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Vorhaben UG2: GEOREAL - Geothermische Experimente im KTB-Tiefenlabor unter Realbedingungen einer Tiefbohrung

GEOREAL - GEOthermal experiments in the KTB deep laboratory under REAL conditions of a deep borehole

To seismically monitor the GEOREAL hydraulic stimulation experiment, that took place during the period 6-15 November 2023, a station network was set up in the vicinity of the Kontinentale Tiefbohrung/ KTB deep crustal lab near Windischeschenbach, Germany. The network comprised both surface stations, shallow borehole (25-150 m deep) stations as well as a borehole chain at 2000 m depth in the main borehole, ca. 200m apart from the pilot borehole. First stations were installed in early 2022 and removed in mid-2024. A total of 600 m³ of water was injected into the 4 km deep pilot borehole (KTB-VB, 12° 7.16' E, 49° 48.98' N, 513.418 m above NN ). This volume was injected through a stuck packer in the cased borehole into the open borehole section a depth of 3.85-4 km. No induced seismicity was observed during the injection experiment. Waveform data is available from the GEOFON data centre, under network code 4R, and is fully open.

Comprehensive data set of in-situ hydraulic stimulation experiments for geothermal purposes at the Äspö Hard Rock Laboratory (Sweden)

This data set contains measurements of an underground hydraulic fracture experiment at Äspö Hard Rock Laboratory in May and June 2015. The experiment tested various injection schemes for rock fracture stimulation and monitored the resulting seismicity. The primary purpose of the experiment is to identify injection schemes that provide rock fracturing while reducing seismicity or at least mitigate larger seismic events. In total, six tests with three different injection schemes were performed in various igneous rock types. Both the injection process and the accompanied seismicity were monitored. For injection monitoring, the water flow and pressure are provided and additional tests for rock permeability. The seismicity was monitored in both triggered and continuous mode during the tests by high-resolution acoustic emission sensors, accelerometers and broadband seismometers. Both waveform data and seismicity catalogs are provided.

Seismic waveforms of fluid-induced seismicity from the 2018 hydraulic stimulation campaign at the OTN-3 well, Helsinki, Finland

This data publication contains seismic waveform data of 507 earthquakes recorded during the St1 Deep Heat project in June and July 2018, where the 6.1 km deep OTN-3 well near Helsinki, Finland, was hydraulically stimulated over 49 days (Kwiatek et al., 2019). The waveforms were recorded on a surrounding seismic monitoring network consisting of 12 stations, deployed at epicentral distances between 0.6 to 8.2 km and at depths between 0.23 to 1.15 km. Each station consists of three-component, 4.5 Hz, Sunfull PSH geophones, sampling at 500 Hz. The 507 earthquakes analysed were chosen from the relocated event catalogue by Leonhardt et al. (2021a). The dataset is supplementary material to the Geophysical Research Letters research article of Holmgren et al. (2022), which applied the Empirical Green’s Function technique to examine microseismic rupture behaviour at the Helsinki site.

Fluid injection experiments on critically stressed sawcut faults in low-permeability granite samples

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Ultrasonic transmission measurements from seven boreholes from the STIMTEC-X experiment, Reiche Zeche Mine, Freiberg (Saxony, Germany)

