Vízügyi Közlemények, 1966 (48. évfolyam)

4. füzet - Rövidebb közlemények és beszámolók

(43) POSSIBILITIES FOR THE DEVELOPMENT OF THERMAL WATER RESOURCES IN HUNGARY By L. Bélteky, Engr. (For the Hungarian text see pp. 165) The first thermal well in Hungary was drilled more than 100 years ago on the left bank of the Danube River. Major development of thermal water resources took place only since 1954. This was greatly promoted by the discovery — due mainly to the increased intensity of natural gas and petroleum exploration -— of the favourable geological and geothermal conditions, which render the development of thermal water resources in Hungary much easier than in the surrounding countries. Conditions favourable to the development of thermal water prevail where waterbearing formations are deeply seated and the geothermal gradient is low. (The geothermal gradient is understood as the distance over which a change in temperature of 1 Centigrade occurs. It is denoted by the symbol Gg, and has the dimension m/C°.) In the sedimentary sequence filling the Hungarian Basin sand and sandstone* i.e., porous water-bearing layers most suitable for water production are situated on the boundary of upper and lower Pannonian formations. At still greater depths karstic, fissured, mesozoic carbonate limestones and dolomites overlying the basic rock substratum for the aquifers, which when overlain by younger thick impermeable strata, yield great quantities of thermal water along fissures, cracks and faults. The upper Pannonian formation, having a bedding plane deeper than 500 m

r from which with a temperature higher than 35 Centigrades can in general be expected, occurs over 65 percent of the country. The greatest depth of the upper Pannonian formation extends down to about 2000 m. Geothermal conditions may be classified favourable, inasmuch as the géothermie gradient over the country is on the average no more than 18 m/C°, whereas in the surrounding countries and on the continent it is 33 m/C°. Consequently thermal water of a certain temperature can be gained in the Hungarian Basin at an appreciably smaller depth and at lower cost. As revealed by evidence gained so far the geothermal anomaly in the Hungarian Basin is a regional feature, but in a number of areas local, i.e., zonal deviations occur. From a great number of temperature readings in deep wells the actual value of the geothermic gradient is fairly well known. 427 actual Gg values have been classified in Fig. 1 by the author into four groups and two kinds of shading have been used to denote areas over which Gg values lower, respectively higher than 18 m/C

c are characteristic. Areas from which little information about temperatures at greater depths is available have been left unshaded. The bottom horizon of the upper Pannonian formation is represented by contour lines in Fig. 2. Three kinds of shading corresponding to 500 m contours have been used here. From the deep seated karstic areas covered by thick sediment the two northern ones are only bounded by structural lines. In the unbounded southern mezozoic strip three wells lowered to 50 to 60 m depth yield from fissures of the carbonate rock thermal water of 62 Centigrades temperature. As will be perceived from the two maps different opportunities prevail over different parts of the country, depending on geological structure and geothermal conditions. The role of geology is in this respect more important than that of the geothermal gradient. The Gg may be low in a sediment filled basin, yet if the upper Pannonian formation is not sufficiently thick, the temperature of water remains below 30 Centigrades. On the other hand, where the bottom horizon of the upper Pannonian formation is situated at around 2000 m depth, thermal water of 80 to 90 Centigrades temperature may be found even if the Gg has a value of 20 to 21. Possible utilizations of thermal water in Hungary fall into the following categories : a

) central heating of flats, public buildings and factories (above 70 Centigrades), b) hot water supply for domestic and industrial purposes (above 45 Centigrades),