RESEARCH ON THE MECHANICAL CHARACTERISTICS OF LAMINATED SHALE BASED ON SCRATCH TESTS

Shale laminae are recognized as a critical governing factor influencing both mechanical properties and fracture propagation behaviors in sedimentary formations. However, conventional rock mechanics testing methodologies utilizing standard cylindrical specimens demonstrate significant limitations in characterizing these laminated structures. Measurement resolution constraints at sub-millimeter scales often result in data scattering and impede the development of systematic trend analysis. This paper presents an innovative approach employing non-destructive scratch testing techniques to systematically investigate the continuous spatial variation of mechanical properties in laminated shale. Furthermore, we propose a new quantitative characterization framework that combines scratch curves with fractal dimension theory to objectively evaluate the intensity of laminar development. The results show that for shale with high clay content, the characteristics of clear high-frequency thin inter-bedded structures can be seen on the entire scratch surface, and a large number of failure surfaces appear on both sides of the scratch, forming a “Fish-bone” structure. However, for hard shale, the scratch damage is not obvious, and the sample surface is smoother. For shale with high clay content, the fracture toughness and hardness values are lower, while the development degree of lamination is high; conversely, the fracture toughness and hardness values are higher, and the development degree of lamination is lower. This provides an important reference for in-depth understanding of the mechanical properties of shale under different mineral component laminations and provides new theoretical support for shale oil and gas exploration.