Der Einfluss heterogener Störungszonen auf den Thermalwasserfluss im Aquifer des Malms im Bayerischen Molassebecken – Eine Sensitivitätsanalyse durch hydraulische Simulationen
O 12.2 in Thermal groundwater utilization
14.04.2016, 10:30-10:45, Audimax A, Geb. 30.95
For the geothermal exploration the Malmaquifer located in the northern foreland basin of the Alps is really important as a groundwater reservoir. The reasons for that are its orientation and properties, which imply a big geothermal potential that is already used in thirteen locations in the area of Munich. Several new exploration sites are under construction or being planned. This work supports the investigation of a new site in the southwest of Munich carried out by the company Erdwärme Bayern. Therefor the flow in a faultsystem that is known from seismic data is analyzed by the use of a detailed numerical model. The model is nearly 1650 meters long, 1000 meters wide and about 650 meters high. To accomplish that the open source software OpenGeoSys is being used. By applying an unstructured mesh OpenGeoSys allows to implement faults into the model that have a complex shape in 3D space without simplifying any geometry which is derived from seismic data. Besides the planned drilling path the model considers three geological units. These units contain the rocks from Malm-Alpha to -Gamma, Malm-Delta & -Epsilon and Malm-Zeta together with Purbeck. Furthermore the researched faultsystem represents a graben structure, which is defined by a synthetic main normal fault and a antithetic normal fault. Those faults are represented in the model by a 5 meter wide fault core and a 80 meter wide damage zone. The groundwater flow is studied by permeability variation of all fault elements based on literature values of the corresponding matrix and by monitoring the pressure behavior over time in the wellhead. In case of a highly permeable fault core a discrete 2D-Element is used. Simulations in OpenGeoSys have shown that with the available boundary conditions and with their special adjustment it is not possible to prevent the unwanted influence caused from the boundaries. Due to that fact the exact pressure drawdown values as well as the resulting productivity indices are not meaningful. Despite that qualitative conclusions about the influence of the individual model areas could be made and questions about the planned drilling path could be derived. In general the software test revealed that it is possible to simulate the reservoir flow in detail on small scale with OpenGeoSys. However to use the simulation results quantitative the further development of the boundary conditions is required. That was not possible due to time limitations in the process of this work.
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