Hydrogeological by nuša mecilošek

OPERATIONAL PROGRAMME SLOVENIA-HUNGARY 2007-2013

HYDROGEOLOGICAL CONCEPTUAL MODEL

within the framework of project

Screening of the geothermal utilization, evaluation of the thermal groundwater bodies and preparation of the joint aquifer management plan in the Mura‐Zala basin

T‐JAM

Contents

1. Introduction

2. Groundwater flow systems in the T-JAM project area

2.1. Situation in Hungary

2.2 Situation in Slovenia

3. Hydraulic boundaries and model delineation

4. Main hydrostratigraphic units identification

4.1 Situation in Hungary

4.2 Situation in Slovenia

5. Hydrogeological parameters of the hydrostratigraphic units

5.1 Situation in Hungary

5.2 Situation in Slovenia

6. Conclusions

7. References

Introduction

The main aim of the T-JAM project is to set up a joint thermal water management strategy for the Mura-Zala basin. This will foster sustainable use of transboundary geothermal resources management between Slovenia and Hungary, which is currently not the case. Although transboundary Tertiary geothermal aquifers are not officially delineated we had to prepare a conceptual hydrogeological model which supports the theory of their existence at the beginning of our research. The project addresses the key problem of using natural resources shared by different countries in a sustainable way. Natural resources, such as geothermal energy, whose main carrying medium are deep groundwaters along regional flow paths, are strongly linked to geological structures that do not stop at state borders (Fig. 1). Therefore only a transboundary approach and the establishment of a joint, multi-national management system may handle the assessment of geothermal energy and the limits of use in a region, irrespective of political state borders. This is especially true for transboundary aquifers, where water extraction at a national level without cross-border harmonized management strategies may cause negative impacts (depletion or overexploitation) leading to unnecessary economic and political tensions between countries. The need for complex assessment in transboundary regions is in line with water protection policy and rational water use as set up in the Water Framework Directive (2000/60/EC).

Fig. 1 Sketch of the Pannonian basin geothermal system

One of the tools which can help to solve these problems is a hydrogeological conceptual model of the Tertiary geothermal aquifers in which hydrogeological characteristics of the potential systems have to be described and evaluated within a uniform scheme. The model also needs to include a critical overview of the relevant previous information followed by a 1

spatial delineation of hydrostratigraphic units, important tectonic elements etc. After determination of boundary conditions an assessment of potential flow paths can be given. The regional conceptual hydrogeological model should explain natural flow and transport processes, while their quantification can be done only by numerical models.

Groundwater flow systems in the T-JAM project area

2.1 Situation in Hungary On the T-JAM project area the following flow and transport processes have to be taken into account. The main aquifer zones of the basement comprise the uppermost weathered and karstified parts. Karstic groundwater table aquifers in the mountainous area supply the major part of recharge for the gravity driven flow system. This has two major types on the project area: a) the simple gravity-driven cold karst flow system discharging through the cold water springs at the basin margins or within the mountain area (local or intermediate flow system), b) the mixed gravity- and geothermal (density)-driven flow system (regional karst flow system) which flows under the basin fill sediments and discharges through lukewarm and thermal springs at the basin margins. In addition to these two major types, the fractured, karstified system might be linked to the flow system of the covering strata, might get or give water to them. The cold and lukewarm karst springs represent the simple gravity-driven system at the southern margin of the Keszthely mountain at the Lake Balaton (Erzsébet, János and Festetich springs), with several tens of litres per second discharge, or with the westernmost cold spring at the spring-cave of the Lake Hévíz. The major outlet of the regional mixed gravity- and geothermal (density)-driven system is the Lake Héviz, one of the largest thermal spring-lakes in the world. Its discharge rate before the 1960-ies was over 500 l/s, but the huge karst water abstraction at the nearby bauxite mine decreased this value to approximately 300 l/s (1970-1990). After the mining activities finished some regeneration has occurred and the discharge has stabilized at the 390-420 l/s. The difference between the original natural and present state is a consequence of the decreasing recharge caused by the climate change, plus some remaining (drinking) water production at the former mine site in Nyirád. The majority of the recharged water from the South Bakony and Keszthely mountains is not directed to the springs, but to the deepest parts of the basement, flowing through the upper karstified zone of the Triassic and Cretaceous carbonate rocks. The cold groundwater warms up along its flow path and therewith its density reduces. Where the fault zones have high vertical permeability and are of a large vertical extent there is a possibility that they form so called geothermal heat chimneys (open convection cells). In the heat chimney the hot water rises up. Based on the observed geothermal anomalies, some heat chimneys are supposed to exist in the Zala basin down to a depth of 3000-3500 m, especially W-NW from the Nagylengyel area. The groundwater flows collect heat from a large subsurface area, then uprise through the »chimney« towards the springs, a much smaller area compared to the territory of the »heat-recharge«. In the upwelling path thermal waters cool down to some extent, but still show a 20-40 ºC heat excess, compared to the normal geothermal conditions of the area. The gravity- and geothermal driven flow system of the Zala region is characterized by potential values lower than that of the covering strata. The occurrence of the low salinity, Ca2

