Critical technical parameters of large-diameter multi-stage casing drilling for mine rescue

ObjectiveThis study aims to meet the needs of mine rescue in cave-in accidents occurring in narrow underground spaces and to address the contradiction between equipment miniaturization and the drilling of large-diameter rescue boreholes under complex collapse conditions. Based on the goal of constructing a 60-m-long rescue passageway, this study developed a dual-power, composite drilling process based on multi-stage casing drilling technology for large-diameter horizontal rescue boreholes under complex collapse conditions. Furthermore, this study investigated the critical drilling parameters, aiming to provide a basis for the function development and parameter formulation of rescue equipment. MethodsThis study designed supporting three-stage large-diameter casings and large-diameter spiral drill rods, followed by a mechanical analysis of large-diameter casings in the composite casing drilling process. Accordingly, this study established a model for the movement and mechanical analysis of drilling tools. Using this mode, this study analyzed the variation patterns of the axial frictional resistance and frictional moment of the large-diameter first-, second-, and third-stage casings under varying rotational speeds and rates of penetration (ROPs). Results and ConclusionsThe results indicate that for large-diameter composite casing drilling, the ROP and rotational speed of casings were identified as the major factors influencing their axial frictional resistance and moment of frictional fraction. The variation patterns of the frictional resistance of casings in the composite casing drilling process indicate that, under rotational speeds ranging from 0 r/min to 2 r/min, a slight increase in the rotational speed led to a significant decrease in the axial friction resistance. In contrast, under rotational speeds ranging from 0 r/min to 1.5 r/min, a slight increase in the rotational speed induced a rapid increase in the moment of rotational friction. An analysis based on the law of casings’ frictional resistance that critical parameters of the large-diameter casing drilling technology should be: propulsive force ≥ 2000 kN, rated torque ≥ 5000 kN·m, and the maximum rotational speed of casings ≥ 1 r/min under the maximum torque in the drilling process. These parameters allow for effective resistance reduction in the process of casing rotation. The results of this study serve as a significant reference for drilling rig development and drilling parameter formulation for underground mine rescue.