Recent Deep Exploration Results at the Margins of the Larderello-Travale Geothermal System

Abstract

Within the framework of research in the marginal areas of the LarderelloñTravale geothermal system, several exploration wells have disclosed an extension of the deep reservoir even below zones of medium or low superficial thermal anomaly. NE of the Larderello field, Sesta_6bis well crossed a known low temperature (100?C) CO2 saturated carbonate aquifer, but, at greater depth, in the phyllitic metamorphic basement, a steam reservoir has been discovered at 2400ñ2800 m. The temperature and pressure are similar to those recorded at the Travale field (300?C and 70 bar). Two other wells have been drilled in the area south of Travale characterized by large outcrops of permeable carbonate rocks. These constitute the shallow reservoir, bearing fresh meteoric waters, which mask any deeper thermal information. The well Travale Sud_1 crossed several steam productive layers between 2280 and 2890 m in thermometamorphic and granitic rocks. The reservoir temperature and pressure are 300?C and 70 bar. The well Montieri_4 crossed a thick carbonate sequence and then a granitic body from 2000 m to the bottom hole (3700 m), with rather low permeability but with the same temperature and pressure as the deep Travale reservoir. Surprisingly, injection and acidification tests have improved the hydraulic connection with the reservoir. All the above-mentioned exploration wells have proved to be productive and confirmed the extension of the deep steamdominated reservoir in marginal areas where the superficial thermal gradient is low. The deep reservoir is located at a depth of about 3 km inside the metamorphic basement and the granitic body. On the basis of these results, the exploration has been extended and specific development projects have been planned.