Mg-HCO 3 type “simple karst” waters also depict regional flow paths and support the theory of large mixing regional flow system. The thermal springs at Lake Hévíz with high discharge and temperature of 40-41 ºC represent a high amount of heat derived from the depth, which indicates the extent of the groundwater flow system in the basement. From the geothermal utilization point of view, it is very important to preserve the heat chimneys (controlled convection systems), which can be done on the basis of the regional flow and heat transport evaluations like the numerical modelling. The linked flow system of the fractured, karstified rocks and the covering clastic strata is represented by the W-ern and N-ern surroundings of the Lake Hévíz, where karstified and fractured Triassic rocks are directly overlain by Pannonian aquifers. In the surroundings of Zalacsány the Pannonian delta front sandy aquifers directly supply the underlying thermal karstic reservoir. Mixing of the waters with different chemical characters contributes to the special chemical composition of thermal groundwater in Lake Hévíz and nearby. This mixing also causes karstic corrosion which resulted the enhanced permeability of rocks in the W-ern, NW-ern surroundings of Lake Hévíz, which fosters further enhanced mixing of different groundwaters with different temperature and chemical characters. Groundwater observation wells in this mixing zone correspond well to the discharge of Lake Hévíz. At the moment the present groundwater management decisions in this region (controls, restrictions for abstraction) are based on these monitoring data which are available through the internet. The older Miocene aquifers (abrasional and shore sands, gravels, reef carbonates, etc.) directly overlying the basement rocks form a joint hydraulic unit with them. Delineation and selection of the potential basement geothermal reservoirs should consider the areal extent and thickness of these Miocene rocks (especially Badenian and Sarmatian aquifers), as well as their hydrogeological parameters. Different well-tests of hydrocarbon exploration wells, measured pressure fields, hydrogeochemical characters also suggested, that the older miocene aquifers which form a joint hydrodynamic system with the basement reservoirs have an outstanding importance in the Zala basin. On areas far away from the gravitational flow systems stagnant or very slow flows operate. These groundwaters generally originate from the sea-water of the last transgression of the geological evolution of the area, i.e. they are fossil confined groundwaters. In the basin areas the presence of the overpressured zones has to be taken into consideration. These are generally formed on areas where thick clays and clayey marls are present (‘Miocene’‘Pannonian’ clayey marls); mainly compactional and/or tectonic, diagenetic processes may take part in their formation. The slow fluid migration by cross-flows from the overpressured zones towards the basement, or to the upper aquifers is important from the hydrogeochemical point of view. The amount of water deriving from these units is generally much smaller than the water budget of the main aquifers, but the high dissolved solids content of the overpressured zone’s water significantly contributes to the hydrogeochemical character of the exploited thermal waters and often determines their balneological value. The overpressured zones are proved by the DST measurements in the eastern margin of the Zala basin. They are usually connected to the sandstone layers inside the thick ‘Miocene’-‘Lower Pannonian’ clayey complexes. At the southern and south-western margins the hydrogeochemical interpretations indicate the existence of the overpressured zones, but no DST measurements exist. When the geometry (vertical or subvertical permeable zone of the closed basement aquifers, i.e.conduit channels along larger fault zones) make it possible, a closed thermal convection 3

(free convection) may develop. At the Zala basin there are some areas with geothermal anomalies, where the basement contains the same salty waters as identified in the covering porous layers. These anomalies can indicate a free convection system in the basement. During the designing of a geothermal plant it is worth to study how these convection systems can be best utilized. It is worth to put the abstraction wells close to the upwelling part and the injection wells close to the falling part of the convection system, thus the area of heat mining can be maximized. We do not have enough information on the hydrogeological and hydrodynamic role of those Lower Miocene coarse-grained porous sediments of the deep basins that are not connected directly to the basement aquifers and that of the Miocene and Pliocene volcanites. They have importance only where they directly join the other flow systems therefore we do not study them in this project. Within the thick clayey-marly basin fill complex (aquiclude/aquitard) the separated turbiditic sand bodies with restricted areal extent and low permeability have to be divided, as they often contain fluids with high temperature and high total dissolved solids. The natural flow processes within the turbiditic sands can be neglected; however, their significance from the other aspects (e.g. hydrocarbons, CO 2 storage and exploitation of the utilizable dissolved content) makes them important. The gravitational flow systems of the basin areas can be divided into regional, intermediate and local systems. The deepest regional flow system penetrates till the delta-front and the delta-plain sands of the Upper Pannonian Újfalu formation on the area. Locally, the overlying Zagyva formation can also be a part of this system (the Lenti area). The thermal waters with temperatures above 25-30°C discharge from this unit. The sedimentary and post-depositional erosion processes may significantly modify the stratification of these units, and as a result the forced flow paths and recharge/discharge conditions, too. Under favourable conditions the sandy aquifer units of the Újfalu and Zagyva formations are in direct contact with the hilly areas with a higher hydraulic potential, therefore providing a fairly quick and direct recharge. The majority of the thermal wells in the Zala basin extract water from the regional and intermediate flow systems. According to the previous model results, the main recharge zones are at the hilly parts at western margin of the basin, in Slovenia, Austria and Hungary. The main discharge zones are in the Croatian and Hungarian part of the Drava valley and partly at the Hévíz Lake, at the mixing porous and karst water zone mentioned above. The system is characterized by a strong anisotropy (Kh/Kv often higher than 5000) at a larger, regional scale due to frequent alternation of the sand-silt-clay layers. However due to the uplift and the resulted erosion in the Zala basin, the layers of the Zagyva and Újfalu formations can be in direct horizontal connection with the shallow groundwater system. The intermediate systems encompass the multi-level sandy aquifers of the Zagyva (and to a smaller extent Újfalu) formations in the area. They provide the majority of the drinking water in the Zala basin and play a role in the recharge of the porous and karstified/fractured basement geothermal aquifers. In the Zala basin, the drinking water supply of several larger towns (e.g. Zalaegerszeg, Nagykanizsa and Szombathely) is provided by this intermediate flow system. The drawdown resulting from the drinking water abstraction can significantly affect the geothermal regional flow systems, too. The shallowest groundwater (local) flow system can be divided into two main types. On the hilly areas the precipitation percolating through the Pre-Quaternary weathered or coarse4

grained sediments feed the Quaternary (mostly Holocene) alluvium of the valleys. Here this local flow often meets the intermediate and regional flow systems. The larger streams and deeper and larger alluvial aquifers of the Mura River form the other type, which is a discharge of the deeper flow systems. This is the most favourable situation for shallow geothermal energy utilization with geothermal heat pumps (GTHP). However, it has to be considered that these aquifers provide drinking water and are also subject of other different interventions (e.g. construction of deep garages). It is important that the shallow groundwater systems should be jointly studied and evaluated with the surface waters.

