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Geomechanical characterisation of organic-rich calcareous shale using AFM and nanoindentation

Graham, S.P.; Rouainia, M.; Aplin, A.C.; Cubillas, P.; Fender, T.D.; Armitage, P.J.

Geomechanical characterisation of organic-rich calcareous shale using AFM and nanoindentation Thumbnail


Authors

S.P. Graham

M. Rouainia

P. Cubillas

T.D. Fender

P.J. Armitage



Abstract

The geomechanical integrity of shale overburden is a highly significant geological risk factor for a range of engineering and energy-related applications including CO2 storage and unconventional hydrocarbon production. This paper aims to provide a comprehensive set of high-quality nano- and micro-mechanical data on shale samples to better constrain the macroscopic mechanical properties that result from the microstructural constituents of shale. We present the first study of the mechanical responses of a calcareous shale over length scales of 10 nm to 100 μm, combining approaches involving atomic force microscopy (AFM), and both low-load and high-load nanoindentation. PeakForce quantitative nanomechanical mapping AFM (PF-QNM) and quantitative imaging (QI-AFM) give similar results for Young’s modulus up to 25 GPa, with both techniques generating values for organic matter of 5–10 GPa. Of the two AFM techniques, only PF-QNM generates robust results at higher moduli, giving similar results to low-load nanoindentation up to 60 GPa. Measured moduli for clay, calcite, and quartz-feldspar are 22±2 GPa, 42±8 GPa, and 55±10 GPa respectively. For calcite and quartz-feldspar, these values are significantly lower than measurements made on highly crystalline phases. High-load nanoindentation generates an unimodal mechanical response in the range of 40–50 GPa for both samples studied here, consistent with calcite being the dominant mineral phase. Voigt and Reuss bounds calculated from low-load nanoindentation results for individual phases generate the expected composite value measured by high-load nanoindentation at length scales of 100–600 μm. In contrast, moduli measured on more highly crystalline mineral phases using data from literature do not match the composite value. More emphasis should, therefore, be placed on the use of nano- and micro-scale data as the inputs to effective medium models and homogenisation schemes to predict the bulk shale mechanical response.

Citation

Graham, S., Rouainia, M., Aplin, A., Cubillas, P., Fender, T., & Armitage, P. (2021). Geomechanical characterisation of organic-rich calcareous shale using AFM and nanoindentation. Rock Mechanics and Rock Engineering, 54, 303-320. https://doi.org/10.1007/s00603-020-02261-6

Journal Article Type Article
Acceptance Date Sep 23, 2020
Online Publication Date Oct 19, 2020
Publication Date 2021
Deposit Date Oct 20, 2020
Publicly Available Date Mar 29, 2021
Journal Rock Mechanics and Rock Engineering
Print ISSN 0723-2632
Electronic ISSN 1434-453X
Publisher Springer
Peer Reviewed Peer Reviewed
Volume 54
Pages 303-320
DOI https://doi.org/10.1007/s00603-020-02261-6

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Publisher Licence URL
http://creativecommons.org/licenses/by/4.0/

Copyright Statement
Advance online version This article is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons licence, and indicate if changes were made. The images or other third party material in this article are included in the article's Creative Commons licence, unless indicated otherwise in a credit line to the material. If material is not included in the article's Creative Commons licence and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this licence, visit http://creativecommons.org/licenses/by/4.0/.




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