The nestos delta geothermal field and its relation to the associated self potential (sp) field

Abstract

Prospecting for geothermal reservoirs by geophysical methods has proved to be a challenge in recent years. In the case of Nestos geothermal field, considered to be a blind field (no surface manifestation), the geological and geophysical data were studied and intercorrelated. The geophysical results from SP, gravity, and VES data were compared with basement morphology and tectonics, as well as with the high temperatures measured in the area of main geothermal interest. As a result, the highly conductive subsurface zone and high temperatures observed on the ground surface were closely associated with a specific fracturing system. The latter was successfully mapped by the SP method. The SP method also defined certain fracture zones which, being highly electrically polarized, are hypothesized as future geothermal targets. All existing geophysical data have been re-evaluated, along with the SP data acquired over the geothermal field, and compared with the thermal contour maps and regional tectonics of the area. A deep borehole, drilled earlier in the area of the geothermal field, detected high temperatures in the basement (115°C), but very low flowrate of the geothermal fluids. According to the results of this study, this is due to the fact that the borehole was located outside the area of the main fracture zones of geothermal interest.