Vízügyi Közlemények, 1973 (55. évfolyam)
4. füzet - Rövidebb közlemények és beszámolók
(70) STUDIES ON THE THERMAL WATER AQUIFER SYSTEM AT SZENTES By Dr. Korim, Kálmán, Geologist and Liebe, Pál, Civ. Engr. (For the Hungarian text see pp. 290) One of the most significant and at the same time representative areas of thermal water production and of geothermic energy utilization in Hungary is situated along the central section of the Tisza River, on the left-hand bank at Szentes and the environment (Fig. 5). The exploration of the thermal water field was started in 1957 and at present there are 22 thermal wells in the round 100 sq. km large area. The wells are arranged in a heterogeneous pattern. In view of the fact that in the area considered thermal water is withdrawn under undisturbed conditions, without interfering external factors, the system appears eminently suited for studying the hydrodynamic processes and phenomena taking place in the thermal water reservoir (Figs. 1. to 4). Chapter 1 is devoted to the discussion of the deep geological formations and the reservoir conditions in the area. The formation yielding the thermal water is according to explorations the sequence of sand-sandstone layers of Middle-Pliocene (Upper Pannonian) origin situated between 1500 and 2400 metres depth. The sandstone layers are separated by interbedded clay-marl strata. The type of reservoir most commonly encountered is the closed lens form of limited extent, but owing to the extensive sand formation in many parts reservoir units of large size are also encountered in many locations. The average porosity of the thermal water storing formations is 15 to 25%, the average transmissibility being 200 to 400 millidarcy. These petrophysical parameters decrease with depth. The original static reservoir pressure of the thermal water bearing formation is hydrostatic in character ( Fig. 8). The 22 wells in the area considered are flowing, or positive thermal wells, the necessary driving force being provided by factors of reservoir energy (high formation temperature, the dissolved gas content of water and the elastic expansion of the water body). The 100 deg. C. geoisotherm surface is situated at 1800 m depth (Fig. 9). The gas: water ratio (GWR) was initially 0.02 to 0.50 m 3/m 3 (Fig. 10/b ). The thermal waters are of the sodium-hydrogencarbonate type. The total dissolved components range from 1562 to 3263, the low (6 to 43 mg/lit) value of the chloride ion being typical (Fig. 10/c). Since the first well was drilled at Szentes in 1957, a total of 40.89 million eu. m of thermal water were withdrawn up to August 31, 1972, while the number of wells has increased to 22. The geographical pattern of thermal water production is shown in Fig. 11/a, whereas that of the reservoir energy level in Fig. 11/b As a consequence of the thermal water volume withdrawn thus far the following experiences were made: — The yield related to the 0.5 atmospheres positive outflow level remained in general unchanged, a reduction in yield having been observed in no more than 5 wells. — There was a slight reduction in the static pressures at the well heads and at depth (0.2 to 0.5 at/million eu. m water per well). — The temperature of the (flowing) water and of the formation remained substantially constant. — The dissolved gas content of water showed changes in exceptional cases only. — Changes in the chemistry of water occurred likewise in rarest instances only (Chapters 2 and 3 ). For exploring reservoir continuity and occasional communication between the wells an interference study was made with the results shown in Fig. 12 and Table IV. Considering the thermal water field as a whole, a slow migration of the formation fluid is indicated by the fact that the values of the reservoir energy level are higher in the western part, further that the pressures at the well head, the salt concentration, gas content and temperature at depth increase from the west towards the East.
