Numerical Simulation of Rock Breaking Mechanism Analysis of Drill Bit with Central Stinger in Axial Percussive Drilling

Abstract

ABSTRACT: The drill bit with central stinger element assisted by axial vibration has achieved a good rate of penetration in granite and diorite formation in China, but the study on the theoretical rock breaking mechanism of this bit is still insufficient. To better understand the rock-breaking mechanism of drill bit with central stinger and provide a theoretical basis for practical engineering, this paper presents numerical modelling with the finite element method of dynamic cutting processes under 50-200Hz loads. The rock breaking model with three 16mm plain cutters and a 16mm central stinger cutter is established, the cutters break a certain depth of granite at the fixed weight on bit and rotate speed. The rock failure mode, cutting force, mechanical specific energy (MSE) is analyzed and then compared with the steady load breaking condition. Also, the influence of cutter’s location has been analyzed and results indicate that, for 16mm cutter, when the cutting radius of the first plane cutter is less than 13.1mm, there is almost no cutting force on stinger cutter. When the radius is greater than 13.1mm, the force on stinger cutter always increases with the increase of the radius and exists a maximum value. Compared with the steady load, the average cutting force and MSE of stinger cutter under 100Hz load decrease by 11%. Meanwhile the fluctuation of the cutting force of stinger and other three cutters are significantly smaller, the maximum cutting force is reduced by over 19%, which reduces the occurrence of stick-slip. The findings contribute to understand theoretical rock breaking mechanism of central stinger bit, also optimize the bit selection and percussive drilling parameters. 1. INTRODUCTION In drilling operation of petroleum engineering, the Polycrystalline Diamond Compact (PDC) bits are becoming much more widely used and important tools for directional wells, extended reach wells, deep wells and even the ultra-deep wells due to its good efficiency and economy of being able to repair. Nowadays the PDC bits have dominated almost all the footages in drilling operation of oil and gas wells, the efficiency of PDC bits has become a key part of the economics of the drilling operation (Cheng et al., 2018, 2019; Zhang et al., 2020). Therefore, the methods to design efficient and durable PDC drill bits have become the most important direction in drill bit development.