Electromagnetic methods for exploration and monitoring of enhanced geothermal systems - A virtual experiment

We present the concept of virtual electromagnetic experiments, which aims at setting up and optimizing the monitoring design for a potential stimulated geothermal energy reservoir. The concept builds on existing 3D geologic models, which are processed, meshed, assigned realistic electrical parameters and used for our finite element simulations on unstructured tetrahedral grids. The available simulation codes are able to cope with the high degree of geometric complexity in close-to-reality scenarios. To demonstrate the procedure and the capabilities of our method, we show the model preparation and the simulation results for the transient electromagnetic method in the context of a prospective enhanced deep geothermal energy site at the fault 'Roter Kamm' near Schneeberg in Saxony/eastern Germany. We show the changes in the measuring signal caused by the stimulated fracture system in more than 5000 m depth for a range of electrical resistivity contrasts, which represent different porosity, pore connectivity or fluid resistivity variations. When a borehole receiver is advantageously placed at depth, percentage changes in the measuring signal of 25% can be expected. Our study demonstrates, that the optimal positioning of source and receiver is crucial for a successful monitoring and may only be achieved with advanced simulation techniques. (C) 2015 Elsevier Ltd. All rights reserved.