| Title | Geothermal Evaluation of the Bayramhacýlý and Tekgöz-Çiftgöz Area, Central Anatolia, Turkey by a New Conceptual Reservoir Model |
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| Authors | Uður Erdem DOKUZ, Mehmet ÇELÝK, Yusuf Kaðan KADIOÐLU, Maren BREHME, Hilal ENGÝN |
| Year | 2015 |
| Conference | World Geothermal Congress |
| Keywords | hydrogeochemistry, conceptual model, water-rock interaction, Central Anatolia |
| Abstract | More than 250 low to medium enthalpy geothermal fields in turkey cover an estimated potential of 60,000 MWt. The Central Anatolian Volcanic Province hosts twelve geothermal areas. One of these fields is located near to Kayseri City, SE of Ankara. In order to evaluate the geothermal area with a focus on hydrochemical characteristics hot and cold springs, as well as wells and rivers were sampled during dry and wet season. Water samples were analysed for major and minor elements. Rock analyses disclose the detailed petrography and alteration patterns, revealing the hydrothermal influence. Discontinuity measurements on fractures were done as faults and fractures are assumed to be the controlling factor on geothermal groundwater flow. Calculations of saturation states and geothermometers complete the evaluation considering the water-rock interaction in the area. The main outcome of this study is a conceptual reservoir model of the adjacent areas Bayramhacýlý and Tekgöz-Çiftgöz. A considerable part of the water infiltrates downward through the fractured marbles, other discontinuities and the permeable and semi-permeable areas. But also the rise of fluids is controlled by fractures. Both the Tekgöz-Çiftgöz and Bayramhacýlý springs are generally aligned at NE-SW and NW-SE trending faults. Residence times of Bayramhacýlý springs are 45-50 years based on tritium. During circulation, the infiltrated waters are hydrochemically enriched and heated by both the geothermal gradient and the magmatism feeding Erciyes volcano. The groundwaters circulating in marbles are partially also in contact with volcanosedimentary cover units and with the syenites. As a result, they are enriched with Na by ion exchange. A Na/K vs. K/Rb plot shows that thermal waters are in equilibrium with the basement metamorphic rock units. The elevated concentrations of Ca and HCO3 and decrease of pH in springs are mainly related to the high CO2 contents that result from interactions with carbonate rocks. In conclusion, the formation and development of the mineral composition of Bayramhacýlý, Tekgöz and Çiftgöz geothermal springs are influenced primarily by the geological setting, effectiveness of the active faults and high geothermal gradient based on magmatic activity. The Bayramhacýlý springs are recharged by a regional hydrogeological system that is deep and wide, while the Tekgöz and Çiftgöz springs are recharged by a local shallower system. In the previous studies, only marbles were taken into consideration during geothermal reservoir exploration in the area but obviously syenites and basalts play a major role as well. This conceptual geothermal reservoir model is a new contribution to studies in the Central Anatolian area and general geothermal studies in Turkey as it explains general processes of subsurface fluid flow and water-rock interaction in geothermal systems. |