定向随钻扩孔PDC钻头优化设计及应用

油气井定向随钻扩孔钻井技术主要用于优化井身结构、提高固井质量及预防复杂地层缩颈卡钻等事故的发生，适用于该钻井技术的破岩工具为扩孔钻头。根据塔河油田深井定向随钻扩孔钻井的实际需要，开展了新型钻头的研发。通过对PDC（polycrystalline diamond compacts，聚晶金刚石）钻头扩孔结构、冠部形状、布齿结构等方面进行优化设计，开发出CK306B型定向随钻扩孔PDC钻头，其中钻头扩孔结构采用二级扩孔设计方案，钻头领眼段的冠部采用“微凸冠顶”结构，钻头的布齿结构根据自平衡原理设置，并对新型随钻扩孔PDC钻头进行稳定性和水力特性的仿真分析。该型钻头在塔河油田深井定向随钻扩孔钻井工程的实际应用中取得良好的使用效果：扩孔井径大于170 mm的设计扩孔井径要求，造斜率达到9.9°/30 m；扩孔钻头平均进尺达到93 m，机械钻速为1.24 m/h，分别比国外同类钻头提高50%和4%。研究结果表明：新型定向随钻扩孔钻头在深井条件下钻进是可行的，能够满足井眼轨迹控制和定向扩孔的要求，且将钻头的不平衡系数控制在0.05以内，能提高钻头的稳定性，减少钻头异常失效现象，从而延长钻头的使用寿命。

Optimization design and application of PDC bit for directional reaming-while-drilling

The technology of directional reaming while-drilling for oil and gas wells is mainly used to optimize the well structure, improve the cementing quality and avoid drill pipe sticking caused by wellbore shrinkage. The applicable rock breaking tool for this drilling technology is reaming bit. The research and development of a novel reaming bit was conducted based on the actual demands of directional reaming while-drilling for deep wells in Tahe oilfield. Based on the optimization design of reaming structure, crown profile and cutter distribution, the CK306B PDC (polycrystalline diamond compacts) bit for directional reaming while-drilling was developed. Specifically, the basic reaming structure was designed with two-stage, and the crown profile of the pilot bit was designed as a slight-raised curve and the cutters were distributed on the basis of the self-balancing principle. The simulation analysis of stability and hydraulic characteristics of novel reaming while-drilling PDC bit was carried out. Field application in directional reaming while-drilling for deep wells in Tahe oilfield showed that the bit had a good performance, wherein, the reaming diameter was larger than 170 mm while the build-up rate reached 9.9°/30 m, which indicated that either the reaming ability or the build-up ability of the bit satisfied the engineering requirement. Moreover, the average footage of reaming bit was 93 m and the ROP (rate of penetration) of the bit was 1.24 m/h, which were 50% and 4% higher than foreign congeneric bits used in similar well section, respectively. The research result shows that it is feasible to use the novel PDC bit for directional reaming while-drilling in deep-well because the novel bit can meet both the requirements of well track control and directional reaming. Besides, the lateral imbalanced coefficient of the novel reaming bit can be controlled within 0.05, which will improve the stability of the bit, reduce the bit failure risk and prolong service life of the bit.