Research on overall drilling and protection technology ofgas drainage borehole in deep soft coal seam

In view of the problems such as deep soft coal seams, and the widespread deformatin and collapse of gas well drilling, as well as the difficulties in gas drainage in the Pingdingshan Mining Area, the research on drilling and protection integration technology and equipment is carried out. The Kelvin creep model of finite element software ANSYS is used to analyze the influence of creep of coal body on the stress distribution of borehole at different times, and the maximum vertical stress distribution around the soft coal boreholes is obtained. Average borehole shrinkage due to creep effect (the average of the vertical inner diameter and the horizontal inner diameter) is about 61%, and the average period of action is about 20 days. Based on the above numerical analysis, a magnetic tooth chip limit flip PDC pipe drill bit and a tubular drill pipe are developed with PE pipe as preferred protecting pipe and the field tests were launched in the Shoushan No.1 Mine of the Pingdingshan Mining Area.The test results show that the average flow rate of single-hole per 100 m gas is increased from 0.003 6 m3/(min·hm) to 0.010 82 m3/(min·hm) after the integration technology of gas extraction and drainage in deep soft coal seam.