Hungary (approx. 8000 km2), (ii) to find potential areas for hydraulic trapping in the study area, (iii) to explore the hydraulic connection between Hajdúszoboszló and Ebes gas fields and their surroundings. First the hydrostratigraphic build-up was determined based on borehole sequences, seismic horizons and sections. Then mapping of the fluid-potential field was carried out based on measured hydraulic (pressure and hydraulic head) data by pressure vs. elevation profiles, tomographic fluid-potential maps, and hydraulic cross sections. This evaluation was complemented by water chemical and temperature data analyses by TDS (total dissolved solids content) and temperature vs. elevation profiles, tomographic isoconcentration and isotherm maps, as well as cross sections. Based on the results of the data processing two distinct flow systems were identified and characterized, namely the nearly hydrostatic, gravitational, and the overpressured flow system, which are well known in the Pannonian Basin (eg. Tóth & Almási, 2001). Beneath the main recharge area (Nyírség), gravitational downward flow is superimposed to the deeper upward flow and thus a potential minimum zone evolves. This zone can function as a hydraulic trap, so this can be the upper limit of vertical hydrocarbon migration (Czauner & Mádl-Szőnyi, 2013). As the aim of this research, the connection between the flow systems and the areas of Hajdúszoboszló and Ebes gas fields were analysed in detail. The favourable hydraulic conditions of entrapment and accumulation right here are provided by coincidences of different factors. Namely, in the area of the Hajdúszoboszló gas field upward gravity-driven flow dominates from the elevated Pre-Neogene basement, which may focus flows of the underpinning overpressured system from the South, up to the land surface. This upward flow zone could force the dominantly horizontal SW-directed gravitational flows to turn upward, whilst pressure and temperature drop, as well as salinity increases and these together decrease the solubility of hydrocarbons in groundwater. Furthermore the differences related to the topography of the Pre-Neogene basement between the Hajdúszoboszló–Ebes High and the Derecske Trough were described, as they determine the pressure and heat dissipation and secondary migration pathways as well. In addition these findings can help to find geothermal resources with greater economical confidence (Mádl-Szőnyi & Simon, 2016). These conclusions demonstrate the significance of hydraulic studies in the understanding of secondary hydrocarbon migration and accumulation. Combining these methods with the otherwise used industrial practice as a hand-in-hand experience, they can help to reach better scores in hydrocarbon exploration, as well as in geothermal research. These results are part of a project that has received funding from the European Union’s Horizon 2020 research and innovation programme under grant agreement No 810980 and was supported by József and Erzsébet Tóth Endowed Hydrogeology Chair and Fundation, as well as Vermilion Hungary Ltd.

Sedimentary basins depending on their temperature conditions are targets for installation of geothermal power plants and for direct-use of thermal water. The necessary elements of a fluid–based geothermal systems are the reservoir with sufficient hydraulic parameters, the favourable quantity of heat and the production fluids which can transport heat during abstraction (Dickson and Fanelli 2004). These elements should be investigated for the study area during reconnaissance phase of geothermal exploration whether they are available or not. However, the availability of fluids not only depends on the permeability of the reservoir but also on the regional flow systems and hydrodynamic conditions. The hydrogeological aspects of geothermal energy utilization are in the focus of interest nowadays, nevertheless, our knowledge regarding geothermal resources in the context of basin-scale flow systems, especially in deep confined carbonates is very restricted. This study intended to highlight the importance of basin hydrodynamic character in planning of geothermal interventions. The geology, basin depth and geometry can modify the groundwater flow and heat pattern, as well, these constraints have important role in evolution of heat accumulation for geothermal utilization. Several cases in various geologic settings across Hungary could demonstrate the hydrodynamic conditions acting as a main agent determining the geothermal potential and utilisation possibilities. Especially for deep carbonate aquifers, the results showed that the siliciclastic cover is responsible for heat accumulation in carbonates. Therefore position of unconfined and confined parts is decisive in geothermal heat utilization in carbonates. The unconfined carbonates have potential only for shallow geothermal utilization, e.g. heat pump, however at confined regions economic geothermal production is feasible. These outcomes have benefits for geothermal exploration and utilization. Evaluation of hydrodynamic situation is not a conventional element of a geothermal reconnaissance, but it is also important for economic production. Basin-scale hydrogeological studies can reveal the hydrodynamic conditions which affect the feasibility and efficiency fluid-based geothermal systems. This research is part of a project that has received funding from the European Union’s Horizon 2020 research and innovation program under grant agreement No 810980. References: Dickson, M. H. & Fanelli, M. 2004. What is geothermal energy? International Geothermal Association