2.2 Situation in Slovenia The shallowest regional groundwater flow occurs in the upper, active aquifer system in the Quaternary, Plio-Quaternary, Pliocene and Pontian sediments and rocks. If continuity of the aquifers is assumed regionally, we believe that groundwater level decreases towards south and east, following the surface water net. This indicates a regional gravitational fresh water flow, enhanced by topography and relative height difference between Goričko hills and Mura river plain, in total 220 m. Recharge of these aquifers is believed to come from the infiltrating rainwater in the north and west (Goričko hills), and the south part of the Slovenske gorice hills (Kralj, 1999; Pezdič et al., 2006; Lapanje, 2007). Natural outflow from the unconfined Quaternary and Plio-Quaternary aquifers is limited to the surface water flows (rivers, lakes) but evapotranspiration also affects them. Springs occur at the bottom of the valleys. The semi-confined Ptuj-Grad and Mura formations aquifers reach the surface in the Goričko hills and some valleys or plains, where discharge may occur therefore it is supposed that their natural outflow occurs mainly as hidden underground discharge to the overlying Quaternary aquifers, but this has yet not been confirmed by any research. This type of flow has been confirmed by some numerical modelling with TOUGH2 (Rman, 2007) and MODFLOW (Pezdič et al. 2006) simulators. The geothermal aquifers in the Lendava and Špilje&Haloze formations, Mesozoic carbonates and Paleozoic metamorphic rocks probably do not take an important part in the regional flow system but contain mostly stagnant groundwater with minor recharge, which is limited to the fault zones (Lapanje, 2007). In the central part of the Mura-Zala basin faults often act as barriers as they cut, move and isolate water-bearing layers between each other (Radenci, Petišovci and Dankovci). The regional Ljutomer fault identified in the SW-NE direction north of Lendava probably acts as a hydraulic barrier for deeper – older formations’ aquifers, while in shallower (the Mura formation and younger) it only winds layers but does not represent a barrier for groundwater flow. In the Goričko hills some basalt dikes spreading in the N-S direction are identified near Grad. The same sand and gravel layers are captured in the wells Grad-1, DSL-1 and VID-1. As the recharge is assumed from NW to SE, the first two wells, positioned west of the dyke, have lots of water, while VID-1, positioned east of the dyke, has poor yield. From this it can be concluded that the basalt dyke acts as a hydraulic barrier (Matoz et al., 2002). The described regional flow mechanisms cause deeper penetrating water to heat up and therefore a regional thermal water flow also develops. Its driving force is the density difference between the warm mineralized and cold fresh water. This regional flow is governed by the well permeable layers, the presence of open fissures and channels and the permeable contact between the basement metamorphic rocks and the overlying Tertiary rocks (Pezdič, 1991; Kralj & Kralj, 2000b; Kralj, 2004). Due to the higher horizontal than vertical permeability the flow direction parallel to the stratification is enhanced. The high pressure in the central part of the basin is assumed to result in the thermal water flow towards the basin 5

margins (Pezdič, 1991). There natural outflow features occur with typical natural mineral water springs (slatina), known for centuries in Slovenske gorice, Radenci and Nuskova. The Mura formation geothermal aquifers outcrop in Radenci, plus due to numerous faults positioned in the Raba fault zone (Žlebnik, 1978; Lapanje, 2007) the permeability is locally enhanced and outflow occurs. The hidden underground thermal water discharge into the fresh water Quaternary and Plio-Quaternary aquifers is also expected, but yet not proven. Locally, enhanced vertical permeability by faults results in development of free convection cells within the fault zones, as in Benedikt. Due to the fresh, mineral and thermal water extraction from the production wells, the forced groundwater flow is expected locally, which does not follow the regional flow direction. The number of shallow (cold) groundwater wells is unknown but an approximate number of water permits exceeds 7000. There are also 26 active geothermal wells identified in the T-JAM project area in Slovenia with no reinjection applied (Rman&Lapanje, 2008a).

3. Hydraulic boundaries and model delineation Regionally (Fig. 2), the Tertiary aquifers in the Mura-Zala basin are limited to the north by the very low permeable Paleozoic metamorphic rocks of the South Burgenland swell in the Goričko hills continuing towards the NE to Hungary. To the west the outcropping metamorphic and magmatic Pohorje massive also forms a closed hydraulic boundary. Towards the east the structure is open to Hungary while to the south the structure continues to Croatia therefore the hydraulic boundaries are opened or are regarded as constant-pressure. The delineated area covers the regions of Pomurje and partly Podravje in Slovenia and Vas and Zala counties with surroundings in Hungary.

Fig. 2 Delination of the T-JAM project area

In the Hungarian part the results of the XL Pannon groundwater flow model (Jocháné Edelényi et al., 2005, Tóth 2009) were used for delineation of the model area along the recharge boundaries of the main thermal aquifers. Based on the evolution of the Hévíz Lake and its surroundings (Cserny et al., 2009) we incorporated those parts (e.g. Keszthely mountains) which are necessary for the understanding the groundwater flow system in the Zala basin. In Hungary, all boundaries are handled as open, in the porous and even in the basement systems. It means that the modelled area is smaller than the regional flow system as a whole. Due to the regional WNW-ESE regional groundwater flow directions in the Pannonian porous thermal aquifer, the boundaries along the Austrian-Hungarian border and at the SW border of the model area (border of the Zala county) were regarded as open ones. The upper boundary of the model coincides with the surface topography, because the role of recharge from precipitation will be examined as well.

4. Main hydrostratigraphic units identification The hydrostratigraphic units represent rock bodies with similar hydrogeological properties.

4.1 Situation in Hungary The pre-Tertiary basement is composed of the Paleozoic metamorphic rocks and the Mesozoic sedimentary formations with various lithological features. The Paleozoic rocks have best permeability at their weathered upper parts, or related to larger fault zones. The Mesozoic consists of the Triassic karstified carbonate rocks (dolomite and limestone) in a large extent and the Upper Cretaceous karstified limestones. In the uppermost part of the basement, the different hydrostratigraphic units can be outlined based on similar lithologies. Below the basement surface a 100 or 200 m thick model layer will be used to represent the weathered and karstified zone, which has better permeability than the underlying unaltered rocks. Below this, to 8000 m b.s.l., which is the bottom of the model, no more model layers will be outlined. The pre-Tertiary basement is overlain by the Miocene, Pliocene and Quaternary sedimentary sequences. From bottom up the main hydrostratigraphic units are: the ‘Miocene’ and lowermost ‘Pannonian’ sandstone formations, the Szolnok formation (Lower ‘Pannonian’) turbiditic sands and the Újfalu formation (Upper ‘Pannonian’) delta-front to delta-plain sediments. The delta-front sands are the best geothermal aquifers in the region. The Újfalu formation is overlain by the Zagyva Formation (Pontian – Lower Pliocene) delta-plain sands, silts and coal-bearing clays. The uppermost Quaternary sequence with good hydraulic conductivity represents the shallowest aquifer.

