Application of chemical geothermometers to low temperature fields in Southern Bulgaria

Abstract

Bulgaria is quite rich in thermal waters with temperatures between 20 and 100 C. In Southern Bulgaria there are more than 600 hot springs and wells in about 120 localities. This report made use of 203 chemical analyses from different hot springs and wells. The chemical composition of the thermal waters from 18 fields were interpreted by chemical geothermometers. Four fields, Burgas, Kazanlak, Razlog and Sofia, were selected as suitable areas for interpretation of all samples. The main results of this report are predicted temperatures for about 200 samples using various quantitative chemical geothermometers (chalcedony, Na-K, Na-Li, Na-K-Ca and K-Mg). Chemical equilibrium calculations were made using the computer programme WATCH and plotting the log(Q/K) diagram. It was found that water with temperatures 10-20 C higher than are now found, could be obtained by drilling in several areas in Southern Bulgaria. It is likely that about 10% of the geothermal occurrences could be used directly for heating because they have temperatures above 70 C. This might mean expanded utilization of hot water in Southern Bulgaria, which at present is used directly and indirectly in spas, swimming pools, greenhouses but only in a few cases for heating.