Experimental Study on Rock-Breaking Characteristics of Conglomerate with Special-Shaped PDC Cutters Under High Confining Pressure
Authors: Chen Xiaoyuan , Li Xinlong , He Wenhao , Wang Wei , Huang Zhongwei , Shi Huaizhong , Xiong Chao , Chen Han , Chen Zhenliang 
Published: August 2024

ABSTRACT:
The characteristics of conglomerate non-uniformity and complex pore structure lead to severe wear and low rock-breaking efficiency of PDC bits when drilling into conglomerate formations. In this paper, the characteristics of breaking conglomerate of three kinds of PDC cutters such as planar cutter, triple-ridged cutter and axe-shaped cutter are studied under high confining pressure. By designing and carrying out experiments of breaking conglomerate with the planar cutter, axe-shaped cutter and triple-ridged cutter under high confining pressure, the characteristics of cutting force, rock breaking volume, MSE of rock breaking and distribution of cuttings of PDC fractured conglomerate, and the surface topography of the cutting groove of PDC fractured conglomerate are compared. The experimental results show that the cutting force of the triple-ridged cutter is the most stable and the mechanical specific energy of the axe-shaped cutter is the least under the condition of high confining pressure. In addition, the grooving boundary of the triple-ridged cutter is more obvious, and the ability of triple-ridged cutter to peel the whole gravel is stronger under the condition of large cutting depth. In the design of PDC bits in conglomerate formations, the triple-ridged cutter can be selected as the front cutter of the nose and shoulder. The research provides theoretical support for the cutter selection design of hybrid-cutters PDC bit in conglomerate formation to improve rock breaking efficiency and lifespan of conglomerate formation drilling.

1. INTRODUCTION
After years of oil exploration and exploitation, it is increasingly difficult to find new large oil and gas reservoirs in the middle and shallow strata, the oil and gas exploration has been extended to deep (4500∼6000 m) and ultra-deep (&gt;6000 m) around the world(Bian et al., 2022). Petroleum drilling technology is gradually entering the stage of "efficient drilling of deep and ultra-deep complex formations". PDC (polycrystalline diamond bit) bits are widely used in the drilling process in oil & gas industries. According to statistics, the drilling length of PDC bits has exceeded 90% of the total drilling length in the world, accounting for about 80% of the global market(Huang et al., 2017). However, when drilling into hard, highly abrasive, and heterogeneous formations, planar PDC drill bits suffer from problems such as low mechanical drilling speed, and the severe wear of PDC cutters, greatly limiting the service life of a single drill bit(Cheng, 2019). In recent years, special-shaped PDC cutters of different shapes, such as triple-ridged, axe-shaped, wedge (V) shape and chisel shape, have been continuously developed to transform PDC bits from the original shear rock-breaking mode to the mixed-rock breaking mode with multiple rock breaking functions, such as shear and plough, which greatly improves the drilling ability and rock breaking efficiency of PDC bits in hard, abrasive and heterogeneous layers.