4.2 Situation in Slovenia The Mura –Zala basin has a distinctive vertical stratification of the geothermal aquifers (Žlebnik, 1978; Pezdič, 1991; Kralj & Kralj, 2000b). The deepest are the fissured aquifers in the Pre-Tertiary metamorphic and carbonate rocks. The karstic basement aquifers which are characteristic for the Hungarian part of the T-JAM project area are probably not developed in Slovenia. The Tertiary layers are deposited on it in multiple sequences and generally dip and thicken towards S and SE. From bottom up it follows: the Špilje & Haloze, Lendava, Mura and Ptuj-Grad (previously unnamed) formations (Jelen et al., 2006, Jelen & Rifelj, 2010). The Quaternary Mura gravel is the youngest and stratigraphically the highest aquifer, of 15 m thickness in average. This regional unconfined intergranular aquifer is continuous and well 7

permeable with groundwater flow in the NW-SE direction. Between Dobrovnik and Dolga vas it is covered by low permeable sediments in thickness of few meters and 1-2 km in width (Mioč & Marković, 1998). Elsewhere, it is open for surface recharge and hydraulically connected to the river Mura, and captured in numerous drinking and technological water wells.

Fig. 3 The main captured geothermal aquifers and borehole activity in the NE Slovenia

Under the Mura gravel, between Ljutomer and Dolga vas in the south, and Veržej, Beltinci and Dobrovnik in the north, a 60 m thick package of the Plio-Quaternary stiff coarse grained greyish gravel (Lapanje et al., 2009a) with iron hydroxides is deposited. The aquifer is unconfined, continuous and hydraulically connected to the Mura gravel (Krivic, 2009). It is captured in a few wells: Hr-2/03, Žižki-1v, ČRE-2v, Trnje-1v, VP-1v, Bistrica-3v/96, Bistrica-4v/97 and observation wells in the Krapje gravel pit. This aquifer continues to Hungary. In the area between Jošavski prekop and Lendava hills the groundwater is expected to flow in the opposite direction, from Hungary to Slovenia. The Quaternary aquifers are usually separated from the underlying Tertiary ones with thick sequences of clay and argillaceous sand (Kralj, 1999). The Pliocene and Miocene sediments consist of coal, marl, silty clay, silt, sand and gravel, and the latter three represent the potential water-bearing layers. The lithification and compaction increase with depth. The Tertiary aquifers are semi-confined with the recharge limited to areas where permeable layers outcrop or are in contact with the Quaternary aquifers. The confined character gets stronger with distance towards the layer’s sinking direction. The piezometric water level is not continuous between these aquifers. From bottom up it follows as stated: the Špilje & Haloze, Lendava, Mura and Ptuj-Grad formations aquifers.

The low-mineralized water in the intergranular (geothermal) aquifer in the Ptuj-Grad (Jelen & Rifelj, 2010) formation (Pontian-Pliocene) is captured in minor sand and gravel lenses. Below, the intergranular geothermal aquifer in the lower part of the Mura formation (Pannonian-Pontian) comprises of well permeable and hydraulically connected sand and gravel lenses with effective thickness app. 100 m and which thickens towards east. It spreads over the whole Mura-Zala basin, while the Ljutomer fault influence on water migration is yet not clear but probably negligible. Underneath, up to 1 km thick Lendava formation (Pannonian) is deposited. Its water-bearing layers are only a few meters thick and cemented, therefore fissured porosity prevails. Below the Lendava formation a thick sequence of the Špilje & Haloze formation (Carpathian to Lower Pannonian) with predominant fissured porosity of the basal breccia and sandstone intercalations exists. The permeable layers of the Lendava and Špilje & Haloze formations are often isolated, which is confirmed by their oil and gas deposits. The formations have low thermal water yields. These Tertiary aquifers are often isolated from the surroundings due to the lithological and tectonic settings. The turbidite water-bearing layers of the described formations are lithologically limited. The basement of the Tertiary sediments comprises the remnants of the Mesozoic limestone and dolomite and predominately of the various Paleozoic metamorphic rocks. The thermomineral carbonate aquifer in the Radgona-Vas tectonic half-trench (Jelen et al., 2006) spreads in the SW-NE direction in a narrow area of the Raba fault zone over the Slovenske gorice hills, Radgona and Goričko hills to Hungary. It is identified in boreholes Rad-2 and TH-3/3a (Austria), Kor-1gα/08, St-1, Peč-1, Dan-1, Pan-1 and Šal-2 in Slovenia. Its thickness is less than 100 m. At Kungota some erosional remnants outcrop, while in Radgona it occurs at 1,7 km depth and deepens eastward to 3,2 km in Šalovci. It is expected to exceed 4 km depth in Hungary (Lapanje & Rman, 2008). Fissured and channel porosity prevail here. The aquifer is probably recharged from the east, from the Transdanubian Mountains, north of the Lake Balaton in Hungary. Some of the water can originate from leakage from the overlaying Tertiary sediments. In the SE part of this tectonic half-trench isolated carbonate reservoirs are developed and cut by normal faults. They were identified as potential gas storage sites (the Pečarovci structure) (Lapanje & Rman, 2009b). Some fissured aquifers in the Paleozoic metamorphic rocks are identified in fault zones and the intercalated carbonate lenses. In Benedikt, the Tertiary rocks are deposited directly on the metamorphic basement (Kralj & Vršič, 2007). The borehole Be-2/04 captures water from up to 30 m thick lenses of the dolomite marble probably within the fault zone. The rocks have fracture porosity and the well has great yield but thermal water contains much CO 2 gas. In Maribor, the metamorphic rocks are fissured but have little recharge therefore the yield and even more dramatically the water level have decreased significantly during the years of production and is very small at the moment, with simultaneous large drop of the water level in the boreholes.

