NOTICE CONCERNING COPYRIGHT RESTRICTIONS

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1 NOTICE CONCERNING COPYRIGHT RESTRICTIONS This document may contain copyrighted materials. These materials have been made available for use in research, teaching, and private study, but may not be used for any commercial purpose. Users may not otherwise copy, reproduce, retransmit, distribute, publish, commercially exploit or otherwise transfer any material. The copyright law of the United States (Title 17, United States Code) governs the making of photocopies or other reproductions of copyrighted material. Under certain conditions specified in the law, libraries and archives are authorized to furnish a photocopy or other reproduction. One of these specific conditions is that the photocopy or reproduction is not to be "used for any purpose other than private study, scholarship, or research." If a user makes a request for, or later uses, a photocopy or reproduction for purposes in excess of "fair use," that user may be liable for copyright infringement. This institution reserves the right to refuse to accept a copying order if, in its judgment, fulfillment of the order would involve violation of copyright law.

2 Geothermal Resources Council TRANSACTIONS, Vol. 14, Part It, August 1990 GEOTHERMAL ENERGY IN CENTRAL DEPRESSION OF DANUBE (PANNONIAN) BASIN 0. Frank&'> M. Fendek(i)A. RemSik'l-) M. Krril (2) (1) Geologickq listav D. $t6ra, Mlynsks dolina 1, Bratislava (2) Geofyzika, Geologickri 18, Bratislava ABSTRACT The central depression of the Danube Basin is the greatest geothermal water reservoir in Czecho-Slovakia. In twenty geothermal boreholes m deep were drilled in the area (Tab. 1). Geothermal water aquifers (Dacian-Pannonian sands) in the boreholes were tested by short-term, long-term and hydrodynamical check measurements (Frank0 et al. 1989). The evaluation of the resulting data gives the idea of the spatial distribution of aquifers and waters, of thermal and heat fields. It enables the evaluation of the heat-energetic potential of. geothermal waters. SPATIAL DELIMITATION OF RESERVOIR The structure extends between Bratislava-Galanta-Surany-Nov6 Zrimky-KomBrno and the Danube river (Fig. 1). It is dish-shaped, brachysynclinca1.the geothermal water reservoir is bordered from the bottom and from sides by an impermeable basement a complex of aquicludes, and from above - by a horizontal plain in the depth of 1000 m.3the volume of the reservoir is 4031 ky of which the aquifers occupy 1371 km (34 %). In this structure the geothermal waters are associated with Pannonian-Dacian sands. The amount of aquifers increases towards the basin Margin, which is associated with the depth-controlled fading-out of aquifers (Fig. 1). The reservoir pressure is practically identic with static values of hydrostatic pressures. The NW-SE thermal water flow direction is in the northern part of the reservoir, in other parts of the depression the waters flow to its centre (Fig. 2) Table 1. Geothermal bore-holes realized in (rril'ovi 3ri 5enci ropoyiiky (omirno Salan t a rvrdo- Sovce iornij '0th histov Ivory?ad Zitavou JlCany ZabCi- (OVO ;a lan t a 3ohePov GPB-1 3unaj. ztreda Zalovo jenec liakov- ;e Jov6 :&mky,alovo :ala - FGS-1/1 FGT-1 FGK-1 FGG-1 FGTV-1 FGHP-1 FGC-~ FGDZ-~ FGV-1 FGGa-1 FGG-2 Exploratory wells O 23.O O O observation well T.D.S. (g/l) ,O Exploratory-t iloitation wells DS ' C-1 BS-1 DI GNZ c O HTS

