The growing interest in geothermal energy as attractive supply of base load energy is
demanding technological progress and more sophisticated analyses of the available
resources. Former geothermal evaluation methods traditionally used interpretation
methods based on a one-dimensional layered medium. Recent computational progress,
allows application of 3D numerical models, for visualization and calculations. As
such, GEOWATT AG has integrated available geothermal data into GOACAD models covering
multiple areas of the Swiss Plateau of approximately 30x30 km2 size. The models focus
on well-known aquifer systems like Upper Marine Molasse, Cretaceous Malm, Upper
Muschelkalk and Crystalline Basement. In order to extrapolate the temperature from
individual boreholes to arbitrary subsurface points an extensive numerical procedure
was chosen. The 3-D geological model was transformed into a finite element mesh. By
discretizing the subsurface into tetrahedra the geological structures were exactly
reproduced. After calibrating the numerical model with measured temperature data, the
temperature of individual aquifers can be reproduced. This allows a classification
into formations that are promising for pure heat utilization (T<100°C) or for
combined heat and electricity production (T>100°C, higher temperatures yielding
higher efficiencies). The future utilization of high temperature systems depends on
the identification of appropriate formations. The recent experience from existing
geothermal projects in the Rhine Graben (Soultz, Landau) highlights the importance of
naturally fractured systems for the success of geothermal systems. An important
concern is therefore the identification and characterization of subsurface
permeability. Here, the geothermal mapping allows one to identify these systems by
evaluating possible advective signatures in the temperature field. Well-permeable
systems are often evident from a convective fluid pattern that have an important
impact on the thermal energy distribution in subsurface.  Various examples of
circulation systems will be shown. The swiss resource geothermal resource atlas
indicates a possible annually extractable energy of 10 PJ per km3 that would
potentially cover a broad range of Swiss energy needs.

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