| Abstract |
The project I-GET (Integrated Geophysical Exploration Technologies for deep fractured geothermal systems) is co-funded by the European Commission within the 6th Framework Programme for Research and Technological Development. Within the project, 11 partners from 6 European countries have joined forces with the objective to develop a methodology to improve the detection, prior to drilling, of fluid bearing zones in naturally and/or artificially fractured geothermal reservoirs. The basic idea is to integrate data and measurements from several existing geophysical methods into one final reservoir model. This new approach has been tested at four European geothermal systems (Figure 1) with different geological and thermodynamic reservoir characteristics: two high enthalpy (metamorphic rocks in Travale, Italy and volcanic rocks at Hengill, Iceland), and two middle enthalpy geothermal systems (deep sedimentary rocks in Gross Schönebeck, Germany and Skierniewice, Poland). The high-enthalpy site Travale in Italy is part of the extensive reservoir used since 1904 for energy production at Larderello. The productive zones of the deep reservoir occur mainly within contact metamorphic carbonate rocks above a granite intrusion. Less productive fractured levels are also found inside deeper granitic bodies, where temperatures do not exceed 330°C. Deep wells did not meet productive levels where recorded temperatures exceed 350 °C. The lowest boundary of this reservoir still represents an open question. At Travale, existing seismic lines from a 3-D seismic dataset were reprocessed for a joint interpretation with magnetotelluric (MT) data acquired within the project (Figure 2, overleaf, Manzella et al., 2006). In addition, advanced analysis of the seismic data (azimuthal analysis of the seismic signal amplitudes reflected from the geothermal targets and AVO analysis on a selected 2D profile from the 3D seismic volume) provides information about preferred fracture orientation. These measurements visualize the target horizon as a distinct reflector (Fiordelisi et al., 2005) and low conductivity zone (Mayorga & Manzella, 2007) independet of the lithology, which coincides with a productive zone containing dry steam. |