Research on discrete element modeling and numerical simulation of cutting rock behavior under impact load

Abstract

Combining well-drilling hammers with polycrystalline diamond compact bits to break rock under cutting load and impact load is an effective way to improve drilling efficiency. Although impact load can enhance the cutting efficiency of the cutter, excessive impact can also cause the cutter to be subjected to additional vibrations, which can decrease its working life. Knowledge of laws governing the changes in the cutting force of the cutter under impact load is essential for the design and selection of well-drilling hammers. Based on rock scratch tests and finite element rock cutting model, a discrete element modeling (DEM) rock cutting model was established to analyze the rock breaking and cutting force. Then, the material parameters of rock samples were determined, and the simulation parameters were corrected.Finally, a DEM rock cutting model under an impact load was established. The results showed that when there was an obvious difference between the average cutting force and mean peak cutting force, which corresponded to the rockbreaking transition from ductile to brittle, with introduction of the impact load leading to an earlier transition. The cutting force variance was proportional to the impact amplitude, and the increase in the cutting force variance became more obvious when the static load exceeded the critical transition weight.When the ratio of the impact amplitude to the static load was greater than 50%, the mean and variance of the cutting force increased rapidly. Under the same impact amplitude, the impact frequency had little effect on the average cutting force, but a higher frequency could significantly reduce the variance of the cutting force under a high static load (i.e., it could alleviate the fluctuation of the cutting force). These results provide a reference for the selection of welldrilling hammers and optimization of the impact load. K E Y W O R D S discrete element modeling, impact drilling, PDC bit, rock cutting force, well-drilling hammer