Geomechanical behaviour of Opalinus Clay at multiple scales: results from Mont Terri rock laboratory (Switzerland)

Amann, Florian; Wild, Katrin M.; Loew, Simon; Yong, Salina; Thoeny, Reto; Frank, E.

doi:10.1007/978-3-319-70458-6_8

Cited by 10 publications

(11 citation statements)

References 25 publications

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“…Displacement amplitudes are of 0.3 to 1 mm, the norm of displacement vector in March 2019 being estimated to 0.95 mm after 5 months of monitoring (more than 70% of the displacement occurred after about 1.5 month). These values are in reasonable accordance with strain relaxation effects associated to borehole or gallery excavation observed in other Mt-Terri experiments (Amann et al, 2017). The SIMFIP data show displacement variations in all the three EW, NS and Z directions, highlighting the three-dimensional characteristics of such relaxation effects.…”

Section: Borehole Stability Monitoring In Bcs-d7supporting

confidence: 90%

Fault sealing and caprock integrity for CO<sub>2</sub> storage: an in-situ injection experiment

Zappone¹,

Rinaldi²,

Grab³

et al. 2020

Preprint

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Abstract. The success of geological carbon storage depends on the assurance of a permanent confinement of the injected CO2 in the storage formation at depth. One of the critical elements of the safekeeping of CO2 is the sealing capacity of the caprock overlying the storage formation, despite faults and/or fractures, which may occur in it. In this work, we present an ongoing injection experiment performed in a fault hosted in clay at the Mont Terri underground rock laboratory (NW Switzerland). The experiment aims at improving our understanding on the main physical and chemical mechanisms controlling i) the migration of CO2 through a fault damage zone, ii) the interaction of the CO2 with the neighbouring intact rock, and iii) the impact of the injection on the transmissivity in the fault. To this end, we inject a CO2-saturated saline water in the top of a 3 m think fault in the Opalinus Clay, a clay formation that is a good analogue of common caprock for CO2 storage at depth. The mobility of the CO2 within the fault is studied at decameter scale, by using a comprehensive monitoring system. Our experiment aims to the closing of the knowledge gap between laboratory and reservoir scales. Therefore, an important aspect of the experiment is the decameter scale and the prolonged duration of observations over many months. We collect observations and data from a wide range of monitoring systems, such as a seismic network, pressure temperature and electrical conductivity sensors, fiber optics, extensometers, and an in situ mass spectrometer for dissolved gas monitoring. The observations are complemented by laboratory data on collected fluids and rock samples. Here we show the details of the experimental concept and installed instrumentation, as well as the first results of the preliminary characterization. Analysis of borehole logging allow identifying potential hydraulic transmissive structures within the fault zone. A preliminary analysis of the injection tests helped estimating the transmissivity of such structures within the fault zone, as well as the pressure required to mechanically open such features. The preliminary tests did not record any induced microseismic events. Active seismic tomography enabled a sharp imaging the fault zone.

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Section: Borehole Stability Monitoring In Bcs-d7supporting

confidence: 90%

Fault sealing and caprock integrity for CO<sub>2</sub> storage: an in-situ injection experiment

Zappone¹,

Rinaldi²,

Grab³

et al. 2020

Preprint

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“…The shallow deformation lie within the ‘excavation damage zone’ (EDZ; Amann et al., 2018). The EDZ around the CS‐D niche (where our boreholes are located) was stable by the time of the Gallery 18 breakthrough detailed in this work (Corkum & Martin, 2007).…”

Section: Resultsmentioning

confidence: 99%

“…However, apart from qualitative observations, a complicated modeling exercise will be required to shed more light on the patterns shown in Figure 4b. The reader is referred to (Amann et al., 2018) for a detailed analysis of the strain response of EDZs to excavations at Mont Terri.…”

Section: Resultsmentioning

confidence: 99%

“…Looking at the decameter scale around underground galleries in the Opalinus clay shales in the Mont Terri Rock Laboratory (MTRL) (Switzerland), Amann et al. (2018) highlight that a high density of bedding planes and faults strongly influences macroscopic failure through shearing along preexisting planes coupled to newly created extensional fractures. Compiling laboratory determined mechanical properties of various types of shales, Bourg (2015) shows a factor of 20 decrease of the unconfined compressive strength (UCS) of shales that contain ∼1/3 phyllosilicate (clay mineral) mass fraction.…”

