Katrin Plenkers

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Plenkers

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Katrin

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0000-0002-7739-2554

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Publications1 - 10 of 27

Analysis of the pico-seismic response of a fractured rock volume to fluid injections in the Bedretto Underground Laboratory, Switzerland
Durand, Virginie; Rosskopf, Martina; Plenkers, Katrin; et al. (2022)
EGUsphere
The Bedretto Underground Laboratory for Geoenergies and Geosciences (BULGG) is a multidisciplinary laboratory on the hundred meter scale run by ETH Zurich. It is located in the Swiss Alps, in the middle of a 5.2km long horizontal tunnel, 1.0km below the surface. Seven 250-300m long boreholes have been equipped with different instruments: Acoustic Emission Sensors, Accelerometers, Fiber Optics (allowing simultaneous DTS, DSS and DAS measurements), Strainmeters and Pore Pressure Sensors. The variety of the instrumentation allows a multidisciplinary analysis of the response of the rock volume to fluid injections. The fluid injections are realized through a 400m injection borehole located in the center of the instrument network. It is divided into 14 intervals, allowing us to make injections at different depths. We will first present the methods used to generate a pico-seismic catalog with precise locations and a magnitude of completeness as low as -5, and the associated challenges. Then, we show a preliminary analysis of the spatio-temporal evolution of the pico-seismicity generated by different injection protocols. We interpret the evolution of the seismicity in comparison with the injection parameters (i.e., injection pressure and rate) and the stimulated intervals.
High-Resolution Seismo-hydromechnic Monitoring in Mesoscale Multi-stage Stimulation Experiment
Plenkers, Katrin; Krietsch, Hannes; Gischig, Valentin; et al. (2019)
AGU Fall Meeting Abstracts
Supplementary material to "Seismic monitoring of the STIMTEC hydraulic stimulation experiment in anisotropic metamorphic gneiss"
Boese, Carolin M.; Kwiatek, Grzegorz; Fischer, Thomas; et al. (2022)
Solid Earth
Hydraulic stimulation and fluid circulation experiments in underground laboratories: Stepping up the scale towards engineered geothermal systems
Gischig, Valentin S.; Giardini, Domenico; Amann, Florian; et al. (2020)
Geomechanics for Energy and the Environment
Ultra-Sensitive, High-Bandwidth Photonic-Mems Seismic Sensor
Ebrahimi Argi, Farnaz; Manzoor, Ayman; Sattari, Hamed; et al. (2025)
IEEE International Conference on Micro Electro Mechanical Systems ~ 2025 IEEE 38th International Conference on Micro Electro Mechanical Systems (MEMS)
The study of microcrack development in rocks, the need for advances in seismology, the monitoring of micro-earthquakes induced by geothermal projects, as well as the assessment of structural health in bridges, necessitate the deployment of sensor arrays capable of measuring radiated seismic waves. These sensors must be well-calibrated, passive, compact, highly sensitive and designed with tailored bandwidths. In this work, a novel accelerometer design is presented, based on vacuum-packaged Photonics-MEMS technology, which offers superior performance compared to current solutions thanks to a high quality factor (Q) mechanical resonator and an integrated optical detection and amplification. The target is to achieve low thermal noise, while ensuring a large bandwidth, using high-stress, high Q-factor Silicon Nitride (Si$_3$N$_4$) tethers (the spring element of the resonator). A radial distribution of the tethers and a centrally concentrated mass distribution of the inertial element are included to improve directionality and avoid unwanted resonant modes. The proof mass vibration is detected using optical evanescence with an integrated Mach-Zehnder Interferometer (MZI). Different accelerometers have been designed with various bandwidth-sensitivity trade-offs. The targeted specifications are as follows: noise floor <100 ng/$\sqrt{Hz}$, 1 kHz - 50 kHz frequency range, dynamic range >140 dB (24 bits), and off-axis rejection >20 dB. A first generation of the sensors has been fabricated, and the initial characterization of the sensors mechanical behavior shows performances in-line with the predictions from simulations.
Multi-Disciplinary Monitoring Networks for Mesoscale Underground Experiments: Advances in the Bedretto Reservoir Project
Plenkers, Katrin; Reinicke, Andreas; Obermann, Anne; et al. (2023)
Sensors
The Bedretto Underground Laboratory for Geosciences and Geoenergies (BULGG) allows the implementation of hectometer (>100 m) scale in situ experiments to study ambitious research questions. The first experiment on hectometer scale is the Bedretto Reservoir Project (BRP), which studies geothermal exploration. Compared with decameter scale experiments, the financial and organizational costs are significantly increased in hectometer scale experiments and the implementation of high-resolution monitoring comes with considerable risks. We discuss in detail risks for monitoring equipment in hectometer scale experiments and introduce the BRP monitoring network, a multi-component monitoring system combining sensors from seismology, applied geophysics, hydrology, and geomechanics. The multi-sensor network is installed inside long boreholes (up to 300 m length), drilled from the Bedretto tunnel. Boreholes are sealed with a purpose-made cementing system to reach (as far as possible) rock integrity within the experiment volume. The approach incorporates different sensor types, namely, piezoelectric accelerometers, in situ acoustic emission (AE) sensors, fiber-optic cables for distributed acoustic sensing (DAS), distributed strain sensing (DSS) and distributed temperature sensing (DTS), fiber Bragg grating (FBG) sensors, geophones, ultrasonic transmitters, and pore pressure sensors. The network was realized after intense technical development, including the development of the following key elements: rotatable centralizer with integrated cable clamp, multi-sensor in situ AE sensor chain, and cementable tube pore pressure sensor.
