Goaf gas drainage

Optimal gas drainage must recognise the gas drainage mechanisms and all influencing factors. Based on our comprehensive field investigation of the coupled dynamics of strata, groundwater and gas, as well as the CFD simulations of goaf gas dynamics, we have obtained many insights into gas drainage mechanisms under various mining conditions.

One excellent example is longwall horizontal gas drainage through goaf gas pressure control. As a result of the characterisation of longwall goaf environment, a new gas drainage system using underground directional boreholes was designed at the Blakefield South mine to replace most of the conventional vertical wells in the initial mining stage. Such a system has delivered significant benefits, including:

• an increase in methane drainage efficiency in the initial mining stage from 30-60% up to 80%
• a capability to reduce GHG up to 0.42 Mt CO2-e every year
• savings in excess of $10M per year from increased productivity


The designed horizontal drainage boreholes (left) and the effectiveness of reducing gas-out delays (right).