THE APPLICATION OF THE TRANSIENT EM METHOD INTO THE GEOTHERMAL FIELD EXPLORATION

Abstract

In this work we examine the potential of the time-domain electromagnetic method (Transient EM) in the exploration of geothermal field and the study of the geological environment. The method was applied in the geothermal field of Aristino (Alexandroupolis), westwards of the Traianoupolis, where the known hot springs exist. The EM method and more specifically magnetotellurics (MT), it has been applied in the past in Greece by various researchers, but it is the first time the TEM method is applied for geothermal exploration purposes. As it has been shown by previous works, in the wider region of Aristino an important geothermal field is developed, with geothermal fluid temperature of 30°-90° and high content of dissolved salts of 10gr/lt. These factors result to the appearance of highly conductive geoelectrical anomalies which are directly related to the geothermal field. The existence of two drillholes in the region allowed the calibration and the control of the effectiveness of the TEM method. The geophysical survey has delimited the area of local geothermal interest that is formed by hot aquifer at a relatively shallow depth, extended North of Aristino and between the main faults of the region. The two main faults are responsible for the creation of a tectonic graben in the intermediary region and the development of a highly conductive formation which correlates well with the hot aquifer tank. The geothermal fluid circulates through the faulting system having high temperature caused by the contact with magmatic masses. The application of TEM proved the operational advantages of the method in the geothermal field exploration. The relatively limited number of TEM soundings presented here does not allow the export of safe conclusions regarding the geothermal field of the wider region, although the evaluation of results based on the geological and geoelectrical data of the region is extremely encouraging and justifies the use of the TEM method in the systematic study and mapping of geothermal fields.