Influence mechanism of the rubbing of drilling pipe for the stability of hole wall

The hole wall appears because of the gas drainage of the coal seam, the hole wall is divided for the elastic area and plastic area, according to the elastic mechanics and rock mechanics established borehole wall stress model, caused by gas drilling secondary stress makes the hole wall instability are analyzed, also on the borehole wall by drill pipe contact friction caused by hole wall instability mechanism was studied and obtained the main reason which causing the borehole wall instability is the impact of drill pipe.