Study On The Regularity Of PDC Bit Cutting Structure And Rock Interaction Based On The Bottom Hole Shape

Drill bit is the main tool for oil and gas drilling.To improve the rock breaking efficiency of drill bit is one of the most effective ways to improve oil and gas drilling efficiency.The current bit usage of PDC bits has accounted for more than 60% of the total.How to improve the service life and rock breaking efficiency of PDC bits is an urgent problem to be solved in the design of PDC bit.To improve the service life and rock breaking efficiency of PDC bit,it is necessary to study from the material of drill bit and the structural design of drill bit.The optimization design of cutting structure is the main way to improve the service life and rock breaking efficiency of the PDC bit.The rock breaking mechanism of PDC bit is the basis of PDC bit cutting structure design.In this paper,the influence of bottom hole shape is considered into the study of PDC bit cutting structure and rock interaction mechanism,and a PDC bit cutting structure design method based on the bottom hole shape is formed.This paper mainly studies the following contents:1.The effect of bottom hole shape on the rock breaking effect of the PDC bit cutting structure was studied.By analyzing the rock stress state in different areas of bottom hole,we can obtain the difficulty of rock breaking in different areas of bottom hole.The rock is difficult to break in outer cone area,and the rock is easy to break in inner cone area.The inner cone area is simplified to a cylindrical rock with different radii of curvature,and the outer cone area is simplified to a cylindrical rock with different radii of curvature.2.The evaluation index of the rock-breaking effect on PDC bit cutting structure based on the bottom hole shape is proposed.Through the analysis of the rock breaking process of the PDC bit cutting structure,we can establish the mathematical model of the rock breaking stress of bottom hole.By establishing the relationship between the rock breaking stress and the evaluation index of the rock-breaking.The influence of bottom hole shape is applied to the optimized design of the PDC bit cutting structure.3.The rock breaking experiment of the PDC bit cutting structure based on bottom hole shape was carried out,and the law of the interaction between cutting structure of the PDC bit and rock based on the bottom hole shape was obtained.Whenthe PDC cutting teeth break the rock in the outer cone area.The rock breaking stress gradually decreases as the curvature radius increases.When the PDC cutting teeth break the rock in the inner cone area.The rock breaking stress gradually increases as the curvature radius increases.Due to the complexity of the factors affecting the rock breaking process of the PDC bit.Studying on the interaction law between PDC bit cutting structure and rock require a large number of repetitive experiments,Therefore,based on the numerical simulation method,a mathematical model for the interaction between PDC bit cutting structure and rock is established.4.An optimized design method for the cutting structure of PDC bit based on the bottom hole shape is proposed.The PDC bit cutting structure is optimized for the minimum specific rock energy per revolution of the crown.PSO particle swarm optimization algorithm is used to optimize the cutting structure of PDC bit.Combined with the constraints of clear rock effect and bit machining,and the PDC bit cutting structure design method suitable for different strata is established.