Micromechanical characterisation of overburden shales in the Horn River Basin through nanoindentation

• Published in: IOP Conference Series: Earth and Environmental Science
• Main Authors: Charlton, T S, Rouainia, M, Aplin, A C, Fisher, Q J, Bowen, L
• Format: Article in Journal/Newspaper
• Language: unknown
• Published: IOP Publishing 2023
• Subjects: Canada; Fort Simpson; Horn River
• Online Access: http://dx.doi.org/10.1088/1755-1315/1124/1/012087; https://iopscience.iop.org/article/10.1088/1755-1315/1124/1/012087; https://iopscience.iop.org/article/10.1088/1755-1315/1124/1/012087/pdf

Abstract The paper presents a micromechanical characterisation of Fort Simpson shale, which overlies unconventional gas-producing lithologies in the Horn River Basin, NW Canada. The Fort Simpson formation is clay-rich and microseismic data recorded during hydraulic fracturing events in the underlying reservoir has shown the formation acts as a barrier to fracture development, with a notably anisotropic seismic response. Samples were prepared from core fragments and the composition and texture of the shale was characterised using X-ray diffraction, mercury injection porosimetry and scanning electron microscopy (SEM). Nanoindentation testing was used to obtain the mechanical response of the shale microstructure, at grain-scale. The indentation was conducted on a grid pattern and samples were oriented both parallel and perpendicular to the bedding plane to assess the inherent mechanical anisotropy. Chemical analysis of the grids was also undertaken through SEM/EDS (energy dispersive X-ray spectroscopy) and the coupled chemo-mechanical data was used to characterise the material phases of the shale through a statistical clustering procedure. The results show that Fort Simpson shale broadly consists of a soft clay phase, with strongly anisotropic elastic stiffness, and stiffer but effectively isotropic grains of quartz and feldspar. A simple upscaling scheme was also applied to link the grain-scale elastic stiffness to the field-scale microseismic data.