Productivity zoning and petrophysical assessment in the Munich metropolitan area for hydro-geothermal utilization using multivariate methods

The North Alpine Foreland Basin in Bavaria is one of Europe’s most important deep reservoirs for hydrogeothermal energy utilization for district heating. Most of the plants are located in the Munich metropolitan region, where there are both favorable geological conditions and a high demand for heat due to the urban character. However, the region's potential is far from fully utilized and extensive geothermal development is thus planned in the city of Munich and the surrounding municipalities. Reliable productivity prognoses help to ensure that this development is sustainable and efficient. We use the dense and comprehensive drilling data set in the region to derive a productivity zonation using multivariate methods. To do this, we derive geophysical and hydraulic parameters from the existing borehole measurements and combine them with hydrochemical, historical and technical data to derive a set of 24 individual parameters. For this parameter set, we carry out a principal component analysis (PCA) and single linkage hierarchical cluster analysis (HCA). The PCA reduces the data set to six main factors, which explain 80% of the data set variability. Of those, the most important factors fa1, fa2, and fa3, which explain 53% of the data set variability, contain mainly geological (fa1), hydrochemical (fa2), and technical parameters (fa3). The HCA reveals four main clusters, with clusters 3 and 2 in the north, 1 in the center of the study area, and 4 in the south. The spatial location of these clusters fits very well with the zoning assumed in the previous assessment analysis ‘Masterplan Geothermal Energy‘. Cluster 2 behaves very similar to cluster 3, but is separated from it by a different hydrochemistry (fa2). In addition, two outliers were identified at two doublets in the north of the study area, which are distinguished from the main clusters in one case by differing hydrochemistry and in the other case by differing hydraulic and thermal conditions. Furthermore, a sub-cluster of cluster 4 is the only one that scatters across the entire study area. However, this can be explained by factors that do not directly influence the productivity of the boreholes concerned. Our results indicate that we can divide the reservoir from north to south into three productivity types A to C, where we derive different outflow temperatures and porosities from regression equations of depth trends.

Graphical Abstract