Variational collapse instability

ABSTRACT In order to reveal the collision behavior regularity between the drill pipe and the coal hole wall in the process of gas extraction drilling, the nonlinear dynamic equations of the drill pipe and the finite element model of the collision between the drill pipe and the hole wall are established. The collision stress variation between the drill pipe and the hole wall with different diameters are analyzed. The results show that with the decrease of the coal hole diameter, the collision stress value between the drill pipe and the hole wall increases and the hole wall is more instability to collapse. When the hole diameter increases to a certain extent, the collision stress variation become gentle and the hole wall become stable. The research provides the theoretical law to select the proper drilling parameters, which can improve the coal hole wall stability in the process of the gas extraction drilling. 

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