基于分区法的扩眼器刀翼布齿优化研究

扩眼器在破岩时,刀翼处受力不均会产生不平衡侧向力,引起井下钻具振动,影响井眼质量和钻具使用寿命,对扩眼作业造成不利影响。为了准确分析井底形状和刀翼切削受力的变化,提出分区法来分析扩眼器刀翼的切削过程。基于分区法,扩眼器旋转切削一圈的过程可以分为几个不同的切削阶段,每个切削阶段对应一组切削参数。借鉴PDC钻头的受力模型,建立了以扩眼器全阶段侧向力最小为目标,以各个切削齿后倾角为优化变量的多目标优化模型。利用非支配排序遗传算法2 (NSGA-Ⅱ)对优化模型进行求解,得到最优Pareto解集,利用模糊综合评价法对Pareto解集中的个体解进行评价,并从中选取最优个体解。以三刀翼扩眼器为例进行了布齿优化设计,优化结果表明,基于分区法的布齿优化方法可以有效减小每个切削阶段的侧向力,且保证了各个阶段的侧向力与钻压比值都在5%以内,从而实现扩眼器全切削阶段的侧向力平衡。研究结果对扩眼器的设计具有一定的指导意义。

Cutter Layout Optimization of Reamer Based on Zoning Method

When the reamer breaks the rock,the uneven force on the blade will produce unbalanced lateral force,which will cause the downhole drilling tool vibration,affect the wellbore quality and the service life of the tool,and adversely affect the reaming operation. To accurately analyze the changes in the shape of the well bottom and the cutting force of the blade,the zoning method is proposed to analyze the cutting process of the reamer.Based on the zoning method,the process of the reamer cutting a circle can be divided into several different cutting stages,and each cutting stage corresponds to a set of cutting parameters. Using the force model of the PDC bit for reference,a multi-objective optimization model with the minimum lateral force of the reamer at all stages as the goal and the back rake angle of each cutter as the optimization variable is established. The optimal Pareto solution set is obtained by using the non-dominated sorting genetic algorithm 2( NSGA-Ⅱ) algorithm to solve the optimization model. The individual solutions in the Pareto solution set are evaluated by the fuzzy comprehensive evaluation method to select the optimal individual solution. Taking the three-blade reamer for case study,the optimization design of the reamer cutter layout is carried out. The results show that the cutter layout optimization method based on the zoning method can effectively reduce the lateral force of each cutting stage,and ensure that the lateral force and the WOB ratios are all within 5%,so as to achieve the lateral force balance of the reamer during the entire cutting stage. The study has certain guiding significance for the design of reamer.