Geothermal potential of sedimentary basins, especially of the Swiss molasse basin

Abstract

Sedimentary basins usually have significant geothermal potential. Deep aquifers are key components. The factors, conditions, and processes that define and control the potential are on one hand the processes during basin formation like sedimentation, karstification, fracturing; for utilisation on the other the reservoir rock properties porosity, permeability; depth/temperature; the hydrogeology and nowadays the production sustainability (“specific characteristics”) are decisive. These latter characteristics are demonstrated on selected examples: USA basins, Paris Basin, Molasse Basin. Of the latter, the French, German and Austrian parts are described first and then the Swiss Molasse Basin (SMB) in more detail. The various efforts undertaken to assess and quantify the SMB potential are described, with example maps presented. The realisations of the SMB potential so far are really modest: of 10 deep drilling projects performed in various locations to date only one is successful and two are partial success. On the other hand, the geothermal heat pump systems develop mainly in the SMB, in a globally leading way. The official Swiss energy strategy EN2050 includes electricity supply in the future; this assigns 4.4 TWh to geothermal sources in 2050. This would be delivered from geothermal power plants, foreseen are 250 MWe installed capacity from hydrothermal reservoirs, and another 250 MWe from petrothermal (EGS) sources. Only the SMB could host hydrothermal resources, but the current data do not show much potential. In principle, EGS plants could take heat (and convert it to electricity) from below the SMB. The EGS technology itself has great potential but it is still in the proof of concept stage. Intensive R&D is ongoing in several countries, however very substantial funding will be needed to answer the many questions still open.