NANOINDENTATION EXPERIMENTS TO STUDY THE MICROMECHANICAL PROPERTIES OF STRATIFIED SHALE

The micromechanical properties of stratified shale are critical for understanding wellbore stability and hydraulic fracture extension patterns. Based on nanoindentation experiments and data analysis, the mechanical parameters of shale specimens from two laminar directions of the Jimsar Lucaogou Formation in Xinjiang are measured from a microscopic perspective in this paper. The mechanical parameters of multiple indentation points are obtained using grid indentation. The mineral composition of the samples is quantified using field emission scanning electron microscopy (SEM) and XRD ray diffraction. The results show that the shale mechanical parameters have a good linear relationship with each other at the nanoscale. However, the relationship between horizontal bedding and vertical bedding is quite different. The average elastic modulus, average hardness, and average fracture toughness of the parallel laminated specimens are 22.94 GPa, 1.04 GPa, and 1.19 MPa·m^1/2, respectively. The average elastic modulus, average hardness, and average fracture toughness of the vertical laminated specimens are 35.23 GPa, 3.47 GPa, and 1.32 MPa·m^1/2, respectively. The shale mechanical parameters in the vertical bedding direction are higher than those in the horizontal laminae. The mechanical parameters at the nanoscale are related to the orientation of the laminae. The shale is anisotropic at the nanoscale and the anisotropy of different mechanical parameters behaves differently. The microscopic elastic modulus, hardness, and fracture toughness of shale conform to Weibull distribution. The dispersion of hardness is the highest. The results can help analyze the relationship between shale mechanical properties and laminar orientation.