3D Seismic Surveying for the Detection of Fractured Geothermal Reservoirs in the Upper Rhine Graben
Dr. Lotz, Ulrich
The Upper Rhine Graben (URG) is one of the most favorable geothermal provinces in Europe. A combination of increased geothermal heat flow, several potential host rock formations and intensive tectonic deformation provide a high probability to detect fractured geothermal reservoirs, large and productive enough to serve as energy source for geothermal plants.
The URG, however, yields a very complex geomechanical setting, which is basically defined by a tectonic horizontal stress caused by the northward migration of the Alps. In this stress environment the URG as a whole reacts in a sinistral strike slip movement. As consequence, compressive and extensive zones are closely associated within the graben itself.
A thorough knowledge about the position of the fault and deformation zones forming the fractured geothermal reservoirs and also the geomechanical “environment” of these zones is therefore essential for successful geothermal projects, which require minimum rates of production of geothermal water/ brine of 70 to 90 liters/sec. The degree of tectonic deformation and the orientation of the fault zones relative to the recent subsurface stress field define the (fracture) permeability of the fault zones and thus the potential production rates.
In the past most geothermal projects in the URG have been planned with 2D seismic data only – causing several projects to be not successful with respect to production rates and/ or having restrictions to production due to the occurrence of induced seismicity because the accessed reservoir zones have insufficient permeability.
Therefore the new approach is to apply 3D seismic data to reveal the tectonic and geomechanical subsurface situation as clear as possible with an available modern technique. This seminar course deals with the aims, the execution and the results of a 3D seismic survey executed in the Waghäusel-Philippsburg-Area north of Karlsruhe in den central URG.