Lateral Force-balance Analysis And Optimal Design For Cutter-layout Of PDC Bit Based On Dynamic Wear Of Cutters

PDC Bit is widely used in drilling industry.It is one of the principal drilling tools because of its low weight on bit(WOB),high drilling rate.However,the PDC bit is easy to failure when it meets the hard formation.The main failure reason is the unbalanced lateral force during drilling process.So far,traditional cutter layout design based on balanced lateral force not considers the cutter wearing.The cutting parameters will be changed when the cutter wear,and then the lateral force of PDC bit will be changed.The status of force balance will be broken.The vibration will be enhanced,and the PDC bit will failure easy.Therefore,the lateral force balance analysis and cutter layout optimization design will be carried out to increase the service life and improve drilling efficiency.The main content and results are shown in the following.(1)The study of the cutting geometric parameters considering the dynamic wear of cuttersMathematical models of the worn and unworn cutters are established.The cutting parameters such as cutting arc length,cutting section area,cutting volume are researched.The zero point traverse method is proposed in the research of the algorithms to solve the cutting parameters.The related error is only 0.035%between the zero point traverse method and the Pro/E method.The mathematical model of PDC cutters and the zero point traverse method are the theory basis for the following research work.(2)The analysis of the sensibility of lateral force based on dynamic wear of cuttersThe effect of the dynamic wear of cutters on lateral force of PDC bit is performed.And the results show that the lateral force increases with wear volume of cutters during drilling process.The ratio of lateral force on WOB is more than 5%.At this moment,the PDC bit is unstable,and it does not conform to the principle of lateral force balance;the results of the analysis of the sensibility of lateral force show that the sensibility of lateral force on wearing volume of cutter are strongest.So,it is unreasonable to make a cutter layout design of force balance without considering the wear tooth.(3)The optimization design research of cutter layout under the wearing conditionThe mathematical model of the balance of traverse force of PDC bit is set up.The Optimization of Latin hypercube and Kriging surrogate model are used to simply the original optimization model.And then,the particle swarm optimization method is used to solve the Kriging model.At last,the PDC bit which has the optimal cutter layout structure has a small lateral force during the dynamic wearing of cutters,and the ratio of lateral force to WOB is always less than 5%.The PDC bit is stable during drilling,and this is important for stability of rock breaking.(4)The research of balance property of lateral force of original and optimized PDC bitThe dynamic properties of the original and optimized PDC bit are studies by the Abaqus simulation platform.The results show that the differences of the forces of the original and optimized PDC bit are small.However,when the cutters are worn,the PDC bit has a high lateral force and large fluctuation range if the wear condition is not considered.This will lead to extreme vibration and low drilling efficiency of PDC bit.However,the lateral force and the fluctuation range keep small if the wear condition is considered in the cutter layout design process.This conforms to the principle of the design of lateral force balance,and verifies the correctness of the results of optimal design of cutter layout.(5)The experiment of the lateral force balanced design for PDC bitWe make 2 PDC bits.They are original PDC bit and new PDC bit.The original PDC bit not considers the wear condition;while the new PDC bit considers the wear condition.Do an experiment on a vertical driller.The results demonstrate that the two bits have small lateral force when cutters are not wearing.After cutters wear,the force of original PDC bit cannot keep balance.Additionally,the new PDC bit conforms the balanced principle of lateral force.Besides,the error of force model in this thesis is less than 8%compared with the experiment result.This illustrates that the optimal cutter-layout design method of lateral force balance can be used in the cutter layout of practical PDC bit.(6)Development of the software "PDC bit cutter-layout optimization design software".The software mainly includes cutter contact analysis,bit force analysis and so on.It can aid the design optimization of the lateral force balance of PDC cutter-layout,improving the efficiency of cutter-layout.