Triaxial permeability testing and microstructure study of hard-to-drain coal from Sydney Basin, Australia

Several mines operating in the Bulli seam of the Sydney Basin, Australia have coal seam zones that are difficult to drain. Metropolitan Colliery being one of such mines, has experienced difficulties in reducing gas content within the available drainage lead time; as the coal seam would not drain even with additional drainage boreholes. A research study using coal permeability testing and microstructure analysis was carried out to investigate the hard-to-drain problem. The permeability test was conducted using two different apparatus. The methods of permeability testing of coal under different triaxial conditions are discussed. Both the tests' results and the calculated values of permeability are in agreement. Coal microstructure results based on SEM imaging technology for coal samples from hard-to-drain areas were examined and the microstructures of the tested coal samples appear to be tight and some of the coal pores are filled with coal particles and mineral matter.