Geological structure of a long‐living geothermal system, Larderello, Italy

Abstract

We have examined the data of 600 geothermal wells and reinterpreted approximately 500 km seismic profiles through the field of Larderello, Italy. We conclude that the two main seismic reflectors present below the geothermal area host two different fluids: (1) superheated steam in the upper H-horizon (reached by drillholes) and (2) supercritical fluid in the deeper K-horizon (reached by few unproductive or damaged wells). The superheated steam has the physical and chemical connotation of the geothermal fluid exploited so far at Larderello, whereas the supercritical fluid represents a potential unconventional deep-seated resource still to be assessed. The high temperatures existing in correspondence of the K-horizon suggest that the silica-rich rocks are close to a plastic state and the fluids should remain confined in a medium sealed to the confining rocks, unless occasional fluid overpressure and abrupt high strain rates occur.

Hengill geothermal volcanic complex (Iceland) characterized by integrated geophysical observations

“…In the Larderello geothermal field, supercritical fluids were found at the K-Horizon (3-4 km depth), and due to the high temperature prevailing at that depth, rocks are close to a plastic state (Bertini et al, 2006). Brittle-plastic conditions are strongly dependent on both temperatures and strain rates.…”

Experimental Investigation of Biotite-Rich Schist Reacting with B-Bearing Fluids at Upper Crustal Conditions and Correlated Tourmaline Formation

“…Such a system, imaged by geophysics, would constitute a super-hot reservoir present below the presently exploited Larderello-Travale geothermal reservoirs and constitute a potentially valuable exploration target. Plio-Pleistocene granites under the Larderello-Travale intruded a metamorphic complex similar to that existing in eastern Elba Island [36,62]. Thus, also in the Larderello-Travale the interaction between biotite-bearing rocks and B-rich saline fluids, exsolved from acidic intrusion, caused extensive tourmalinisation, as indicated by the finding of schorl-dravite-ferridravite tourmalines in the deep wells of the Larderello-Travale geothermal field [8,17].…”

Migration of geothermal fluids in extensional terrains: the ore deposits of the Boccheggiano-Montieri area (southern Tuscany, Italy)

“…With this goal, several methodologies have been proposed in presently active geothermal systems: from numerical simulations of fluid circulation (e.g., Bertani and Cappetti 1995;Zhang and Sanderson 1996;Kloditz and Clauser 1998) to integrated interpretation of geochemical (e.g., D'Amore and Bolognesi, 1994;Minissale et al 2000;Magro et al 2003) and geophysical and structural data (e.g., Werner and Kahle 1980;Rowland and Sibson 2004;Accaino et al 2005;Lüschen 2005;Brogi et al 2005;Bertini et al 2006;Finetti 2006). The integration among these approaches leads to fluid flow models describing the relationship between the crustal structures and the geothermal resources (Younker et al 1982;Clauser and Villinger 1990;Muraoka et al 1998;Furuya et al 2000;Bellani et al 2004).…”