The Gömör-Torna Karst (known also as Aggtelek Karst and Slovak Karst) is an unconfined transboundary aquifer located on the border of Hungary and Slovakia. Thanks to its complex natural heritage, which includes surface karst forms, caves and sinkholes, the region is under the protection of the Aggtelek National Park and the Slovak Karst National Park. The aquifer consists of karstified Triassic carbonates, partially covered with Quaternary clayey sediments. The karst springs provide the drinking water for the inhabitants of the area. The high sensitivity of these resources thus requires an effective and accurate protection strategy. In the past decades, the Gömör-Torna Karst was in the focus of numerous studies, including hydrogeological investigations and local-scale groundwater vulnerability assessments. For the significant springs of the area records of long term daily observations (1964-1993) are available. This detailed hydrometeorological database provides an appropriate base for data-driven analysis of the factors influencing groundwater vulnerability. The Weights of Evidence (WofE) technique is a well-known spatial statistical method successfully applied for mineral exploration, landslide hazard zonation, groundwater productivity potential or vulnerability assessment. WofE is a method based on the Bayesian conditional probability, which enables observations of the individual role and the combined effect of different geological, geophysical or geochemical features to assess the spatial distribution of a natural phenomenon. Here, we attempt to apply the WofE technique for: i) the evaluation of factors influencing the spring distribution in the karst area and ii) the assessment of a reliable groundwater vulnerability map. The spatial statistical analysis can provide a reliable support in the evaluation of geological and hydrogeological factors influencing groundwater vulnerability in the karst system. This result is part of a project that has received funding from the European Union's Horizon 2020 research and innovation programme under grant agreement No 810980".

Numerical model calculations were carried out in order to investigate the relevance of the interaction of water table configuration and heat transfer as driving forces of regional groundwater flow (Szijártó et al., 2019). Effect of the growing geothermal gradient, regional relief, model depth and anisotropy of hydraulic conductivity were examined on the groundwater flow pattern and the temperature field corresponding to the thermal Rayleigh number (Ra=0-6336) and the modified Péclet number (Pe*=0-323). Transition from topography-driven forced thermal convection to mixed thermal convection system appears when the Rayleigh and the modified Péclet number is Ra=500-1100, and Pe*=10-20, respectively. Below these intervals, advective heat transfer is the dominant driving force, thus the flow converges towards a steady-state solution (Fig. 1). However, above those intervals, additional effect of buoyancy force (free thermal convection) increases the vigorousness of the flow system, which causes time-dependent mixed thermal convection in the numerical models. Obviously, free thermal convection is facilitated by higher geothermal gradient and greater model depth, while increasing regional relief and anisotropy strengthen the formation of forced thermal convection. Besides these systematic investigations, influence of artificial thermal and flow boundary conditions were tested along the sides, on the top and the bottom of the model. Based on conclusions of the theoretical studies, combined effect of the two mentioned driving forces was examined along a two-dimensional west-east geological section across Buda Hills (Rózsadomb) to Gödöllő Hills (Fodor, 2011). Three simulation scenarios were carried out to investigate the effect of driving forces separately: (a) a purely topography-driven groundwater flow, (b) a topography-driven groundwater flow with forced thermal convection and (c) a time-dependent groundwater flow with mixed thermal convection. The verification of the model was completed in agreement with the annual amount of precipitation, the estimated heat fluxes and the result of basin-scale hydraulic evaluation of Mádl-Szőnyi (2019). Generally, the thermal convection increases the heat flux compared to the conductive model which is shown by the nondimensional Nusselt number from 1.5 to 5 in model (b) and (c), respectively. Forced thermal convection causes a large hot upwelling with a surface temperature of 50–70 °C beneath the River Danube in agreement with the interpreted temperature depth profiles and appearances of thermal springs (Mádl-Szőnyi, 2019). The buoyancy force also facilitates the formation of small hot upwellings and convection cells in the Mesozoic carbonate sequences (Fig. 2). Mixed thermal convection induces a time-dependent, but quasi-stationary groundwater flow in the model, which might elucidate the heat anomalies in temperature maps and profiles. Calculated temperature depth profiles and measured data were compared along three vertical sections in the numerical model. This study draws attention to the importance of theoretical and ‘practical’ investigation of different driving forces in groundwater flow systems. Comparison of the numerical results and the observation data could improve understanding the fluid-matrix interaction caused by mixed thermal convection in karstified carbonate sequences and adjoining siliciclastic sedimentary basins. However, there are still some open questions: how can the climate change influence a complex groundwater flow pattern; how can we improve the understanding of the influence of geological evolution on fluid flow, temperature and solute transport processes etc.? This research is a part of a project that has received funding from the European Union’s Horizon 2020 research and innovation program under grant agreement No 810980. The project was supported by the Hungarian Scientific Research Fund (K 129279).

