Updating the Geothermal Database and the Heat Flow Density Map of Hungary
Laszlo LENKEY, Janos MIHALYKA, Petra PAROCZI
[Eötvös Lorand University, Hungary]
The heat flow density map of Hungary was presented in the Atlas of Geothermal Resources in Europe in 2002 and was last updated in 2005. Since that time several geothermal projects, e.g. TransEnergy (2010-13), assessment of the geothermal potential of the Drava basin (2013) Paks-II, NPP (2016) and continuous drilling activity in the country have been in progress. Large amount of temperature data became available, which allowed the update of the Geothermal Database of Hungary. The Geothermal Database of Hungary presently contains more than 14000 single temperature data and numerous temperature logs from about 5000 boreholes and wells. The temperature data derive from different types of measurements: BHT, DST, temperature of water entering into the well at the screening, outflowing water temperature at the well head and well logs. The measured temperatures are corrected for the disturbing effects, e.g. cooling due to drilling (BHT) or cooling of the water due to upwelling in the well. The corrected temperature data are ranked into nine classes depending on the quality of the data and the applied corrections. The database also contains the lithology of the boreholes and wells in order to estimate the thermal conductivity of rocks. The thermal conductivity of the rocks is known from laboratory measurements made on core samples. In case of Neogene and Quaternary clastic sediments, which constitute the subsurface rock types in 70 % of the country, the thermal conductivity versus depth functions established for sands and shales are used. The heat flow density is calculated using the Bullard-plot technique in which the temperature data are weighted according to their quality. The heat flow density data are not corrected for the topography and the paleoclimatic variations. The heat flow density map is constructed using 2000 heat flow density data. The mean heat flow density in Hungary is 90 mW/m2, varying between 30 mW/m2 and 120 mW/m2. The high values are found over buried basement highs in the eastern and southern part of the country, while the low values are located in the recharge areas of karstic flow systems. In the sedimentary basins, where the thickness of the Neogene and Quaternary sediments reaches 5-7 km, the heat flow is slightly below the mean value (80-90 mW/m2) due to the transient effect of sedimentation. These basins contain the main thermal water aquifer in Hungary utilized for district heating and green house heating. The buried basement highs are characterized by high heat flow (100-120 mW/m2), and these areas are the potential sites for EGS utilization. The heat flow map of the country and the temperature data are the most important input data or control data in 3D numerical modelling aimed to identify or characterize geothermal reservoirs or predict deep temperatures in EGS exploration.
|        Topic: Geophysics||Paper Number: 13115|