Abstract: The high cost of shale coring limits the application of the Schmidt hardness method based on core samples. This study employs cuttings sieving, sample preparation, and point load testing to reveal variation patterns in the ultimate compressive strength of cuttings with different fragment shapes and sizes, establishing a conversion model between cuttings and core Schmidt hardness. Experimental results show that: (1) Shale cuttings are categorized into four shapes: blocky, wide flaky, elongated, and narrow flaky. (2) The ultimate compressive strength of blocky and wide flaky cuttings decreases with increasing dimensions of the long, intermediate, and short axes, and then stabilizes. No significant pattern is observed for narrow flaky and elongated cuttings. (3) The initial dimensions of the stable stage of ultimate compressive strength are 8.2 mm for the long axis, 5.9 mm for the intermediate axis, and 3.2 mm for the short axis, and results beyond these dimensions exhibit strong stability. (4) The Schmidt hardness of cuttings is lower than that of the core test results. However, a strong correlation exists between the two, with a correlation coefficient exceeding 0.9. The findings provide a low-cost, real-time evaluation method and standard for shale Schmidt hardness, offering a basis for drilling optimization.

Key words: Schmidt hardness, shale cuttings, cuttings fragment shape, ultimate compressive