This section provides a brief summary of available information on coal and hydrocarbons in the Galilee subregion. More specific information will be presented in the forthcoming coal seam gas and coal resource assessment for the Galilee subregion bioregional assessment.
In the Galilee Basin, significant coal-bearing sequences occur in the Early Permian Aramac Coal Measures, the Late Permian Betts Creek beds, the Bandanna Formation and the Colinlea Sandstone (Figure 20). In the Lovelle Depression, the Aramac Coal Measures can be up to 272 m thick with aggregate coal thickness of up to 60 m (Scott et al., 1995). Vitrinite reflectance data suggest that the Aramac Coal Measures have, for the most part, reached thermal maturity for oil generation (Hawkins and Green, 1993).
The Betts Creek beds (and its equivalents) are widespread in the Galilee Basin, and are up to 200 m thick in the Koburra Trough and 120 m thick in the Lovelle Depression (Hawkins and Green, 1993). Areas of maximum coal development within Betts Creek beds (and its equivalents) tend to occur towards the central Lovelle Depression and Koburra Trough, with individual seams and aggregate coal thicknesses up to 20 m and 45 m respectively (Scott et al., 1995). Hawkins and Green (1993) report that Betts Creek beds and equivalents reached thermal maturity for oil generation in deeper sections of Koburra Trough and Lovelle Depression and adjacent to the Maneroo Platform.
The Betts Creek beds, Bandanna Formation and Colinlea Sandstone outcrop along the eastern margin of the Galilee Basin. The coals are classified as high volatile sub-bituminous coals. In the Lovelle Depression, the coal measures are less developed in the southern parts compared to the northern sections (Radke, 2009).
As of December 2013, two development proposals had been approved, and a further four were undergoing the development approval process (Figure 21). The Colinlea Sandstone is the host unit for mineable coal resources at the proposed Alpha coal development (Hancock Prospecting, 2010). At the South Galilee Coal Project the mineable coal resources lie within the Bandanna Formation (AMCI 2012).
Sub-bituminous coals occur in the Winton Formation in the Eromanga Basin. Although these may be considered a secondary target by some exploration companies, very significant tonnages are delineated around Blackall and at the South Blackall deposit.
Exploration for hydrocarbons in the Galilee subregion commenced in the late 1950s with initial focus on conventional oil and gas reservoirs. Overall about 130 wells have been drilled in the Galilee subregion for hydrocarbons, of which about 52 targeted coal seam gas. Most conventional petroleum wells targeted reservoirs in the Powell Depression, the Lovelle Depression, or along the western margin of the Galilee Basin.
Most recent exploration has focused on coal seam gas. To date, almost all coal seam gas drilling has occurred within the northern Galilee Basin, in particular the Aramac Trough, Koburra Trough, and the Lovelle Depression. Two coal seam gas production pilot well fields have been established in the vicinity of the Aramac Trough. The Glenaras production pilot CSG project has recently commenced operations (Galilee Energy, 2013).
To date, the only commercial conventional hydrocarbon discovery in the Galilee subregion is the Gilmore Gas Field in the Lissoy Sandstone reservoir. The Lissoy Sandstone is in the Adavale Basin, which is beneath the Galilee Basin.
Hawkins and Green (1993) provided details on potential conventional petroleum reservoirs and possible source rocks in the Galilee Basin. Reservoirs and traps may be developed in Aramac Coal Measures and Betts Creek beds, and potentially some Triassic sequences. The best source rocks for hydrocarbons in Galilee subregion are coals in the Aramac Coal Measures and Betts Creek beds.
Shale gas and oil in the Toolebuc Formation in the overlying Eromanga Basin is considered to be another potential hydrocarbon target (Galilee Energy, 2013). Conventional hydrocarbons are also targeted in the Eromanga Basin, within the Galilee subregion.
Figure 20 Distribution of the coal-bearing formations in the Permian Galilee Basin
Source data: modified from Figures 9, 10, 13 and 14 of Scott et al. (1995)
Figure 21 Significant coal and coal seam gas developments in the Galilee subregion
EIS is an acronym for environmental impact statement. All coal and coal seam gas developments, unless otherwise specified, occur within the Galilee Basin sedimentary sequence.
