为了解决下行定向钻孔煤屑堵塞、瓦斯抽采有浓度无流量技术瓶颈难题，提出下行定向钻孔氮气泡沫幂律多相流携渣、解堵技术，采用理论分析、数值模拟、现场工业试验等方法，对煤矿井下下行定向钻孔瓦斯抽采引起煤屑堵塞的原因、下行定向钻孔环空氮气泡沫幂律多相流携渣理论及实践应用进行了研究。通过含壁函数的湍流模型数值模拟耦合瓦斯流动和煤体变形，钻孔抽采后流体压力变化引起的孔壁弹性位移。通过三维库仑失效准则模型数值模拟求解抽采引起的压力变化以及压力变化引发的应力、应变、位移变化及下行定向钻孔塌孔风险。通过幂律多相流理论分析氮气泡沫的稳定性、泡沫在钻杆内、钻头处、环空间隙的流动性、泡沫中煤粉悬浮性能、环空间隙泡沫排渣的压力损失、泡沫向上排渣受力情况。在下行定向钻孔环空氮气泡沫幂律多相流携渣理论分析的基础上，设计了稳定氮气泡沫发生器、泡沫发生灌注系统、下行定向钻孔氮气泡沫钻进工艺、瓦斯抽采钻孔氮气泡沫二次解堵工艺，并进行下行定向钻孔氮气泡沫排渣现场工业试验。研究结果表明钻孔壁摩擦曳力和弯曲处的离心力会造成煤屑颗粒聚集及孔壁坍塌风险增大，瓦斯携带的煤粉颗粒会撞击孔壁使孔壁变形或剥离，进而导致抽采钻孔塌孔堵塞；建立的涵括氮气泡沫稳定性、流动性、煤粉悬浮性能、环空间隙泡沫压力损失、排渣受力分析的下行定向钻孔环空氮气泡沫幂律多相流携渣、解堵技术理论体系能很好的为下行定向钻孔氮气泡沫排渣提供理论支撑；现场工业试验中氮气泡沫排渣钻孔相比水排钻孔，初始混合量和纯量分别提高了6.5和6.4倍，40 d混合量和纯量分别提高了10倍左右，说明氮气泡沫携渣、解赌技术可显著提高下行定向钻孔的瓦斯抽采效率。

In order to solve the technical bottleneck problem of downward directional drilling coal cuttings blockage and gas drainage with concentration but no flow, the nitrogen foam power law multiphase flow slag carrying and unblocking technology of downward directional drilling was proposed. Theoretical analysis, numerical simulation, om-site industrial experiments and other methods were used to research the causes of coal cuttings blockage caused by downward directional drilling gas drainage in coal mines, and the theory and practical application of nitrogen foam power law multiphase flow slag carrying in downward directional drilling annular. Numerical simulation was carried out by a turbulence model containing wall function coupled with gas flow and coal deformation, and the elastic displacement of the borehole wall caused by the fluid pressure after drilling extraction was analyzed. Numerical simulation with a three-dimensional Coulomb failure criterion model solved for the pressure changes caused by extraction, as well as the stress, strain, and displacement changes induced by the pressure changes, and the collapsing risk of downward directional drilling. The stability of nitrogen foam, the fluidity of foam in drill pipe, at the drill bit, in the annulus, the suspension performance of coal powder in foam, the pressure loss of foam slagging in the annulus, and the upward slagging stress on the foam were analyzed by the power law multiphase flow theory. Based on the theoretical analysis of downward directional drilling annulus nitrogen foam power law multiphase flow slag carrying theory, the stable nitrogen foam generator, foam generating injecting system, downward directional drilling nitrogen foam drilling process, and gas drainage drilling nitrogen foam secondary unblocking process were designed, and the downward directional drilling nitrogen foam slag removal on-site industrial experiment was conducted. The results indicated that, the frictional drag force of the borehole wall and the centrifugal force at the bends could cause the aggregation of coal particles and increase the risk of borehole wall collapse. The coal powder particles carried by the gas will collide with the borehole wall to deform or detach the borehole wall, which would lead to the collapse and blockage of the extraction borehole. The theoretical system of downward directional drilling annulus nitrogen foam power law multiphase flow slag carrying and unblocking technology, which included nitrogen foam stability, fluidity, coal powder suspension performance, annular space foam pressure loss, and analysis of slag removal force, can well provide theoretical support for downward directional drilling nitrogen foam slag removal. In the on-site industrial experiments, the initial mixing and pure amount of the nitrogen foam slag removal drilling hole increased by 6.5 and 6.4 times, respectively, compared with the water drainage drilling hole, and the mixing and pure amount increased by about 10 times in 40 days, which indicated that the nitrogen foam slag carrying and unblocking technology can significantly improve the gas drainage efficiency of the downward directional drilling hole.