3D Seismic for the Deep Exploration of the Travale Geothermal Field (Italy): I-GET Project Results

摘要

In 2003-2004 Enel carried out the acquisition of 3D seismic surveys in a few areas of the Larderello-Travale geothermal system. In the framework of the European project "Integrated Geophysical Exploration Technologies for deep fractured geothermal system" (I-GET), advanced analyses have been applied to 3D seismic data of the Travale test site, where a deep superheated steam reservoir is hosted in metamorphic/intrusive formations at a depth greater than 3000m. Reservoir productivity is linked to fractured and permeable levels that are rather confined and not uniformly distributed and that often give rise to high amplitude seismic reflections. Thus, seismic data processing was aimed at the proper treatment of signal amplitudes and at the detection of the peculiar seismic signatures, as well as at the reconstruction of subsurface seismic images. All the available surface and well data of the Travale site have been utilized for an integrated interpretation that was initially oriented to update the geological and structural model. Geophysical well logs were acquired in the framework of the IGET project, and together with all the other available logs, were very useful for calibrating surface seismic. A second interpretative step was the detection of deep seismic markers that can be interpreted as potential targets for explorative wells. To this end, pre-stack and post-stack signal amplitude analyses were focused on identifying areas characterized by anomalous amplitude values. As testified by a significant number of wells, the most important deep seismic reflector in the study area is represented by the "H" horizon that, from a geological point of view, is the expression of a contact metamorphic aureole characterized by a higher fracture density. In order to assess the reliability of this seismic marker as a drilling and productive target, a detailed study has been carried out comparing the steam production from fractures occurring inside and outside the seismic horizon. As a result of this analysis the production supplied by fractures within the H marker was more than 70percent of the total.