engleski

Possibilities of finding geothermal water for heating purposes in the Town of Vukovar (Croatia)

Initial study of the possibilities of finding geothermal water was conducted in the Town of Vukovar, which is interested in utilizing this renewable energy resource and reduce the dependence on expensive imported gas for district heating purposes. The initial study was done based on the existing data from hydrocarbon research (seismic reflection, borehole data and water sampling). Unfortunately, seismic reflection profiles were not available for the area of the town itself. Since it is of interest to drill a well on the territory of the town and as close as possible to the future users (central heating stations), the profiles were not considered in the interpretation. Rocks and sediments with satisfactory hydraulic properties have been determined during hydrocarbon research of the Vukovar area, and it is expected that the Upper Pannonian Abichi deposits (sands and sandstones) represent geothermal aquifers. On the basis of the data from resistivity and spontaneous potential logging, favourable intervals have been determined at depths ranging from 800 to 1700 m. Geothermal gradient was determined on the basis of thermal logging and maximum temperature measurements. Usually the gradient obtained by using TMAX is higher than the one obtained by logging, due to the technology of measurement. In Vukovar area, data from seven boreholes were available: 6 thermal logs and 1 TMAX. The determined values were 34-43 °C/km. Slightly elevated geothermal gradient was determined, which is in accordance with the position of research area on the southern rim of the Pannonian Basin System, a known positive geothermal anomaly due to crustal thinning. Data for the wider Vukovar area (Eastern Slavonia Basin) have shown gradients of 51-53 °C/km. Water samples were only taken in one out of seven boreholes, at two depths. Waters show a similar hydrochemical facies (Na-Cl type) which, in the context of hydrochemical model of Pannonian Basin System, represents waters that infiltrated formations during Miocene transgression and achieved chemical equilibrium with rock matrix. Anionic composition also shows characteristics of mature waters, i.e. waters with long residence time which achieved chemical equilibrium with the surrounding porous medium. After analysing the existing data, guidelines for the next phase of research were given.

geothermal prospection, hydrocarbon wells, permeable intervals, geothermal gradient, hydrogeochemistry

nije evidentirano