| Title | Magnetotelluric exploration of the Gross Schönebeck |
|---|---|
| Authors | Gerard Muñoz, Oliver Ritter, Inga Moeck |
| Year | 2010 |
| Conference | World Geothermal Congress |
| Keywords | Magnetotellurics, Electrical conductivity, 2D Inversion, Low enthalpy geothermal system, Northeast German basin |
| Abstract | Electrical conductivity is a key parameter for the exploration and characterization of geothermal reservoirs as (hot) mineralized formation water of (active) geothermal areas usually exhibits significantly higher electrical conductivity than the surrounding host rock. In this work we present results of a magnetotelluric (MT) exploration experiment carried out in the vicinity of the Groß Schönebeck (Germany) geothermal test site, where a doublet system has been drilled to establish an in situ laboratory to investigate the potential for geothermal energy production. The MT data were recorded along a 40-km long main profile, centred on the doublet, and a 20-km long parallel profile, located 3 km to the east. Classical two-dimensional smooth inversion of the MT data reveals a shallow conductive layer which delineates an antiform-like shape above a Permian thick evaporitic layer. This result is consistent with information from regional geology and seismic images. However, at the northernmost part of the profiles, the conductivity models resolve deep reaching conductive structures which appear uncorrelated with existing (geophysical or geological) data. Incorporating seismic and well data as independent constraints for the 2D inversions of the MT data allows us to examine the model space rigorously but target-oriented, introducing a certain degree of subjectivity. Employing so-called tear zone inversions we can effectively derive an alternative class of models, which are consistent with the MT observations but also with the additional information. We speculate that the zones of high conductivity imaged at the level of the reservoir at approximately 4-5 km depth are related to salt lows (areas of reduced salt thickness) of the overlaying evaporite layer. The enhanced conductivity of these regions can be explained by higher porosity (fracture density) in anhydritic areas and/or generally lower resistivity of the pore fluid. |