Numerical Simulation on Damage Characteristics of Carbonate Rock Under Axial-Torsional Coupled Impact by PDC Cutters

ABSTRACT Carbonate rock is an important oil and gas reservoir rock. Deep carbonate rocks are of high strength, hardness, abrasiveness and poor drillability, which will cause various problems as follows: PDC cutter collapse, serious wear and low drilling efficiency. Axial-torsional coupled percussive drilling can improve the drilling speed of deep hard rocks including carbonate rock. Therefore, a numerical model of axial-torsional coupled impact rock breakage was established for carbonate rocks. The damage characteristics of carbonate rock caused by spherical cutter and axe-shaped cutter under different impact parameters were analyzed. The simulation results reveal that the impact force of two kinds of cutters increases with the increase of impact speed. The torque of PDC cutters increases with the increase of torque amplitude. Under the same conditions, the tensile damage of carbonate rock caused by axe-shaped cutter is more obvious under the action of axial-torsional coupled impact and the tensile damage area under axe-shaped cutter tends to be connected. Additionally, the damage caused by PDC cutter to carbonate rocks is mainly tensile damage, supplemented by compressive damage. This work is instructive in revealing the effect of PDC cutter on breaking carbonate rocks under different impact parameters. INTRODUCTION As an important oil and gas reservoir rock, 50% of the world's proven oil and gas resources are stored in carbonate rocks (Al-Shargabi et al., 2022). Deep carbonate rocks are of high strength, hardness, abrasiveness and poor drillability. Conventional rotary bit drilling method has many problems in rock breaking, such as serious wear and low drilling efficiency (Jamali et al., 2019). Axial-torsional coupled percussive drilling has higher penetration rate in breaking hard rock, such as carbonate rock (Saai et al., 2020). And some oil companies designed some special-shaped PDC cutters (Zhu et al., 2022), such as axe-shaped cutter and spherical cutter. However, the characteristics of breaking carbonate rock by PDC cutters under the action of axial-torsional coupled impact is not clear. Therefore, it is of great significance to investigate the effect of different impact parameters on breaking carbonate rock by PDC cutters under the action of axial-torsional coupled impact.