Determining the physical and mechanical properties of sedimentary rocks during rotary core drilling using the specific penetration index derived from a fully automated coring machine’s parameters

The primary goal of this study was to assess the use of the Specific Penetration Index (SPI) for determining the physical and mechanical properties of rock during rotary drilling. To accomplish this, three types of rock blocks with different physical and mechanical properties (30 cm × 30 cm × 40 cm) were prepared, along with four synthetic blocks (50 cm × 50 cm × 37.5 cm) consisting of layered sequences with varying characteristics. Drilling tests were performed on both the rock blocks and synthetic blocks using a fully automated coring machine equipped with a 60 mm outer diameter and 54 mm inner diameter drill bit at rates of penetration of 0.10, 0.15, 0.20, and 0.25 mm/s. SPI was calculated based on the thrust at each rate of penetration during drilling in various types. The relationship between the SPI and the physical and mechanical properties of the rocks, as well as those of the layers in the synthetic blocks, was then analyzed through regression analysis. The results demonstrate that the SPI can be a reliable and practical tool for estimating the physical and mechanical properties of rock.