Study on emission law and disaster-causing mechanism of floor oil-type gas in coal-oil-gas symbiotic mines—A case study of No.2 Coal Mine in Huangling Mining Area

Abstract

Aiming at abnormal emission of floor oil-type gas in No.2 Coal Mine, Huangling Mining Area, this study combines field measurement and FLAC3D numerical simulation to analyze emission laws and disaster-causing mechanisms. Results show that oil-type gas mainly emits from floor heave fractures 5–10 m ahead of the working face, with a maximum concentration of 95%. Borehole emission follows a power-law pattern and attenuates rapidly within one week, with an attenuation coefficient of 1.24–2.14 d⁻¹ and a fitting correlation coefficient R² of 0.89–0.99. Emission intensity decreases with an increasing distance between the gas reservoir and coal seam. In-situ stress, geological structures, and gas pressure are the three main controlling factors, and 72% of abnormal emission points are located in anticline structures. Mining forms an approximately 40 m pressure-relief gas conduction zone ahead of the working face. Oil-type gas emission occurs only when the reservoir is within this zone. The results provide a key quantitative basis for the prevention and control of oil-type gas hazards in coal-oil-gas symbiotic mines.