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.

gas drainage  /  drilling cuttings  /  minimal start-up speed  /  drilling angle