1.2.1.2.1 Coal seam gas from black coal

There is no history of CSG production from Strzelecki Group black coals in the Gippsland Basin bioregion, and there has been only limited exploration. Black coals to the north of the traditional mining areas of Wonthaggi and Korumburra have been targeted for CSG. The well Megascolides-1 drilled in the Narracan Trough by Karoon Gas intersected around 12 m of Strzelecki Group coals, present as thin (5 cm to 1 m) seams (Grosser, 2005). Most of the thin coal seams did not have butt cleats, although face cleats were commonly seen with spacing ranging in size from 7 to 25 mm (Grosser and Smith, 2008). A single desorption coal sample had air-dried moisture content of 2.9%, ash of 47.4%, volatile matter of 23.7% and fixed carbon of 26.0%. It also had a vitrinite reflectance (VR) range between 0.64 and 0.89 (within the optimum gas-producing range). The desorption gas content was 3.37 cubic metre/tonne dry ash free (DAF) and the gas composition approximately 100% methane, with very low carbon dioxide (Grosser, 2005). Grosser and Smith (2008) concluded at the time, that low total coal thickness and gas contents made this coal unsuitable for a commercial CSG development.

The role of gas in mine disasters that killed miners at the State Coal Mine at Wonthaggi is often cited as evidence for the presence of CSG. Official reports on the disaster indicate that open-flame lamps were routinely used, which suggests that gas influx was not a major concern. A 1936 report by the mine manager quoted in Harper (1987) stated that ‘the mines are not gaseous, and naked light is used, but stone dusting is adopted’. Stone dusting is a form of coal-dust hazard reduction, indicating that coal dust was considered the greater fire and explosion hazard.

Data pertaining to the prospectivity of the Gippsland Basin black coals as a source of CSG are very limited. As a result, there are no identified CSG resources from black coals (i.e. there are no known reserves that are commercially viable at this time), and their prospectivity is considered poor (Goldie Divko, 2015). There remains a large degree of geological uncertainty associated with CSG potential from Strzelecki Group black coals.