3 Franko ct al. Open Outflow Water forms a continuous impermeable basement Locali- Well segment yield tempe-t.d.s, of single hydrogeological complexes and ty from to Q rature actually of the entire hydrogeothermal (m) (1.s-'1 T(OC) (g/l) structure. Galanta FGG The hydrogeological complex 1 repre sents a complex of aquifers - beds of Total gravels and sands (Rumanian-quaternary) In some places are thin discontinuous rious bed complexes with variable typical hydrological characters and properties controlled by lithologic composition of beds in single complexes. The hydrogeological complexes comprise variable portions of sand beds, sandstone or gravel beds representing thermal water aquifers, and clay representing aquicludes. Sandy clays and clayey sands, mostly fine-grained, represent aquitards. Single hydrogeological complexes were in vertical sense distinguished according to lithologic composition of beds and log diagrams of wells. Decisive was the percentage of aquifers and aquicludes, their thickness, alternation of resistance and potential properties of sediments. In horizontal plain the hydrogeological complexes either link up to one another or are interlocked. The borders of hydrogeological complexes in the horizontal level are presumable in wider areas of wells. The spatial delimitation of hydrogeologic complexes is schematical. The idea of their spatial position is presented in level maps (Fig. 2) and sections (Fig. 3). In the depth intzrval m in Gadenian-Quaternary sediments six hydrogeological complexes have been distinguished. The data on the complexes were treated statistically and graphically by the personal computer WANG All complexes are presented in Table 2. The occurrence of the delimitated hydrogeological complexes below 3000 m is presumable. Thickness of single hydrogeological complexes ranges from 5 to 1174 m. Their succession is relatively regular in places and correlable with a wider surroundings. In some places their vertical and horizontal successions are irregular and reflect the complicated Neogene scdimentation in the depression. One hydrogeological complex may occur repeatedly in the vertical well log. Only the complexes 1 arid 2 have a stable succe-. ssion. The complex 1 always has the position of an overlier. The hydrogeological complex 5 preserves a stable position. It is also in the filling of the depression, The hydrogeological complex 2 represents a complex of alternating aquifers and aquicludes in+an approximate equilibrium (tolerance - 13 %). The complex 2 always underlies the complex 1 and occurs also in deeper segments. Its borders in relation to hydrogeological complexes 1, 3,5 are conspicuous, and in relation to complexes 4 and 6 - less conspicuous. The complex ranges from 55 to 1174 m in thickness and occurs in the depth interval m. The percent of aquifers is %, of aquicludes and of aquitards In the upper and lower parts of the complex are thick continuous bodies of Pannonian-Rumanian rocks. The hydrogeological complex 3 is characterized by aquicludes dominant over aquifers with thick clay beds alternating with thin sand beds. Its contact with the complexes 2 and 6 is conspicuous, the contact with the complexes 4 and 5 is less distinct. Its position in relation to the complexes is variable. The thickness of the hydrogeological complex 3 is m. The complex is in the depth interval The percentage of aquicludes is %, of aquifers %, and of aquitards %. The complex 3 forms large continuous bodies of Pontian-Dacian rocks in the centre of the depression. The hydrogeological complex 4 is characterized by aquicludes dominant over aquifers with clay beds alternating with thinner sand or sandstone beds. Its borders in relation to hydrogeological complexes 2 and 3, partly 5 are less conspicuous, but its contact with the complex 6 is distinct. The thickness of the complex is m. The complex is in the depth interval m. The percentage of aquicludes is %, of aquifers %, and aquitards %. The complex 4 forms huge continuous bodies of Sarmatian-Rumanian rocks in various parts of the depression filling. The complex is resembling the com- 880

Franko, et al. plex 3, only it displays dominance of alternating aquicludes and aquifers and the number of aquicludes thicker than 48 m decreases whereas in the complex 3 it increases.

