Research on Fidelity Performance of Coring Bits during Drilling and Cutting in Deep Extreme Environments

Deep rock formations in extreme environments are characterized by complex working conditions, various structures, high hardness, and high resistance to compression. However, existing coring techniques leave the cores of deep rock formations vulnerable to residual stresses, resulting in poor fidelity during deep coring. This paper develops a rock-breaking model for the structural parameters of drill bits. It proposes that a drill bit's structural parameters in terms of back-rake and side-rake angles will affect the core's fidelity performance. In addition, the core's mechanical specific energy and maximum stress will reflect the fidelity effect. The accuracy of the theoretical model was verified via simulation analysis. The simulation results show that the tool's average cutting force and Standard deviation of cutting force increase as the drill bit's back-rake and side-rake angles vary. This leads to increased shear friction on the core, which affects the maximum stress and mechanical specific energy, and, subsequently, the fidelity of the core. The back-rake angles ranged from 15 & DEG; to 25 & DEG;, with the optimum back-rake angle of 21 & DEG; producing a maximum stress and a mechanical specific energy that were 0.69 and 0.85 times higher than the highest point, respectively. The side-rake angles range from 5 & DEG; to 15 & DEG;, with the optimum side-rake angle of 10 & DEG; producing a maximum stress and a mechanical specific energy that were 0.76 and 0.96 times higher than the highest point, respectively. The finite element method error was 1.21%. This work's main results will help reveal the fidelity mechanisms of the drilling process and contribute to the development of fidelity drill bits for complex surface drilling processes.

Automated summary

This study develops a rock-breaking model for drill bit's structural parameters and reveals their impact on the fidelity performance of deep coring. The simulation analysis validates the accuracy of the theoretical model. The results show that variations in the drill bit's back-rake and side-rake angles affect the shear friction on the core, resulting in changes in maximum stress and mechanical specific energy, and ultimately affecting the fidelity of the core.