In the most sedimentary basins, like in the Pannonian Basin the groundwater flow is primarily driven by the altitude differences of the water table, especially in the upper approx. 1 km thick part of the crust. Beyond that, the flow is also influenced by other processes, e.g. buoyancy force due to heterogeneous temperature and/or solute concentration. The elevated geothermal gradient in the Pannonian Basin is able to modify or even dominate the deep flow system in special geological situation, such as in thick, permeable layers with low anisotropy of hydraulic conductivity and moderate water table differences [Szijártó et al. 2019]. In confined karstified carbonate systems the presence of the free thermal convection is presumptive by both observed temperature anomalies [Mádl-Szőnyi 2019] and numerical model results [Havril et al. 2016]. The variation in groundwater salinity is another phenomenon which affects the coupled, topography-, salinity and temperature-driven groundwater flow system. Two-dimensional numerical calculations have been carried out in order to investigate how the salinity-and temperature-driven free convection modifies the flow pattern. The solute concentration and the temperature distribution was compared to the purely topography-driven forced convection. In the first synthetic model set the interaction of the salinity increasing with depth and the water table variation was studied. It was established, that the increase in density contrast between the lower saline and the upper fresh water zone reduces the Darcy flux, and therefore retards the decrease of the solute concentration. Beneath the recharge zone a dense, salt water zone evolves in which sluggish, inner convection forms with a Darcy flux lower by 1-2 orders of magnitude. The increase in the anisotropy coefficient of permeability (horizontal/vertical) stabilizes the deep, dense zone similarly. The mechanical dispersivity has minor effect on the regional flow. Increasing dispersivity enhances the transverse dispersive flux through the bottom boundary and slows down the flow slightly. In the second simulation suit the combined effect of the salinity-and temperature-driven free convection and the topography-driven forced convection was investigated. Initially, the solute concentration increased with depth linearly, while a constant bottom heat flux (90 mW/m 2) was prescribed at the bottom boundary. As the density difference due to salinity increased, the flow slowed down, the advective heat transport was suppressed, thus the thermal buoyancy increased and intensified the convection again. Figure 1 shows the quasi-stationary model solution when the density increase due to high salinity and the density decrease due to high temperature is dynamically balanced. The dynamic equilibrium between the two competitive effects results in intense inner convection within the salt water zone, while the topography-driven regional groundwater flow is constrained in the upper fresh water zone. Finally, a thermohaline convection model was applied along a 2D, west–east hydrogeological section crossing the Buda Thermal Karst [Fodor 2011]. Beneath the western, unconfined part of the karst system the intense topography-driven forced convection effectively reduces the salinity and the surface heat flux. On the other hand, within the eastern, confined karst system a vivid inner thermal convection evolves which preserves the high solute content of the groundwater. Beneath the River Danube, at the boundary of the confined and unconfined carbonates, the observed solute content and temperature anomaly can be elucidated by the mixing of the two types of groundwater. The project was supported by the János Bolyai Research Scholarship of the Hungarian Academy of Science, the ÚNKP-18-3 and ÚNKP-18-4 New National Excellence Program of the Ministry of Human Capacities. The project was also supported by the Hungarian Scientific Research Fund (K129279). This research is part of a project that has received funding from the European Union’s Horizon 2020 research and innovation program under grant agreement No 810980.

