PDC钻头井下流动可视化实验研究与冲蚀分析

在自行开发设计的PDC井下射流实验平台上, 通过丝线法和高速摄影手段进行了PDC钻头井下流场结构的可视化实验。发现井下多股射流的流场为不稳定场, 在靠近钻头肩部的流道附近存在强烈的漩涡; 对流场的可视化研究表明破坏钻头的主要因素可能是随漩涡而冲击钻头壁面的岩屑和气相的溃灭冲蚀以及水力设计不合理而造成流道堵塞; 破坏出现的主要位置应是钻头头部多喷嘴之间的区域、喷嘴本身及其周围区域和筋板及流道的逆压力梯度区。因此, 有必要在多喷嘴射流的钻头上加设一中心喷嘴打破井下的涡结构, 以减轻对钻头中心部位的破坏。

Visualization experiments of flow field of PDC bit and its erosion analysis

Visualization experiments of flow field of PDC bit were made by such experimental techniques as silk-thread showing and high-speed photography. It is found that the bottom-hole flow field is unsteady, and strong eddies appear around the bit shoulder. Visualization investigation shows that, the main factors for bit damage include rock cuttings impact on the bit wall with eddies, air phase erosion and flow passage jamming resulted from unreasonable hydraulic design. Bit damage maybe occur on the area of bit wall around the nozzles, nozzles area and inverse pressure gradient area. Therefore it is suggested an additional nozzle fixed on the bit to change the structure of the eddy and reduce the damage on the central part of the bit.