Publication Name: Eastern Australian Basins Symposium III (EABS 2008)
Authors: S. Thomson, P. Hatherly, S. Hennings and J. Sandford
Date Published: September 2008
Number of Pages: 6
Abstract:
Gas content and gas composition in the Permian coals of the Lower Hunter, Sydney Basin, show evidence of distinct layering that can be attributed to the tectonic history of the coal measures and the effects of meteoric waters. Essentially, coals closest to the surface are more likely to contain methane of biogenic origin, and are more likely to be undersaturated than those at depth. In addition, a mixed gas zone of methane and CO2 occurs below the biogenic methane zone and above a deeper thermogenic methane layer. Domains saturated with CO2 may be explained in terms of magmatic activity, palaeostress fields and structural boundaries. This model is supported by compositional data and isotope analysis. The model explains this variability in terms of burial history, tectonism and groundwater flow paths. The implications of these findings are relevant to an understanding of coal seam gas character in the Hunter Coalfield and for the broader Sydney Basin. The model provides a framework for explaining variability in gas content, composition, saturation and permeability, and has a bearing upon coal seam gas exploration and production strategies.