Research on isotope techniques for exploitation of geothermal reservoirs in Western Turkey

The regional grabens of Western Anatolia of Turkey were formed by neotectonic activities since Miocene. East-west aligned Buyuk Menderes and Afyon Grabens were formed as a result of the doming uplift and mainly north-south tensional forces. The main high enthalpy geothermal fields of Western Anatolia investigated (and their reservoir temperatures) are Denizli-Kizildere (242 deg. C), Aydin-Germencik (232 deg. C). low enthalpy areas are found in Afyon (66-107 deg. C) and Soke (20-42 deg. C) regions. The Kizildere field is situated in the eastern part of the Buyuk Menderes Graben. The power plant with 20 MWe capacity was installed in 1984 by TEAS. Also, a factory started to produce CO2 in 1986 with a capacity of 120.000 ton/year. Besides 20 exploration and production wells, a reinjection well (R1), at a depth of 2261 m. was drilled in 1998 by MTA. The highest reservoir temperature determined for this area is 242 deg. C. The chemical analyses show the water type to be NaHCO3. Germencik geothermal field is located 100 km to the west of Kizildere. The temperatures of the first and second reservoirs are between 203-217 deg. C. The water types are NaCl in well waters but NaCl-NaHCO3 for springs. The geothermal waters are of meteoric origin without significant magmatic inputs. Kizildere and Germencik waters are partially equilibrated and deep reservoir temperatures estimated using different geothermometers are between 240-260 deg. C. Geothermal fluids from deep reservoirs in Kizildere and Germencik fields are slightly acidic with pH values of 5.5-5.9 and 4.9-5.5, respectively. There are clear δ18O shifts from Mediterranean Meteoric Water Line (MMWL) in Kizildere and Germencik fields that are more significant for higher temperature fields. In Soke region low temperature, small isotope shift, shallow circulation and mixing with shallow cold water and seawater are suggested. In Afyon region medium temperature (66-107 deg. C), slight isotope shift, deep and shallow circulation are postulated. (author)