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Nanoindentation of Horn River Basin Shales: The Micromechanical Contrast Between Overburden and Reservoir Formations

Lookup NU author(s): Dr Tom CharltonORCiD, Dr Mohamed Rouainia



This work is licensed under a Creative Commons Attribution 4.0 International License (CC BY 4.0).


© 2023. The Authors.We present a micromechanical characterization of shales from the Horn River Basin, NW Canada. The shales have contrasting mineralogy and microstructures and play different geomechanical roles in the field: the sample set covers an unconventional gas reservoir and the overburden unit that serves as the upper fracture barrier. Composition and texture were characterized using X-ray diffraction, mercury injection porosimetry, and scanning electron microscopy (SEM). Grid nanoindentation testing was used to obtain the mechanical response of the dominant phases in the shale microstructure. Samples were indented parallel and perpendicular to the bedding plane to assess mechanical anisotropy. Chemical analysis of the grids with SEM-EDS (energy dispersive X-ray spectroscopy) was undertaken and the coupled chemo-mechanical data was used in a statistical clustering procedure (Gaussian mixture model) to reveal the mechanical properties of each phase. The results show that the overburden consists of a soft clay matrix with highly anisotropic elastic stiffness, and stiffer but effectively isotropic inclusions of quartz and feldspar; the significant anisotropy of the overburden has been previously observed on a much larger scale using microseismic data. Creep displacement is concentrated in the clay matrix, which is the key phase for fracture barrier and seal applications. The reservoir units are harder and have more isotropic mechanical responses, primarily due to their lower clay content. Despite varied compositions and microstructures, the major phases of these shales (clay/organic matrix, quartz/feldspar, dolomite, and calcite) have unique mechanical signatures, which will aid identification in future micromechanical characterizations and facilitate their use in upscaling schemes.

Publication metadata

Author(s): Charlton TS, Rouainia M, Aplin AC, Fisher QJ, Bowen L

Publication type: Article

Publication status: Published

Journal: Journal of Geophysical Research: Solid Earth

Year: 2023

Volume: 128

Issue: 3

Print publication date: 01/03/2023

Online publication date: 08/03/2023

Acceptance date: 08/03/2023

Date deposited: 12/04/2023

ISSN (print): 2169-9313

ISSN (electronic): 2169-9356

Publisher: John Wiley and Sons Inc


DOI: 10.1029/2022JB025957


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Funder referenceFunder name
NE/R018057/1Natural Environment Research Council (NERC)