Hydrogeological parameters of the hydrostratigraphic units

The above outlined aquifers coincide with the boundaries of different hydrostratigraphic units in most cases. The hydraulic parameters of the basin fill sediments, sedimentary rocks and the basement rocks can be assessed from well tests, expert judgements, as well regional reviews, literature data, modelling results, etc. The available hydrogeological data were gathered in the T-JAM expert database and re-interpreted. Hydrogeological parameters of the representative wells are shown in the T-JAM borehole database (www.t-jam.eu)

5.1 Situation in Hungary The uppermost Quaternary sediments of the main river valleys have the highest transmissivity (conductivity as well). The value for transmissivity varies between 100 and 2500 m2/d. The porosity is also high and varies from 0,1 to 0,35 meanwhile the effective porosity is around 0,15. The porosity, transmissivity, hydraulic conductivity and anisotropy of the Tertiary rocks and sediments usually decrease with age which is more or less proportional to the burial depth. In the Zagyva Formation transmissivity is between 100 and 500 m2/d and porosity varies from 0,1 to 0,2 (effective porosity around 0,1). In the sandstones of the Ă&#x161;jfalu Formation the transmissivity is between 50 in 500 m2/d and the effective porosity around 0,1. In the underlying Szolnok formation the transmissivity is between 0,5 and 20 m2/d while the effective porosity around 0,1. The Mesozoic and Paleozoic rocks form the basement of the sedimentary basin. The Cretaceous and Triassic carbonate rocks are karstified with their transmissivity between 100-2000 m2/d. Although the hydraulic conductivity is usually low for the fractured Mesozoic and Paleozoic rocks, it can locally reach higher values because of their weathered mantle, fissures and faults. Some perspective aquifers were identified also in the Pre-Tertiary fissured formations. The detailed values of numerous hydrogeological parameters of the different Quaternary, Tertiary, Mesozoic and Paleozoic hydrostratigraphic units in Hungary are given in Table 1. The data is summarized from various literature-data and previous modelling studies.

Table 1 Hydrogeological units' properties for Hungary Hydrogeological and geothermal properties Geological units

Formation age

Holocene

Pleistocene

Upper Pannonian

Pannonian

Sarmatian

Aquifer type

Hydraulic and storage parameters

Transport parameters

Geothermal parameters

Formations

intergranular (P), fissured (F), dual porosity (DP), karst (K), aquifer (AF), aquitard (AT), aquiclude(AC), unsaturated zone (UZ)

Transmissivity (m2/d) unconfined zone

Transmissivity (m2/d) confined weathered or karst zone

Hydraulic conductivity (m/d) confined, fresh zone

Transmissivity (m2/d) confined porous zone

Anisotropy coefficient (Kh/Kv)

Porosity

Specific storage (1/m)

Effective porosity

Longitudinal dispersivity (m)

Thermal conductivity (W/m °C)

Water-laid sediments

P; AF-AT; UZ

10-2000

0,1-0,3

0,15

50-100-150

1,5-1,8

Eolian sands

P; AF; UZ

25-250

0,1-0,2

0,15

50-100-150

1,5-1,8

Deluvial, proluvial sediments

P; UZ

0,15-0,35

50-100-150

0,15

50-100-150

1,5-1,8

0,15

50-100-150

1,5-1,8

Fluvial lower terraces

P; AF

100-2000

0,1-0,25

Fluvial higher terraces

P; AF; UZ

(100-1000)

0,1-0,25

P; AF-AT

100-2500

200-500-1000

1,0E-4

0,15

50-100-150

1,5-2,0

P; AF-AT

100-2500

200-500-1000

1,0E-3-1,0E-4

0,15

50-100-150

1,5-2,0

Eolian sands

P; AF; UZ

25-250

0,1-0,2

0,15

50-100-150

1,5-1,8

Eolian loess

P; (AF-AT); UZ

0,5-4

(1)-10

0,25-0,45

0,25

50-100-150

1,2-1,5

Fluvial basinal sediment complex, (upper) Fluvial basinal sediment complex, (lower)

Deluvial, proluvial sediments

P; UZ

0,15-0,35

50-100-150

Zagyvai Fm., fluvial

P; AF-AT

5-50

100-500-(1000)

2000-5000

0,1-0,2

1,0E-4-1,0E-5

0,1

50-100-150

1,5-2,1

Somló-Tihany Fm

P; AF-AT

5-50

100-500-(1000)

2000-5000

0,1-0,2

1,0E-5-1,0E-6

0,1

50-100-150

1,5-2,1

Diás Gravel Fm.

P; AF

10-200

10-100

0,1-0,25

1,0E-3-1,0E-4

0,15

50-100-150

1,5-2,1

Torony Lignite Fm

P; AF-AT

5-50

10-200

100-1000

0,1-0,25

1,0E-3-1,0E-4

0,15

50-100-150

1,5-2,1

Kalla Gravel Fm

P; AF

10-200

10-100

0,1-0,25

1,0E-3-1,0E-4

0,15

50-100-150

1,5-2,1

Újfalu Fm., delta plain

P; AF-AT

5-50

100-500

2000-5000

1,0E-5-1,0E-6

0,1

50-100-150

1,5-2,1

Újfalu Fm., delta front sand, sandstone

P; AF-AT

50-500

2000-5000

1,0E-5-1,0E-6

0,1

50-100-150

1,5-2,1

Kisber Gravel Fm.

P; AF

10-200

10-100

1,0E-3-1,0E-4

0,15

50-100-150

1,5-2,1

Algyo Clay Fm

P; AT-AC

0,01-0,1

2000-5000

1,0E-5-1,0E-6

0,05

50-100-150

1,5-2,1

Szolnok Sandstone Fm (Turbidite sandstone)

P; AF-AT

0,5-20

2000-5000

1,0E-5-1,0E-6

0,1

50-100-150

1,5-2,1

Szak Marl Fm.

