Abstract
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.
Highlights
The coupled hydro-seismo-mechanical characteristics of crystalline basement rock masses have traditionally been of broad scientific and engineering interest
Combining the characterization efforts to date, we evaluate the suitability of the BedrettoLab rock volume as a test-bed to host upcoming experiments and offer an outlook on the challenges and opportunities to advance the understanding of hydro-seismomechanical processes taking place in fractured crystalline rock masses
Since 2018, the Bedretto Tunnel has been made available by its owner, Matterhorn Gotthard Bahn (MGB), to ETH Zürich for long-term research, which prompted the establishment of the BedrettoLab
Summary
The coupled hydro-seismo-mechanical characteristics of crystalline basement rock masses have traditionally been of broad scientific and engineering interest. At full-size reservoir scales, studies on the hydro-seismo-mechanical processes have to be inferred from observations at a sparse spatial resolution (e.g., Basel, Switzerland; Cooper Basin, Australia; Cornwall, UK; Fenton Hill, USA; Helsinki, Finland; Pohang, South Korea; Soultz, France). The experiments at such scales are often constrained at insufficient resolution in order to yield fundamental understanding and wide application. Combining the characterization efforts to date, we evaluate the suitability of the BedrettoLab rock volume as a test-bed to host upcoming experiments and offer an outlook on the challenges and opportunities to advance the understanding of hydro-seismomechanical processes taking place in fractured crystalline rock masses
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