Study on Characteristics of Airflow Spatial Distribution in Abandoned Mine Gob and Its Application in Methane Drainage

At present, there are many known sources of methane resources in abandoned mine gobs. Therefore, investigations into the characteristics of airflow spatial distributions in abandoned mine gobs will be helpful in future methane drainage processes. In this study, a physical simulation experiment was first adopted to simulate the formation processes of abandoned gobs based on the geological conditions of the abandoned Yongan Mine in China. Gas injection experiments were then conducted to study the gas concentration distributions and variations in a simulated gob based on the measured gas concentrations at certain sampling points. The results indicate that the abandoned gob comprises a gas enrichment zone (GEZ), gas diversion zone (GDZ), and gas isolation zone (GIZ) from the bottom to the top in the incline edges of the abandoned gob, respectively. However, only the GEZ and GIZ exist in the incline center of the abandoned gob. The gas concentration in the GEZ is observed to be the highest, although the concentration is also found to be relatively high in the GDZ. Moreover, a shielding is found to exist between the boundaries of the GEZ and GDZ, which results in a dramatic decline in concentration in the latter due to its extremely low permeability. The study results were verified by using the methane drainage data from the surface vertical wells in the abandoned Yongan Mine. The field application indicated that the methane extraction flow rate could potentially increase by 1.5 times when the well bottom traversed the GDZ and entered the GEZ, compared to the flow rate when the well bottom was located in the GDZ.