Geochemistry of the Kizildere- Tekkehamam- Buldan- Pamukkale geothermal fields, Turkey

Abstract

The Kizildere and neighbouring geothermal fields are located in the Büyük Menderes and Gediz grabens and intersection of these grabens. The chemical composition of waters in the study area is governed by rock-water interaction, but does not reflects a peripheral or steam heated origin. The geothermometry temperatures for Kizildere well waters vary between 188°C and 245°C. By comparison with measured temperatures in drillholes at Kizildere it is concluded subsurface temperature in the Kizildere and Tekkehamam areas must be quite similar. In the other areas reservoir temperatures are relatively low. The waters of the Buldan and Pamukkale groups are immature to partly equilibrated, the Tekkehamam and Kizildere waters have evolved close to full equilibrium. The scaling in Kizildere wells is a major problem and causes decline in well productivity. The main scale formation in the wells is calcite. In the flashing zone, loss of CO2 leads to increasing pH and strong supersaturation with respect to calcite and subsequent precipitation of this mineral. The water discharged from Kizildere wells is also supersaturated with respect to calcite. It is the increase in CO3-2 and Ca+2 concentration associated with the boiling degassing and cooling of the aquifer waters that is responsible for the produced calcite supersaturation. Various evidence such as the linear relationship between d18O and Cl, and between Cl and B, and the plots on the Na-K-Mg diagram, indicates that mixing has taken place between cold and hot water in upflow zones. The silica-enthalpy and the chlorine-enthalpy mixing models were applied to estimate subsurface temperatures in the study area. These models give similar reservoir temperatures as the chemical geothermometers.