Coal Geology & Exploration


The stuck and buried drills in underground coal mines often lead to accidents of broken drill pipes in the holes. At present, the success rate of the commonly used fishing methods of male and female fishing tap buckle is low, which not only consumes a lot of manpower and material resources, but also affects the production progress of coal mining. Based on this, a retractable slip overshot with the structural design of the cooperation between the slips and the outer cylinder through the wedge-shaped spiral surface has been proposed, which converts the pull-out force of the drill rod into a slip overshot model that self-locks the holding force of the broken drill rod. The structural design of slips improves the overshot’s ability to hold the broken drilling tool. The keyway structure design of the control ring realizes the retractable operation under complicated working conditions. The relationship between the shear stress generated by the rotating torque of the drilling rig and the strength of the overshot, and the relationship between the normal stress generated by the pulling force of the drilling rig and the strength of the overshot are analyzed, providing theoretical support for the parameter design of the overshot wall thickness. The formula for converting the drilling rig pull-out force into the gripping force of slips on the drill pipe is analyzed to verify the feasibility of the drilling tool in the overshot hole. The trial production and field test of the overshot have been carried out in Xinyuan Coal Mine, Shanxi Province. The successful application of the slip overshot in coal mines shows that its structure design is reasonable and its salvage performance is reliable. This study provides new technical equipment for dealing with complex drilling accidents in underground coal mine and theoretical basis for structural design of fishing tools.


retractable slip overshot, male and female fishing tap, structural design, underground coal mine




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