In 2020 and 2021 the STIMTEC-X hydraulic stimulation experiment was performed at ca.~130 m below surface at the Reiche Zeche underground research laboratory in Freiberg, Saxony/Germany. The project temporally followed the STIMTEC experiment at the same site and aimed at understanding the stress heterogeneity of the anisotropic and metamorphic gneiss rock mass. The STIMTEC-X experiment applied the hydraulic stimulation technique in several boreholes at the mine-scale. Complementary to the stimulations, there were active seismic ultrasonic transmission data acquired before the stimulations. We use a seismic monitoring network consisting of six single-component acoustic emission (AE) sensors (sensitivity 1-60 kHz), six hydrophone-like AE sensors (sensitivity 1-40 kHz) and four to twelve single-component Wilcoxon accelerometers (sensitivity 50 Hz-25 kHz). The AE sensors and remained stationary in sub-horizontal and upwards reaching boreholes, the accelerometers were mostly installed along the tunnel walls with one accelerometer in a shallow borehole in each tunnel, and the hydrophone-like AE sensors were installed in the down-going water filled boreholes, but repositioned for each measurement campaign (Figure 1). This data set of 120 active ultrasonic transmission (UT) measurements is supplementary to Boese et al. (2022, in review), which introduces some of the active measurement campaigns of the STIMTEC-X experiment in detail. The whole data set togetter with the “Ultrasonic transmission measurements from six boreholes from the STIMTEC experiment, Reiche Zeche Mine, Freiberg (Saxony, Germany)” [https://doi.org/10.5880/GFZ.4.2.2021.002] was used to evaluate performance measures such as sensitivity and frequency bandwith, coupling, placement and polarity of the hydrophone-like AE sensor compared to AE sensors. The active seismic data provided here are from seven boreholes (BH01, BH05, BH06, BH10, BH14, BH18, BH19) as shown in Figure 1. There are nine tables provided as metadata of which seven contain the STIMTEC-X sensor coordinates for each measurement campaign, the event information of all the 120 UT measurements and the UT picks. The UT measurements were recorded with a sampling rate of 1 MHz and results from an automatic stack of 1024 UT pulses generated by the ultrasonic transmitter and recorded by the STIMTEC-X sensors. The UT measurements are saved in binary file format (fsf file format). Fsf-files can be processed with FOCI software: https://www.induced.pl/software/foci. Each fsf file contains 32768 samples, which corresponds to 0.032768 seconds. All UT event files were manual inspected and phase arrivals identified. These are stored in the fsf-file header as well as in the table STIMTECX_UT_picks.csv.

Earthquake catalog of induced seismicity associated with 2020 hydraulic stimulation campaign at OTN-2 well in Helsinki, Finland

This data publication contains seismic catalog developed by the analysis of seismicity recorded during hydraulic stimulation campaign performed in May 2020 in the 5.8-km deep OTN-2 well near Helsinki, Finland as part of the St1 Deep Heat project (Kwiatek et al., 2022). The original seismic data to develop the seismic catalog were acquired with the high-resolution seismic network composed of 22 geophones surrounding the project site. The centerpiece of the network was a 10-level borehole array of Geospace OMNI-2400 geophones (3C/15 Hz) sampled at 2 kHz placed in the OTN-3 well adjacent to the OTN-2 injection well, and located at 1.93 - 2.55 km depth, approx. 3km from injection intervals. Additional 12 stations at distances <10 km from project site formed the satellite network that was equipped with short-period 3C 4.5 Hz Sunfull PSH geophones, completing the seismic network. Near-real-time processing of induced seismicity data started on Jan 26, 2020, i.e. about 3 months prior to the onset of the injection, covering entire period of the stimulation campaign in May 2020. The monitoring stopped end of June 2020, about one month after the stimulation finished. The monitoring campaign resulted in initial industrial seismicity catalog containing 6,243 events that was refined and further extended (cf. Kwiatek et al., 2022). The final catalog associated with this data publication contains 6,318 earthquakes, including 197, 5427 and 694 events recorded before, during, and after stimulation campaign. The core catalog data contains origin time, local magnitude, (re)location and focal mechanism data.

Frequency-dependent quality factors of S-coda waves from active ultrasonic transmission measurements in the STIMTEC project, URL Reiche Zeche, Germany

Mean S-wave coda quality factors (mean-Qc) were estimated from active ultrasonic transmission (UT) measurements acquired during the STIMTEC project in the URL Reiche Zeche (Saxony, Germany). We used S-coda waves of 88 selected UT measurements carried out in 3 differently oriented boreholes (BH10, BH12, BH16) to estimate the spatial change of the coda quality factor in the targeted rock volume, an anisotropic metamorphic gneiss. We also analysed temporal variation in attenuation before and after hydraulic stimulations performed in two boreholes (BH10, BH17). We formed in total 8 UT groups (see data table "2022-004_Blanke-and-Boese_mean_UT_event_locations") from neighbouring UT measurements within different depths and from separated time intervals (see also Tab. 1 in Blanke et al. 2023), and compare mean-Qc estimates of centre frequencies ranging 3-21 kHz of octave-width frequency bands. Our results show a characteristic frequency-dependence and we find that mean-Qc estimates reveal temporal-variations of attenuation more significantly than those obtained from velocity measurements. The temporal variations are strongly connected to hydraulic stimulation activities resulting in a reduction of the coda quality factor where AE events occurred. Analysis of mean-Qc estimates after a temporal resting phase (with no activity in the rock volume) suggests that frequencies > 15 kHz indicate healing of small-scale fractures induced by injections. The study shows that coda analysis is a powerful tool for the detection of damage zones and for monitoring changes of the local fracture network within reservoirs important for exploitation or underground storage of gases and liquids.

