1.2.1 Available coal and coal seam gas resources

Summary

The geological Clarence‑Moreton Basin contains substantial coal, coal seam gas (CSG) and conventional gas resources. Within the Clarence‑Moreton bioregion, black coal was first discovered in 1824 in the Ipswich Coal Measures and in 1864 in the Walloon Coal Measures. Coal is also present in other formations, but economic coal deposits are located mainly within the Walloon Coal Measures, the Ipswich Coal Measures and the Nymboida Coal Measures.

The cumulative thickness of coal seams varies considerably throughout the Clarence‑Moreton bioregion, ranging from approximately 1 m near the basin margins to about 120 m in the Casino Trough, a major depositional centre within the Clarence‑Moreton bioregion in NSW where the Walloon Coal Measures are thickest (up to approximately 700 m). The coal rank of the Walloon Coal Measures ranges from high-volatile bituminous to low-volatile bituminous and sub-bituminous, and the coal has been described as slightly higher in rank than the coals in the linked geological Surat Basin.

Both conventional and unconventional gas resources occur in the Clarence‑Moreton bioregion. Methane adsorption tests of coal samples from the Clarence‑Moreton bioregion in NSW demonstrated that the coals are fully saturated or close to full saturation. This is attributed to the low permeability of the coal seams, the interbedded nature of the coal seams, and to the presence of a regional top seal (the Maclean Sandstone). Numerous igneous intrusions have penetrated the coal seams in the Clarence‑Moreton bioregion, and these heating events may have affected the maturity of coal seams and gas generation at the regional scale.

Gas isotope analyses indicate that the gas contained within the coal seams is thermogenic, in contrast to gas in the adjacent Surat Basin where gas is primarily of biogenic origin.

Last updated:
3 August 2016