三牙轮三喷嘴钻头井底射流辅助破岩机理分析

由于井底射流辅助破岩的复杂性，其室内模拟试验和理论分析均有较大难度，所获得的结论多以经验性的、定性的解释为主，还未能建立能用于实际的、确定有效的理论。为此，采用有限元方法模拟分析了三牙轮三喷嘴钻头井底射流流场，结合井底岩石应力状态和岩屑启动机制的分析，探索了井底射流辅助破岩的机理。研究结果表明，三牙轮钻头三个喷嘴直径的不同，致使井底流场高压区和低压区并存，钻头旋转，带动流场局部低压区周期性地覆盖井底，使得岩石破碎强度和岩屑启动的难度降低，钻头的破岩钻进效率提高。喷嘴间直径差别的增大，使得井底流场高压区和低压区之间的压差增大，钻井机械钻速提高。研究结果与现场试验结论一致。

ANALYZE THE ASSISTANT ROCK-BREAKING MECHANISM OF BOTTOM-HOLE JET OF 3-NOZZLE 3-CONE BIT

The bottom-hole jet flow field of 3-nozzle 3-cone bit has been simulated and analyzed by means of finite-element method. Meanwhile, combining the analysis of bottom-hole rock stress condition and cuttings start-up mechanism, the assistant rock-breaking mechanism of bottom-hole jet has been probed. Research results indicate that the different diameters of three jet nozzles on a three-cone bit can result in the coexistence of low-pressure region and high-pressure region in bottom-hole flow field, and the bit revolution will drive the local low-pressure region of bottom-hole flow field to periodically cover the hole bottom, which will lower the rock collapse strength and make the cuttings start-up easier, and will improve the rock breaking and thus the penetration rate of bit. The bigger the differences between the diameters of jet nozzles, the bigger the differential pressure will be between the high-pressure region and low-pressure region at the bottom hole flow field, which results in increasing the penetration rate. This research results conform to field test results.