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

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.