Application Of Aem To Shallow Geothermal Potential Mapping

The “VIGOR” project aims at assessing geothermal resources in 4 regions of Southern Italy. The SkyTEM survey is a part of the planned geophysical activities and has been chosen since it is able to collect resistivity data on wide areas, with great resolution and in short times. To date, the application of AEM methods to geothermal targets has been limited, due to the depth at which the target is usually found. Kirsh and Siemon (2008) suggested its application in low enthalpy study. In this project AEM is tested in an area of known geothermal activities, and where a wealth of ancillary data is also present, in western Sicily. The results are composed in a 3D model of the electrical resistivity of the subsurface, and then interpreted for geothermal potential, following 2 main paths. The first is to produce a model of heat exchange capacity. The second aims at identifying directly conductive anomalies that might be associated to locally shallow hydrothermal fluids. “Termini” area is covered by extensive geological surveys. Since geological conditions of Sicily, even at shallow depth, are very complex, this area provided a good place for defining the resistivity values of the main geological units outcropping in the region. The “Western Sicily” area covers the main thermal manifestations of Western Sicily. Based on near real time preliminary results from the more regional mapping at 1 km line spacing, three infill areas were selected as being the most promising to test the concept. The obtained resistivity volume has then been the base for a detailed lithological and geothermal interpretation. Lithological and geological maps were used to constrain surface condition and to understand the resistivity ranges of the different lithological units. On the base of AEM derived resistivity values, and of laboratory measurements of thermal and electrical conductivity on samples, it was possible to establish the main links between lithology, electrical resistivity and thermal conductivity. The work in progress aims at extending the correlation also at depth, producing a 3D model of thermal exchange capacity for the areas surveyed. This detailed interpretative modeling provides also the basis for detecting resistivity anomalies within carbonate units, which may possibly represent hydrogeological or hydrothermal bodies.