交叉刮切PDC钻头破岩机理及切削力学研究

The parallel track scraping principle of conventional PDC bits largely limits the cutting efficiency and working life in hard formations. A new invented PDC bit has the rock breaking principle of cross scraping by making the helical cutting track and the concentric-circle cutting track overlapped. The research of rock breaking mechanism and cutting mechanics for the new bit would be done, which include: establishing the kinematics theory, and theoretically studying kinematics of cutter cross-cutting trajectory; carrying out the cross-track rock cutting experiments with single cutter, and comparatively analyzing cutting force and energy consumption under the conditions of cross scraping and parallel track scraping; carrying out numerical simulation of single cutter cross-track cutting by means of FEA, establishing rock failure criteria under the condition of cross scraping, calculating and analyzing rock and cutter stress fields, and studying the load distribution on the cutter; comprehensively analyzing the results of experiments and numerical simulation, and studying the influence and its mechanism of the cross angle, cutting angle of PDC cutter, and other factors to cutting force and energy consumption; carrying out drilling experiments of the cross scraping PDC bit for simulation cross-tracking rock breaking, and studying the influential factors and their impact trend to cutter-wheel revolutions, cutting force of cutters, and drilling force of bit; creating cutting force model of PDC cutter and cutter-wheel revolution model under the condition of cross scraping; studying and developing digital simulation system of cross-scraping PDC bit rock breaking, and establishing the analytical means of the bit cutting mechanics. The research can offer theoretical support for the application of the cross-scraping PDC bit, and has great value for enhancing drilling efficiency and saving drilling cost in hard formations.

常规PDC钻头的平行刮切原理在很大程度上限制了钻头在难钻地层的切削效率和工作寿命。交叉刮切PDC钻头是一种能将牙齿螺旋形切削轨迹与同心圆切削轨迹相叠合，从而实现交叉刮切破岩原理的新思想。首先，建立交叉刮切PDC钻头的运动学理论，研究牙齿在井底的交叉刮切运动轨迹规律；其次，研究交叉刮切条件下的岩石失效准则，开展单齿交叉切岩过程的有限元数值模拟和切削力测试实验，对比分析交叉刮切与平行刮切两种模式下的牙齿切削力和切削能耗，研究各种交叉刮切条件下的PDC齿切削力特性和能耗特性，建立牙齿切削力计算模型；再次，开展交叉刮切PDC钻头的室内模拟钻进实验，测试盘刀速比、牙齿载荷以及钻头工作载荷，掌握各种因素对交叉切削轨迹、牙齿载荷及钻头工作载荷的影响规律；最后，研究新型钻头钻岩数字仿真技术，建立钻头切削力学分析手段。该研究能为新型钻头的工程化应用提供基础理论支持，对提高难钻地层的破岩效率具有重要意义。

项目针对现有PDC钻头在深部地层磨损速度快且磨损不均衡、切削齿侵入能力低等弱点，提出一种具有交叉刮切原理的新式PDC钻头。交叉刮切PDC钻头是在常规固定齿PDC钻头上引入大偏移角旋转盘刀而形成的一种新型复合钻头。新型钻头的盘刀上设置有切削齿，盘刀切削齿交替进入切削工作，其螺旋形切削运动轨迹与固定齿的同心圆切削轨迹相叠合，形成网状交叉的井底形貌模式。理论分析和实验测试结果表明，交叉刮切是一种省功、省力的高效破岩方式；旋转盘刀不仅能显著降低钻头切削齿的磨损速度，大幅度改善其磨损不均衡性，而且能显著提高钻头的破岩效率。.项目开展了以下主要内容：.（1）建立了新型钻头的几何学、运动学基础理论，掌握了新型钻头牙齿的交叉切削运动规律；.（2） 通过单齿交叉切岩实验和数值分析，研究了交叉刮切条件下不同影响因子对切削力和切削功耗的作用机理和影响规律；.（3）基于理论分析和单元实验测试结果，提出了交叉刮切条件下的力学模型的建立方法；.（4）通过全尺寸钻头的室内测试，研究了不同影响因子对钻头的盘刀速度比的影响规律，以及钻头工作载荷、钻头破岩效率以及破岩能耗的影响规律；.（5）研究、开发出新型钻头钻岩数字仿真技术，建立了新型钻头切削力学分析手段；.（6）利用数字仿真技术开展各种条件下的仿真实验，并与常规PDC钻头的仿真分析结果相对比，分析、总结了新型钻头的切削力学特性与能耗特点。.项目按照原计划基本完成了研究内容，达到了预期效果。研究结果表明：交叉刮切PDC钻头能够突破常规固定齿PDC存在的性能局限性，具有更高的破岩效率和工作寿命，显示出了非常好的应用前景。