Research on the Rock Cutting Mechanism of Non-Planar PDC Cutters Based on the Drucker-Prager Criterion
Authors: Sun Yuqi , Liu Li , Jiang Haichao , Yu Jinping , Ji Guodong , Wu Qiang , Chen Changchang 
Published: September 2023

ABSTRACT
Non-planar PDC cutters are widely used to solve these problems of wear and breakage of conventional PDC cutters when drilling hard rock formations. In this paper, the finite element method is adopted to study the rock-breaking characteristics of non-planar PDC cutters. The effects of the cutting parameters on the rock-breaking efficiency of a non-planar PDC cutter are analyzed. The mechanical specific energy (MSE) of non-planar PDC cutters is smaller. The rate of penetration (ROP) is higher, and the aggressiveness is stronger. The influence of different cutting parameters on the rock-breaking efficiency of four types of PDC cutters is analyzed. The results indicate that the optimum cutting depth is in the range of 1.5-2 mm, and the optimum cutting angle is in the range of 15°-20°. Based on the finite element simulation results, a personalized PDC bit is designed and successfully applied to Yang101HXX-3 well. The research results can provide a theoretical basis for the selection, structure optimization, drilling bit design, and application of efficient PDC bits.

INTRODUCTION
Oil and natural gas resources are the main energy sources in today's society, which have a bearing on people's livelihoods and national defense security. Polycrystalline diamond compact (PDC) fixed-cutting bits (PDC bits) have continued to evolve and advance since they were first introduced in 1973 and entered the field in 1976. With the increasing level of oil and gas exploration and development, the number of deep and ultra-deep wells is gradually increasing. The geological conditions are becoming more complex. In complex and difficult to drill formations such as deep hard formations, abrasive formations, and soft and hard interlocking formations, conventional PDC drill bits have certain limitations. There are problems such as low mechanical drilling speed, difficulty in drilling, low drilling efficiency, and a short working life (Wang et al., 2021). PDC cutters crushing of rock is divided into two processes. First, PDC cutters intrude into the rock. Then, PDC cutters cause the surrounding rock to crumble into large pieces, and the rock undergoes shear damage (Almenara & Detournay, 1992). The durability of conventional PDC cutters depends on the wear resistance of the diamond (Wang et al., 2019). In addition, the flat working surface of conventional PDC cutters obstructs rock debris transport, which tends to cause repeated cutting. The rock-breaking efficiency of PDC bits is not only influenced by drilling parameters, formation lithology, and PDC bit structure, but also related to the shape of PDC cutters. In recent years, various non-planar PDC cutters have been used in the design of PDC bits, such as ridged PDC cutters, triridged PDC cutters, and stinger PDC cutters, as shown in Fig. 1, which have achieved good speed-up results in specific formations. Non-planar PDC cutters can enhance the impact and wear resistance of PDC bits in hard formations, reduce the mechanical specific energy (MSE) of the rock, and improve the rate of penetration (ROP).