Design and implementation of a traffic light system for deep geothermal well stimulation in Finland
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ORIGINAL ARTICLE
Design and implementation of a traffic light system for deep geothermal well stimulation in Finland Thomas Ader · Michael Chendorain · Matthew Free · Tero Saarno · Pekka Heikkinen · Peter Eric Malin · Peter Leary · Grzegorz Kwiatek · Georg Dresen · Felix Bluemle · Tommi Vuorinen
Received: 11 April 2019 / Accepted: 12 July 2019 © Springer Nature B.V. 2019
Abstract We describe the design and implementation of a traffic light system (TLS) created for the stimulation T. Ader () · M. Chendorain · M. Free Arup, 13 Fitzroy Street, W1T 4BQ, London, UK e-mail: [email protected] M. Chendorain e-mail: [email protected] M. Free e-mail: [email protected] T. Saarno · P. Heikkinen St1 Deep Heat Oy, Purotie 1/PL 100, 00381 Helsinki, Finland P. E. Malin · P. Leary Advanced Seismic Instrumentation & Research, 1311 Waterside, Dallas, TX 75218-4475, USA G. Kwiatek · G. Dresen Helmholtz Centre Potsdam, GFZ German Research Centre for Geosciences, Section 4.2: Geomechanics and Rheology, Potsdam, Germany G. Kwiatek Free University Berlin, Berlin, Germany G. Dresen University of Potsdam, Potsdam, Germany F. Bluemle fastloc GmbH, Berlin, Germany T. Vuorinen Institute of Seismology, University of Helsinki, Helsinki, Finland
phase of a 6.1-km-deep geothermal well in the Helsinki area, Finland. Because of the lack of local seismic data to calibrate the TLS, the TLS thresholds have been proposed on the basis of two parameters: acceptable ground motion levels and probabilities to reach these levels, which were then used to establish TLS magnitudes. A peak ground velocity (PGV) of 1 mm/s associated with a ML ≥ 1 event, or a ML ≥ 1.2 event alone, triggered an Amber alert. A PGV of 7.5 mm/s associated with a ML ≥ 2.1 event triggered a Red alert, where ML was a local “Helsinki” magnitude. Specific thresholds based on PGV and peak ground acceleration were gathered for critical infrastructure sites and related to earthquake magnitudes in a probabilistic way. The implementation of the TLS during the stimulation showed that the selected thresholds were reasonably conservative. Some of the Amber events were reportedly felt or heard, but the public opinion remained very favourable to the project. Measured ground motions were too low to have any impact on the built environment and the stimulation was able to proceed without being impaired by the occurrence of a Red event. Seismic data acquired during the stimulation and lessons learnt are presented and used to revisit the TLS thresholds for potential future stimulations. Keywords Geothermal · Stimulation · Traffic light system · Induced seismicity · GMPE
J Seismol
1 Introduction St1 Deep Heat (St1 DH) is developing a geothermal doublet in Espoo, Finland, for the purpose of supplying deep geothermal heat to local district heat networks. As part of the project, the first well OTN-3 was completed in May 2018 with a true vertical depth of 6.1 km (Fig. 1). In June and July 2018, OTN-3 was stimulated during 7 weeks in order to improve rock permeability (Kwiatek et al. 20
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