一种适用于普通PDC钻头的新型超高压流道设计

为了突破井下水力增压器只能与特制钻头配套使用的局限性，进行了适用于普通PDC钻头的新型超高压流道设计。根据高压管压力损耗计算，设计了新型分流结构，确定了导流管直径和长度；通过超高压水射流分析，优化了喷嘴结构、喷嘴圆锥段收缩角、喷嘴尺寸参数；通过室内系统测试，验证了不同压力下各部件及连接处的密封性能。由理论分析得知，分流机构上端的理论壁厚下限为3.1 mm，综合考虑施工流量和压力影响，设计超高压管道直径8 mm，配合高压软管长度400 mm，高压水射流喷嘴最大流量系数下的收缩角为13°，高压喷嘴出口段圆柱段的长度选取喷嘴出口直径的2~4倍。现场试验表明，新型超高压流道使平均机械钻速提高71.95%。研究得出，超高压双流道直联式流道系统的分流装置、导流装置、超高压喷嘴满足了现场作业要求，井下增压器直接与普通PDC钻头配合使用拓宽了其应用范围。 

A New Design of Ultrahigh Pressure Flow Channel for Common PDC Bit

In order to overcome the limitation that downhole supercharger could only support special PDC bit,a new design of ultrahigh pressure flow channel for common PDC bit was developed.Based on calculation of pressure loss in high-pressure pipe,a new shunt mechanism was designed and the diameter and length of diverter hose were determined.Through analysis of ultrahigh pressure water jet,the nozzle was optimized in structure,contraction angle of cone and its size.By laboratory testing,the sealing performance of all parts and connections under different pressures was verified.Theoretical analysis showed that lower limit of wall thickness at top of the shunt mechanism was 3.1 mm.Considering flow rate and pressure in operation,diameter of ultrahigh pressure pipe was designed as 8 mm,matching 400 mm-long high pressure hose;shrinkage angle of high-pressure water jet nozzle at maximum flow coefficient was designed as 13°;length of cylindrical outlet section of the high-pressure nozzle was defined 2-4 times that of the outlet diameter.Field test demonstrated the new design allowed average ROP to increase by 71.95%.Therefore,shunt device,diverting device and ultrahigh pressure nozzle of the ultrahigh pressure system with direct-connect dual-flow channels meet the requirements in field operation.The downhole supercharger integrating with common PDC bit can broaden its scope of application.