Geology and geothermal potential in the eastern flank of Eger Rift (Litomerice area, Czech Republic)
Abstract
Utilization of geothermal energy in low enthalpy regions is made possible with the use of EGS (Enhanced Geothermal Systems), which utilize a system of two boreholes connected by artificially fractured rock volume providing permeability for heating the cold water injected in one of the boreholes and produced in the other one. We focus on the area of Litomerice in the NW part of Bohemian Massif, where a pilot 2.1 km deep geothermal borehole was drilled in 2007.
We combine existing geological knowledge with newly acquired data to build a conceptual geological model of the area. Temperature logging and thermal characteristics of the collected rock samples provided data for thermal modelling.
The lower part of the borehole samples relatively homogeneous mica-schists, which are overlain by rhyolite ignimbrites, upper-Carboniferous continental siliciclastic sediments and sedimentary cover of Bohemian Cretaceous Basin on the top. Several sets of brittle structures of various ages were identified in the area, however only some of them are prone for reactivation in the present stress field corresponding to NNW-SSE compression.
The prevailing orientation of metamorphic foliation and missing signs for contact metamorphism appear to preclude the possible occurrence of granites in the deeper horizons. Equilibrium temperature in 1.8 km is 57.5 degrees C, which combined with the thermal characteristics of the rocks gives the heat flux of 78 mW/m(2) and temperature prediction of about 140 degrees C in 5 km depth, which ranks the area to typical geothermal provinces of the NW part of the Bohemian Massif.
Further research will be focused on seismic surveys and stress measurements to assess the seismicity potential of the formation.