涡流钻头降压机制及设计原则

Depressurization mechanism and design principles of vortex drilling-bit

涡流钻头通过反向喷嘴和高速旋转形成负压漩涡,降低井底压差,提高钻井的机械钻速.对涡流钻头降压机制进行研究.采用混合网格计算方法分析反向喷嘴的轴向倾角、径向倾角、上返流量、出口高度和旋转速度等对涡流钻头降压性能的影响,并提出涡流钻头的设计原则.结果表明：反向喷嘴下方井底钻井液回流是影响涡流钻头降压能力的主要因素.涡轮钻头设计的理论原则：轴向倾角为150°～ 180°、径向倾角为60°～75°、上返流量大于30％、反向喷嘴的出口高度为100～140 mm,井壁间隙应小于3 mm,尽可能地提高钻头旋转速度.

The drilling practice of oil and gas wells has indicated that reducing the bottom-hole pressure difference can signif-icantly improve the rate of penetration （ROP）. Vortex drilling-bit can reduce the bottom-hole pressure difference via a re-verse nozzle to generate a vortex flow due to the high rotary speed of the drilling-bit. The depressurization mechanism of thevortex bit was analyzed. By using a hybrid mesh method, the key factors that affect the depressurization capacity of the vortexbit were investigated, which include axial angle, radial angle, reverse flow ratio, rotation speed, bit clearance, and distancebetween reverse nozzle outlet and the bottom-hole wall. The results show that backflow below the reverse nozzle outlet is themain reason that can decrease the depressurization effect of the vortex bit. A guideline for the design of the vortex bit is givento maximize the depressurization effect. The optimum axial and radial angles are 150°-180°and 60°-75°respectively, andthe flow ratio of the reverse nozzle is best above 30%. The bit clearance should be kept below 3 mm, and the distance be-tween the reverse nozzle outlet and the bottom-hole surface can be 100-140 mm. The rotation speed of the bit should be aslarge as possible.