水击振荡减阻器力学行为分析

Mechanical Behavior of Fluid Oscillation Drag Reducer

针对提高连续管井下作业延伸极限的振荡减阻工具,根据水击效应建立了振荡减阻器工作时的水击方程,采用渐近线法对水击方程组进行求解,得到装有振荡减阻器的管路内流体压力与流速分布。同时,根据动量定理计算了水击振荡器引起的管柱轴向力和径向力变化,此径向力将改变管柱的法向接触力,进而改变摩阻力。计算结果表明:流体流速幅度从振荡器位置向水平井跟端位置呈阶梯式降低,压力幅度呈阶梯式上升,在阀的每一个开关周期内流体流速和压力都会陡然变化。当流体通过振荡器时,由于流体流速变化,单位质量流体将产生瞬时轴向拉力,将管柱静摩擦转化为动摩擦,有助于连续管在井眼内移动。

The water hammer equations of the fluid oscillation drag reducer for improving the extension limit of coiled tube in downhole operation are established according to the water hammer effect.The water hammer equations are solved by asymptote method,and the distributions of fluid pressure and velocity in the pipeline equipped with the fluid oscillation drag reducer are obtained.The changes of axial force and radial force of pipe string caused by the fluid oscillator are calculated according to the momentum theorem.This radial force will change the normal contact force of the coiled tube string,and then change the friction between coiled tube string and wellbore.The calculation results show that the fluid velocity amplitude decreases step by step and the pressure amplitude increases step by step from the fluid oscillator position to the heel end of the horizontal well.The fluid velocity and pressure will change sharply in each switching cycle of the valve.When the fluid passes through the oscillator,due to the change of fluid velocity,the unit mass fluid will produce instantaneous axial tension,and the static friction between coiled tubing string and wellbore will be converted into dynamic friction,which is helpful for the coiled tube to move in the wellbore.