MICROSTRUCTURAL AND MECHANICAL PROPERTY CHARACTERIZATION OF ARGILLACEOUS, KEROGEN-RICH, AND BITUMINOUS SHALE ROCKS

Shale rocks have become an indispensable natural gas and oil source. Hence, knowledge of the mechanical properties of shales is critical for horizontal drilling and hydraulic fracturing. We selected three types of shales with drastically different compositions and microstructures and conducted detailed microstructural characterization and mechanical property measurements by nanoindentation. The argillaceous and kerogen-rich shales have soft matrix phases. The bituminous shale, on the contrary, is rich in carbonates. The kerogen-rich shale has the lowest mechanical properties, followed by the argillaceous shale, while the bituminous shale is the stiffest and hardest. Young’s modulus is anisotropic for all samples, but hardness does not follow this trend. Young’s modulus decreases at higher indentation depth in the bedding plane-normal direction, but the decrease is not apparent in the bedding plane-parallel direction. Additionally, apparent cracking and spallation were noted in the argillaceous and bituminous shale, but not in the kerogen-rich shale.