Nano-scale mechanical characterization of shale using nanoindentation: an experiment work

Shale’s micromechanical properties can be determined by nanoindentation. We employed the advanced accelerated property mapping mode to obtain the mechanical properties and its spatial distribution of a shale sample. Nanoindentation tests were conducted on the sample surface to obtain the elastic modulus and hardness, offering quantitative mechanical characterization of localized shale. Gaussian mixture model and K-means algorithm were used to fit the data and identify distinct mineral phases from load-displacement curves. Experiment results and analysis show that the nano-mechanics of shale is conditioned by the mineral composition and its distribution. Three clusters of different mineral phases were recognized through nanoindentation curves. It is evident that the shale was highly heterogeneous in nano-to-micron scales based on the spatial distribution mapping of the elastic modulus and hardness. A two-term exponential relationship was observed between the hardness and the plastic work induced in the nanoindentation process. For the tested Marcellus shale, the mechanical weakening was not apparent after 10 days water treatment due to the short time of treatment. Mechanical alteration was observed when the treatment prolonged to 20 days. The elastic modulus of shale exhibited a reduction of 0.6%~15% and the hardness decreased by 8.6%~17.8%.