Naturally discharging springs and water wells have been providing high-quality water as a local drinking water resource in the Bakony Mts.-Balaton Highland area (Central Hungary, Europe) for centuries. On the other hand, the Balaton Highland-Lake Balaton region is a popular tourist destination with an outstanding ecological value of the Lake Balaton and the surrounding wetlands. For the proper and sustainable water management, we need to reveal the groundwater flow systems of the Bakony Mts.-Balaton Highland-Lake Balaton region. It means the understanding of hydraulic connection between the subareas of it, quantity and areal distribution of groundwater recharge, subsurface flow paths through the mainly carbonate formations and also the exploitable amount of groundwater which, meets the human and ecological needs. Therefore, the main aim of the study was to disclose the natural hydrogeological processes in the Lake Balaton region, applying the modern theory of basin hydraulics, considering the special behaviour of carbonate systems and the structural constraints. Hydraulic and hydrochemical connection among Bakony Mts., Balaton Highland, Lake Balaton and Somogy Hills were examined. Water management-related issues were also discussed regarding drinking water resources, sustainable water use and geothermal potential. The study area consists of ~2-3 km thick carbonate formations with hydraulic conductivity of 10-6-10-5 m/s. Two main tectonic events have played important role in determining the hydrogeological conditions: the first has resulted syncline structures before the Late Cretaceous and the second one has produced ~200 km horizontal displacement along strike slip faults during the Miocene. The hydrostratigraphy and the basin geometry modify the flow pattern. The folded basement aquitard restricted the groundwater flow at the boundary of the Bakony Mts. (~5 km deep) and Balaton Highland (0.5-1-km-deep basin) and it caused intensified flow toward the area of the Lake Balaton. The low-permeability thrust-fault caused a hydraulic head drop of 10-30 m at the footwall. South of the Lake Balaton, the carbonates are covered by a <2-km-thick siliciclastic cover. The intensity of groundwater flow is low in this confining layer, and groundwater is directed toward the Lake Balaton because of the water table difference. This could result in a subsurface convergence zone of groundwater flowing from the Northern and Southern basin. Subsurface temperature field reflected the advective heat transport caused by the groundwater flow. The recharging cold water could infiltrate and move down to –3 000 m asl under the Bakony Mts., thermal water (>30 °C) could be found in deeper parts of the basin, except the two near-surface heat accumulations under the boundary of Bakony Mts. and Balaton Highland and under the basin of Lake Balaton. Slightly elevated water temperature (20–23°C) can be found in the region of the Lake Balaton. The regional-scale numerical simulation and hydraulic data evaluation could disclose flow components from the North and South; revealed an asymmetric flow pattern caused by different topographic settings in the Northern and Southern basins; the hydraulic regimes in the broader vicinity of the Lake Balaton; and the groundwater discharge through the lakebed of the Lake Balaton. The constraints of the groundwater flow and heat transport are provided by the distinctly different hydrostratigraphic configuration, basin depth and topographic settings determined by structural evolutionary events. This research is part of a project that has received funding from the European Union’s Horizon 2020 research and innovation program under grant agreement No 810980.

The Gömör-Torna Karst (known also as Aggtelek Karst and Slovak Karst) is an unconfined transboundary aquifer located on the border of Hungary and Slovakia. Thanks to its complex natural heritage, which includes surface karst forms, caves and sinkholes, the region is under the protection of the Aggtelek National Park and the Slovak Karst National Park. The aquifer consists of karstified Triassic carbonates, partially covered with Quaternary clayey sediments. The karst springs provide the drinking water for the inhabitants of the area. The high sensitivity of these resources thus requires an effective and accurate protection strategy. In the past decades, the Gömör-Torna Karst was in the focus of numerous studies, including hydrogeological investigations and local-scale groundwater vulnerability assessments. For the significant springs of the area records of long term daily observations (1964-1993) are available. This detailed hydrometeorological database provides an appropriate base for data-driven analysis of the factors influencing groundwater vulnerability. The Weights of Evidence (WofE) technique is a well-known spatial statistical method successfully applied for mineral exploration, landslide hazard zonation, groundwater productivity potential or vulnerability assessment. WofE is a method based on the Bayesian conditional probability, which enables observations of the individual role and the combined effect of different geological, geophysical or geochemical features to assess the spatial distribution of a natural phenomenon. Here, we attempt to apply the WofE technique for: i) the evaluation of factors influencing the spring distribution in the karst area and ii) the assessment of a reliable groundwater vulnerability map. The spatial statistical analysis can provide a reliable support in the evaluation of geological and hydrogeological factors influencing groundwater vulnerability in the karst system. This result is part of a project that has received funding from the European Union’s Horizon 2020 research and innovation programme under grant agreement No 810980.