Ultrasonic transmission measurements from injection borehole and vertical validation boreholes from the STIMTEC experiment, Reiche Zeche Mine, Freiberg (Saxony, Germany)

Between early 2018 and late 2019 the STIMTEC hydraulic stimulation experiment was performed at ca.~130 m below surface at the Reiche Zeche underground research laboratory in Freiberg, Saxony/Germany. The project aimed at gaining insight into the creation and growth of fractures in anisotropic and heterogeneous metamorphic gneiss , to develop and optimise hydraulic stimulation techniques and to control the associated induced seismicity under in situ conditions at the mine-scale. These aspects of failure and associated seismicity are important for the development of enhanced geothermal energy systems. A combined seismic network consisted of 12 single-component acoustic emission sensors (sensitivity 1-100 kHz) and three single-component Wilcoxon accelerometers (sensitivity 50 Hz-25 kHz) were installed in boreholes drilled into the test volume, surrounding the stimulation site (Figure 1). A stimulation borehole with 63 m length was drilled with 15° northward inclination. This data set of 314 active ultrasonic transmission (UT) measurements is supplementary to Boese et al. (2021, in review), which introduces the STIMTEC experiment and its active measurement campaigns. This data set was used to derive an anisotropic velocity model for the STIMTEC rock volume. The active seismic data provided here are from six boreholes (BH09, BH10, BH12, BH15, BH16, BH17) as shown in Figure 1. of the associated data description. There are three tables provided as metadata that contain the STIMTEC sensor coordinates, event information of the 314 UT measurements and the UT picks. The UT measurements were recorded with a sampling rate of 1 MHz and results from an automatic stack of 1024 UT pulses generated by the ultrasonic transmitter and recorded by the STIMTEC sensors. The UT measurements are saved in binary file format (fsf file format). Fsf-files can be processed with FOCI software: https://www.induced.pl/software/foci Each fsf file contains 32768 samples, which corresponds to 0.032768 seconds. All UT event files were manual inspected and phase arrivals identified. These are stored in the fsf-file header as well as in the table STIMTEC_UT_picks.csv.

Entwicklung eines virtuellen geomechanischen Projektlabors für die Begleitung hydraulischer Stimulationen auf der Grundlage von Prozessexpertise aus Experiment und Modellierung - SHynergie

Ziel des Vorhabens ist die Erhöhung des Steuerungspotentials bei hydraulischen Stimulationen in tiefen Bohrungen im Zuge von Projekten zur Gewinnung tiefer geothermischer Energie durch die Bereitstellung eines interaktiven Simulationswerkzeugs auf der Basis eines verbesserten Prozessverständnisses abgeleitet aus experimentellen, theoretischen und numerischen Untersuchungen. Das Werkzeug zielt darauf ab, Handlungsspielraum aus weitgehender Vorbereitung und optimaler Informationsgewinnung zu gewinnen. Das Vorhabenziel soll durch eine interne Organisation in sechs stark vernetzte Unterprojekte erreicht werden. Jedes Unterprojekt wird von mindestens zwei Experten mit unterschiedlichem Hintergrund bearbeitet (Geo- und Ingenieurwissenschaftler sowie Industrieexpertin für Hydro-Geochemie). Der Ansatz kombiniert die Durchführung innovativer Laborexperimente mit der Entwicklung moderner Modellierungsinstrumente für hydro-mechanische und hydro-chemische Wechselwirkungen. Die Verflechtung paralleler und sequentieller Arbeitsschritte erlaubt die Entwicklung des nutzer-orientierten Werkzeugs zur Projektbegleitung.

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