P; AT-AC

0,01-1

2000-5000

1,0E-5-1,0E-6

0,05

50-100-150

1,5-2,1

Endrod Marl Fm

P; AT-AC

0,01-0,1

2000-5000

1,0E-5-1,0E-6

0,05

50-100-150

1,5-2,1

Békés Gravel Fm

P; AF-AT

5-200

10-100

1,0E-5-1,0E-6

0,05

50-100-150

1,5-2,1

0,05-0,15

1,5-2,1

Kozard Fm

P; AT-AC

0,5-5

0,01-1

2000-5000

1,0E-5-1,0E-6

0,05

50-100-150

Tinnye Fm

P; DP; K; AF-AT

50-1000

0,05-0,1

10-100

1,0E-3-1,0E-4

0,03-0,1

50-100-150

2,2

Galgavolgy Riolittuff Fm

P; AC

0,5-5

500

50-100-150

1,5-2,1

Tinnye-Dudlesz Gravel Fm

P; AF-AT

10-200

10-100

1,0E-3-1,0E-4

0,15

50-100-150

1,5-2,1

Gyulafiratot Fm

Badenian

KarpatianBadenian

Karpatian

EggenburgianOttnangian

Oligocene

Eocene

Upper Cretacious

JurassicCretacious

P; AF-AT-AC

1-200

10-200

500

1,0E-4-1,0E-5

0,1

50-100-150

1,5-2,1 2,0-2,3

Matra Andezit Fm

F; AF-AT

0,5-5-50

0,005-0,01

(1)-10

1,0E-5-1,0E-6

0,01-0,03

50-100-150

Rakos-Lajta Limestone Fm

DP; K; AF-AT

50-1000

0,05-0,1

10-100

1,0E-3-1,0E-4

0,03-0,1

50-100-150

2,2

Hidas Fm

P; AF-AT-AC

0,5-5-50

10-200

500

1,0E-4-1,0E-5

0,03-0,1

50-100-150

2,0-2,3

Szilagy Clayey-marl Fm.

P; AT-AC

0,5-5

0,01-1

2000-5000

1,0E-5-1,0E-6

0,05

50-100-150

1,5-2,1

Tekeres Shlier Fm

P; AT-AC

0,5-5

0,01-1

2000-5000

1,0E-5-1,0E-6

0,05

50-100-150

1,5-2,1

Pecsszabolcs Limestone Fm

DP; K; AF-AT

50-1000

0,05-0,1

10-100

1,0E-4-1,0E-5

0,03-0,1

50-100-150

2,2

Cserszegtomaj Fm

P; AC

50-100-150

Tari Dacite-tuff

P; DP; AF-AT-AC

0,5-5

0,01-1

10-100

50-100-150

1,5-2,1

Budafai Fm

P; AT-AC, (AF)

0,5-5

0,01-1

2000-5000

1,0E-5-1,0E-6

0,05

50-100-150

1,5-2,1

0,5-5-50

500

1,0E-4-1,0E-5

0,1

50-100-150

1,5-2,1

0,5-5-50

10-100

1,0E-5-1,0E-6

50-100-150

0,5-5-50

500

1,0E-4-1,0E-5

0,05

50-100-150

1,5-2,1

0,005-0,01

(1)-10

1,0E-5-1,0E-6

0,01-0,03

50-100-150

2,0-2,3

Somlovasarhely Fm

P; AF-AT-AC

0,5-5-50

Gyulakesz Riolite-tuff

P; DP; AF-AT-AC

Szaszvar Fm

P; AF-AT-AC

Mecseki Andezit Fm

F; AF-AT

0,5-5

0,5-5-50

Szecseny Shlier Fm.

P; AT-AC

0,01-1

2000-5000

1,0E-5-1,0E-6

0,05

50-100-150

1,5-2,1

Csatka Gravel Fm

P; DP; AF-AT-AC

50-1000

500

1,0E-4-1,0E-5

0,1

50-100-150

1,5-2,1

Padrag Marl Fm

P; AT-AC

0,5-5

0,01-1

2000-5000

1,0E-5-1,0E-6

0,05

50-100-150

2,2

Vulkanite (E2-3)

F; AF-AT

0,5-5-50

0,005-0,01

(1)-10

1,0E-5-1,0E-6

0,01-0,03

50-100-150

2,0-2,3

Szentlorinc Fm

P; DP; AF-AT-AC

0,5-5-50

500

1,0E-4-1,0E-5

0,1

50-100-150

1,5-2,1

Szoc Limestone Fm.

K; AF

100-2000

0,05-0,1

1,0E-4-1,0E-5

0,01-0,03

50-100-150

2,4

Dorog Fm

P; AT-AC

0,5-5

0,01-1

1,0E-5-1,0E-6

0,01

50-100-150

2,2

Gant Fm

P; AT-AC

0,5-5

0,01-1

1,0E-5-1,0E-6

50-100-150

2,2

Ugodi Limestone Fm.

K; F; AF

100-2000

0,05-0,1

1,0E-5-1,0E-6

0,01-0,03

50-100-150

2,4 2,2

Jako-Polany Marl Fm.

P; AT-AC

0,5-5

0,001-0,005

100

1,0E-5-1,0E-6

0,01

50-100-150

Halimba-Csehbanya-Ajka Fm.

P; (AF); AT-AC

0,5-5

0,001-0,005

100

1,0E-5-1,0E-6

0,01-0,03

50-100-150

2,2

Senonian pelagic marl

P; AT-AC

0,5-5

0,001-0,005

100

1,0E-5-1,0E-6

0,01

50-100-150

2,2

Ofiolite melange

P; F; AT-AC

0,5-5

0,005-0,01

1,0E-5-1,0E-6

0,01

50-100-150

2,5

Pelagic limestones

F; (K); AF-AT

50-250

0,05-0,1

1,0E-5-1,0E-6

0,01

50-100-150

2,4

Low-grade metamorphytes

F; AF-AT

0,5-5-50

0,005-0,01

1,0E-5-1,0E-6

0,01

50-100-150

2,5

Upper TriassicJurassic

Dachstein Limestone Fm.-Kardosrét Limestone Fm.