4 Franko, et al. plex 3, only it displays dominance of alternating aquicludes and aquifers and the number of aquicludes thicker than 48 m decreases whereas in the complex 3 it increases. The hydrogeological complex 5 is a complex of aquicludes with absolutely dominant thick clay beds with occasional thin sandstone or sandstone or sand beds (8adenian- Rumanian). Its contact with the complexes 2,4, and 6 is conspicuous, with the complex 3 it is less distinct. The complex 5 besides occurring in the depression filling also forms continuous impermeable basement for single hydrogeological complexes and so for the entire geothermal water reservoir. The thickness of the complex is m. It is in the depth interval m. The percentage of the clay beds is % and of sand or sandstone beds %, aquitards are absent. The hydrogeological complex 6 is characterized by aquifers dominant over aquicludes. Thick and thin sandstone or sand beds alternate with thin beds of clay and marls (Sarmatian-Pontian). The contact of the complex 6 with the complexex 3,4,5 is distinct, with the complex 2 less distinct. The complex 6 only occurs in the western part of the depression and around TvrdoSovce. The thickness of the complex is m. It is in the depth interval m. The percentage of aquifers is %, of aquicludes %, and of aquitards %. Thermal water aquifers are ranged to five transmissivity classes with 0.5 order sparing. The absolute transmiss'vity coefficifat Tp ranges from 1.6 xl0"to 1.6 x 10 m, the transmissivity coefficient T = 3.6 x loo3-4.9 x lo-'m.s-', the permeability coefficient kp = 1.1 x 10' mc and hydraulic conductivity kf = 1.1 x 6.0 x 10"m.s". A horizontal decrease of the absolute transmissivity coefficient is seen from the middle of the basin to its margins, the vertical decrease is controlled by depth (Fig. 2,3). The geothermal waters belong to four chemical types. Two types (Na-HCO with T.D.S. to 1 g.l"and Na-HCO with 7.D.S. to 1-5 g.l-') are genetical2y ranged to Table 2. Presence of aquifers, aquitards and aquicludes in hydrogeological complexes of the basin I Aquicludes I Aquitards 1 881

Frank0 et al. waters with petrogenic mineralization, and other two types (Na-HCO -C1 or Na-C1-HC03 with T.D.S. 5-10 g.l-'aad Na-C1 with T.0.S above 10 g.f") to marinogenic waters.