Groundwater flow mobilises, transports and accumulates hydrocarbons, thus the evaluation of recent fluid flow systems contributes to the mapping of hydraulically favourable places for hydrocarbon trapping and preservation. The aim of our research was (i) to understand the recent fluid flow systems and regional pressure field in the broader area of Hajdúszoboszló and Ebes, Hungary, (ii) to find potential areas for hydraulic trapping in the study area and (iii) to explore the hydraulic connection between Hajdúszoboszló and Ebes gas fields and their surroundings. First the hydrostratigraphic build-up was determined based on borehole sequences, seismic horizons and sections. Then mapping of the fluid-potential field was carried out from measured hydraulic (pressure and hydraulic head) data by pressure vs. elevation profiles, tomographic fluid-potential maps, and hydraulic cross sections. This evaluation was complemented by water chemical and temperature data analyses by TDS (total dissolved solids content) and temperature vs. elevation profiles, tomographic isoconcentration and isotherm maps, as well as cross sections. s a result of the data processing, two distinct flow systems were identified and characterized, namely the nearly hydrostatic, gravitational, and the overpressured flow systems, which are well known in the Pannonian Basin. The connection between the flow systems and the areas of Hajdúszoboszló and Ebes gas fields were analysed in detail. The favourable hydraulic conditions of entrapment and accumulation right here are provided by coincidences of different factors. Namely, in the area of the Hajdúszoboszló gas field upward gravity-driven flow dominates from the elevated Pre-Neogene basement, which may focus flows of the underpinning overpressured system from the South, up to the land surface. This upward flow zone could force the dominantly horizontal SW-directed gravitational flows to turn upward, whilst pressure and temperature drop, as well as salinity increase and these together decrease the solubility of hydrocarbons in groundwater. Furthermore the differences related to the topography of the Pre-Neogene basement between the Hajdúszoboszló–Ebes High and the Derecske Trough were took into consideration, as they determine the pressure and heat dissipation and secondary migration pathways for hydrocarbons as well. These conclusions demonstrate the significance of hydraulic studies in the understanding of secondary hydrocarbon migration and accumulation. Combining these methods with the commonly used practice in industry as a hand-in-hand experience, can help to reach better scores in hydrocarbon exploration. These results are contributing to a project that has received funding from the European Union’s Horizon 2020 research and innovation programme under grant agreement No 810980 and was supported by Vermilion Hungary Ltd. as well.

In South Transdanubia (Hungary) there are remarkable geothermal and hydrocarbon resources. Besides the sedimentary basin, the area also includes the Villány Thermal Karst. The karst area is characterized by natural thermal water discharge at the boundary of outcropping carbonate hills and the sedimentary basin, which established the thermal water exploration of Hungary in 1866. These regional discharge areas are favourable sites of hypogenic caves as well. These geofluid systems and groundwater related phenomena are usually investigated separately and their interactions are just neglected. The aim of this study was to give all these resources and phenomena a common framework applying the dynamic system approach and complete the regional hydraulic and hydro-geochemical assessment of the area. During the measured data based hydraulic assessment pressure-elevation (p(z)) profiles, tomographic fluid potential maps and hydraulic cross sections had been constructed to determine the vertical and horizontal fluid flow conditions. The hydrochemical study (concentrationand temperature-elevation profiles, concentration map series) helped to understand the geofluid systems more accurately. Local scale studies focused on groundwater related phenomena: on the research of a spring lake and a hypogenic cave. With geophysical measurements the local geological build-up of the spring lake was explored. Time series of physico-chemical parameters of the spring and in the cave help to understand the local scale dynamics of the system which was verified by numerical simulation. In-situ experiment using carbonate rock slices combined with continuous recording of the physico-chemical parameters reported on the recent processes in the cave.

As conventional methods, spring hydroand physico-chemographs are widely applied. With the help of these graphs, the local dynamics and heterogeneity of the aquifer can be investigated on catchment and aquifer scale. In turn, springs are the natural discharge points of flow systems, they can reflect the subsurface flow and temperature conditions, and therefore they can provide information about the groundwater flow pattern. Namely, the character of springs and their spatial distribution can be indicative for nested groundwater flow systems via the physicochemical parameters of their outflowing water, as well as for geothermal potential via their outflowing water volume and temperature. Similarly, to the groundwater flow pattern evolved in siliciclastic sedimentary basins, carbonate regions can also be characterized by regional subsurface flow field due to gravitational driving force on basin-scale. This study intends to display the methodology of groundwater flow characterization based on springs via the case study of Hungarian hills and highlands, with special emphasis on the Transdanubian Range. It is located in the central part of Hungary and it consists of ~2-3 km thick carbonate formations and there are ~700 naturally discharging springs. Multidimensional data analysis of the springs as natural discharge points could help to understand the natural groundwater flow pattern and hydraulic role of structures. Elevation of spring orifice, water temperature, volume discharge of springs and major ion content as potential indicative parameters for groundwater flow were applied during basin-scale classification. Based on combined cluster and discriminant analysis (CCDA), groups were derived which were ranked into local, intermediate and regional flow systems. Systematic analysis of springs can lead to a comprehensive conceptualization of groundwater flow systems and the consequent characterization regarding the geothermal potential of a carbonate area. This study is part of a project that has received funding from the European Union's Horizon 2020 research and innovation programme under grant agreement No 810980.

