Influence of water injection in burst-prone coal seam on suction and sticking during drilling

When the spiral drill pipe is used to predict and evaluate the dynamic disasters such as rock burst, the drilling dynamic phenomena such as suction and sticking are easy to occur. In order to study the influence of water injection in burst-prone coal seam on suction and sticking, the mechanism of dynamic phenomenon of suction and sticking was analyzed by establishing the mechanical model of drill pipe, pointing out that the stress of coal body and the amount of drilling cuttings are the important factors that affect the occurrence of suction and sticking, deriving the calculation formula of drilling mechanical parameters such as drill pipe thrust and drill pipe torque under different water content, and clarifying the calculation formula. After the coal seam had been injected with water, the law of stress redistribution and the law of the change of the amount of cuttings in the coal body were studied. The multi parameter drilling test system was used to drill the coal body with different water content in the underground, so as to study the law of the change of the drill pipe thrust, the drill pipe torque and the amount of cuttings with the water content of the coal body. Combined with the dynamic phenomenon of suction and sticking observed in the field, the influence of water injection in burst-prone coal seam on the mechanical properties of coal body and the mechanical properties of suction and sticking was studied. The results show that: During suction, the thrust value of the drill pipe decreased obviously, and during sticking, the torque value of the drill pipe increased sharply; The increase range of drill pipe thrust, torque mean and the decrease range of drilling cuttings mean increased first and then decreased with the increase of water content in coal body; The suction and sticking points gradually transfer to the depth of coal wall with the increase of water content in coal body; The data variation characteristics of downhole drill pipe thrust, torque and drilling cuttings amount corresponded well with the stress distribution of coal body. The study can provide some theoretical and engineering guidance for the prediction of rock burst and safe drilling operation.