Geothermics, Vol. 17, No. 2/3, pp. 531-535, 1988. Printed in Great Britain.

0375-6505/88 $3.00 + 0.00 Pergamon Press plc

© 1988 CNR.

G E O T H E R M A L E X P E R I E N C E I N H U N G A R Y

P E T E R O TTLIK

Institute of Energetics, Ostrom v. 23, 1012 Budapest, Hungary

Abstract--Geothermal fluids in Hungary are exploited in 650 wells and connected heating systems. The highest emergence temperature is about 95°C. Scaling problems are being tackled by chemical and physical techniques. Reinjection tests are now under way to comply with environmental regulations.

In Hungary there are large quantities of geothermal fluids, especially in the sandy aquifers of the Pannonian basin. The salt content of thermal waters varies from place to place in Hungary. The chemical composition of the thermal waters coming from aquifers of Pannonian age is mainly of the alkaline-carbonate type and these waters also contain methane and carbon dioxide.

Salt content is on average 3000-5000 mg l-l; gas content varies over a wide range. Because of the methane in the thermal water, explosions have occurred on several occasions. There are very severe regulations controlling the gas content in water supplies. Gas content must not exceed 0.8 NI m -3, but up to a maximum of 5 NI m -3 the water can be utilized in specific circumstances. Above 5 NI m -3 the methane must be separated from the water. Since cold water in Hungary also contains methane, many kinds of degassificators have been developed. In wells producing water with gas, the quantity of gas must be redetermined every two years. The utilization of thermal water is regulated by the Water Authority through a permit. Any person may obtain a permit, so thermal water wells can be owned privately. Oil or gas wells, however, are state-owned. So wells drilled for thermal water that recover gas are taken over by the Government .

The permits issued by the water authorities provide directions on how thermal wells are to be drilled and operated, such as what depth-interval is permitted, how and where to replace waste water. Drilling is assisted by the literature available on oil well operations, but the flow-rate of a new well is difficult to predict beforehand because of variations in granulometry of aquifers even over a short distance.

Well logging techniques are also regulated by law since all data must be comparable. Part of the geothermal wells were drilled for this specific purpose while others were transformed from oil to geothermal wells. The main parameters in geothermal utilization schemes are the temperature and scaling properties of the fluids. The temperature of the water can be predicted within a small error (Fig. 1), depending on the depth of the aquifer.

Scaling properties cannot be predicted with the same probability as temperature, since it depends on the quality and quantity of salt and gas. During production, the physico-chemical characteristics of the geothermal system change, since pressure decreases from several hundred bar to atmospheric pressure and temperature decreases from about 100-120°C to 15-25°C. Consequently the solubilities of the salts and gases also change. The geothermal resources recovered so far in Hungary are of the low enthalpy type. The highest emergence temperature of the water is about 95°C.

Geothermal experience in Hungary is based on the exploitation of 650 geothermal wells and connected heating systems. In systems installed during the last few decades, the thermal water

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was passed directly through the system. Temperatures dropped through these systems by 40-50°C in the best of cases and the water left the system at 40-50°C. Nowadays when waste water has a temperature of about 30°C the system is considered a success.

Operation costs depend mostly on the quality of the water. In Hungary scaling occurred throughout the system. Incrustations restricted heat transfer and water flow-rate, so the efficiency of the system decreased. The system then had to be shut-down to remove the incrustations. Recently inhibitors have been used but the dosage is of extreme importance as very small concentrations will not inhibit scaling, and very large concentrations will make the water very aggressive. The inhibitor has to be added in the well below bubble-point.

An experiment was conducted in Hungary on different inhibitors: NALCO, Hydrogel, Visco, Sago and a Hungarian product to define the concentrations required. The results indicated that all the inhibitors had the most effect at about 6-8 ppm concentration.

Lately experiments have been conducted on combatting scaling by physical methods and equipment. Only short-term tests of the magnetic technique have been carried out. The results seem to be good but details and conclusions cannot be published yet. Experiments with the ultrasonic method are also planned.

Physical methods have some advantages over chemicals; physical techniques are simple, cheap and unaffected by flow rate.

Modifications have recently been made to the design of the geothermal heating systems. Instead of direct systems only indirect systems have been installed, comprising a primary and a secondary circuit, with thermal water in the primary and fresh water in the secondary. The circuits are connected only by a heat exchanger, so that no scaling occurs in the secondary heating circuit. Degassification is achieved in the short primary circuit.

Opinions vary as to the temperature limit for utilization of geothermal waters, with the lower limit set at 30-35°C, but for energy utilization the temperature must be above 50°C. According to the Hungarian Office of Statistics in 1985 the number of geothermal wells and springs is as shown in Table 1.

