Exploration and Exploitation of Geothermal Waters in the Zagreb Area

Abstract

In the sixty's of the last century in the Zagreb area was discover significant geothermal potential by drilling. Today is in use only a part of this geothermal energy potential. By drilling have been discovered some few geothermal aquifers in the depth from 300 to 1000 m. The temperatures in these aquifers are from 30 to 80 0C. Main aquifers are the Triassic dolomitic breccias, dolomite, and dolomite limestone, less important aquifers are the Miocene bioclastic limestone. Geothermal gradients on locations of single boreholes are very different, and the temperatures in the depth of 500 m vary from 27 to 52 0C. After the heat conductivity values, the Tertiary formations in that area represent the heat isolator, while the Triassic dolomite in their base represent the heat conductor. The mean value of the terrestrial heat-flow density is 83,6 mW/m2. The lowest value is 58,6 mW/m2 (well Jarun-1), while the highest amounts are up to 102 mW/m2 (well KBNZ-1B). The most of the calculated terrestrial heat-flow density values in the Zagreb area in the central part of Europe represent the positive anomaly.