Abstract: Continental shale generally consists of layers with varying components, including clay, felsic minerals, and calcite. During hydraulic fracturing stimulation of shale fracture network structure, the interfacial transition zone (ITZ) forms, significantly influencing crack propagation direction and morphology. Currently, effective quantitative methods for determining the ITZ distribution range in shale layers are lacking. This study focuses on the discrete characteristics of shale micro-mechanical parameter curves and employs confidence ellipses to calibrate discrete data within the ITZ range. Linear fitting and the projection length of confidence ellipse intersections are introduced as a new method for quantifying the ITZ in shale layers. Scanning electron microscopy and a mineral quantitative evaluation system were used to obtain shale surface morphology and mineral distribution, analyzing mineral damage forms after scratch experiment. Nano scratch experiment results were used to determine mineral distribution lengths from various rock types via fracture toughness, compared with scanning electron microscopy findings. Results show that plastic minerals such as illite show a damage pattern of debris accumulation on both sides during the scratch test, while brittle minerals such as albite and quartz show jagged damage or point-like chipping. The presence of ITZ causes the distribution length of plastic minerals identified by scanning electron microscopy to exceed the quantitative results from fracture toughness curves. The friction coefficient method is affected by surface roughness, resulting in lower fitting confidence and higher quantitative results. Compared to the friction coefficient method, the fracture toughness method offers higher data continuity and fitting confidence, though it considers relatively fewer factors. Non-dimensional parameters comprehensively account for fracture toughness, hardness, friction coefficient, and scratch depth, reducing curve dispersion and fitting errors. Compared to traditional methods for identifying individual mechanical parameters, the accuracy of ITZ distribution range quantification based on dimensionless parameters is greatly enhanced.

Key words: continental shale, nano scratch experiment, damage pattern, magnitude analysis, interfacial transition zone