Vertical Seismic Profiling in the Krafla Geothermal Field, NE-Iceland

• Main Author: Kästner, Felix
• Other Authors: TU Bergakademie Freiberg, Geowissenschaften, Geotechnik und Bergbau
• Format: Dissertation
• Language: English
• Published: Technische Universitaet Bergakademie Freiberg Universitaetsbibliothek "Georgius Agricola" 2017
• Subjects: VSP; geothermal; imaging; Iceland; ddc:550; Island; Krafla-Spaltenschwarm; Geothermik; Geothermische Energie; Seismik; Seismische Prospektion
• Online Access: http://nbn-resolving.de/urn:nbn:de:bsz:105-qucosa-215820; http://nbn-resolving.de/urn:nbn:de:bsz:105-qucosa-215820; http://www.qucosa.de/fileadmin/data/qucosa/documents/21582/K%C3%A4stner_08122016_Qucosa_1b.pdf

A VSP test experiment at the high temperature geothermal field Krafla in NE-Iceland has been carried out. In two boreholes a zero-, far-, and multi-offset VSP were applied to assess the applicability of VSP as a method for delineating subsurface structures like magmatic bodies, zones of supercritical fluids, superheated steam, and high permeability in volcanic geothermal fields. Because of high well temperatures (>150°C) and high attenuating surface layers, challenging field preparations were necessary. Three-component seismic data were recorded with a sufficient signal-to-noise ratio and dominant signal frequencies around 20 Hz and 40 Hz, down to 2200 m depth, for air gun and explosive sources, respectively. As a result, the data provide a good basis for several processing and imaging techniques. As part of this Master\'s thesis, standard and novel processing techniques of a subset of the data (zero and far-offset VSP in a single well) have been tested and show promising results in accordance with the lithology from well data. Besides velocity profiles and a corridor stack for both P- and S-waves were determined, a 3D Kirchhoff depth migration and Fresnel volume migration have been applied and tested. Already for a single source location, results show structures in the vicinity and below the well, and it can be assumed that further interpretation and data integration will provide a great potential in addition to hitherto applied teleseismic and potential methods. Especially, for geothermal sites it has been shown, that VSP can be applied and provide information of geometries where dipping faults and fracture zones are expected. The research leading to these results has received funding from the European Community\'s Seventh Framework Programme under grant agreement No. 608553 (Project IMAGE).