瓦斯抽采钻孔受限空间内钻屑运移特征

 应用气力输送理论,建立钻屑颗粒群孔内悬浮模型,推导钻屑颗粒群启动最小气流速度求解方程,结合案例分析钻屑颗粒直径、摩擦系数及钻孔倾角对钻屑颗粒群启动速度的影响规律.结果表明,施工俯孔时,最小启动风速存在极值θ_D,θ_D<θ<0 时,伴随钻孔倾角θ绝对值增大,所需最小启动风速v_a逐渐增大,在θ_D～-π/2 范围,伴随钻孔倾角绝对值的增大,所需最小启动风速va呈现小幅度减小趋势;施工仰孔时,存在角度θ_U,当0<θ<θ_U时,伴随仰孔倾角逐渐增大,所需最小启动风速逐渐降低,当θ>θ_U时,钻屑在自重作用下自行滑落;摩擦系数对最小启动风速的影响规律与钻孔倾角类似,当俯孔倾角θ=-π/2 时,不同摩擦系数曲线交于同一点,表明当θ=-π/2 时,最小启动风速与摩擦系数无关.

Transportation characteristics of drilling cuttings in gas drainage borehole

Based on pneumatic conveying theory, the suspension model of drilling cuttings has been established, the minimal startup speed of the drilling cuttings was derived, and the influence of diameter of drilling cuttings, friction coefficient, and drilling angle on the start-up speed was analyzed. The results show that in downward drilling engineering, there existed a drilling angle θ_D when the start-up speed reached its maximum value. When the drilling angle was in the range of θ_D～0, the start-up speed v_a increased with increase of the absolute value of the drilling angle; when the drilling angle was in the range of θ_D～-π/2, v_a decreased slightly with increase of the absolute value of the drilling angle. In upward drilling engineering, there existed a drilling angle θ_U. When the drilling angle was in the range of 0~θ_U, the start-up speed v_a decreased gradually with increase of the drilling angle; when the drilling angle θ＞θ_U, the drilling cuttings will slide under gravity. Similar influence of the friction coefficient on the minimal start-up speed was obtained. When the drilling angle θ=-π/2, different curves met in one point, indicating that the start-up speed had nothing to do with the friction coefficient.