GEOTHERMAL POTENTIAL OF THE SWISS MOLASSE BASIN

The Swiss Molasse Basin (SMB) is characterized by a relatively smooth temperature field (average geothermal gradient 30-degrees-C/km with a slight tendency for the gradient to decrease from north to south). In terms of geothermal energy potential (=''possibilities to use the heat content of the subsurface'') several categories are addressed: a) thermal springs, b) stratiform aquifers, c) artificial systems (shallow geothermics: Vertical earth heat exchangers, VHE; deep geothermics: Hot Dry Rock, HDR). The absence of thermal springs in the SMB is indicative of generally low vertical permeability of Molasse sediments. Several potential regional aquifers can be identified: Obere Meeresmolasse, top Mesozioc carbonates (?), Oberer Muschelkalk. Exploration and development risk increases with depth; a potential assessment with rather optimistic assumptions yields marginal figures. On the other hand, VHE potential is considerable (at least 5000 TJ/a); the SMB exhibits the highest VHE density in the world. The potential of HDR systems is difficult to assess; figures in the range 50000-500000 TJ/a might be conservative. This option still requires intensified research and development efforts.