5 Frank0 et al. waters with petrogenic mineralization, and other two types (Na-HCO -C1 or Na-C1-HC03 with T.D.S g.l-'aad Na-C1 with T.0.S above 10 g.f") to marinogenic waters. With depth the mineralization increases, the Na-HC03 component decreases and the Na-C1 increases. The waters contain CH4, N and co Incrustation properties are mos?ly chgracteristic of Na-C1 type of waters or of waters with an increased C02 content. GEOTHERMIC CONDITIONS Geothermic conditions in the central depression are evaluated within the entire Danube Basin. In the most part of the basin the Neogene basement consists of crystalline complexes. Mesozoic sequences are only in the northern parts of the Ba$in and in the area between Komarno and Stdrovo. Geothermic characteristics of the Danube Basin is based on data from 32 boreholes. To get the maximum amount of information about the heat field we have treated also data on aquifer temperature, resulting from hydrodynamic tests and temperature measurements on the footwall of the borehole. For a complex evaluation of thermal conditions the temperature data by 100 m and geothermal gradient by 100, 500 and 1000 m were statistically treated. Maps of geoisotherms in depths 1000, 1500, 2000, 2500, 3000 and 4000 m below the surface level were compiled for the entire region. A l l availabe data on Hungarian frontier areas and on boreholes in adjacent areas were considered in the construction of temperature maps. Temperatures to the depths 3000 and 4000 m are extrapolated by a calculation considering thermophysical parametres of the environment in these depths. For the purpose of detailed thermal characteristics of the central depression the average temperature by 100 m are given to the depth 2500 m and by extrapolation to 4000 m. Thermal gradient in the central depression at the depth m is changing in the interval 35.6OC/km "C/km with the average value 39.1 "C/km. The character of thermal field in the depth 1000 m (Fig. 4) is as follow: The average temperature for the entire basin is 47OC. High temperatures are around elevation structure? in the basement near Komdrno (55'C), Stlirovo (50-55 OC), between Chorvdtsky Grob and Rusovce (51-57OC). Low temperatures occurred in a depression between Samorin, GabEikovo and Calovo (43-44 "C). Eastwards of the zone of lower temperatures the temperature is about 50 C, westward-around Senec- the average temperature at the depth 1000 m is 49'C. Towards SE slopes of the Mal6 Karpaty Mts. the temperature rapidly dropped to about 40 OC. The second anomaly of low temperatures is in the area of the Kom4rno elevated block (20-24OC in depth 1000 m). It is due to an intense disturbance of the field by cold carst waters flowing from the Transdanubian Midmountains. The temperature maps to the depth 4000 m show that the thermal conditions in the Oanube Basin to the depth m are markedly influenced by the basement elevation with a much higher heat conductivity than in the Neogene complex. A thicker Neogene complex represents a thermal aquiclude, and therefore the temperatures in the central depression are higher than on the basin periphery. It is in maps of temperatures at greater depth. So the highest temperature should be in the centre of the depression with the thickest sediments. But it is not proved by boreholes in GabCikovo, Bohel'ov and Calovo. It is due to cold surface waters infiltrating into relatively thick Quaternary sequences and flowing into the centre, resulting in the downward cooling of the rock environment. The anomaly of increased temperatures between TopoPniky, VlCany, TvrdoSovce, Kol4rovo and Dvory nad zitavou even in the depth 4000 m is indicative of its association with the deep geologic structure. In the geothermal boreholes the drill cores were sampled on approximately every 100 m and the heat conductivity coefficient was determined. The heat conductivity of rocks increased with the growing sand content and decreases with the growing clay content. A detailed study of heat conductivity of single petrographic rock types shows that it is controlled by depth. The relation of heat conductivity to depth is evaluated by the moving average method on the basis of the equation kyy2 = k + 4 k !< k + 3 +k t 4 16 where i = 1... n ki+j kyy2 (1) = heat conductivity (i+j) of the sample, j = 0,1,2,3, 4 = smoothed value of heat conductivity by the method of moving averages of 5 neighbouring values Since the heat conductivity of Neogene sediments depends upon clay contents and deposition depth, we have based the determination of the average conductivity of the Neogene complex in a depth interval upon logs for the determination of clay content. The clay content was determined from the gamma log according to the formula 882

$The average heat conductivity in the depth interval explored was determined as the weighted mean in relation to the clayey or sandy fraction.$

