A theoretical goaf resistance model based on gas production analysis in goaf gas drainage

Abstract

Over the past few years, the Australian coal mines heavily relied on drilling vertical goafholes to capture coal mine methane and monitor methane levels, which is named goaf gas drainage. The suction pressure applied on the surface goafholes may change goaf pressure distribution and goaf gas flow pathways. Besides, high suction pressure may cause more air leakage in the goaf and increase the risk of gas explosion and spontaneous combustion, posing a significant threat to mine safety. This paper focuses on analysing goaf gas production data from different goafholes in two active Australian longwall panels. The correlation between suction pressure, total flow rate, gas flow rate and air leakage rate were analysed in detail as the face-to-hole distance changed. Suction pressure is found to be positively correlated with total flow rate, and their correlation also varies at different goaf locations due to various goaf compaction and flow resistance. As a result, instant control strategies are suggested for different scenarios based on adjusting goafhole suction pressure. This paper also proposed a theoretical method to calculate the goaf resistance of ventilation air leakage pathways. The model results suggested that the resistance of air leakage pathways from the working face to individual goafholes increased with the face-to-hole distance, and the resistance results can be used to calculate the corresponding permeability at the same goaf position. These results may be applied to calibrate other geomechanical models and as input data for CFD or Ventsim models with a clear understanding of simulation tool limitations.