14:30-15:00 Uhr - Workshop 3/2

Active cross-well survey at geothermal site Schäftlarnstraße

Emmanuel Gaucher

Emmanuel Gaucher1, Jerome Azzola1, Katja Thiemann2, Ulrich Steiner2, Michael Meinecke3

1Karlsruher Institut für Technologie, Deutschland; 2Erdwerk GmbH; 3Stadtwerke München Services GmbH

In the frame of the INSIDE project (supported by BMWi), scientific investigations to assess the impact of the geothermal exploitation on induced seismicity are carried out. The Schäftlarnstraße geothermal field is one of the target site. To do so, deployment of networks to record seismic events is necessary. At Schäftlarnstraße, two fibre optic cables have been deployed thanks to TUM and SWM, one behind the casing of well Th3 and the other one in the well Th4. Hence, Distributed Acoustic Sensing (DAS) acquisition and processing techniques can be applied on these fibres. Following data recording, location of the events constitutes a major result from which further processing and interpretation can start. It is well known that the seismic velocity model plays a major role in the accurate determination of the seismic event hypocentres. Consequently, the characterization of such propagation medium is of importance.

To explore this, it was decided to carry out an active cross-well survey at Schäftlarnstraße. The first objective is to “calibrate” the velocity model with a shot positioned as deep as possible in the well Th6. This shot is supposed to mimic a seismic event that would occur at the well level in the geothermal reservoir. Since real location and timing of the active source are controlled, calibration of the velocity model between the source and the fibre optic cables should be possible. The second objective is to perform a cross-well tomography to go beyond the calibration and to image the velocity model between the source well and the receiver wells.

At submission of this abstract, design of the active campaign, which is planned for mid-October 2020, is still on going. The active source will likely be a repeatable sparker source of weak energy. Results of the recent VSP survey acquired at Schäftlarnstraße on the fibre optic cable, in the frame of GeoMare project, can be used in this design phase. During this workshop, we wish we will be able to present more than the design work of the survey.

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