Based on field observations and previous numerical simulations, combined effect of external forces (e.g. water table elevation) and buoyancy forces can cause a complex groundwater flow pattern characterized by mixed thermal convection, not only in siliciclastic sedimentary basins, but also in adjoining karstified deep carbonates. The interaction of different driving forces was examined along a two-dimensional west-east geological section across Buda Hills (Rózsadomb) to Gödöllő Hills. On the course of this study three simulation scenarios were systematically examined in the last evolutionary stage of Buda Thermal Karst: (a) a purely topography-driven steady-state groundwater flow, (b) a topography-driven steady-state flow system with forced thermal convection, and (c) a time-dependent flow system with mixed thermal convection. The numerical model was verified using the results of basin-scale hydraulic evaluation (observed pressure elevation profiles, tomographic potentiometric maps) of Mádl-Szőnyi (2019) complemented by estimated recharge rates, and calculated heat fluxes. The effect of different flow and thermal boundary conditions was systematically tested during the simulations. Effect of thermal convection was studied in order to examine its influence on the temperature distribution and on the groundwater flow pattern. It was established that existence of thermal convection increases the heat flux compared to the conductive model in agreement with values of the Nusselt number from 1.5 to 5 in model (b) and (c), respectively. The pure advective heat transfer due to forced convection causes a large hot upwelling with a surface temperature of 60-80 ℃ beneath the regional discharge area in agreement with the temperature depth profiles and appearances of thermal springs. However, the effect of time-dependent free thermal convection also facilitates small hot upwellings in the unconfined karstified carbonate system which might elucidate the unexplained heat anomalies in temperature maps and profiles. In addition, the effect of free thermal convection increases the value of the monitoring parameters in the models (e.g. Darcy flux, temperature and hydraulic head). These simulations draw attention to the importance of different driving forces of groundwater flow, especially at the margin of unconfined and confined carbonate sequences, such as in Buda Thermal Karst. Thorough comparison of the numerical results and the observation data could improve understanding the interaction caused by mixed thermal convection.

The hydrogeological conditions of Hungary would be suitable for the more enhanced application of MAR systems for water management purposes. Recently there are two classical examples (aside from frequent IBF sites) of infiltration ponds for drinking water supply in Borsodszirák (Mikita and Kovács 2014) and in the area of Bátonyterenye Waterwork. The groundwater model of the Borsodszirák area could prove that 2‒3 meters increase in water level can be achieved for the center and 0.2‒1 m for a wider area in the gravel aquifers. The MAR concept was used for theoretical simulations in the area of Debrecen Great Forest. The study deals with the potential remediation of an overproduced area here. The potential technical solutions can be infiltration drains and an infiltration pond with different recharge capacities (Szűcs et al, 2007). The MAR concept also can be used in local discharge areas to flood the area and keep up water levels at the surface or in the soil layer to store the water for the purposes of agriculture and for natural vegetation. The artificial recharge of cleaned wastewater can be also an option but it is not favoured by Hungarian experts yet due to the restrictions in the legislation. In addition, future prospects along with a MAR potential of an area which is constantly fighting against water shortage will be discussed. We will present MAR potential maps for an area where water supply is planned in a natural conservation area.

Managed Aquifer Recharge is an evolving technique worldwide to sustain groundwater level and preserve groundwater resources in the long term between changing climatic conditions. The web-based global inventory of managed aquifer recharge is a remarkable initiation (Stefan & Ansems, 2017) and it displays more than 1200 MAR sites from all over the world. However, IAH-MAR and INOWAS has only limited information about Hungarian MAR sites (eg. Homonnay, 2002). In addition, there are two fundamental questions about the already functioning MAR sites: their sustainability and their related costs. The bank filtration as a technique is handled as a MAR, and it has been long-term tradition in Hungary since 1868. Although there are 4 induced bank filtration (IBF) sites along the Danube River related to Hungary in the international database but there are several more represented only in the Hungarian literature. The oldest IBF sites are more than 100 years old and they are still working and ensure the drinking water supply of Budapest, the capital of