Temporal evolution of fault systems in the Upper Jurassic of the Central German Molasse Basin: case study Unterhaching

The structural evolution of faults in foreland basins is linked to a complex basin history ranging from extension to contraction and inversion tectonics. Faults in the Upper Jurassic of the German Molasse Basin, a Cenozoic Alpine foreland basin, play a significant role for geothermal exploration and are therefore imaged, interpreted and studied by 3D seismic reflection data. Beyond this applied aspect, the analysis of these seismic data help to better understand the temporal evolution of faults and respective stress fields. In 2009, a 27 km2 3D seismic reflection survey was conducted around the Unterhaching Gt 2 well, south of Munich. The main focus of this study is an in-depth analysis of a prominent v-shaped fault block structure located at the center of the 3D seismic survey. Two methods were used to study the periodic fault activity and its relative age of the detected faults: (1) horizon flattening and (2) analysis of incremental fault throws. Slip and dilation tendency analyses were conducted afterwards to determine the stresses resolved on the faults in the current stress field. Two possible kinematic models explain the structural evolution: One model assumes a left-lateral strike slip fault in a transpressional regime resulting in a positive flower structure. The other model incorporates crossing conjugate normal faults within a transtensional regime. The interpreted successive fault formation prefers the latter model. The episodic fault activity may enhance fault zone permeability hence reservoir productivity implying that the analysis of periodically active faults represents an important part in successfully targeting geothermal wells

3D seismic survey for geothermal exploration in crystalline rocks in Saxony, Germany: 3D seismic survey for geothermal exploration

A 3D seismic survey was recorded in 2012 to explore a petrothermal reservoir in a late‐Variscan granitic pluton within the Erzgebirge (Ore Mountains) in Saxony, Germany. The main objective was to test this area in the context of the Enhanced Geothermal System concept and to test the 3D seismic technique as an exploration tool. The intention and challenge are to image and characterize potentially permeable fracture zones at target depths of 5–6 km, with temperatures above 150 °C. Unconventional methods were applied for field acquisition and data processing. The vibroseis technique was used in the core experiment, accompanied by a special explosive seismic experiment. Field acquisition was characterized by severe noise conditions and a highly irregular layout. These conditions required extensive preprocessing and data conditioning. The imaging started with conventional Common Midpoint processing for quality control and for a first reference. Better images were obtained by Common Reflection Surface processing with subsequent post‐stack time migration. Prestack time migration was also used for comparison. Outstanding results were obtained by the ‘operator‐oriented’ version of the Common Reflection Surface technique. A rich repertoire of structures within the granite pluton was imaged, including steeply dipping fault zones and conjugate faults. Images and indications of fracture and crack porosity of a prominent fault zone provide the background to define an optimum drill path. This is considered as the next stage for a possible geothermal plant, if a decision is taken to drill a research well in the future. The 3D seismic reflection technique was shown to be an indispensable tool for geothermal exploration, even in crystalline basement rocks

Geothermische Charakterisierung von karstig-klüftigen Aquiferen im Großraum München : Endbericht ; Laufzeit des Vorhabens: 01.05.2008 - 31.12.2011

[no abstract available