Micromechanical characterization of shales through nanoindentation and energy dispersive x-ray spectrometry

Journal Article · Wed Mar 01 00:00:00 EST 2017 · Geomechanics for Energy and the Environment

DOI:https://doi.org/10.1016/j.gete.2016.10.004· OSTI ID:1340233

Veytskin, Yuriy B. ^[1]; Tammina, Vamsi K.  ^[2]; Bobko, Christopher P.  ^[3]; Hartley, Patrick G. ^[4]; Clennell, Michael B. ^[5]; Dewhurst, David N. ^[5]; Dagastine, Raymond R. ^[6]

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1. Sandia National Lab. (SNL-NM), Albuquerque, NM (United States). Structural Dynamics
2. LGM Consultants Engineering Services, Tarrytown, NY (United States)
3. North Carolina State Univ., Raleigh, NC (United States). Dept. of Civil, Construction, and Environmental Engineering
4. CSIRO Energy, Clayton, VIC (Australia). Ian Wark Lab.
5. Australian Resources Research Centre, Kensington, WA (Australia)
6. Univ. of Melbourne (Australia). Dept. of Chemical and Biomolecular Engineering

Shales are heterogeneous sedimentary rocks which typically comprise a variable mineralogy (including compacted clay particles sub-micrometer in size), silt grains, and nanometer sized pores collectively arranged with transversely isotropic symmetry. Moreover, a detailed understanding of the micro- and sub-microscale geomechanics of these minerals is required to improve models of shale strength and stiffness properties. In this paper, we propose a linked experimental–computational approach and validate a combination of grid nanoindentation and Scanning Electron Microscopy (SEM) with Energy and Wavelength Dispersive X-ray Spectrometry (EDS/WDS) at the same spatial locations to identify both the nano-mechanical morphology and local mineralogy of these nanocomposites. The experimental parameters of each method are chosen to assess a similar volume of material. By considering three different shales of varying mineralogy and mechanical diversity, we show through the EMMIX statistical iterative technique that the constituent phases, including highly compacted plate- or sheet-like clay particles, carbonates, silicates, and sulfides, have distinct nano-mechanical morphologies and associated indentation moduli and hardness. Nanoindentation-based strength homogenization analysis determines an average clay packing density, friction coefficient, and solid cohesion for each tested shale sample. Comparison of bulk to microscale geomechanical properties, through bulk porosimetry measurements, reveals a close correspondence between bulk and microscale clay packing densities. Determining the mechanical microstructure and material properties is useful for predictive microporomechanical models of the stiffness and strength properties of shale. Furthermore, the experimental and computational approaches presented here also apply to other chemically and mechanically complex materials exhibiting nanogranular, composite behavior.

• Research Organization: Sandia National Lab. (SNL-NM), Albuquerque, NM (United States)
• Sponsoring Organization: USDOE National Nuclear Security Administration (NNSA)
• Grant/Contract Number: AC04-94AL85000
• OSTI ID: 1340233
• Report Number(s): SAND-2016-2837J; PII: S2352380816300843
• Journal Information: Geomechanics for Energy and the Environment, Vol. 9, Issue C; ISSN 2352-3808
• Publisher: Elsevier
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
58 GEOSCIENCES
Micromechanical characterization
Shale
Nanoindentation
Energy and wavelength dispersive x-ray spectrometry
Scanning electron microscopy
Strength homogenization
Cathodoluminescence