Gas drainage improvement in underground coal mines

Effective gas management is vital to the success of the longwall mining in the Bulli seam, in the Southern Coalfield, Sydney Basin, NSW, Australia. The evolution of gas drainage methods and practices are discussed with respect to gas type, gas drainage lead time and prevailing geological conditions. Both underground to inseam drilling and surface to inseam drilling techniques are described at both pre and post-drainage conditions. Post-drainage of gas from longwall is discussed for its effectiveness, practicability and efficiency. The long term benefit of the method selected is examined with respect to gas capture efficiency. An alternative method of surface based goaf drainage, using medium radius drilling technology to drill horizontal boreholes above and/or below the production seam into the partial caving zone prior to longwall goaf formation is proposed.