Study On New Types Of PDC Cutters And Their Optimization Designs

PDC cutters have always been one of the research hotspots of PDC bit,whose rockbreaking characteristics and service life directly affect the rock-breaking efficiency of PDC bit.There are technical problems of low rock breaking efficiency and low ROP of PDC cutter in hard,heterogeneous and other difficult-to-drill formations.Theoretical analysis,numerical simulation and laboratory experiments are used to study the mechanical properties and rock breaking of PDC cutters considering the passivated cutting edge with chamfer,polycrystalline diamond material,special-shaped cutter design and other factors.On this basis,two new types of PDC cutters have been developed:concave axe-shaped cutter and multi-ridge shaped cutter.Considering the chamfering factor,a theoretical prediction model of cutting force is revised for plane cylinder-shaped cutter,and the prediction model is verified by the the single cutter rotating tests.The influence law of chamfering on the tangential force and normal force of the plane cylinder-shaped cutter is revealed.It is found that the normal force increased with the increase of chamfer by about 10 times of the tangential force.Furthermore,based on laboratory experiments,the effect of chamfering and polycrystalline diamond material on the wear resistance and overall performance of PDC cutter has also been studied.And the effect of polycrystalline diamond material on wear resistance and thermal stability of PDC cutter is more significant than that of chamfer.Drilling in hard and heterogeneous formations,the application effect of axe-shaped cutter has significantly improved compared with that of plane cylinder-shaped cutter.In laboratory experiments,the cutting state is divided into two states: initial invasion process and stable cutting process.The rock-breaking characteristics of axe-shaped cutter on cutting hard rock(granite)are studied.The influence law of ridge-shaped structure on cutting efficiency and mechanical properties(wear resistance and impact resistance)of PDC cutter is studied.The research results show that the ridge-shaped structure of the axe-shaped cutter is not only beneficial to improve the wear resistance and impact resistance,but also to improve the cutting efficiency.For the application of PDC bit in hard plastic mudstone formation,a new concave axe-shaped cutter is developed,and an approximate experimental method for single cutter cutting hard plastic mudstone is established.Taking the factors of cutting force,cutting quality and track length as the criterion,the rock-breaking mechanism of the new concave axe-shaped cutter to break the hard-plastic mudstone is clarified.Aiming at the problems of premature failure of PDC bit and low ROP in hard formation,a PDC cutter with multi-ridge geometry is developed by combining the conclusion that reasonable narrow cutter spacing helps improve rock breaking efficiency and the design of special-shaped cutter.And a three-ridge shaped cutter has been selected.The numerical simulation of the rock-breaking process of the axe-shape cutter and the three-ridge shaped cutter is carried out by using finite element software.Combined with the rock breaking by single cutter tests in laborary tests,rock breaking simulation experiment,the stress concentration and stress diffusion in the rock during the rock breaking process of the three-ridge cutter are analyzed.Based on the experimental results of cuttings fractal,cutting force and performance test,the influence of the new multi-edge structure on the cutting efficiency and mechanical properties of the PDC cutter is revealed.The study found that the simultaneous rock breaking mode of the three-ridge cutter can significantly improve the cutting efficiency.The field test results deomonstrate that threeridge cutters improve the drilling efficiency of the PDC bit.