Exploring for geo-energy resources in the geneva basin (Western Switzerland): Opportunities and challenges

A regional-scale evaluation of geothermal energy resources and subsurface heat-storage potential are being carried in the westernmost part of Switzerland and the nearby surrounding France (Haute-Savoie and Ain Departments) in the framework of the 'GEo-therme2020' and Swiss national SCCER SoE programs. These activities are promoted by the Canton authorities and the Services Industriels de Geneve. A large data set of 2D seismic lines from different surveys and vintages have been collected, in some cases, reprocessed and integrated in a single data base with newly acquired seismic and borehole data. This forms the basis for the definition of the subsurface stratigraphy and the identification of regional variability of key geological formations. The latter span from the Permo-Carboniferous to the Cainozoic time period, including potential geothermal reservoirs such as the Palaeozoic and Tri- A ssic sandstones and several limestones intervals throughout the Mesozoic series. A detailed mapping of fault systems is being carried out with specific focus on the deeply rooted lineaments which may allow connectivity between the crystalline basement and shallower stratigraphic formations. In particular, attention has been given to the lineaments controlling the Permo-Carboniferous extensional structures and their possible reactivation at later stages during the Alpine inversion and the present day tectonic regime as normal, inverse or transpressive faults. Downhole temperatures from deep boreholes drilled in the study area suggest a gradient ranging between 25 and 30 °C/km. These data have been used in junction with regional and newly acquired Bou-ger-anomaly gravity maps, distribution of historical and recorded earthquakes epicentres and results of ongoing passive seismic monitoring. The ongoing examination of these different data sets aims at definig both geothermal and hydrocarbon plays in support of further evaluation and risk assessment, including the possible undesired occurrence of hydrocarbons, of the regional geothermal potential. This will ultimately assists in the identification of a number of most suitable subsurface targets for both direct use of heat and heat-storage. © 2019 Ver. Schweizerischer Petroleum Geol. und Ing.. All rights reserved.