大直径水平定向钻低流速层流下岩屑运移规律

The migration law of cuttings in the case of low-velocity laminar flow during large-diameter horizontal directional drilling

大直径水平定向钻钻孔直径可达到钻杆直径的10倍以上,钻孔环形空间泥浆不仅处于不利于岩屑运移的层流状态,而且流速极低,岩屑极易在孔底形成稳定的岩屑床,造成孔内事故。针对该问题,首先推导出柱坐标系下环空泥浆的运动微分方程组,然后使用环空岩屑运移综合模拟实验装置进行多次模拟实验,最后通过数值模拟揭示环空泥浆流场分布及岩屑运移规律。结果表明:增加泥浆PAM含量对提高大粒径岩屑运移效率效果不明显;提高环空泥浆流速,在一定程度上能够提高单颗岩屑运移效率,但同时会增加岩屑床末端回流区尺寸,使岩屑床内部压差增大。研究成果对水平定向钻施工具有指导意义。(图5,表2,参20)

The hole diameter of large-diameter horizontal directional drilling can be more than 10 times the diameter of drilling pipe. The mud in the annulus of drilling hole is not only in the laminar state which is not conducive to the migration of cuttings, but also at very low flowing velocity. The migration efficiency of cuttings in the annulus is very low and a stable cuttings bed is formed at the bottom of the hole, so accidents tend to happen easily in the hole. In order to solve this problem, the differential equations on the motion of annular mud in cylindrical coordinate system were firstly derived. Then, several simulation experiments were carded out by using the comprehensive simulation experimental device for the cuttings migration in the annulus. Finally, the distribution of annular mud flow field and the migration law of cuttings were revealed by means of numerical simulation. It is shown that the migration efficiency of large diameter cuttings isn＇t improved significantly by increasing the PAM content of mud. And the increasing of annular mud velocity can improve the migration efficiency of single cuttings to a certain extent while increasing the back flow area at the end of the cuttings bed, and consequently the pressure difference inside the bed is increased. The research results provide the theoretical analysis and experimental conclusion for the construction of horizontal directional drilling and have the practical significance for engineering guidance. （5 Figures, 2 Tables, 20 References）