水平定向钻扩孔反循环形成机理及其应用研究

Horizontal Directional Drilling (HDD) is a trenchless construction method typically used for the installation of pipelines and conduits, especially in rivers, lakes or other areas where open-cut construction is not allowed. Before the pipeline installation, a pilot hole is drilled and then reamed. .As the pilot hole is enlarged, the growth of borehole diameter significantly decreases the mud velocity, as a result of which the cuttings transport efficiency is greatly reduced. For its unique cuttings transport mechanism, reverse circulation technology has been successfully applied in pile foundations as well as oil drillings, and has produced enormous economic benefits. Inspired by its successful application in pile foundations and oil drillings, an attempt to adopt reverse circulation in horizontal directional drilling is thus made in this research. Combining the characteristics of horizontal directional drilling and by means of theoretical analysis, laboratory test, field test as well as numerical simulation, the mechanism and formation condition of reverse circulation are investigated in the present research. This investigation is divided into three parts including the study of the flow field of reverse circulation and its variation, the study of cuttings transport under the coupling of the flow field of reverse circulation and gravity field, as well as the study of the energy loss of solid-liquid flow inside the rotating pipe. The objective of this research is to establish the mathematical relationship of cuttings size, cuttings volume ratio with the critical parameters of reverse circulation, and to uncover the dynamic features of solid-liquid flow in rotating pipe. The research findings will provide a theoretical basis for the application of reverse circulation technology in horizontal directional drilling, and also provide experimental data for the design of reamer as well as the determination of operation parameters.

水平定向钻是穿越河流、湖泊等无法或不利于开挖区域铺设管道的一项重要技术，其扩孔阶段环空泥浆流速随钻孔直径增加明显降低，岩屑运移异常困难。反循环以其特殊的岩屑运移机理在钻探和工程领域取得了良好的应用效果，为解决水平定向钻岩屑运移问题提出了一个新的研究方向。本项目基于水平定向钻的工艺特点，拟采用理论分析、数值模拟、室内模型实验和现场实验等方法，研究大孔径比环空反循环形成机理及条件；通过抽吸口静态、旋转实验和固-液混合介质运移实验探究大孔径比环空反循环流场分布及其变化规律、固体颗粒在多场耦合作用下的运移规律、固-液混合介质在转动管道内的流动模式及其能量损失。在此基础上，建立大孔径比环空反循环关键参数与环空固体颗粒尺寸、浓度之间的匹配关系，揭示固-液混合介质在转动管道内的动力学特征，为反循环技术在水平定向钻领域的应用提供理论基础，并为水平定向钻反循环扩孔设备设计和施工参数选取提供实验数据。

水平定向钻是穿越河流、湖泊等无法或不宜采用开挖铺设管道的关键技术之一，大直径水平定向钻孔径可达到钻杆直径的十倍以上，这导致钻孔环形空间泥浆返速极低，低流速状态下岩屑沉降快、易堆积形成岩屑床，急剧降低岩屑运移效率。反循环以其特殊的岩屑运移机理在钻探和石油领域取得了良好的效果，是加快岩屑运移效率的重要技术手段，但其在水平定向钻中应用的基础理论和实验研究非常有限，大孔径比条件下的环空反循环流场分布、固体颗粒在反循环流场中的运移规律、固-液混合介质在运动管道内的流动模式及其能量损失特征均不清楚，本项目针对上述问题首先通过理论分析和数值模拟确定了大孔径比环形空间反循环流场的分布规律和变化特征，证明了反循环抽吸口能通过抽吸作用产生低压区域的反循环流场，从理论上确定了水平定向钻反循环的可行性，然后研究通过抽吸口静态实验、抽吸口旋转实验和数值模拟掌握了大孔径比环空固体颗粒在反循环流场中的运移规律，并通过岩屑运移的模型实验和数值模拟揭示了自转状态下管道内固-液混合介质的流动模式及能量损失特征，确定了水平定向钻反循环扩孔技术的最佳输送流速应介于不淤流速和悬浮流速之间，论证了反循环排渣的高效性。此外，实验结果还发现水平定向反循环效率与钻杆旋转和偏心运动有关，但钻杆的低转速旋转对于钻杆内部流场几乎无影响，水平方向岩屑颗粒体积浓度分布仍呈对称状态；管道底部岩屑颗粒体积浓度出现一个梯度变化，当钻杆开始旋转时底部岩屑颗粒向钻杆旋转方向偏移，但是沿径向岩屑颗粒体积浓度几乎无变化。本研究证明了水平定向钻反循环的高效性，确定了实现反循环的临界流速、最优泥浆和扩孔钻具的重要设计参数，为实现反循环提供了理论和实验支撑，为解决大直径长距离水平定向钻岩屑运移瓶颈提供了最有效的解决方案。