Consolidated-undrained triaxial testing of Opalinus Clay: Results and method validation

Giger, Silvio B.; Ewy, Russell T.; Favero, Valentina; Stankovic, Rudy; Keller, Lukas M.

doi:10.1016/j.gete.2018.01.003

Cited by 39 publications

(46 citation statements)

References 11 publications

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“…Argillaceous rocks, claystones or shales mainly consist of clay minerals typically with ≥ 50 volume percent (vol%) of particles sized < 62.5 µm (e.g., Folk 1980). They account for roughly two-thirds of the sedimentary rock record (Milliken 2014), and are encountered in different natural settings such as sedimentary basins (Hornby et al 1994) and accretionary wedges (Yamaguchi et al 2011;Chester et al 2013;Morley et al 2017).…”

Section: Introductionmentioning

confidence: 99%

Experimental Deformation of Opalinus Clay at Elevated Temperature and Pressure Conditions: Mechanical Properties and the Influence of Rock Fabric

et al. 2021

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The mechanical behavior of the sandy facies of Opalinus Clay (OPA) was investigated in 42 triaxial tests performed on dry samples at unconsolidated, undrained conditions at confining pressures (pc) of 50–100 MPa, temperatures (T) between 25 and 200 °C and strain rates ($$\dot{\varepsilon }$$ ε ˙ ) of 1 × 10–3–5 × 10–6 s−1. Using a Paterson-type deformation apparatus, samples oriented at 0°, 45° and 90° to bedding were deformed up to about 15% axial strain. Additionally, the influence of water content, drainage condition and pre-consolidation was investigated at fixed pc–T conditions, using dry and re-saturated samples. Deformed samples display brittle to semi-brittle deformation behavior, characterized by cataclastic flow in quartz-rich sandy layers and granular flow in phyllosilicate-rich layers. Samples loaded parallel to bedding are less compliant compared to the other loading directions. With the exception of samples deformed 45° and 90° to bedding at pc = 100 MPa, strain is localized in discrete shear zones. Compressive strength (σmax) increases with increasing pc, resulting in an internal friction coefficient of ≈ 0.31 for samples deformed at 45° and 90° to bedding, and ≈ 0.44 for samples deformed parallel to bedding. In contrast, pre-consolidation, drainage condition, T and $$\dot{\varepsilon }$$ ε ˙ do not significantly affect deformation behavior of dried samples. However, σmax and Young’s modulus (E) decrease substantially with increasing water saturation. Compared to the clay-rich shaly facies of OPA, sandy facies specimens display higher strength σmax and Young’s modulus E at similar deformation conditions. Strength and Young’s modulus of samples deformed 90° and 45° to bedding are close to the iso-stress Reuss bound, suggesting a strong influence of weak clay-rich layers on the deformation behavior.

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Section: Introductionmentioning

confidence: 99%

Experimental Deformation of Opalinus Clay at Elevated Temperature and Pressure Conditions: Mechanical Properties and the Influence of Rock Fabric

et al. 2021

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“…Ewy (2018) presented examples of this approach and illustrated how pre-conditioning samples to high relative humidity (RH) make this a convenient method for shale testing. Giger et al (2018) and Minardi et al (2019Minardi et al ( , 2020 successfully adopted this procedure for Opalinus Clay (sandy and shaly facies). The same technique was applied by Schuster et al (2021) to test wet samples of Opalinus Clay.…”

Section: Pore Pressure Generationmentioning

confidence: 99%

“…By applying confining stresses in the order of tens of MPa to pre-conditioned shale samples (with RH > 90%), positive pore pressure, in the order of several MPa is developed (Ewy 2018;Giger et al 2018;Minardi et al 2020). For the saturated samples in the work of Schuster et al (2021) nonnegligible pore overpressures must have been developed as isotropic confining pressure of 50 MPa was applied.…”

Section: Pore Pressure Generationmentioning

confidence: 99%

“…The strain rate at which a sample is sheared impacts the pore water redistribution and pressure generation (Head and Epps 2014;Giger et al 2018). Measurements of the pore pressure evolution would allow computing the effective stress path during each test.…”

Section: Strain Ratementioning

confidence: 99%

“…In the work of Giger et al (2018), it is shown that for undrained testing, a strain rate one order of magnitude greater than the one theoretically appropriate for pore pressure equilibration led to an apparent strength increase of 15-20%. A strain rate two orders of magnitude faster caused an overestimation of shear strength of 40% and Poisson's ratio underestimation of 70%.…”

Section: Strain Ratementioning

confidence: 99%

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Discussion on “Experimental Deformation of Opalinus Clay at Elevated Temperature and Pressure Conditions: Mechanical Properties and the Influence of Rock Fabric” of Schuster, V., Rybacki, E., Bonnelye, A., Herrmann, J., Schleicher, A.M., Dresen, G.

2021

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The testing procedure and results on saturated samples of Opalinus Clay in the work of Schuster et al. (Rock Mech Rock Eng https://doi.org/10.1007/s00603-021-02474-3, 2021) were conducted and presented using strain rates two to four orders of magnitudes higher than the rates needed to allow pore pressure equilibrium in the material, both in drained and undrained conditions. This leads to an erroneous estimation of the mechanical properties in saturated conditions. We discuss this aspect in the context of shale testing. We also discuss the effect of drying-induced fissuring on the mechanical properties of geomaterials tested in dry conditions.

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The quantitative evaluation of fault sealing during the Cenozoic in Gaoyou Depression, Subei Basin

2022

Geological Journal

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The quantitative evaluation of fault sealing is conducted based on comprehensive analysis of mechanism and type analysis of fault seal, fault seal evaluation, and case study analysis. The results indicate that the properties of fault sealing are the interaction of fault order, net-to-gross ratio, fault activity, mud distribution on fault walls, fault dip, and buried depth. In addition, there are three types of fault sealing, including juxtaposition seal, fault rock seal, and cementation seal. Furthermore, the opening and closing of faults play an essential role in controlling hydrocarbon migration and accumulation. Finally, the fault sealing plays a controlling role in reservoir preservation.

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Consolidated-undrained triaxial testing of Opalinus Clay: Results and method validation

Cited by 39 publications

References 11 publications

Experimental Deformation of Opalinus Clay at Elevated Temperature and Pressure Conditions: Mechanical Properties and the Influence of Rock Fabric

Experimental Deformation of Opalinus Clay at Elevated Temperature and Pressure Conditions: Mechanical Properties and the Influence of Rock Fabric

Discussion on “Experimental Deformation of Opalinus Clay at Elevated Temperature and Pressure Conditions: Mechanical Properties and the Influence of Rock Fabric” of Schuster, V., Rybacki, E., Bonnelye, A., Herrmann, J., Schleicher, A.M., Dresen, G.

The quantitative evaluation of fault sealing during the Cenozoic in Gaoyou Depression, Subei Basin

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