K; (F); AF

100-2000

0,05-0,1

1,0E-4-1,0E-5

0,01-0,03

50-100-150

2,4

Triassic-Jurassic

Low grade metamorphytes, slope and basinal sediments

F; AF-AT

0,005-0,01

1,0E-5-1,0E-6

0,01

50-100-150

2,5

Kössen Marl Fm

P; DP; AT-AC

0,5-5

100

1,0E-5-1,0E-6

0,01

50-100-150

Main dolomite (Hauptdolomite) Fm

K; F; AF

100-2000

1,0E-4-1,0E-5

0,01-0,03

50-100-150

Jurassic

Upper-middle Triassic

0,5-5-50

0,05-0,1

3,8

Lower Triassic

Upper Perm Lower Perm

Pre-Perm, Paleozoic

Veszprem Marl, Sandorhegy Limestone Fms.

P; DP; AT-AC

0,5-5

0,001-0,005

100

1,0E-5-1,0E-6

0,01-0,03

50-100-150

2,2

Aszofő, , Iszkahegy, Megyehegy Fms.

K; F; AF

100-1000

0,05-0,1

100

1,0E-4-1,0E-5

0,01-0,03

50-100-150

3,5

Som, Táska, Igal Limestone Fms.

K; F; AF

100-1000

0,05-0,1

0,01-0,03

50-100-150

2,4

Csopak Marl Fm.

P; DP; AT-AC

0,5-5

0,001-0,005

100

1,0E-5-1,0E-6

0,01-0,03

50-100-150

2,2

Buzsak Fm

P; DP; AT-AC

0,5-5

0,001-0,005

100

1,0E-5-1,0E-6

0,01-0,03

50-100-150

2,2

(New) Red Sandstone Fm

F; AF-AT

10-100

0,005-0,01

100

1,0E-5-1,0E-6

0,01

50-100-150

2,2

Shallow marine, silciclastic sediments, carbonates

F; DP; AT-(AF)

0,5-5-50

0,005-0,01

100

1,0E-5-1,0E-6

0,01

50-100-150

2,4

Granitoids

F; AT-(AF)

0,5-5-50

0,005-0,01

1,0E-5-1,0E-6

0,01

50-100-150

2,6

Bük carbonates

F; (K); AF-AT

100-1000

0,05-0,1

1,0E-4-1,0E-5

0,01-0,03

50-100-150

2,4

Low-grade metamorphytes

F; AT-(AF)

0,5-5-50

0,005-0,01

1,0E-5-1,0E-6

0,01

50-100-150

2,3

fillonite, milonite

F; AT-(AF)

0,5-5-50

0,005-0,01

1,0E-5-1,0E-6

0,01

50-100-150

2,3

Kőszárhegy, Polgárd, Litér Fm

F; K; AF-AT

100-1000

0,05-0,1

1,0E-4-1,0E-5

0,01-0,03

50-100-150

2,4

5.2 Situation in Slovenia Based on the data gathered in the T-JAM database, different hydrogeological parameters were compared and are presented in the following figures. They show the total porosity, laboratory horizontal and vertical permeabilities of cores, hydraulic conductivity from pumping tests, water temperature and yield distribution with depth and their relations. The laboratory measurements are given at the precise depths (below the wellhead), while the field measurements (Q, T, K) are reported at mean screened interval depth. The total porosity reduces with depth (Fig. 4), which is a result of rocks greater age and therewith longer cementation and compaction processes. The highest total porosity is reported for clays, while the highest effective porosity is reached in the Quaternary and the Mura formation sands. They are poorly lithified therefore laboratory measurements are very difficult to perform, and often only more lithified parts were measured giving too low results. High secondary porosity is measured on some cores of fissured carbonate or metamorphic rocks, while in general these rocks exhibit rather low porosity.

Fig. 4 Total porosity distribution with depth (326 measurements)

The permeability is compared from three types of measurements. The laboratory horizontal and vertical permeability are measured on cores, using an oedometer, while the field measurements are reported from different pumping and DST tests. These values are transformed from m/s to m2 by approximate equation 10-15m2=10-8 m/s, and no temperature corrections were applied. Due to the rather medium water temperatures we assumed that the correction for water density does not affect the order of magnitude of permeability calculated from the transformation from m/s to m2, therefore they are directly compared as showed on Fig. 4 and 5. The permeability shows lognormal distribution with depth, with reduction factor of 1000. The laboratory determined permeability on poorly lithified cores from the Quaternary and Mura formation aquifer layers is lower than the actual, due to the same reason as already stated by the porosity description. A large number of very low permeable samples, shown on Fig.5, is a result of testing the potential gas storage reservoirs and determination of the properties of the barrier hanging and foot wall. The most accurate 14

permeability values are reported from the pumping tests, when hydraulic conductivity is determined.

Fig. 5 Permeability distribution with depth (460 measurements)

Fig. 6 Laboratory vertical and horizontal permeability ratio of the Tertiary rocks (23 measurements)

Fig.6 shows that the empirical ratio between the horizontal and vertical permeability, (the anisotropy coefficient) of the sandstones and marlstones in the Ĺ pilje & Haloze formation is between 1 and 50. From this it can be concluded that the vertical permeability is lower than the horizontal. As the number of measurements is small and the rocks very heterogeneous, 15

the results should not be generalized. We expect that if more samples of mostly sandstones from different formation aquifers are measured, the anisotropy would be even higher. From this we expect that the groundwater flow is preferably parallel to the layering. The vertical flow is enhanced in the areas with hydrostatic pressure higher than normal, where leakage occurs, as well as in the fissures and faults where the secondary porosity enhances the vertical flow.

Fig. 7 Statistical parameters of hydraulic conductivity of different formations (99 measurements)

The statistical distribution of hydraulic conductivity on Fig.7 shows that it decreases with formation age (usually proportional with burial depth). The extremes are very variable, partly depending on the purpose of testing (research of water-bearing or water-barrier layers), but the median values show the decreasing trend clearly. It is also noticeable that the higher number of measurements (black line) reduces the influence of the extreme values. This can be explained on an example of the Mura and Lendava formations, where the latter shows the higher median of hydraulic conductivity. However, in reality the Mura formation is much more permeable and exhibits greater yields than the Lendava formation. The high momentary yields are reported mostly for the Quaternary sediments and the Mura formation. High yields are also reported locally for the fissured carbonate rocks, while other formations exhibit at least one order of magnitude lower rates (Fig.8).

