166 Geophysics in Geothermal Exploration and the depth of the target. The resource exploration phase and in particular that which leads to the selection of drilling targets, the estimation of the resource volume and its future performance, conditions investors’ decision-making. The key challenge is to maximize the probability of a project’s success. This document focuses on the upstream phase, resource exploration and in particular the use of geophysics to limit costs at 1 km depth maximum. This depth is well suited to a few medium-sized enthalpy projects, offering operators a favorable depth/temperature combination for heating or cooling installations, depending on the season. In specific geological contexts, these depths may also be compatible with power-generating geothermal plants. 5.2 Why electrical resistivity tomography is useful? Electrical Resistivity Tomography (ERT) is a rather low-cost geophysical method, even when it comes to obtaining a three-dimensional image of the subsurface. The method highlights the electrical conductivity of the different parts of the subsoil. Over and above the intrinsic properties of geological formations, it is sensitive to weathering processes, water content and temperature. It has proved its worth not only in tabular geological environments, but also in geological systems with more complex geometries. 5.3 Deep electrical resistivity tomography for geothermal exploration – an Italian example This article describes an example of a geophysical campaign performed by GEG Experts in Central Italy, in particular a Deep Electrical Resistivity Tomography (DERT) campaign, the aim of which is to gain a better understanding of the subsoil in order to assist operators of the medium-depth geothermal resource, while taking care not to disturb the upper aquifer. The shallow aquifer, located around 300 m from the surface, is used to capture freshwater for domestic use. The deeper aquifer is potentially saturated in hypothermal water (temperature between 20 and 30 °C) or thermal water (temperature between 30 and 40 °C). The initial ambition was to have a better knowledge over 1 km2, at a maximum depth of 800 m.
RkJQdWJsaXNoZXIy NjA3NzQ=