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a The study area in Hungary, the location of evaluated thermal wells and the track of the geological cross section. The age and lithology of the screened formations in the evaluated thermal wells are also indicated [topography based on the SRTM model (Farr et al. 2007)].
Source publication
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 i...
Contexts in source publication
Context 1
... study area is divided by the River Danube into western and eastern parts (Fig. 1a, b). From the hydrogeological point of view, the Danube represents the boundary between the semi-unconfined (Buda Hills), and the confined carbonate aquifer systems (Gödöllő Hills and Pest side) . The dominantly Triassic carbonate formations partially outcrop and are partially covered by an Oligocene aquitard and Early-Middle Miocene ...
Context 2
... covering formations are east of the Danube the Upper-Miocene-Pliocene and Quaternary formations behave as aquifer units (Fig. 1b). The Triassic and Eocene carbonate formations of the area, made up of dolomite, limestone and calcareous marl, are characterized by double porosity. In contrast, the siliciclastic Upper Miocene-Pliocene sandstone formations behave as a granular aquifer and display primary ...
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... the preformance of tests for new wells. These wells were screened to different aquifers described as Upper Miocene-Pliocene sandstone, as well as in Middle Triassic dolomite, Upper Triassic dolomite, limestone and Upper Eocene-Lower Oligocene calcareous marl, respectively. The tested wells were unevenly distributed throughout the research area (Fig. ...
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... head, production yield, production time, etc. Moreover, with regard to wells sunk into carbonate rocks, it was a common occurrence that when the drilling of the well reached an open fracture, its water level recovery was almost immediate. Therefore, after disregarding inadequate data series, 12 wells were identified as suitable for processing ( Fig. 1a; Table 1). The density contrast is negligible in thermal wells due to the low TDS content of the examined aquifers. Consequently, no density contrast was taken into consideration during the carrying out of the aquifer ...
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... depth of the well is 20 m, it was deepened in the Main Dolomite (T3 Main Dolomite Fm.) aquifer (Figs. 1a, b, ...
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... depth of Well 8, Pécel, is 670 m (Figs. 1a, 6). In the surroundings of the screened section, fine and medium sand, silt, silt loam and silty clay alternate. In Well 8, three screens can be found. The upper screens are open to fine and medium sand, while the lower two screens to medium sand. Above and between the screened sections, primarily silty clay is reported in the wellbore ...
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Citations
... The geology of the area was grouped into five hydrostratigraphic units (HsU) complemented by the original pore fluid content (Table 3): the karstified Triassic carbonate (HsU1); the Eocene limestone (HsU2); the clayey Oligocene aquitard (HsU3); the siliciclastic Miocene aquiferaquitard group (HsU4) and the undifferentiated Upper Miocene-Pliocene-Quaternary group (HsU5) (Mádlné Szőnyi, 2020). In the hydrostratigraphic division, HsU1 and HsU5 are considered as the main aquifers, and HsU3 represents the main aquitard based on geological and hydrogeological descriptions and evaluation of pumping test data (Rman and Tóth, 2011;Garamhegyi et al., 2020). The hydrostratigraphic section of the study area and the location of faults are originally based on seismic interpretation of MOL Plc. ...
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.
... For the goals of the numerical simulations, the complex geology and different lithological units were converted to 11 hydrostratigraphic units (HS) on the basis of a priori data and previous studies. These units were characterized by the necessary input physical parameters for the simulations (Fig. 2b and c; Bodri, 1981;Dövényi and Horváth, 1988;Rman and Tóth, 2011 (T-JAM project); Mádl-Szőnyi and Tóth, 2015Havril et al., 2016;Békési et al., 2018;Mádl-Szőnyi et al., 2018Tóth, 2018;Mádl-Szőnyi, 2019;Garamhegyi et al., 2020). Contrary to studies referring to karst systems, here we focused on the understanding of basin-scale flow patterns and heat transport processes. ...
... There, the negative temperature anomaly might also have evolved due to the time-dependent mixed thermal convection which was suggested by the numerical simulations. On the eastern side of the studied section (x>40 km), a shallow advective cooling effect is identified (z>-400 masl) which changes to a mainly conductive temperature field with depth due to the possible anisotropy of the Miocene aquifers (HS1 and HS2) (Garamhegyi et al., 2020). ...
... Garamhegyi et al., 2020; (2)Rman and Tóth, 2011 (T-JAM project);(3)Tóth, 2018; (4) Máld-Szőnyi et al., 2019; (5) Eppelbaum et al., 2014; (6) Bodri, 1981; (7) Dövényi and Horváth, 1988; (8) Békési et al., 2018. ...
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.
In this study we propose a new method called the cessation time approach (CTA) for interpreting recovery tests in confined aquifers, which is based on the Theis solution. The CTA method involves selecting a residual drawdown measurement from the recovery phase and linking it to its dimensionless counterpart through simple algebraic steps. This approach is then incorporated with a regression model to estimate aquifer parameters. The performance of several parametric polynomial and non-parametric machine learning regression models was investigated using various datasets. Results show that CTA with third-order multivariable polynomials produced highly accurate parameter estimates with a normalized root mean squared error (NRMSE) within 0.5% for a field dataset. Among the machine learning algorithms tested, the radial basis function and Gaussian process regression achieved the highest accuracy with NRMSEs of 0.6%. We conclude that CTA can be a viable interpretation tool for recovery tests due to its accuracy and simplicity.
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.
