基于DPM模型的双级PDC钻头流场特性研究

Study of Dual-Stage PDC Bit Flow Field Based on Discrete Phase Model

针对双级PDC钻头领眼钻头井眼空间上返的钻井液与扩眼钻头井底流场相互干扰的问题,通过在分流传力总成上增加级间喷嘴形成了一种新的双级PDC钻头水力结构。基于FLUENT软件中的DPM模型,模拟计算了井底钻井液流速、井底压降及井底岩屑质量浓度分布,证实了级间喷嘴对于流场改善的有效性,并在此基础上分析了级间结构对双级PDC钻头井底流场的影响规律。仿真结果表明:级间喷嘴倾角为75°时钻井液清洗效果相对较好;领眼钻头与扩眼钻头的刀翼位置应尽量重叠,这样形成了自下而上的流动通道,利于岩屑的快速上返;领眼钻头与扩眼钻头级间段长增大到40 mm时,级间喷嘴的抽吸作用最显著而后逐渐减弱;领眼钻头与扩眼钻头喷嘴流量比值的增大,提高了领眼钻头井底流场清洗效率,降低了扩眼钻头井底流场清洗效率,领眼与扩眼体喷嘴间最佳流量分配比例为5∶5。研究结果可为双级PDC钻头的水力结构设计及井底流场特征研究提供理论依据。

To address the interferes of the flowback drilling fluid from the pilot bit of the dual-stage PDC bit with the flow field of the reaming bit,a new dual-stage bit hydraulic structure is formed by adding the inter-stage nozzle on the flow distribution assembly. Based on the DPM( Discrete Phase Model) model in FLUENT,the bottomhole drilling fluid flow rate,bottomhole pressure drop and bottomhole cuttings concentration distribution are simulated. The effectiveness of the inter-stage nozzle for flow field improvement is verified. Based on this,the interstage structure influence on the bottom flow field of the dual-stage PDC bit is analyzed. The simulation results show that the drilling fluid cleaning performance is great when the inter-stage nozzle angle is 75°. The positions of the blade of the pilot bit and the reaming bit should be inline as much as possible,thus forming a bottom-up flow passage that facilitates the rapid return of the cuttings. When the length between the pilot bit and the reaming bit increases to 40 mm,the suction of the inter-stage nozzle is most pronounced and then gradually weakened. The increase of the flow ratio of the pilot bit and the reaming bit nozzle improves the cleaning efficiency of the pilot bit bottomhole flow field and reduces the cleaning efficiency of the reaming bit bottomhole flow field. The optimal flow distribution ratio between the pilot and the reaming bit nozzle is 5 ∶ 5.