Methane research in the Sydney Coalfield

For centuries, human society has relied on coal as a principal source of fu el for heat and power. Extraction of this valuable fuel has always been inf luenced by control over hazards such as wafer inflows and potentially explo sive dust and methane gas. Following a fatal methane explosion in 1979 at N o. 26 Colliery in Cape Breton, Nova Scotia, growing safety concerns in thes e undersea workings fed 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 b een on methane including: methane properties of seams; in-situ! and laborat ory 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 Coalfield are classified as gassy, having specific emissions in the 10 m(2) to 15 m(3)/t onne range. CANMET arid CBDC have both worked very closely and as methane-e missions increase with depth, research has concentrated on these deeper wor kings, The goal ir to develop, jointly, safe and appropriate methane contro ls far single entry retreat walls, covering both bleeder and "sewergate" ve ntilation systems. This paper gives an overview of recent CSL methane research covering the fo llowing aspects: defining coal seam characteristics: specific emissions - the relationship b etween methane content, coal 'rank' and depth; the gee-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 affecti ng 'sewergate' performance. This research has helped CBDC to control methane-related production delays to tolerable levels. in particular, two principal factors have influenced m ethane emissions on 7 East longwall at Phalen Colliery: the predominant thi ckness >20 mi and proximity of the lower Sandstone Unit (<4 m) and the pres ence 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 l ongwalls below 850 m in depth, when workings will be in virgin conditions.