Conceptual Geological Model of the Bedretto Underground Laboratory for Geoenergies

Castilla, Raymi; Krietsch, Hannes; Jordan, Douglas W.; Ma, Xiaodong; Serbeto, Francisco; Shakas, Alexis; Guntli, P.; Bröker, Kai; Löw, Simon; Hertrich, Marian; Bethmann, Falko; Meier, Peter

doi:10.3997/2214-4609.202011912

Cited by 3 publications

(7 citation statements)

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“…5 and 7). The whole cluster potentially traces back to the tunnel wall and coincides with the major fault zone observed between TM 1950-1993 (Castilla et al, 2020). Major fault zones of this scale seem to be repeatedly present along the Bedretto Tunnel for every few hundreds of meters (Schneider, 1985), and they are generally trending perpendicular to the tunnel (NE-SW) and/or E-W.…”

Section: Heterogeneous Rock Mass Representative Test Volumesupporting

confidence: 56%

Multi-disciplinary characterizations of the BedrettoLab – a new underground geoscience research facility

Hertrich

Amann

et al. 2022

Solid Earth

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Abstract. The increased interest in subsurface development (e.g., unconventional hydrocarbon, engineered geothermal systems (EGSs), waste disposal) and the associated (triggered or induced) seismicity calls for a better understanding of the hydro-seismo-mechanical coupling in fractured rock masses. Being able to bridge the knowledge gap between laboratory and reservoir scales, controllable meso-scale in situ experiments are deemed indispensable. In an effort to access and instrument rock masses of hectometer size, the Bedretto Underground Laboratory for Geosciences and Geoenergies (“BedrettoLab”) was established in 2018 in the existing Bedretto Tunnel (Ticino, Switzerland), with an average overburden of 1000 m. In this paper, we introduce the BedrettoLab, its general setting and current status. Combined geological, geomechanical and geophysical methods were employed in a hectometer-scale rock mass explored by several boreholes to characterize the in situ conditions and internal structures of the rock volume. The rock volume features three distinct units, with the middle fault zone sandwiched by two relatively intact units. The middle fault zone unit appears to be a representative feature of the site, as similar structures repeat every several hundreds of meters along the tunnel. The lithological variations across the characterization boreholes manifest the complexity and heterogeneity of the rock volume and are accompanied by compartmentalized hydrostructures and significant stress rotations. With this complexity, the characterized rock volume is considered characteristic of the heterogeneity that is typically encountered in subsurface exploration and development. The BedrettoLab can adequately serve as a test-bed that allows for in-depth study of the hydro-seismo-mechanical response of fractured crystalline rock masses.

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Section: Heterogeneous Rock Mass Representative Test Volumesupporting

confidence: 56%

Multi-disciplinary characterizations of the BedrettoLab – a new underground geoscience research facility

Hertrich

Amann

et al. 2022

Solid Earth

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“…The intensive ductile shear zones and fractures concentrated in the fault zones imply that, the major fault zone may consist of multiple fault cores bounding internal lenses of intact rock and overlapping damage zones. Such a complex structure has been validated by the recovered borehole cores in CB1, CB2, and CB3 (Castilla et al, 2020;Ma et al, 2022) and is similar to the wide fault zone model proposed by Faulkner et al (2003). Therefore, it is reasonable to expect different deformation response of these components to the ambient stress fields.…”

Section: Characterization Of Fault Zonessupporting

confidence: 68%

“…Synthesizing borehole logs and core observations, Castilla et al. (2020) confirmed the continuity of the major fault zone between boreholes CB1, 2, and 3. Since MB8 is located between CB2 and CB3, it is inferred that it also penetrates the same major fault zone, which can be confirmed according to the concentration of fractures between 125 and 175 m MD.…”

Section: Fracture Mapping and Fault Zone Characterizationmentioning

confidence: 84%

“…For example, from the tunnel wall down to the first brittle fault zone, a cluster of fractures (marked as pink interval) is encountered in the middle six boreholes (CB1, CB2, MB8, CB3, ST1, and MB5), manifested as a significant increase of fracture density from the background level. According to their lithologies and the spatial continuity across these boreholes, these fractures probably belong to the same fault zone (Castilla et al., 2020). Depending on the specific borehole, more specifically, this fault zone is presumedly penetrated by the northernmost (leftmost) seven boreholes at the depth of about 50–100 m MD (pink intervals).…”

Section: Fracture Mapping and Fault Zone Characterizationmentioning

confidence: 99%

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Fault Zone Spatial Stress Variations in a Granitic Rock Mass: Revealed by Breakouts Within an Array of Boreholes

Zhang

Bröker

et al. 2023

JGR Solid Earth

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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.

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“…Although this middle fault zone unit is composed of several fault branches, it is found that these branches are generally sub-parallel to each other and form a cluster (Figures 5 and 7). The whole cluster potentially traces back to the tunnel wall and coincides with the major fault zone observed between TM 1950-1993(Castilla et al, 2020. Major fault zones of this scale seem to be repeatedly present along the Bedretto Tunnel for every few hundreds of meters (Schneider, 1985), and they are generally trending perpendicular to the tunnel (NE-SW) and/or E-W.…”

Section: Heterogeneous Rock Mass Representative Test Volumesupporting

confidence: 52%

Multi-disciplinary characterizations of the Bedretto Lab – a unique underground geoscience research facility

Hertrich

Amann

et al. 2021

Preprint

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Abstract. The increased interest in subsurface development (e.g., unconventional hydrocarbon, deep geothermal, waste disposal) and the associated (triggered or induced) seismicity calls for a better understanding of the hydro-seismo-mechanical coupling in fractured rock masses. Being able to bridge the knowledge gap between laboratory and reservoir scales, controllable meso-scale in situ experiments are deemed indispensable. In an effort to access and instrument rock masses of hectometer size, the Bedretto Underground Laboratory for Geosciences and Geoenergies (‘Bedretto Lab’) was established in 2018 in the existing Bedretto Tunnel (Ticino, Switzerland), with an average overburden of 1000 m. In this paper, we introduce the Bedretto Lab, its general setting and current status. Combined geological, geomechanical and geophysical methods were employed in a hectometer-scale rock mass explored by several boreholes to characterize the in situ conditions and internal structures of the rock volume. The rock volume features three distinct units, with the middle fault zone sandwiched by two relatively intact units. The middle fault zone unit appears to be a representative feature of the site, as similar structures repeat every several hundreds of meters along the tunnel. The lithological variations across the characterization boreholes manifest the complexity and heterogeneity of the rock volume, and are accompanied by compartmentalized hydrostructures and significant stress rotations. With this complexity, the characterized rock volume is considered characteristic of the heterogeneity that is typically encountered in subsurface exploration and development. The Bedretto Lab can adequately serve as a test-bed that allows for in-depth study of the hydro-seismo-mechanical response of fractured crystalline rock masses.

show abstract

Conceptual Geological Model of the Bedretto Underground Laboratory for Geoenergies

Cited by 3 publications

References 0 publications

Multi-disciplinary characterizations of the BedrettoLab – a new underground geoscience research facility

Multi-disciplinary characterizations of the BedrettoLab – a new underground geoscience research facility

Fault Zone Spatial Stress Variations in a Granitic Rock Mass: Revealed by Breakouts Within an Array of Boreholes

Multi-disciplinary characterizations of the Bedretto Lab – a unique underground geoscience research facility

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