Evaluation of Horna Nitra Geothermal Reservoir (Central part of Slovak Republic)

Abstract

Geothermal waters in the Horna Nitra Basin are bound to Triassic carbonates of the Choc and Krina nappes, which are overlain bu the basal Paleogene (breccias, conglomerates) above which are flyschoid facies and Neogene layers. Geothermal activity of the area is demonstrated on the surface by natural outflows at Chalmova (water temperature of 39oC) and at Bojnice 945oC). The mean value of heat flow density is 70mW/m2. Statistical methods and mathematical modeling by analytical and numerical models were uses for analysis of regime and interrelationships of fresh groundwater and geothermal waters. Statistical analysis of data showed a seasonal character of groundwater level fluctuation in wells tapping geothermal waters at Bojnice. The influence of shallower cold groundwater was documented by groundwater level fluctuation in the well BR-4. A two dimensional numerical model was used for evaluation of the geothermal resources of the reservoir. This model confirmed that the regime of level fluctuating in Bojnice is dependent mainly on geothermal water exploitation, and does not depend on precipitation directly. The model demonstrated that the exploitation rate from Bojnice should not exceed 27 1/s if the groundwater is to be stabilized at present levels. The total amount of geothermal energy of the Horna Nitra Basin was estimated to be 19.6 MW.