| Abstract |
A total of 7 geothermal fields, covering a west-to-east transect of about 530 km along the North Anatolian Fault Zone (NAFZ), were sampled in 2000 and 2001 in an attempt to assess their geothermal potential. The studied fields are, from west to east, Efteni, Mudurnu, Bolu, Seben, Kur?unlu, Gˆzlek and Re?adiye. Both production wells and natural springs were utilized during sampling. The temperature of thermal waters ranges between 38 and 73 oC, and the pH values between 5.6 and 7.5. TDS content varies, by a factor of about 25, from 433 to 11074 mg/l. Thermal waters are almost all Na-HCO3 type except those from Bolu and Mudurnu which are Ca-Mg-SO4 and Ca-HCO3 type waters, respectively. The waters appear to have acquired their chemical character mainly through the dissolution of their reservoir rocks that are dominantly Mesozoic limestones, and/or through ion-exchange reactions on the way to surface. The chemical composition of waters, when examined together with their discharge temperatures, suggests the occurrence of subsurface mixing and conductive cooling in the geothermal fields of Kur?unlu, Seben and Mudurnu. Cation geothermometers yielded overestimated, whereas amorphous silica, cristobalite and opal CT geothermometers yielded underestimated temperatures for most of the geothermal fields. Chalcedony temperatures are almost similar to the discharge temperatures. The estimates from quartz geothermometer appeared to be more representative as they are also supported by silica-enthalpy and chloride-enthalpy mixing models applied to Kur?unlu and Seben fields. In this respect, the likely reservoir temperatures are in the range of 88-115 oC for Kur?unlu, 85-88 oC for Bolu, 143-150 oC for Efteni, 77-86 oC for Mudurnu, 110-149 oC for Seben, 97-99 oC for Re?adiye and 67-72 oC for Gˆzlek geothermal fields. From the point of geothermal potential, Efteni and Seben fields appear to be more promising for geothermal energy development. However, precautions should be taken against possible silica and calcite scaling. |