6 Franko, et al. Gh - G v i - - Gi - Gp where Gh = intensity of gamma radiation of bed serched, Gp = of the bed of pure sand and Gi of the bed of pure clay. The average heat conductivity in the depth interval explored was determined as the weighted mean in relation to the clayey or sandy fraction. The average heat conductivity values of Neogene sequences calculated from the above formula were corrected and used for the calculation of heat flows. In cases of boreholes without cores and data on heat conductivity the heat flow was determined according to the statistic data on heat conductivity and their depth relations for single petrographic rock types. The correction on clay content according to gamma log is a method of correcting the heat conductivity of a sandy-clayey complex in relation to the clayey or sandy fraction. Such correction is evidently necessary for the heat flow calc!lation in Neogene basins (MaruSiak-Lizon 1974) because at random sampling the sand/clay ratio is not preserved and great errors may occur in the determination of average heat conductivity of the Neogene complex and consequently in the heat flow calculation. The heat flow Q in all boreholes was always calculated in two ways: at first as sum of the average heat conductivity and the average thermal gradient according to the equation (2) and then by summation of heat resistivity according to (3). The results of both procedures were almost identic in all wells Q kstr Gstr (2) where k is the average value of heat conducthsfty and G is the average value of thermal graalgnt in the bored Neogene complex. q = - A T h hi I- i ki (3) where Q is the heat flow in the depth interval explored. A T is the temperature difference in the interval, h. is the thickness of a bed with the avkrage heat conductivity k.. A map of heat flow of the Danube Basin (Fig. 4) was constructed from the heat flow values. The minimum heat flow value-t was in boreholes around Senec (67.70 mwm and the maximum value in boreholes K-2 Koli4rovo and FGDZ-1 Dvory nad zitavou (87 mwm-'1. The average value of heat flow in the central depression is 76 mwm-' 1. EVALUATION OF HEAT-ENERGY POTENTIAL (HEP) Hydrodynamical research of aquifers was based on the method of unstable groundwater flow and on consequent calculation of hydraulic parameters. Hydraulic parameters were calculated from the recovery test curves, using the Theiss equation, modified by Jacob transformation. I n the vertical sense the beds were tested separately gradually by single segments (open by jet perforation) from the bottom to the top. The aquifers were thus tested in the depth interval m. The thickness of single tested segments in the depth interval mentioned was m. The thickness of productive aquifers ranged from 34 to 192 m. The absolute transmissivity coefficient (T ) ranges from '"to "'m3 'and under these conditions it corresponds to thf transmisfivity coeff i- cient (TI ' m'.s'. We expect the storativity coefficient of aquifers to range from "to 1.0 lo-'. It is roved by the storativity va lue (9.0 10' P at the first measurement of pressure oneset and 5.5 at the secon measurement), calculated on the borehole FGG-2 serving as an observation well during hydrodynamical tests on the borehol e FGG-3 in Galanta. The calculated hydraulic parameters were presented in hydroge 0- thermal sections and maps showing their spatial distribution (Fig. 2,3). A two dimensional model for the determination of prognostic resources has been compiled on the basis of the application of a theory (Mucha - Shestakov 1987). It is the method of superposition to study the influence of discharge (natural or artificial water issues on the surface) and of the recharge (of natural or artificial recharge of aquifers) to the course of the piezometric surface for unstable flow. The law of superposition is based on the Laplace equation which may also be solved by the sum of partial solutions and by the sum of partial solutions multiplied by arbitrarily selected constants. So if the aquifer comprises several discharges and recharges then the course of piezometric 1e.ve1 of the geothermal water pressure will be equal to the algebraic sum of piezometric levels controlled by single discharges or recharges messured from the original state from the course of geo- 003

7 Franko et al. thermal water level prior to the discharge and recharge activities. The total decrease of pressure for the calculation node IJ is calculated for time t as t t 43 = + p:+l,j-l + I-1,J + I-l,J+l t t t t + 1,J-1 + I,J + I,J+l + I+l,J-l+ t t + 1-1,J I-l,J+l (1) where I = No of calculation node in the x direction J = No of calculation node in the y direction and single depressions are calculated according to the equation y. T. t P = P - Q. In 4%. Tp p- S. r (2) where 3 Q - yield (m.s- ) p - dynamic water viscosity (Pa.s- ) Tp - absolute transmissivity coefficient <m3> f- specific gravity (N.m3) r - diameter of a fictitious source in calculation node (m) S - storativity coefficient (dimensionless number). The relation for the calculation of total depression is valid if the interference in the nearest fictitious resources is considered (influence over one pace distance in direction I and J). At present the program enables solution considering the interference over fivc stcp distance in direction I and J. The maximum drawdown given for the calculation of the yield comes from depressions measured on single wells. There still is some reserve in the calculated yields of single calculation nodes. It is because the static values of aquifer pressures have not been measured and the depressions are smaler. The amount of water pumped from individual calculation nodes was selected so as to prevent irreal values. Prognostic resources are calculatcd for the depth m (Fig. 2) because almost all open intervals of aquifer producing water in the existing wells occur at about this depth levcl. Most data on hydraulic parameters of aquifers and on chemicaltechnological properties of water concern the depth level m. A comparison of data about yields in single intervals shows a gradual stabilization in equal cal- 2 culation nodes and of total yields. It follows that after continuous even exploitation of fictitious sources in single calculation nodes after 185 days the prognostic resources represent l.s- The yields in single calculation nodes are comparable with the yields proved by regime monitoring. At the temperature drop 45OC the power is 193 MW (Tab. 3). Seasonal exploitation concerns the winter when the thermal energy is utilized for heating in agriculture and housing. The heat balance made for this structure shows that the groundwater exploitation by free outflow will not evoke the heat deficit. Geothermal power of the wells is utilized for the heating of 3 buildings (a sports-hall in TopoPniky, and other buildings in OunajskS Streda, restaurant with lodging-house in Oiakovce), about 15 ha of glass-houses, and about 30 swimming pools. In Galanta a housing-quarter comprising 1100 flats, a hospital and a pensioner house will be heated. Table 3. Heat energetic potential of the geothermal resources Rough potential REFERENCES 56. -_ technologically utilizable potential Franko, 0. - BodiS, 0. - Fendek, M. - RemSik, A. - JanCi, J. - Kr51, M. 1989: Methods of research and evaluation of geothermal resources in pore environment of Pannonian Bagin. Zgpadne Karpafy, s6ris hydrogeologia 8, Geol. Ust. 0. Stlira, Bratislava, MaruSiak, I. - Lizo:, I. 1974: Problem v)ipoctu tepelneho toku v sedimentirnych panvsch. Geol. prozkum 3, XVI, SNTL, Praha, p Mucha, I. - Shestakov, V. M. 1987: Hydraulika podzemn)ich v8d. Alfa, Bratislava. 884