Fig. 8 Maximum momentary yield distribution with depth (345 measurements)

Additional geothermal information is given in Fig.9, which shows an almost linear wellhead temperature increase with the mean production (screened) depth. This is probably connected to the geothermal system type, which is predominately conductive, as convection cells are only rarely identified in Slovenia (only in Benedikt).

Fig. 9 Wellhead temperature distribution with depth (231 measurements)

Based on the presented research the characteristic hydrogeological column of the Mura-Zala basin was elaborated (Table 2).

Table 2 Characteristic hydrogeological column of typical formations in the Mura-Zala basin

Formation

Average aquifer thickness (m)

Effective porosity

Hydraulic conductivity (m/s)

Quaternary Mura gravel Q-Pl gravel Ptuj-Grad formation Mura formation Lendava formation Špilje&Haloze formation Mesozoic carbonates

App. 15 App. 60 Few 10 < 100 Few 10 Few 10 < 100 Unknown, narrow subvertical fault zones

0.15 0.15 <0.1 <0.2 <0.1 <0.1 <0.1

10-3 to 10-4 10-3 to 10-4 10-5 to 10-6 10-5 to 10-6 10-5 to 10-7 10-6 to 10-9 10-4 to 10-6

<0.01

unknown

Paleozoic metamorphic rocks

Beside the hydrogeological properties the spatial distribution and aquifer’s continuity is also important. The regional delineation and research of the geothermal aquifer in the Mura formation, named also Termal 1 (Kralj & Kralj, 2000b), was done in years 1989-1991, when wells Mt-6, Sob-1, Sob-2, T-1, T-2, T-3 and T-4 were investigated. It was noticed that the porosity decreases with depth, while the TDS increases. The mineralization is dependant mostly on dissolved CO 2 gas, which is connected to the fissured areas, while depth is of minor importance (Kralj, 1980). The regional hydraulic connection between the wells Sob-1, Sob-2 and V-66 was proven by pressure decrease in an inactive well V-66 which exceeded 70 mbar (1989/90) and 40 mbar (1990/91) during the winter heating season (Kralj, 1991). The interference was noticed also in other wells capturing the Mura formation aquifer: Pt-18, Pt20 and Pt-74; Le-1g and Le-2g; Le-2g and Le-3g; Sob-1 and Sob-2; Mt-6 and Mt-7; Do-1 and Do-3g (Rman et al., 2008b). The transboundary effects have not been investigated yet, but are expected at the Slovenian-Hungarian border. The natural hydraulic connection between different aquifers has not been proven yet and due to the rather thick intercalations of clay and claystone it is less probable. It may be limited to the areas where permeable layers are in direct contact or where the fault zones with permeable channels allow the forced convection flow. As in many Slovenian wells more than one formation aquifer is captured we believe that the artificial hydraulic connections within the borehole itself may exist (Sob-1, Sob-2, Fi-14, Le-1g, Mo-2g, Pt-20, Ve-2, Ve-3) (Žlebnik et al., 1988; Rman et al. 2008b). The changes in geothermal aquifers were observed by many authors (Kralj, 1992; Kralj & Kralj, 2000a; Kralj, 2001; Pezdič, 2003, Rman et al. 2008b). In Murska Sobota, wells Sob-1 and Sob-2 have problems with high gas content and periodic outblows (Kralj et al., 1998), lower transmissivity and changed chemistry. In Radenci, the inflow of older meteoric waters into the mineral water production area was proven by the oxygen and sulphate isotopes (Pezdič, 2003). The last regional research (Rman et al. 2008b) shows continuous water level decrease (Mt-1, Mt-4, Mt-5, Mt-6…), changes from naturally outflowing wells to pumping wells (Pt-20, Pt-74, Le-1g, Ve-3, Sob-1, Sob-2) or water level decrease when the pump had to be lowered to produce the same needed quantity (Mt-6, Ve-2, P-3). Where new wells were drilled (Mo-2g) the yield in the old ones decreased (Mo-1) and interference between the wells (Moravske Toplice) are reported.

Conclusions

The hydrogeological data overview revealed that there are some rules on the hydrogeological characteristics of the rocks and sediments that can be applied throughout the Mura-Zala basin area in the both T-JAM project countries. The main hydrogeological parameters such as porosity, transmissivity and hydraulic conductivity of the geothermal aquifers usually decrease with formation age, which is proportional to the burial depth, lithification and cementation processes. From the comparison of the hydrogeological properties of the most exploited geothermal aquifers in the NE Slovenia and SW Hungary we managed to identify the potential transboundary geothermal aquifers in the Tertiary sequences. The deepest Tertiary aquifers probably contain stagnant, fossil groundwater and are identified as the ‘Miocene’ and ‘Lower Pannonian’ aquifers on the Hungarian side and the Špilje & Haloze formation aquifer on the Slovenian side. The covering Szolnok /Lendava formation aquifers may locally be a part of the active regional groundwater flow systems but it is more probable that they are also rather isolated (proved by the oil and gas field at Petišovci – Dolina in Slovenia which continues to the Hungarian Zala fields). The deep regional groundwater flow system is most probably developed in the Újfalu and Mura formation aquifers, which represent the best and the most exploited geothermal aquifers in the T-JAM project region. The overlaying Zagyva /Ptuj-Grad formation aquifers are a part of the intermediate flow system, and contain thermal water in the deeper parts while from the shallower parts drinking and industrial water is produced. It is possible that they are hydraulically connected to the underlaying Újfalu /Mura formation and serve as their recharge. The uppermost (shallow) Quaternary aquifers extend over the whole research area and are more or less continuous throughout the region. The potential transboundary Tertiary geothermal aquifers which are delineated based on the T-JAM hydrogeological research are: - The Quaternary aquifers - The Zagyva / Ptuj-Grad formation aquifers - The Újfalu / Mura formation aquifers - The Szolnok / Lendava formation aquifers. The numerical groundwater flow modelling performed during the T-JAM project will be a continuation of this conceptual model. It will help us to provide a better understanding and a quantitative description of the most important transboundary geothermal aquifers in the Tertiary sedimentary sequences. Therewith it will form strong scientific grounds for the development of the joint transboundary geothermal aquifers management strategies.

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