Microstructure and composition of brittle faults in claystones of the Mont Terri rock laboratory (Switzerland): New data from petrographic studies, geophysical borehole logging and permeability tests

Kneuker, Tilo; Hammer, Jörg; Shao, Hua; Schuster, Kristof; Furche, Markus; Zulauf, Gernold

doi:10.1016/j.enggeo.2017.10.016

Cited by 21 publications

(20 citation statements)

References 51 publications

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“…The different facies types of the Opa-linus Clay can be recognized by the different shades of brown and yellow; the new Gallery 18 is highlighted in green. Map modified from Mont Terri Consortium (swisstopo) Kneuker et al 2017), which are confirmed by the mineralogical-geochemical analyses, ideally applied in combination (e.g. Clauer et al 2017;Kneuker et al 2020).…”

Section: Introductionmentioning

confidence: 84%

Capturing the structural and compositional variability of Opalinus Clay: constraints from multidisciplinary investigations of Mont Terri drill cores (Switzerland)

Kneuker

Furche

2021

Environ Earth Sci

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Opalinus Clay is considered a potential host rock for radioactive waste disposal. The Jurassic claystone formation is composed of several facies and subfacies types, which are characterized by varying amounts of quartz, carbonates (cements and fossils) and clay minerals. To provide samples for ongoing experimental and numerical studies, a complete core section was drilled in the Mont Terri rock laboratory. The lithological and structural variability (including tectonic fault structures) from borehole BAD-2 was investigated using a multidisciplinary approach including high-resolution geoelectric in situ borehole measurements, mineralogical/geochemical and (micro)structural analyses.The lithological–compositional variability was captured by successfully applying a modified subfacies approach, which is independently confirmed by the geochemical data and ERT (Electrical Resistivity Tomography) measurements. The variability on the cm to dm scale perpendicular to bedding can be determined based on the mean resistivity and variation of amplitude. In particular, the facies transitions could be precisely located. The new results suggest that both shaly facies types form the homogenous part of the investigated section, whereas the sandy facies and especially the carbonate-rich sandy facies represent the more heterogeneous lithofacies types of the Opalinus Clay. The varying resistivity can be attributed to differences in clay mineral and carbonate content. Regarding the structural variability, brittle faults were observed with varying frequency throughout the investigated section. Most fault planes occur in the shaly facies types, some of them concentrate along heterogeneities on the subfacies scale. The striking reproducibility of the measurements and observations was confirmed by a comparison with boreholes drilled in parallel, indicating a rather low compositional–structural variability parallel to bedding. The applied multidisciplinary approach is well suited to depict the vertical and lateral variability of a claystone formation, allowing an assessment of the degree of homogeneity/heterogeneity based on the subfacies concept.

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Section: Introductionmentioning

confidence: 84%

Capturing the structural and compositional variability of Opalinus Clay: constraints from multidisciplinary investigations of Mont Terri drill cores (Switzerland)

Kneuker

Furche

2021

Environ Earth Sci

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“…A literature review of existing petrographic descriptions has been performed to evaluate the lithological heterogeneity within the OPA at different scales, such as described and highlighted by different authors (Bläsi, 1987(Bläsi, , 2002Matter et al, 1987Matter et al, , 1988Etter, 1990;Bläsi et al, 1991Bläsi et al, , 1996Allia, 1996;Allia, 2000, 2003;Nagra, 2001Nagra, , 2002Peters et al, 2011;Houben et al, 2013Houben et al, , 2014Bossart, 2014, 2016;Lerouge et al, 2014Lerouge et al, , 2015Reisdorf et al, 2014Reisdorf et al, , 2016Hostettler et al, 2017;Kneuker et al, 2017Kneuker et al, , 2020Lauper et al, 2018;Mazurek and Aschwanden, 2020).…”

Section: Petrographymentioning

confidence: 92%

“…Larger fossils, such as belemnites, ammonites or other organisms, are occasionally observed (see examples in Etter, 1990Etter, , 2004Reisdorf et al, 2014Reisdorf et al, , 2016Hostettler et al, 2020). Structural features, such as fault planes and shear zones, as well as induced excavation damaged zones and artificial discontinuities can occur, but are not further discussed within the scope of this study (see e.g., Kneuker et al, 2017). Furthermore, mineral alteration at the surface of longexposed drill core sections or outcrops may typically modify the appearance of the rock.…”

Section: Frequent Sideritic Patchesmentioning

confidence: 99%

“…Many studies at Mont Terri have emphasized the tight relations between various rock properties, lithology and texture. Typical examples include the small-scale heterogeneity of geomechanical properties (Klinkenberg et al, 2009;Kaufhold et al, 2013;Siegesmund et al, 2014), the distribution of micro-porosity (Houben et al, 2013(Houben et al, , 2014Keller et al, 2013;Philipp et al, 2017), sorption processes and radionuclides diffusive transport (Hennig et al, 2020;Hennig and Kühn, 2021), the responses of seismic P-wave velocity (Kneuker et al, 2017;Schuster et al, 2017;Lauper et al, 2018), and more generally, the overall (geochemical, petrophysical and hydro-mechanical) anisotropic behavior of the OPA (Van Loon et al, 2004;Wenk et al, 2008;Favero et al, 2018). Jaeggi and Bossart (2014) provide an overview of the main rock properties (petrophysical, hydrogeological, rock mechanical, thermic, geochemical/pore water composition, and gas entry pressure parameters) of the OPA at Mont Terri and their relationship with lithology.…”

Section: Subfacies Types and Rock Propertiesmentioning

confidence: 99%

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Quantification of Lithological Heterogeneity Within Opalinus Clay: Toward a Uniform Subfacies Classification Scheme Using a Novel Automated Core Image Recognition Tool

Lauper

Zimmerli

Jaeggi³

et al. 2021

Front. Earth Sci.