8 Franko et al. Spatial delimitation of geothermal water reservoir in central depression of Danube Basin 1 - Pannonian base isolines, 2 - percentage of acquifers, 3 - geothermal well, 4 - oil well km L a..., Fig. 2 Hydrogeothermal map of m level 1 - hydrogeothermal complex 2-complex with approximate equllibrium /tolerance 13 %/ of equl-?ere end equlcludee /alternating eende, grevele, oleye and eendy cleye/, 2 - hydrogeologicel complex 3-dth equlcludee dominant over aquifere /alternation of thiok m oley bede with thln m eend beds/, 3 - hydrogeologicel complex 4-with aquioludee dominant over equifare /alternation of leee thlck m clay bede with thinner m eend and eendetone bede/, 4 - hydrogeologicel complex 5-complex of equicludee /thick clay bed6 ebeolutely dominant over eceroe thin eend end eendetone beam/, 5 - hydrogeologicel complex C-with aqulfere dominant over equloludee /alternating thiok end thin send end eendetone bede with thin clay end marl bede/, 6 - trenemieeioity of equifere, T,=1,04,5.10'%?, 7 - trenemleeivity of equlfere with Tp-0,5- -l,o.lo-%?, 0 - tranemieeivity of equifere with Tp(0,5.1611n?, 9 - eeotion line, 10 - ieobere in MPa, 11 - couree of geothermal water flow, 12 - geoieotherma in OC, 13 - geothermal reeeerch well, 14 - geothermal producing well, 15 - geothermlo obeervetion well, 16 - etructurel geologioel borehole, 17 - celculetion nodee 005

9 Franko et al. L 0 V d Y ~e rl 886

10 Franko et al. 1 Fig. 4 Map of heat activity in Oanube Basin I - Neogene, 2 - Nwvolcanics, latricum- 3 - envelope series. 4 - crystalllne conplexes 5 - Fatricum (KtfZna nappe). 6 - Hronlcm (m nappe). 7 - Paleogene, 8 - Fault systems, 9 - Geoisoihem at depth I 000'1~ (OC), IO - Mat flow (mu'. m-2) Wells 007

NOTICE CONCERNING COPYRIGHT RESTRICTIONS

NOTICE CONCERNING COPYRIGHT RESTRICTIONS This document may contain copyrighted materials These materials have been made available for use in research, teaching, and private study, but may not be used for