Simulation Study On Rock Breaking Of PDC Bit Assisted By Composite Impact System

With the development of oil drilling industry,the drilling depth has gradually increased.In order to improve the rock breaking efficiency of drilling machinery and improve the working performance of PDC(Polycrystalline Diamond Composite)bit in the deep stratum,the low-frequency composite impact system is designed to assist PDC bit to accelerate rock breaking.To further study the process of PDC bit in composite impact system.This paper analyzes the intrusion of PDC bit,constructs composite impact system,establishes simulation model by discrete element,and explores the changing parameters of PDC bit under various conditions.The main studies are as follows:(1)To analyze the rock breaking theory of PDC bit and composite rock breaking conditions,Establish a composite impact system with drilling fluid as the energy medium and axial and torsional shocks,to analyze different frequency conditions of composite impact system with AMEsim shows that the system can assist the drill bit to complete low frequency impact and reset function and stable operation.(2)The drill rock breaking model was established by discrete element method,analyzed the effect of one-way impact conditions using the control variable method,and established the factors affecting the axial impact,torsion impact and impact frequency,and concluded that the axial impact significantly improves the rock breaking efficiency and reduces the energy consumption.Based on the basis of factors,the orthogonal experimental scheme is designed to explore the rules of rock efficiency,energy consumption and working load during different axial shocks,different torsion shocks and different impact frequencies.(3)Taking rock breaking efficiency and unit energy consumption as indicators,When the composite impact conditions are Axial impact 3.5mm?Torsional impact 6deg?Impact frequency5 Hz,The rock breaking efficiency is the highest;Axial impact 3.5mm?torsional impact 4deg?impact frequency 3Hz,Minimum energy consumption of unit rock breaking;Taking the two-index ratio as the new evaluation method,When The axial impact is 2.5mm?Torsional impact5deg? Impact frequency 4Hz,Maximum ratio of the two indicators,Best working performance;Based on the equivalent rock medium model,The impact conditions are compared with the normal operating conditions,Rock breaking efficiency improved by 19.56%,Energy consumption per unit of rock breaking has decreased by 26.04%,Feft depth raised by 15.5%,Rock strength decreased in horizontal and vertical direction decreased by 8.94% and 6.28%respectively.The working performance of drilling rock is significantly better than the conventional conditions.There are 46 pictures,15 tables and 74 references.