A review of geothermal exploration by magnetotelluric imaging in Tenerife

Abstract

The geothermal potential of the Canary archipelago has been extensively studied since the mid-seventies, with a particular focus on Tenerife. Several agencies and institutions conducted magnetotelluric surveys in Tenerife characterizing the electrical resistivity distribution of the subsurface. The resultant 3D resistivity model shows the classical geoelectrical distribution of a high-temperature geothermal system, with a conspicuous low resistivity structure interpreted as the hydrothermal alteration zone (clay cap) that sits above a more resistive zone, which may correspond to rocks at higher temperatures. This paper is a review of the MT studies carried out in Tenerife for geothermal exploration, including the results obtained when correlating the resistivity model with other geophysical and geochemical data. Additionally, a second-derivative model of the resulting MT model has been used to define the main interfaces between the geoelectrical structures. Geothermal exploration in the Canary Islands dates back to the mid-Seventies, when the Spanish Geological Survey (IGME) started a nationwide project to study this resource in the whole Spanish territory. This archipelago was the main target of this study owing to its active volcanism. The works were focused particularly on the islands of Gran Canaria, Lanzarote, La Palma and Tenerife, including volcanological, petrological, geochemical and geophysical studies. In the particular case of Tenerife, the main activity took place in the last stage of this nationwide project. Among the studies performed during these years, two magnetotelluric (MT) surveys were conducted in 1987 and 1991, covering the centre of the island. As a result of these works, four major areas of interest were defined, and the gradient well, Tenerife-1, was drilled in the north-west of the island. The geothermal exploration in the Canary Islands stopped in 1993. In 2007 Petratherm S.L and the Technological Institute of Renewable Energy (ITER) started a new project encouraged by the geothermal potential revealed by the previous studies. The collection of vintage data, as well as new geostructural, geochemical and geophysical surveys, were the main activities conducted in this new research stage (Hidalgo, 2010). Tenerife was, once again, the main target of the geothermal investigation. During this period several MT surveys were conducted in the island, in 2009, 2012 and 2013. The resulting 3D resistivity model images the internal structure of the island help us to characterize the seal/reservoir system.