Methane research in the Sydney Coalfield

For centuries, human society has relied on coal as a principal source of fuel for heat and power. Extraction of this valuable fuel has always been influenced by control over hazards such as water inflows and potentially explosive dust and methane gas. Following a fatal methane explosion in 1979 at No. 26 Colliery in Cape Breton, Nova Scotia, growing safety concerns in these undersea workings led to a new focus on research and development and the establishment in 1981 of the Cape Breton Coal Research laboratory (CBCRL), now the CANMET Sydney Laboratory (CSL). A major focus of the research has been on methane including: methane properties of seams; in-situ and laboratory testing; methane emissions; investigation of operational issues (e.g., Phalen 7 East); and refinement of prediction models. Below 600 m depth, the Phalen and Harbour Seams in the Sydney Coal field are classified as gassy, having specific emissions in the 10 m 3 to 15 m 3 /tonne range. CANMET and CBDC have both worked very closely and as methane emissions increase with depth, research has concentrated on these deeper workings. The goal is to develop, jointly, safe and appropriate methane controls for single entry retreat walls, covering both bleeder and sewergate ventilation systems. This paper gives an overview of recent CSL methane research covering the following aspects: ○ defining coal seam characteristics: specific emissions - the relationship between methane content, coal 'rank' and depth; the geo-thermal gradient; in-situ gas pressure; and associated hydrocarbon content of mine air samples analyzed; and ○ defining the performance of 'sewergate' ventilation, particularly on Phalen 7 East. 'Sewergate' ventilation is a marriage between a typical U and a bleeder ventilation system. Undergound measurements, including a novel use of tube-bundles, have provided a clearer understanding of factors affecting 'sewergate' performance. This research has helped CBDC to control methane-related production delays to tolerable levels. In particular, two principal factors have influenced methane emissions on 7 East long-wall at Phalen Colliery: the predominant thickness (>20 m) and proximity of the Lower Sandstone Unit (<4 m) and the presence of unworked remnant pillars in the Harbour Seam above. In the future, methane drainage will have to be considered if Phalen Colliery is to mine longwalls below 850 m in depth, when workings will be in virgin conditions.