Rock Indentation Characteristics Induced by Spherical Button Subjected to Dynamic and quasi-static Loads.

Rock indentation and fragmentation behavior under dynamic and quasi-static loads have significant impacts on the exploration drilling for oil, gas, and geothermal energy. In this study, the mechanical response of rock indentation subjected to dynamic and quasi-static loads was investigated in terms of the interaction between the button and the rock in percussion drilling. The effect of rock type, grain size, and mineralogical composition on rock fragmentation and penetration response was compared, and the cracking characteristics of the rock and crack propagation paths were analyzed. The results show that the damage characteristics of rocks under quasi-static load are similar to those under dynamic load, but the penetration performance under dynamic load is better than that under quasi-static load. The brittleness index can be used to assess the fragmentation performance of different rocks. When the brittleness index of the rock is less than 20, the rock fragmentation performance is particularly sensitive to the brittleness index. The mineral grain size will affect the period of rock failure, when the mineral grain size is less than 900 µm, there is no significant difference in crater depth or volume. The mineralogical composition has a significant effect on the penetration characteristics. When the content of feldspar is more than 5 times that of quartz, the fragmentation performance will not be much different. The relationship between the axial force and the penetration depth follows the power-law relationship, which can be used to describe the dynamic mechanical response of bit and rock in the process of percussion drilling. Highlights: The mechanical response of rock indentation subjected to dynamic and quasi-static loads was investigated and compared. The influence of rock type, grain size, and mineralogical composition on rock fragmentation was evaluated. The rock fragmentation process under quasi-static load can be regarded as a slow motion of rock fragmentation under dynamic load. The relationship between the axial force and the penetration depth in the elastic deformation stage follows a power-law relationship. [ABSTRACT FROM AUTHOR]