APPLICATION OF THE ELECTROMAGNETIC GEOTHERMOMETER IN GEOTHERMICS AND GEOTHERMAL EXPLORATION
V.V. Spichak, O.K. Zakharova
Geoelectromagnetic Research Centre of the Schmidt Institute of Physics of the Earth, Russian Academy of Sciences, Troitsk, Moskovskaya obl., 108840, Russia
Keywords: Electromagnetic geothermometer, temperature, electromagnetic sounding, heat source, supercritical fluids, boreholes
Abstract
The latest results on electromagnetic geothermometry and its use in geothermics and geothermal exploration have been covered. Temperature models for the well-known geothermal areas, Larderello-Travale (Italy), Soultz-sous-Forêts (France) and Hengill (Iceland), constructed from electromagnetic sounding data and temperature well logs have been analyzed. 2D temperature model built along the magnetotelluric profile crossing the Travale (Italy) geothermal system allowed to locate a potential supercritical reservoir at the depth between two isotherms, TSCF ~ 400 °C and TBDT ~ 600 °C, coinciding with the seismic reflectors, detected earlier. 3D temperature model of the Hengill (Iceland) geothermal area built up to the depth 20 km, using electromagnetic sounding data, allowed us to locate high-temperature magma pockets at shallow depth (2-5 km); these magma pockets can be regarded as targets for geothermal exploration. Joint analysis of the specific resistivity and temperature models, taking into account gravity anomalies, allowed us to locate the zones of different thermal regimes within the crust; this, in turn, explained the observed seismicity pattern by thermo-mechanical properties, rather than by crust spreading. Deep temperature model, built for the Soultz-sous-Forêts (France) geothermal area from magnetotelluric data and temperature well logs, used to locate deep heat sources and predict heat transfer mechanism at depth up to 8 km.
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