Corrigendum to “Hydraulic stimulation and fluid circulation experiments in underground laboratories: Stepping up the scale towards engineered geothermal systems” by Gischig et al. https://doi.org/10.1016/j.gete.2019.100175
Gischig, Valentin S.; Giardini, Domenico; Amann, Florian; et al. (2020)
Geomechanics for Energy and the Environment
Low signal-to-noise event detection based on waveform stacking and cross-correlation: application to a stimulation experiment
Plenkers, Katrin; Ritter, Joachim R. R.; Schindler, Marion (2013)
Journal of Seismology
We study the microseismicity (M L < 2) in the region of Landau, SW Germany. Here, due to thick sediments (~3 km) and high cultural seismic noise, the signal-to-noise ratio is in general very low for microearthquakes. To gain new insights into the occurrence of very small seismic events, we apply a three-step detection approach and are able to identify 207 microseismic events (−1 < M L < ~1) with signal-to-noise ratios smaller than 3. Recordings from a temporary broadband network are used with station distances of approximately 10 km. First, we apply a short-term to long-term average detection algorithm for data reduction. The detection algorithm is affected severely by transient noise signals. Therefore, the most promising detections, selected by coinciding triggers and high-amplitude measures, are reviewed manually. Thirteen seismic events are identified in this way. Finally, we conduct a cross-correlation analysis. As master template, we use the stacked waveforms of five manually detected seismic events with a repeating waveform. This search reveals additional 194 events with a cross-correlation coefficient exceeding 0.65 which ensures a stable identification. Our analysis shows that the repeating events occurred during the stimulation of a geothermal reservoir within a source region of only about 0.5 km3. Natural background seismicity exceeding our detection level of M L ~ 0.7 is not found in the region of Landau by our analysis. © Springer Science+Business Media B.V. 2012
Seismic Response of Hectometer-Scale Fracture Systems to Hydraulic Stimulation in the Bedretto Underground Laboratory, Switzerland
Obermann, Anne; Rosskopf, Martina; Durand, Virginie; et al. (2024)
Journal of Geophysical Research: Solid Earth
We performed a series of hydraulic stimulations at 1.1 km depth in the Bedretto underground laboratory, Switzerland, as part of an overall research strategy attempting to understand induced seismicity on different scales. Using an ultra-high frequency seismic network we detect seismic events as small as Mw < −4, revealing intricate details of a complex fracture network extending over 100 m from the injection sites. Here, we outline the experimental approach and present seismic catalogs as well as a comparative analysis of event number per injection, magnitudes, b-values, seismogenic index and reactivation pressures. In our first-order seismicity analysis, we could make the following observations: The rock volume impacted by the stimulations in different intervals differs significantly with a lateral extent from a few meters to more than 150 m. In most intervals multiple fractures were reactivated. The seismicity typically propagates upwards toward shallower depth on parallel oriented planes that are consistent with the stress field and seem to a large extent associated with preexisting open fractures. This experiment confirms the diversity in seismic behavior independent from the injection protocol. The overall seismicity patterns demonstrate that multi-stage stimulations using zonal isolation allow developing an extended fracture network in a 3D rock volume, which is necessary for enhanced geothermal systems. Our stimulations covering two orders of magnitude in terms of injected volume will give insights into upscaling of induced seismicity from underground laboratory scale to field scale.
Insights from Subsurface Monitoring for Engineering of the Stimulation Pattern in Fractured Reservoirs
Gholizadeh Doonechaly, Nima; Bröker, Kai Erich Norbert; Hertrich, Marian; et al. (2024)
Stimulation operations enhance the performance of geothermal reservoirs by boosting fluid flow and heat transfer. Predicting stimulation outcomes is challenging due to complexity of reservoir properties and limited observations given by operational conditions. Factors like stress state, natural structures, pressure distribution, and injection patterns play crucial roles in engineering of a stimulation operation. This study provides in-depth observations from a hectometer-scale stimulation experiment conducted at the Bedretto Underground Laboratory for Geosciences and Geoenergies within a densely monitored crystalline rock volume with an overburden of more than 1 km. We found that hydraulic connectivity, pressure compartments, and the characteristics of existing geological structures play pivotal roles in the propagation patterns of seismic events. Notably, the initiation and distribution of seismicity are markedly influenced by the zonal isolation and the structured propagation of pressure front across the reservoir. The research highlights the necessity of adapting stimulation strategies to the unique geomechanical as well as geological characteristics of the reservoir, as evident from the distinct activation patterns observed between the first and second injection cycles. The spatial extent of the stimulated volume can be partially guided by the number of stimulation cycles and injection pressure level, as farther structures are increasingly likely to be activated in the subsequent cycles. The results also indicate that the Kaiser effect is more pronounced in regions closer to the injection borehole. However, this effect can be attenuated due to stress changes caused by stimulation, consistent with a proposition from a recent study. Our findings underscore the critical importance of understanding the interplay between hydraulic pressures and stress states to optimize the stimulation of geothermal reservoirs effectively.

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Katrin Plenkers

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