Thermal features of the Pisa plain, a neogenic basin in central Italy.

The town of Pisa lies in the alluvial plain of the Arno river, in the north-western part of Tuscany, north-central Italy. The clastic aquifers of the plain are characterized by a slight thermal anomaly, as testified by the presence of thermal springs in the range 20-40°C distributed along the contact between the carbonate formations of the Pisan Mounts and the deposits of the plain, eastwards of the town. These springs are fed, through direct faults, by a Mesozoic carbonate-evaporitic reservoir, which underlies at depth the Whole area. The presence of this reservoir, that tops at depths around 700-1000 m, was shown by geophysical data and by deep hydrocarbon exploratory wells drilled in the 1970s' - 80s'. Thermal data from gradient wells, from water wells tapping aquifers at different depths and from hydrocarbon exploratory wells (down to 3000 m) indicate geothermal gradients in the range 50-60 °Ckm-1, and calculated heat flow values up to 100 mWm-2. This fostered the idea of a potential for medium-low enthalpy geothermal resources in the Pisa plain area, leading to a first exploratory drilling in the late 1990s'. The well turned out to be un-exploitable due to technical problems, but confirmed the potential in terms of temperature and yield. We present a 2-D thermal modeling of the plain, along two different seismic profiles, with the aim to outline the best suitable areas for a possible geothermal development.