在一些复杂地质条件近距离煤层群矿井中，下向钻孔抽采方法成为近距离煤层卸压瓦斯抽采的主要措施。针对下向钻孔抽采下邻近层卸压瓦斯存在孔内残留钻屑量大、水力排渣不彻底影响瓦斯抽采效果的问题，采用理论分析、数值模拟及实验室实验相结合的研究方法，分析下向钻孔泡沫幂律流体携渣机理，研究下向钻孔环空间内泡沫流体的携渣能力，完成排渣泡沫的配制及性能评价，提出基于泡沫流体的下向钻孔排渣方法，并开展了下向钻孔泡沫排渣的现场试验。取得的主要研究成果如下：

应用流体力学与多相流理论，构建了以应力表述的下向钻孔环空间泡沫流体流动模型，分析了环空间泡沫流体流动特征，基于多相流中流动的颗粒受力分析的基础上研究了环空间内煤渣颗粒的运动规律，阐明了下向钻孔环空间泡沫幂律流体携渣运输机理。结果表明，当泡沫流体的流速大于煤渣颗粒沉降速度时，泡沫流体可将煤渣颗粒携带运输并排出钻孔；煤渣颗粒的运输速度主要与煤渣颗粒的粒径、泡沫流体的粘度有关，煤渣粒径越大其运输速度越小，泡沫流体粘度越大煤渣颗粒运输速度越大。

利用Fluent数值模拟软件，模拟研究了下向钻孔环空间内煤渣颗粒的运输规律，获得了流体流速和粘度对煤渣颗粒上返运输速度的影响规律。结果表明，流体的流速和粘度越大，煤渣颗粒上返运输速度越高；随着流体粘度的增加，煤渣颗粒的上返速度显著增高，增大流体粘度有利于颗粒的上返运输，提高下向钻孔的排渣效果。

选用K-12、BS-12、OB-2、OP-10等作为发泡剂及CMC作为稳定剂，按照不同的浓度配置排渣泡沫冲洗液，开展排渣泡沫发泡实验，测试了泡沫体积、泡沫半衰期及粘度等排渣泡沫性能指标。结果表明，K-12发泡剂的发泡能力最强；低浓度CMC稳定剂的添加能够提高泡沫的稳定性及粘度；优选出适用下向钻孔排渣泡沫的配比为0.7%K-12+0.5%CMC。

在邵寨煤矿2502工作面开展了下向钻孔泡沫流体排渣试验，考察了下向钻孔泡沫幂律流体排渣技术的排渣效果及排水排渣后下向钻孔的瓦斯抽采效果。结果表明，与水力法排渣相比，泡沫排渣效率提升了31.7%，瓦斯抽采纯量提升了1倍，为下向钻孔瓦斯高效抽采提供了有力保障。

In some complex geological conditions, the downward drilling and gas extraction method has become the main measure for pressure relief and gas extraction in close range coal seams. In view of the problem that there is a large amount of residual drilling cuttings in the hole and incomplete hydraulic slag removal in the pressure relief gas extraction of the lower adjacent layer by downward drilling, the research method combining theoretical analysis, numerical simulation and laboratory experiments was used to analyze the slag carrying mechanism of downward drilling foam power-law fluid, study the slag carrying capacity of foam fluid in the downward drilling annulus, complete the preparation and performance evaluation of slag foam, propose a downward drilling slag removal method based on foam fluid, and carry out the field test of downward drilling foam slag removal. The main research results obtained are as follows:

Based on the theory of fluid mechanics and multiphase flow, the flow model of foam fluid in the annular space of downward drilling was constructed, and the flow characteristics of foam fluid in the annular space were analyzed. The results show that when the velocity of foam fluid is greater than the settling velocity of coal cinder particles, foam fluid can carry the coal cinder particles and discharge them from the borehole; The transport speed of cinder particles is mainly related to the particle size of cinder particles and the viscosity of foam fluid. The larger the particle size of cinder, the smaller the transport speed, and the larger the viscosity of foam fluid, the greater the transport speed of cinder particles.

Using Fluent numerical simulation software, the transportation law of coal slag particles in the downward drilling annular space was simulated and studied, and the influence of fluid velocity and viscosity on the upward transportation speed of coal slag particles was obtained. The results show that the higher the flow rate and viscosity of the fluid, the higher the upward transportation speed of coal slag particles; With the increase of fluid viscosity, the upward velocity of coal slag particles significantly increases. Increasing fluid viscosity is beneficial for the upward transportation of particles and improves the slag discharge effect of downward drilling.

Select K-12 BS-12, OB-2, OP-10, etc. are used as foaming agents and CMC is used as stabilizer. Slag discharge foam flushing fluid is prepared according to different concentrations. Slag discharge foam foaming experiments are carried out. Slag discharge foam performance indicators such as foam volume, foam half-life and viscosity are tested. The results indicate that, K-12 foaming agent has the strongest foaming ability; The addition of low concentration CMC stabilizer can improve the stability and viscosity of foam; The optimal ratio of foam for downward drilling slag discharge is 0.7% K-12+0.5% CMC.

In the 2502 working face of Shaozhai Coal Mine, the slag removal test of downward drilling foam fluid was carried out, and the slag removal effect of downward drilling foam power law fluid slag removal technology and the gas drainage effect of downward drilling after drainage and slag removal were investigated. The results show that compared with the hydraulic method, the foam slag removal efficiency is increased by 31.7%, and the gas extraction purity is doubled, which provides a strong guarantee for the efficient gas extraction of downward drilling

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