Imaging the deep structures of the Larderello geothermal field (Italy) by electrical resistivity measurements: the IMAGE experiment

Abstract

We are developing an integrated method for exploring deep geothermal systems based on electrical resistivity surveys. The test site is the Larderello geothermal field (Italy).
Despite the amount of geological and geophysical data acquired in the frame of previous exploration projects in the area, several critical issues are still matter of debate, e.g., permeability distribution in the hydrothermal reservoir and the presence of fluids at supercritical condition at depth.
We have recently carried out a new broadband magnetotelluric (MT) survey in the western sector of the Larderello field. MT soundings (22) were acquired using a remote site in Capraia Island (Tuscan Archipelago) as Remote Reference measurements; this was necessary to overcome the anthropic electromagnetic noise affecting the data.
We have designed an experimental high resolution Surface-Hole Deep Electrical Resistivity Tomography (SHDERT), in order to constrain the resistivity response at the depth of the hydrothermal reservoir hosted in the crystalline units. A deep geothermal well kindly provided by Enel GP and located in the central sector of the MT survey area, was used for the experiment.
The design of the in-hole experiment and the preliminary results of the MT survey are hereby presented. The experiment represents a challenge and an opportunity for the applied geophysics.