Conceptual model of the Savat (Artvin/NE Turkey) Geothermal Field developed with hydrogeochemical, isotopic, and geophysical studies


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GÜLTEKİN F. , Temizel E. H. , BABACAN A. E. , KIRMACI M. Z. , Ersoy A. F. , Subasi B. M.

GEOTHERMAL ENERGY, cilt.7, 2019 (SCI İndekslerine Giren Dergi) identifier identifier

Özet

The Savat (Artvin, Turkey) Geothermal Field (SGF) is located on the northeastern border of Turkey. This field is characterized by thermal and mineralized springs and travertine. The temperature of the thermal water is 36 degrees C, whereas that of the mineralized spring in the area is approximately 11 degrees C. The Na-HCO3-Cl-type thermal water has a pH value of 6.83 and an EC value of 5731 mu S/cm. The aim of this study is to characterize the geothermal system by using geological, geophysical, and hydrogeochemical data and to determine its hydrochemical properties. A conceptual hydrogeological model is developed for the hydrogeological flow system in the SGF. According to the hydrogeological conceptual model created by geological, geophysical, and hydrogeochemical studies, the reservoir comprises volcanogenic sandstone and volcanic rocks. The cap rock for the geothermal system is composed of turbiditic deposits consisting of mudstone-siltstone-sandstone alternations. An increase in the geothermal gradient is mainly due to Pleistocene volcanic activity in the field. The isotopic values of thermal water (O-18, H-2, H-3) indicate a deeply circulating meteoric origin. The estimated reservoir temperature calculated by silica geothermometers is 100-150 degrees C, and the mixing rate of cold groundwater with geothermal waters is approximately 70%. It may be possible to obtain warmer fluids from a 300-m-deep borehole cutting through a fracture zone identified by geophysical studies. Heating by conduction via the geothermal gradient resulting from young volcanic activity drives geothermal waters upwards along faults and fractures that act as hydrothermal pathways. The positive C-13(VPDB) value (+4.31 parts per thousand) indicates a metamorphic origin for the thermal water. The S-34(CDT) value (similar to 10 parts per thousand) shows that the sulfur in the geothermal water is derived from volcanic sulfur (SO2).