定向喷嘴布置对PDC钻头井底流场影响研究

Directional Nozzle Layout of PDC Bit Bottom-hole Flow Field Impact Study

定向喷嘴布置的方式对PDC钻头的井底流场将有很大的影响,尤其是能改变PDC钻头的水力性能,因而研究定向喷嘴布置具有重要的意义。本文分析了喷嘴的不同布置方法,并通过数值方法模拟其对PDC钻头井底流场的影响。结果表明:在不完全对称布置方案的冲击区,在射流刚开始从喷嘴处流出去,但还未接触井底,各喷嘴射流处于衰减地带之内,这样的话将对钻头的清洗和携带岩屑离开井底非常有效果;在漩涡区,喷射角大、距钻头中心远的喷嘴射流则对清洗和携带井壁附近的岩屑起主要作用,喷射角小、距钻头中心近的喷嘴射流则对清洗和携带井底中心的岩屑起主要作用;在刀翼上的附面层由于周围喷嘴的影响,刀翼切削面低速区明显减少,剪应力增大,更好地预防、清除PDC钻头的泥包。最终达到提高机械钻速的效果。

The directional nozzle arrangement in PDC bit has strongly affected to flow field at the bottom hole,especially when there is a possibility to change the PDC bit hydraulic performance.Therefore,the study on directional nozzle arrangement has the vital significance.The various nozzles layout method was analyzed and numerical simulation of its PDC bits bottom flow field was carried on.The results showed that：in the jet impact area of incompletely symmetrical layout,the jet blowing from the nozzle to the bottom hole,and before reaching the bottom hole,the jet is located in the attenuation zone.This plays an important impact for the cleaning bit and transport drill cuttings out of the well;In the vortex,when jet angle is large and distance from drill center to the nozzle is far,the jet is merely used for cleaning and carrying drill cuttings in the vicinity of bottom hole,when the jet angle is small,the distance from the drill center to the nozzle is relatively close,the jet is merely used for cleaning and carrying drill cuttings on the center of bottom hole;In the blade boundary layer on the nozzle due to surrounding effect,in the surface close to the blade,due to the surround nozzles,the cutting surface low velocity zone is obviously reduced led to shear stress increases,creating favorable conditions in preventing and cleaning drilling balls on PDC bit.The final outcome is increase the mechanical drilling efficiency.