脉冲射流提速配套PDC钻头流场数值模拟研究

为了最大限度地发挥脉冲式井底交变流场提速工具的性能,采用数值模拟的方法对与提速工具配套的PDC钻头进行研究,模拟钻井液通过其产生的井底交变流场,研究了钻头刀翼类型、刀翼数量和喷嘴数量对钻井液井底冲击力和井底清岩效果的影响,并对钻头结构进行了优选。研究结果表明:螺旋刀翼、7喷嘴、6刀翼钻头产生的脉冲射流具有较高的平均静压冲击力和井底冲击力振幅;6直刀翼6喷嘴钻头对应的井底动压冲击力波动最大,达到7.0 kN以上,5直刀翼7喷嘴钻头对应的井底静压冲击力波动最大,为2.8 k N;5直刀翼5喷嘴钻头的清岩效果最好,其产生的井底最小岩屑质量浓度和平均岩屑质量浓度最低,且井底岩屑质量浓度的波动幅值最大,达到1.6 kg/m^3;对于软到中硬地层,配合使用脉冲式井底交变流场提速工具,选择5直刀翼5喷嘴PDC钻头清岩和携岩效果较好;对于硬地层,选用6直刀翼6喷嘴PDC钻头提速效果较好。所得结论可为脉冲射流钻井提速工具配套PDC钻头结构设计及应用提供参考。

Numerical Simulation of the Flow Field of the PDC Bit Supporting the Pulse Jet Based ROP Improvement Tool

In order to give full play to the performance of the ROP improvement tool based on pulsed downhole alternating flow field,this paper studied its support PDC bit by means of numerical simulation.The downhole alternating flow field generated by drilling fluid through the PDC bit was simulated.The influences of bit blade type,blade quantity and nozzle quantity on the downhole impact force and downhole cuttings cleaning effect of drilling fluid were investigated.What’s more,the bit was structurally optimized.And the following research results were obtained.First,the pulse jet generated by the bit with 6 spiral blades and 7 nozzles has greater average static impact force and downhole impact force amplitude.Second,the bit with 6 straight blades and 6 nozzles is the largest in the fluctuation of downhole dynamic impact force,which is more than 7.0 k N;while the bit with 5 straight blades and 7 nozzles is the largest in the fluctuation of downhole static impact force,which is 2.8 kN.Third,the PDC bit with 5 straight blades and 5 nozzles is the best in cuttings cleaning effect,the lowest in downhole minimum cuttings concentration and average cuttings concentration and the greatest in the fluctuation amplitude of downhole cuttings concentration,reaching 1.6 kg/m^3.Fourth,as for soft and medium strata,the PDC bit with 5 straight blades and 5 nozzles,combined with the ROP improvement tool based on pulsed downhole alternating flow field,can achieve better cuttings cleaning and carrying effect.As for hard strata,the PDC bit with 6 straight blades and 6 nozzles presents better ROP improvement effect.The research results provide the reference for the structural design and application of the PDC bit supporting the pulse jet based ROP improvement tool.