Spontaneous combustion influenced by surface methane drainage and its prediction by rescaled range analysis

This study established numerical modeling using COMSOL™ to examine the influence of horizontal location and drainage ability of surface borehole on spontaneous combustion in longwall working face gob. Rescaled Range Analysis (R/S analysis) was employed to investigate the chaos characteristic of N2/O2 ratio from a surface borehole in 10416 working face gob, Yangliu Colliery, China. The simulation results show that there is always a circular “dissipation zone” around the drainage borehole and an elliptic “spontaneous combustion zone” in deep gob. Little influence was found on spontaneous combustion zone on the intake side of the gob but the width of spontaneous combustion zone in middle gob is enlarged, while the depth of spontaneous combustion zone near the return side is reduced. The R/S analysis indicates that the influence of surface borehole on spontaneous combustion can be divided into two stages by the chaos feature of N2/O2: safety drainage stage and spontaneous combustion initiating stage. It can be concluded that the methane drainage from gob through surface borehole can intervene in the distribution of spontaneous combustion zone in gob and the chaos feature of N2/O2 from surface borehole can effectively reflect coal spontaneous combustion condition in gob. Keywords: Coal spontaneous combustion, Surface drainage borehole, Hurst index, Rescaled range analysis, Methane drainage, Symbiotic disaste