Stability Characteristics Analysis of Large Diameter Surface Drilling Wellbore and Engineering Control

Under the condition of high intensity mining, surface boreholes are easily damaged affected by severe mining. By using the finite difference program FLAC^3D, the force of different diameter well casing was simulated and calculated under the condition of mining. The results show that the casing deformation is larger at the interface of rocks. The larger diameter of the casing, its deformation and under-stress is smaller, and the drilling diameter is increased to reduce the risk of failure. According to the serious damage problem affected by mining, which occurred in the extraction process of the conventional diameter drilling, Yuwu Coal Company carried out engineering test of large-diameter surface drilling gob gas extraction and achieved good results. The field test results show that using large diameter surface drilling can avoid drilling complete failure and extend the validity of drilling drainage.