潜孔锤反循环钻进中心通道内岩屑运移数学模型

Mathematical model for cuttings migration in center channel of DTH hammer of reverse circulation drilling

针对潜孔锤反循环钻进中上返岩屑回落堵塞中心通道问题,将气力输送理论应用于反循环携屑。采用气力输送理论对潜孔锤反循环钻进中心通道内岩屑颗粒进行受力分析;从动力学角度建立潜孔锤反循环钻井中心通道内岩屑运移数学模型;通过编程计算求解岩屑在不同初始条件下速度随时间、空间变化特性。结果表明:初速度大于沉降末速度的岩屑颗粒作减速运动,初速度小于沉降末速度的岩屑颗粒作加速运动,最终岩屑颗粒沉降末速度趋于同一个值,与初速度无关;气固速度比与岩屑尺寸有关,随着岩屑颗粒直径增大,气固比降低。该数学模型为改善反循环钻进携屑能力提供了理论依据。

Returned cuttings block the center channel,it is a major problem of carrying cuttings in DTH hammer reverse circulation drilling.In the paper,pneumatic conveying theory is used to analyze cutting carrying of reverse circulation.The cutting particles in center channel of DTH hammer reverse circulation drilling are analyzed mechanically with the pneumatic conveying theory.From the kinetic point,cutting migration mathematical model in center channel of DTH hammer of reverse circulation drilling is built.Through program calculation,the characteristics of speed change of cuttings with time and space under different initial conditions have been gotten.The results show that when the initial spped is greater than the sedimentation rate,the cutting particles make slowing down movement,and when the initial velocity is less than the sedimentation rate,the cutting particles make acceleration movement.Eventually,the sedimentation rate tends to the same value,which has nothing to do with the initial velocity.The speed ratio of gas-solid is related to the cutting size,and with the size increasing,the speed ratio of gas-solid is decreasing.