Research of the methan content effecting on gas-draine efficiency in the stope when boreholes are left in uncontrollable workings - S. P. Mineev; V. N. Kocherga; Ju. A. Korneev; A. S. Janzhula; A. A. Gulaj; P. M. Samopalenko (Geo-Technical Mechanics, 2018)