Optimal design method of sealing depth in methane drainage boreholes to realize efficient drainage

Abstract

The purpose of underground methane drainage technology is to eliminate methane disasters and enable the efficient use of coal mine methane (CMM). The sealing depth is a key factor that affects the underground methane drainage performance. In this work, the layouts of bedding and crossing boreholes were considered to analyze the stress distribution and failure characteristics of roadway surrounding rocks through a numerical simulation and field stress investigation to determine a reasonable sealing depth. The results demonstrated that the depths of the plastic zone and elastic zone in the Xutuan and Qinan coal mines were 16 m and 20 m, respectively. Borehole sealing could minimize the air leakage through the fractures around the roadway when the sealing material covered the failure and plastic zones. In addition, the field test results of CMM drainage at different sealing depths indicated that the CMM drainage efficiency increased with an increase in the sealing depth and not change when the sealing depth exceeded the plastic zone. Moreover, sealing in the high permeability roadway surrounding rock did not strongly influence the borehole sealing performance. Considering these findings, a new CMM drainage system for a specific sealing depth and length was developed, which could effectively improve the CMM drainage efficiency and prolong the high concentration CMM drainage period. The proposed approach can be a valuable quantitative analysis method to select the optimized sealing parameters for underground methane drainage, which can considerably improve the drainage and utilization rates of CMM.