Reconstruction of Fault Architecture in the Natural Thermal Spring Area of Daruvar Hydrothermal System Using Surface Geophysical Investigations (Croatia)

Ivan Kosović, Maja Briški, Mirja Pavić (), Božo Padovan, Ivica Pavičić, Bojan Matoš, Marco Pola and Staša Borović
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Ivan Kosović: Croatian Geological Survey, Ulica Milana Sachsa 2, 10000 Zagreb, Croatia
Maja Briški: Croatian Geological Survey, Ulica Milana Sachsa 2, 10000 Zagreb, Croatia
Mirja Pavić: Croatian Geological Survey, Ulica Milana Sachsa 2, 10000 Zagreb, Croatia
Božo Padovan: Terra Compacta Ltd., Ulica Psunjska 3, 10000 Zagreb, Croatia
Ivica Pavičić: Faculty of Mining, Geology and Petroleum Engineering, University of Zagreb, Ulica Pierottijeva 6, 10000 Zagreb, Croatia
Bojan Matoš: Faculty of Mining, Geology and Petroleum Engineering, University of Zagreb, Ulica Pierottijeva 6, 10000 Zagreb, Croatia
Marco Pola: Croatian Geological Survey, Ulica Milana Sachsa 2, 10000 Zagreb, Croatia
Staša Borović: Croatian Geological Survey, Ulica Milana Sachsa 2, 10000 Zagreb, Croatia

Sustainability, 2023, vol. 15, issue 16, 1-22

Abstract: The sustainable utilization of geothermal energy mostly depends on the characteristics of the geothermal resource from which it is extracted. Among others, detailed geological modeling is a key factor for estimating the potential of a geothermal resource. This research focuses on the modeling and reconstruction of the geological setting of the Daruvar thermal spring area using geophysical techniques. An integrated geophysical approach based on electrical resistivity tomography (ERT) and both active and passive seismic (MASW and HVSR) methods was used. Based on ERT results and the stratigraphic logs of the wells in Daruvar, three resistivity layers/geological units were identified. The deepest layer with resistivity < 150 Ωm is the Triassic carbonate that constitutes the thermal aquifer. Sharp lateral variations in the resistivity distributions within the bedrock were interpreted as fault damage zones saturated with thermal waters. Integrating the results of the seismic methods, the thickness of the first seismic layer that corresponds to the Quaternary cover was estimated from 5 to 20 m. Here, results of the geophysical investigations were combined into a 3D geological model highlighting the occurrence of subvertical N-S and E-W trending faults in the Daruvar spring area. The N-S-trending fault was interpreted as a fault plane parallel to the regionally mapped Daruvar fault. This fault juxtaposes the Triassic carbonate complex of the thermal aquifer with a Neogene sedimentary sequence of significantly lower permeability. Neogene–Quaternary tectonic activity further increased the fracturing and the permeability field in the Daruvar spring area, as proven by the smaller scale E-W faults and the well logs. This fracture network permits a quick upwelling of thermal fluids resulting in thermal springs with temperatures up to 50 °C. This work proves that the construction of a detailed geological model is crucial for assessing the reservoir and fault geometries in thermal systems hosted in fractured carbonate rocks.

Keywords: ERT; active and passive seismic; fault architecture; Triassic carbonate complex; 3D geological model; Croatia (search for similar items in EconPapers)
JEL-codes: O13 Q Q0 Q2 Q3 Q5 Q56 (search for similar items in EconPapers)
Date: 2023
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