Section: Introductionmentioning

confidence: 99%

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The Effect of Fault Architecture on Slip Behavior in Shale Revealed by Distributed Fiber Optic Strain Sensing

et al. 2022

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We use Distributed Strain Sensing (DSS) through Brillouin scattering measurements to characterize the reactivation of a fault zone in shale (Opalinus clay), caused by the excavation of a gallery at ∼400 m depth in the Mont Terri Underground Laboratory (Switzerland). DSS fibers are cemented behind casing in six boreholes cross‐cutting the fault zone. We compare the DSS data with co‐located measurements of displacement from a chain potentiometer and a three‐dimensional displacement sensor (SIMFIP). DSS proves to be able to detect in‐ and off‐fault strain variations induced by the gallery excavated 30–50 m away. The total permanent displacement of the fault is ∼200 microns at rates up to 1.5 nm/s. DSS is sensitive to longitudinal and shear strain with measurements showing that fault shear is concentrated at the top and bottom interfaces of the fault zone with little deformation within the fault zone itself. Such a localized pattern of strain relates to the architecture of the fault that is characterized by a thick “layer” including an anastomosing network of polished surfaces where clay‐rich rock splits into progressively smaller flakes conferring the entire zone very little cohesion and friction (weak zone), and favoring slipping at the edges of the “layer”. Overall, DSS shows that slow slip may activate everywhere there is a weak fault within a shale series. Thus, our work demonstrates the importance of shear strain on faults caused by remote loading, highlighting the utility of DSS systems to detect and quantify these effects at large reservoir scales.

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“…The strain response upon loading suggests a yielding stress threshold that coincides with the onset of dilation. Microacoustic measurements on both laboratory and field scale suggest that the onset of dilatancy is associated with microacoustic events, which is typically observed for brittle rocks (Amann et al, 2011(Amann et al, , 2018Wild et al, 2015).…”

Section: Introductionmentioning

confidence: 96%

Micromechanisms leading to shear failure of Opalinus Clay in a triaxial test: a high-resolution BIB–SEM study

et al. 2021

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Abstract. A microphysics-based understanding of mechanical and hydraulic processes in clay shales is required for developing advanced constitutive models, which can be extrapolated to long-term deformation. Although many geomechanical tests have been performed to characterise the bulk mechanical, hydro-mechanical, and failure behaviour of Opalinus Clay, important questions remain about micromechanisms: how do microstructural evolution and deformation mechanisms control the complex rheology? What is the in situ microstructural shear evolution, and can it be mimicked in the laboratory? In this contribution, scanning electron microscopy (SEM) was used to image microstructures in an Opalinus Clay sample deformed in an unconsolidated–undrained triaxial compression test at 4 MPa confining stress followed by argon broad ion beam (BIB) polishing. Axial load was applied (sub-)perpendicular to bedding until the sample failed. The test was terminated at an axial strain of 1.35 %. Volumetric strain measurements showed bulk compaction throughout the compression test. Observations on the centimetre to micrometre scale showed that the samples exhibited shear failure and that deformation localised by forming a network of micrometre-wide fractures, which are oriented with angles of 50∘ with respect to horizontal. In BIB–SEM at the grain scale, macroscale fractures are shown to be incipient shear bands, which show dilatant intergranular and intragranular microfracturing, granular flow, bending of phyllosilicate grains, and pore collapse in fossils. Outside these zones, no deformation microstructures were observed, indicating only localised permanent deformation. Thus, micromechanisms of deformation appear to be controlled by both brittle and ductile processes along preferred deformation bands. Anastomosing networks of fractures develop into the main deformation bands with widths up to tens of micrometres along which the sample fails. Microstructural observations and the stress–strain behaviour were integrated into a deformation model with three different stages of damage accumulation representative for the deformation of the compressed Opalinus Clay sample. Results on the microscale explain how the sample locally dilates, while bulk measurement shows compaction, with an inferred major effect on permeability by an increase in hydraulic conductivity within the deformation band. Comparison with the microstructure of highly strained Opalinus Clay in fault zones shows partial similarity and suggests that during long-term deformation additional solution–precipitation processes operate.

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Geomechanical behaviour of Opalinus Clay at multiple scales: results from Mont Terri rock laboratory (Switzerland)

Cited by 10 publications

References 25 publications

Fault sealing and caprock integrity for CO<sub>2</sub> storage: an in-situ injection experiment

Fault sealing and caprock integrity for CO<sub>2</sub> storage: an in-situ injection experiment

The Effect of Fault Architecture on Slip Behavior in Shale Revealed by Distributed Fiber Optic Strain Sensing

Micromechanisms leading to shear failure of Opalinus Clay in a triaxial test: a high-resolution BIB–SEM study

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Geomechanical behaviour of Opalinus Clay at multiple scales: results from Mont Terri rock laboratory (Switzerland)

Cited by 10 publications

References 25 publications

Fault sealing and caprock integrity for CO&lt;sub&gt;2&lt;/sub&gt; storage: an in-situ injection experiment

Fault sealing and caprock integrity for CO&lt;sub&gt;2&lt;/sub&gt; storage: an in-situ injection experiment

The Effect of Fault Architecture on Slip Behavior in Shale Revealed by Distributed Fiber Optic Strain Sensing

Micromechanisms leading to shear failure of Opalinus Clay in a triaxial test: a high-resolution BIB–SEM study

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Fault sealing and caprock integrity for CO<sub>2</sub> storage: an in-situ injection experiment

Fault sealing and caprock integrity for CO<sub>2</sub> storage: an in-situ injection experiment