Florian Duschl1, Michael Drews1, Harald Stollhofen2
1Technische Universität München, Deutschland; 2Friedrich-Alexander-Universität Erlangen-Nürnberg
Comprehensive knowledge on current stress fields is crucial for predicting geomechanical behavior and fault response during drilling. Where data from existing drill sites is scarce, the current stress conditions in a geothermal reservoir can be approximately determined from the structural evolution of the basin. Therefore, detailed information on tectonic styles and (paleo-)stress fields in sedimentary basins are obtained from fault and fracture patterns, and kinematic indicators such as stylolites and slickensides.
This study compares the tectonic styles and stress fields of two geothermal provinces in Bavaria based on paleo kinematic data and fault and fracture pattern analysis: a) the Molasse Basin (MB), as part of the North Alpine Foreland Basin, and b) the adjacent Franconian Basin (FB). While the MB has been subject to geothermal exploration for several years, the FB locally shows promising potential but is yet underexplored. Apart from the analysis of thermal anomalies and of the structural framework, no specific investigations with regard to geothermal use have been carried out in the FB so far.
Our focus lies on the central and southern part of the FB and the northern MB where solid data on maximum horizontal stress are lacking (Reiter et al. 2016), which underlines the need for a reevaluation of the structural inventory. The study area marks the transition zone between the tectonic regimes of the Alps in the south and of the Bohemian Massif in the northeast, where N-S directional horizontal stress (MB) are replaced by NW-SE directional horizontal stress (FB). While the MB is characterized by mostly clastic sediments that represent the erosional products of the emerging Alpine Orogenic Belt in the Cenozoic, the formation of the FB dates back to the collapse of the Variscan Belt in late Paleozoic times. Despite their different age and geologic history, the basins were affected by the compressional tectonics of the Late Cretaceous inversion (FB) and the Alpine Orogeny (FB/MB) (Kley & Voigt 2008), which had a massive impact on their structural evolution.
We define similarities in terms of structural inventory and fault kinematics between the two basins that allow us to better understand current stress fields as well as to predict fault and fracture-controlled bypass-systems and failure mechanisms in potential geothermal reservoirs in respective basin systems. We use published data of known maximum horizontal stress and of fault systems in order to compare them to fracture patterns derived from our own DEM-based lineament analysis.
Jonas Kley, Thomas Voigt; Late Cretaceous intraplate thrusting in central Europe: Effect of Africa-Iberia-Europe convergence, not Alpine collision. Geology ; 36 (11): 839–842. doi: doi.org/10.1130/G24930A.1
Reiter, Karsten; Heidbach, Oliver; Müller, Birgit; Reinecker, John; Röckel, Thomas (2016): Stress Map Germany 2016. GFZ Data Services. doi.org/10.5880/WSM.Germany2016_en
