Marian Hertrich

Last Name

Hertrich

First Name

Marian

ORCID

0000-0001-9525-4609

Organisational unit

03476 - Giardini, Domenico (emeritus) / Giardini, Domenico (emeritus)

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Publications 1 - 10 of 37

Heat Propagation Through Fractures During Hydraulic Stimulation in Crystalline Rock
Wenning, Quinn; Gholizadeh Doonechaly, Nima; Shakas, Alexis; et al. (2022)
Proceedings of the 56th U.S. Rock Mechanics/Geomechanics Symposium
The Bedretto Underground Laboratory for Geosciences and Geoenergies (BULGG) is located in central Switzerland and serves as a test bed for geothermal energy research. Several boreholes were drilled from the laboratory section (ca. 1.1 km overburden) to serve as injection boreholes for stimulation and geophysical monitoring boreholes. During a hydraulic stimulation injection in winter 2020 into injection borehole ST2 interval ranging from 313 to 320 m, we observe a thermal perturbation using distributed fiber optic temperature sensing in a neighboring open borehole (MB1) at a depth of 275 m to 295 m. Prior to injection, there is a thermal anomaly in MB1 at about 289 m due to natural fracture fluid flow. Below this depth the temperature is approximately 1.5 °C higher than above. During injection there is a gradual upward movement of the thermal anomaly to ca. 278 m depth. After injection is stopped, the thermal signal gradually recovers to the original depth. The cause for such a temperature change is potentially due to increased warm water flow reaching the base of MB1 from deeper ST2 or poro-elastic fracture closure of the cold-water conducting fractures at 278 and 289 m depth in MB1 during stimulation.
Modeling Coupled Hydro-Mechanical Processes During Hydraulic Stimulation at the Bedretto Underground Laboratory
Clasen Repollés, Victor; Jiang, Danyang; Rinaldi, Antonio Pio; et al. (2024)
58th U.S. Rock Mechanics/Geomechanics Symposium
In the framework of Enhanced Geothermal Systems (EGS), hydraulic stimulations play an important role in increasing the permeability of the host rock, facilitating more efficient heat extraction. However, these stimulations unavoidably induce reactivation of faults and earthquakes. The induced seismicity serves as proxy for the enhanced fracture network's spatial extent, but at the same time could pose a risk to nearby populations if the earthquakes' magnitude is large. To address this challenge, understanding the coupled physical processes generating fault reactivation and seismicity is crucial, and the development of forecasting tools could help mitigating the risk. Numerous numerical simulators capable of modeling complex coupled processes exist, yet their computational demands hinder their application in real-time induced seismicity forecasting. In this work, we present the development of two distinct categories of models: the first category encompasses a simplified hybrid hydromechanical model tailored for real-time applications, while the second category comprises a more detailed 3D numerical model designed to advance the fundamental understanding of the physical processes at play. By applying these models to reproduce a hydraulic stimulation at the Bedretto Underground Laboratory, we demonstrate that we can simulate first-order observations (e.g. pressure changes, seismicity rate, strain) without introducing excessive complexity.
The Bedretto Underground Laboratory for Geosciences and Geoenergies (BULGG) Seismic Network, Switzerland
Mesimeri, Maria; Scarabello, Luca; Zimmermann, Eric; et al. (2023)
XXVIII General Assembly of the International Union of Geodesy and Geophysics (IUGG)
The Bedretto Underground Laboratory for Geoenergies and Geosciences (BULGG) is a unique research infrastructure located in the middle of a 5.2 kilometers long tunnel that connects Ticino with the Furka railway tunnel, in south-central Switzerland. BULGG is equipped with state of the art instruments that allow to conduct experimental research in various fields. From a seismological point of view, we aim to monitor seismicity that occurs during experiments, as well as monitoring local earthquakes, and possibly induced or run-away seismic events. To accomplish that we set up two real-time monitoring systems based on the SeisComP software, i.e. (i) background seismicity monitoring, and (ii) experimental monitoring. The background monitoring, which is the backbone network, consists of surface and tunnel broadband stations, short period sensors, accelerometers, and geophones sampled at various frequencies (200-2000Hz). Acoustic emission sensors, and an accelerometer sampled at 200kHZ constitute the experimental instance. All sensors stream to a common seedlink server which provides data to multiple clients for processing, real-time visualization, archiving, and risk control via dedicated software. A standard workflow is applied to both background and experimental monitoring that includes, automatic picking, automatic phase association and location, and magnitude estimation. Advanced methods are also applied in real-time, such as, real time double-difference relocation, and real-time earthquake detection based on waveform cross-correlation (template matching). Overall, BULGG is a unique environment to test several types of instruments and implement novel methods on observational and network seismology across scales. Bedretto Team: (see http://www.bedrettolab.ethz.ch/en/home/ for more details)
Multistage hydraulic stimulation at the Bedretto Underground Laboratory, Switzerland: First results from a geomechanical perspective
Bröker, Kai Erich Norbert; Ma, Xiaodong; Gholizadeh Doonechaly, Nima; et al. (2022)
A Prospective Evaluation of Borehole Distributed Acoustic Sensing Technologies for Detecting and Locating Out‐of‐Network Microseismicity
Lanza, Federica; Tuinstra, Katinka B.; Rinaldi, Antonio P.; et al. (2024)
Geophysical Monograph Series ~ Distributed Acoustic Sensing in Borehole Geophysics