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The Opalinus Clay is notable in Switzerland as being the selected host rock for deep geological disposal of radioactive waste. Since the early 1990’s, this argillaceous mudstone formation of Jurassic age has been intensively studied within the framework of national and international projects to characterize its geological, hydrological, mechanical, thermal, chemical, and biological properties. While there is no formal stratigraphic subdivision, the Opalinus Clay lithology is classically divided into several, dam- to m-scale sub-units (or facies), depending on location. Recent multi-proxy studies (combining petrographic, petrophysical, geochemical, and mineralogical analyses) have however demonstrated that high, intra-facies, lithological heterogeneity occurs at the dm- to cm-scale. To constrain this small-scale heterogeneity into distinct lithological units (subfacies), the present study aims at defining and presenting a convenient subfacies classification scheme covering the overall Opalinus Clay lithology across northern Switzerland. Petrographic (macro- and microfacies), mineralogical (X-ray diffraction) and textural (image analysis, machine learning and 3D X-ray computed tomography) analyses are performed on diverse drill cores from the Mont Terri rock laboratory (northwestern Switzerland), and results are extended further to the east (Riniken, Weiach, and Benken). Most of the investigated Opalinus Clay can be described by the use of five distinctive subfacies types (SF1 to SF5), which are visually and quantitatively distinguishable by texture (grain size, bedding, fabric, and color) and composition (nature and mineralogy of components). The five subfacies types can be further refined by additional attributes and sedimentary characteristics (biogenic, diagenetic, and structural). Eventually, the widespread and consistent use of standardized Opalinus Clay subfacies types provides the means to harmonize petrographic descriptions within multidisciplinary research projects, enhance reproducibility of in situ experiments, and further evidence the tight relations between lithology and various rock properties.

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“…Detecting a rock domain with low effective permeability using borehole investigations is essential when investigating suitable radioactive waste disposal sites. Thus, when faults/fractures develop within rock formations it is important to detect the domains where hydraulic fault/fracture‐connectivity is limited, although the permeability of faults/fractures may be comparable to that of the matrix (Boisson et al, ; Constantin et al, ; Kneuker et al, ; Laurich et al, ; Marschall et al, ). However, it is difficult to accurately evaluate hydraulic fault/fracture‐connectivity at the formation scale (e.g., several tens to hundreds of meters) because such connectivity cannot be directly measured.…”

Section: Introductionmentioning

confidence: 99%

Assessment of Hydraulic Connectivity of Fractures in Mudstones by Single‐Borehole Investigations

Ishii

2018

Water Resources Research

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Assessing the hydraulic connectivity of fractures by single-borehole investigations is crucial to radioactive waste disposal but is still a challenge as such connectivity is difficult to measure directly. This study presents geological, hydrological, hydrochemical, and rock-mechanical data for three faulted/ fractured mudstones (the Koetoi, Wakkanai, and Palfris Formations) and proposes a new methodology for assessing the hydraulic connectivity of fractures. The methodology consists of three steps: (a) dividing the formation into two domains with a ductility index (DI) of >2 and <2 (DI is defined as the effective mean stress normalized to the tensile strength of intact rock), (b) estimating the hydraulic connectivity of fractures by analyzing pressure change obtained by packer tests and geological interpretation, and (c) verifying the estimation using pore pressure and water chemistry/geochemistry. The first step is necessary because the failure mode of damage-zone fractures in fault zones can differ between the DI > 2 and DI < 2 domains, which may lead to significant differences in the hydraulic connectivity of fractures. During the second step, potential domains in which the hydraulic connectivity of fractures is limited are identified where upward trends, characterized by slopes of 0.5-1.0, are observed during the middle to late period of elapsed time on log-log plots of pressure derivatives. Although the third step can be performed in various ways, this study employs the observation of pressure anomalies and the detection of young external water. Analyses of the three formations demonstrate the applicability and reliability of the proposed methodology.

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Microstructure and composition of brittle faults in claystones of the Mont Terri rock laboratory (Switzerland): New data from petrographic studies, geophysical borehole logging and permeability tests

Cited by 21 publications

References 51 publications

Capturing the structural and compositional variability of Opalinus Clay: constraints from multidisciplinary investigations of Mont Terri drill cores (Switzerland)

Capturing the structural and compositional variability of Opalinus Clay: constraints from multidisciplinary investigations of Mont Terri drill cores (Switzerland)

Quantification of Lithological Heterogeneity Within Opalinus Clay: Toward a Uniform Subfacies Classification Scheme Using a Novel Automated Core Image Recognition Tool

Assessment of Hydraulic Connectivity of Fractures in Mudstones by Single‐Borehole Investigations

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