A New Deep Exploration Program and Preliminary Results of a 3D Seismic Survey in the Larderello-Travale Geothermal Area (Italy)

Abstract

A deep exploration program at the margins and inside of mining licenses in the Larderello-Travale geothermal system has been scheduled in order to increase the steam production for supplying existing power plants with additional fluid and, in case of particular success, to supply new power plants.
Six areas, where previous deep drillings have already ascertained a temperature of about 300?C at a depth of 3000 m, have been selected for this program.
Since a statistically meaningful correlation between deep seismic signatures and fractured/productive horizons has been verified in many wells of the Larderello-Travale geothermal system, 3D seismic reflection surveys have been scheduled in order to improve a detailed individuation of these horizons and, as a consequence, to reduce the drilling mining risk.
A first survey has been carried out in the Gabbro-Sesta area (NE of the Larderello-Travale geothermal system) using dynamite as energy source and a bin size of 25 x 40 m. In spite of the rough morphology of the area, the theoretical full fold of 1600% requested at the depth of the geothermal targets (4500 m b.s.l.) has been guaranteed as average value of the interesting surveyed area.
The survey has been performed on a surface of about 60 km2 with more than 1400 shot holes drilled with at depth of about 12 m and with more than 800000 stations (12 geophones per stations) deployed. A good seismic signal resolution has been guaranteed by a maximum dynamite charge of 3 kg per hole.
The 2D stack lines processed at the end of the acquisition phase show good quality signals and very interesting reflective markers related either to the H and K horizons which are well known seismic evidences of the Larderello-Travale geothermal system. The quality of the acquired data should guarantee good results of the 3D processing phase which is still in progress.