大尺寸牙轮钻头结构设计问题的分析

ANALYSIS ON STRUCTURAL DESIGN OF ROCK BIT WITH LARGE SIZE/

针对深井上部大直径井段中牙轮钻头机械钻速低的问题，从设计角度对目前大尺寸牙轮钻头的齿面结构和水力结构进行了分析和讨论。与Φ２１５．９ｍｍ钻头相比，在相同地层条件下，Φ４４４．５ｍｍ钻头牙齿与井底岩石的最大接触应力低１８％～２８％，相同齿圈上的齿顶间距增大７０％～８０％，井底面积覆盖率减小了近５０％，平均单齿破岩量增加了１．７４倍，因而在硬地层和砾石层中破岩效率要低。在相同机泵条件下，Φ４４４．５ｍｍ钻头的井底比水功率远低于Φ２１５．９ｍｍ钻头，井底和钻头清洗状况不良，影响了机械钻速。因此，应根据大尺寸牙轮钻头的具体情况，对齿面结构和水力结构进行改造，以提高钻头的破岩效率和清洗效率。同时应增加钻头类型，完善钻头系列。

The cutting structure and hydraulic structure of a large size of rock bit were analyzed, regarding the existing problems of low penetration rate in deep well drilling. The maximum contact stress between rock and tooth of a 444.5 mm diameter insert bit is 18%～28% lower than that of a 215.9 mm diameter insert bit under the same formation conditions. For a 444.5 mm diameter rock bit, the tooth intervals in a tooth row increases by 70%～80%, and the crater area overlapping ratio of bottomhole decreases by about 50%, and rock breakage volume per tooth increases by 174%, comparing with a 215.9 mm diameter insert bit. These cause low rock breakage efficiency in hard formations or gravel formations. The specific hydraulic workrate of a 444.5 mm diameter insert bit is much lower than that of a 215.9 mm diameter insert bit, which resultes in poor cleaning conditions and serious bit balling in the soft formations. Therefore, it is necessary to improve the cutting structure and hydraulic structure of large sizes of rock bits in order to raise rock breakage efficiency and bit cleaning efficiency.