Optimal Design Method Research Of PDC Drill Bit Crown Shape Based On Bottom Hole Stress State

The crown shape is an important part of the PDC bit.The crown shape of the PDC bit determines the bottom hole shape,and further affects the difficulty of rock-breaking.The study of the stress state of rock with different bottom hole shapes can provide guidance for the optimization of the crown shape.The thesis innovatively starts with the relationship between bottom hole shape and the rock-breaking stress of different parts of rock at bottom hole.The optimal design theory of crown shape of PDC bit is systematically expounded,and the general shape of the crown can be fitted with the form of three typical crown shapes(fishtail,flat and cannonball),and the stress distribution at the bottom of the well is characterized by the rock breakable strength.The LS-DYNA finite element simulation software is used to simulate the rock breaking process of single tooth,single blade and single row tooth,and the influence of cutting angle,cutting depth and cutting speed on rock breaking strength under different lithology conditions,and the distribution law of rock breaking strength of typical bottom hole shape are obtained.By establishing the expression of rock breaking strength and bottom hole shape,the optimal design model of crown shape of PDC bit is proposed.This paper develops the research idea of crown design and promotes the development of rock breaking theory.