Downhole distributed acoustic sensing (DAS) has proven effective in monitoring microseismicity produced during hydraulic stimulations. It is also a promising tool for monitoring microseismicity occurring beyond the stimulation region. Downhole DAS arrays exhibit reduced sensitivity to surface noise compared to surface deployments, and they can remain in place undisturbed after operations cease, unlike downhole geophones. Identifying and locating microseismicity occurring at remote distances is crucial for reservoir monitoring, allowing us to assess stress conditions and the presence of pre-existing faults. Here, we evaluate the potential of downhole DAS in detecting and locating out-of-network microseismicity through two case studies: a field-scale investigation at the Frontier Observatory for Research in Geothermal Energy (FORGE) site in Utah and a mesoscale experiment in the Bedretto Underground Laboratory for Geosciences and Geoenergies (BULGG) in Switzerland. We demonstrate that DAS data have sufficient quality to detect and locate low-magnitude earthquakes (M < 0) occurring several hundred meters away. However, azimuthal ambiguity is unavoidable when only a single vertical borehole is available. We show that DAS signal characteristics and location capabilities perform equally at different scales, ranging from full-reservoir scale to mesoscale. Our evaluation supports the employment of longer-term experiments to explore downhole DAS suitability for passive microseismic monitoring.
Multiphysics monitoring of cementation operation: implications for wellbore integrity and hydrogeological characterization
Gholizadeh Doonechaly, Nima; Reinicke, Andreas; Hertrich, Marian; et al. (2024)
Environmental Earth Sciences
The application of optical fibers for assessing cemented wellbore’s integrity attracted considerable attention recently, because of low cost, decent temporal/spatial resolution and absence of downhole electronics. This study presents an integrated approach to compare measurements from distributed temperature sensing (DTS), distributed strain sensing (DSS) and fiber Bragg grating (FBG), at different stages of the wellbore cementation at Bedretto Underground Laboratory for Geosciences and Geoenergies. Before the cementation, the measurements from DTS provided information about the hydrogeological settings of the wellbore, including the major flow zones, and presence of a highly conductive hydraulic shortcut to a nearby wellbore. During the cement injection, the temperature sensors (DTS and temperature FBG) clearly detected the evolution of the top of the cement. While the mechanical deformation sensors (DSS and strain FBG) did not provide significant insights during this stage, their role became more pronounced in subsequent phases. Results show that the irregularities on the wall have minor influence on the thermo-mechanical response of the wellbore, both during and after cementation. After cementation, the temperature sensors (DTS and temperature FBG) traced different phases of cement-hardening process, while DSS measurements identified areas of major deformation, primarily in fracture/fault zones. It was also observed that localized elevation of temperature and extensional deformation along the wellbore during the cement-hardening are correlated with the presence of permeable structures, most likely due to continuous supply of water. Results of this study show that monitoring of the cemented wellbores using optical fibers, in particular during cement hardening, not only can be used to efficiently assess the wellbore integrity but also can provide us additional important information about the hydrogeological settings of the target reservoir volume.
Source Characterization with DAS in Multiple-Borehole Settings: an Application from the BedrettoLab
Tuinstra, Katinka Barbara; Lanza, Federica; Fichtner, Andreas; et al. (2023)
AGU Fall Meeting Abstracts
Hydromechanical characterization of a fractured crystalline rock volume during multi-stage hydraulic stimulations at the BedrettoLab
Bröker, Kai Erich Norbert; Ma, Xiaodong; Gholizadeh Doonechaly, Nima; et al. (2024)
Geothermics
Multi-stage hydraulic stimulation experiments were conducted at the Bedretto Geothermal Testbed (Switzerland) at a depth of over 1 km to study seismo-hydromechanical processes at the hectometer scale. Eight intervals with a total length of 206 m were stimulated within a densely monitored, fractured granitic rock volume. Geological characterization shows that all intervals contain NE-SW striking, steeply dipping fractures, but the transmissivity and natural inflow vary between intervals. Reactivation pressures estimated from injectivity increases during stimulation indicate shear reactivation rather than hydraulic jacking, suggesting reactivation of pre-existing non-filled fractures. Overall, the seismo-hydromechanical response to stimulation is heterogeneous and indicates channelized flow.
Fault Zone Spatial Stress Variations in a Granitic Rock Mass: Revealed by Breakouts Within an Array of Boreholes
Zhang, Shihuai; Ma, Xiaodong; Bröker, Kai Erich Norbert; et al. (2023)
Journal of Geophysical Research: Solid Earth
The in situ stress state within fault zones is technically challenging to characterize. At the Bedretto Underground Laboratory in the Swiss Alps, the breakouts observed in an array of eight inclined boreholes penetrating a fault zone offer a unique opportunity to characterize the fault-associated spatial stress variations. Synthesizing multiple geophysical logs, natural geologic structures intersecting these boreholes are identified, revealing a hierarchy of a major fault zone along with secondary structures. Within the boreholes, breakout rotations occur over multiple scales, spanning individual fractures and the entire major fault zone. We first estimate and rule out the effect of the fracture-induced anisotropy on the breakout rotations, which are attributed mainly to the stress variations. Based on the stress field around a circular borehole and Mohr-Coulomb failure criterion, the observed breakout azimuths are used to invert the stress information. Results show that the stress field outside the fault zone features a stress ratio (quantifying the relative stress magnitude) of about 0.9, an inclined overburden stress (inclination: 12°∼18°), and a maximum horizontal principal stress (SHmax) oriented N100∼120°E. Within the fault zone, a substantial reduction of the stress ratio and complicated stress rotations are constrained, likely induced by the stress drop on local fractures. As a result, less critical stress state inside the major fault zone is expected. Our work provides a semi-quantitative estimation of the in-situ stress variations around fault zones in the absence of direct stress measurements, which is beneficial to a number of scientific and engineering applications
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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Marian Hertrich

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