The number of wells and percentage of water utilized in the different applications are shown in Table 2.

In 1981 a first assessment was made of the geothermal potential of Hungary. Several thousand data from oil wells were analysed, and used to calculate how much geothermal water could be produced by pumps from a depth of 200 m beneath the surface. They also estimated the distribution of reserves, the quantity of water already exploited and the quantity of reserves which could be exploited in the future. Tablc 3 reports the present production levels, estimates for the future, savings in oil and the advantages of cooling the water to 25°C.

Geothermal energy is supported by the State under a national Energy Program, which includes a project for promoting the utilization of geothermal energy. As part of this project an

Table 1. Geothermal wells and springs in Hungary by 1985

Temperature of water Number of wells Mineral springs Flow rate

(°C) 1975 1980 1985 1975 1980 1985 ( 1000 m 3)

<35 257 297 325 23 25 29 45(16 35-44 223 243 273 8 I I 14 2842 45-59 159 168 196 16 20 22 8474 611 69 57 75 87 8 8 14 7272 70-79 411 5(I 53 6 8 8 3752

>811 57 65 82 7 8 I1 3(1(19 Total 793 898 1016 68 80 98 29,855

Geothermal Experience in Hungary

Table 2. NumberofwellsinHungaryandpercentageofwaterutilizedindifferentapplications

535

Number of wells Utilization 1975 1980 1984 1985 (%)

Spas 221 240 262 277 27.3 Drinking water supply 351 416 366 236 23.2 Agricultural heating 81 97 160 258 25.4 Community heating and 20 20 19 14 1.4

hot water supply Industrial water 15 21 64 70 6.9 Others 21 46 94 128 12.6 Closed temporarily 84 58 44 33 3.2

Total 793 898 1009 1016 100.0

Table 3. Present status and future prospects of the utilization of geothermal fluids in Hungary

Temperature of the water (°C) at emergence 50-60 60-70 70-80 80-90 90 Total

1. Producedwater(lO3m3day 1) 2. Water to be exploited in 103 m 3 day-i 3. % utilized

MW day 1 attainable by cooling to 25°C

Savings in t day i attainable in TOE

48 59 33 38 46 224 432 343 195 97 77 1144

11.1 17.2 16.9 39.1 59.7 19.6

2510 2419 1394 349 - - 6672 12,558 13,535 9943 6420 5819 48,275 15,068 15,954 11,292 6769 5819 54,902

216 208 120 30 - - 574 1080 1164 855 552 500.5 4151.5 1296 1372 975 582 500.5 4725.5

e x p e r i m e n t a l hea t ing sys tem was ins ta l led , in which the coo led wa te r was r e in j ec t ed into the aquifer . Dur ing a p r e l i m i n a r y s tage the C C C s imula t ion m o d e l f rom the Unive r s i ty of A r i z o n a was a d a p t e d to H u n g a r i a n condi t ions . S imula t ion gave very i m p o r t a n t and in te res t ing resul ts on the effects of r e in jec t ion .

The ob jec t ive of the e x p e r i m e n t was to d e t e r m i n e the condi t ions r equ i r ed for re in jec t ion . The only da t a avai lab le p rev ious ly came f rom the oil indus t ry where condi t ions are not c o m p a r a b l e with those e n c o u n t e r e d in g e o t h e r m a l wells.

R e i n j e c t i o n tests were also conduc t ed because this t echno logy is the only means of comply ing with e n v i r o n m e n t a l r egu la t ions and those gove rn ing wa te r m a n a g e m e n t and p roduc t ion .

Al l o t h e r t echn iques p e r m i t t e d by the W a t e r A u t h o r i t y do not comply fully with the above regula t ions . The p r o b l e m of waste wa te r d isposa l b e c o m e s increas ingly i m p o r t a n t as the e n v i r o n m e n t a l laws b e c o m e increas ingly more severe . In fu ture g e o t h e r m a l u t i l iza t ion could be res t r i c t ed or p r o h i b i t e d because the waste wa te r canno t be d i sposed of wi thou t e n v i r o n m e n t a l po l lu t ion .

The p ro j ec t also e n a b l e d us to col lect all da t a on e xpe r ime n t s , t echn iques , i n s t rume n ta t i on and e q u i p m e n t known and used in H u n g a r y in g e o t h e r m a l research and ut i l izat ion. This ma te r i a l has been ed i t ed in five vo lumes , unde r the t i t le "S tudy-a id for p lann ing the ut i l iza t ion of g e o t h e r m a l ene rgy" .