A numerical approach to verify the reservoir temperature of the Afyon geothermal fields, Turkey

Authors: ÖZGÜR KARAOĞLU

Abstract: Geothermal energy constitutes an important renewable resource in Turkey that has been extensively utilized for heating buildings, power generation, greenhouse farming and various other industries. One of the most remarkable geothermal locations in Turkey is the low-enthalpy area of Afyon, where five main low-temperature (30-110 °C) geothermal fields are exploited. However, further exploration drilling sites have proven inconclusive, casting doubts on the effective presence of high-temperature geothermal systems in the region. Part of the challenge is that the geometry, size and depth of the heat source of the geothermal system is poorly constrained. It is documented that the Afyon region hosts voluminous and well-preserved potassic/ultrapotassic volcanic successions that formed between 15 and 8 Ma. It is also well known that volcanoes are fed by magma chambers and reservoirs which can be linked to fault zones and geothermal systems. In this study, the origin of the geothermal systems in Afyon is explored by considering the maximum recorded well-head temperature of 110 °C and the estimated reservoir temperature of 125 °C from hydrochemistry data. The calculated and measured temperatures are interpreted in terms of thermal finite element method models.Various thermal models illustrate the possible temperature distribution throughout the crust assuming an arrangement of a crustal magma chamber and a geothermal gradient of 30 °C/km. Results show that the temperature of the fluids at the measured well-head temperature of 110 °C, or estimated reservoir temperature of 125 °C, require the presence of a magma chamber with a temperature in the range 600-800 °C at a depth of 5-7.5 km. These two-dimensional models that simulate crustal geothermal gradients can be used with suitable modifications, to advance the understanding of other geothermal fields.

Keywords: Magma reservoir, temperature, geothermal systems, longevity, heat transfer

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