Surface Goaf Hole Drainage Trials at Illawarra Coal

Surface goaf gas extraction methods are successfully applied at a number of Australian and overseas underground coal mines. BHPB Illawarra Coal has recently undertaken a trial program to determine the effectiveness of surface goaf wells to reduce gas concentrations within the longwall ventilation circuit, and minimise gas related production delays. Three trial wells have been completed within the Bulli Seam operations. Considerable production variation between the three wells was recorded. A goaf gas reservoir model is discussed which describes a sequence of permeability changes within the different goaf strata, dictated by stress changes associated with caving, then recompaction. A requirement for further work is identified to improve understanding on the 3-D properties of the goaf in terms of permeability variations and pressure distributions. An overview of the surface goaf extraction trials including descriptions of the gas plants and well production results is provided.