History of Exploration and Exploitation of Geothermal Energy in the Zagreb Geothermal Area (Croatia)

Abstract

Zagreb Geothermal Area (ZGA) with its history of exploration and exploitation of geothermal waters, currently known geothermal energy potential and actual quantity of geothermal energy is presented in this work. The sixties of the last century saw the discovery of significant geothermal potential as a result of intense drilling in the area. In the course of over 40 years 17 exploration and exploitation boreholes have been drilled to the depths of 500 to 2200 m. Geothermal aquifers were drilled in many cases. A few geothermal aquifers have been discovered at the depth of 300 to 1000 m with temperature of 30 to 80 0C. There are two types of aquifers. The main type is represented by the Triassic dolomite breccias, dolomite and dolomite limestone while the less important type includes the Miocene bioclastic limestone. On some locations both types occur. Water from the boreholes is widely used for the purpose of heating, breeding fish as well as for greenhouses and warming the swimming pools. Currently, the geothermal waters are in use on four locations in ZGA but their geothermal potential is only partly utilized.