Re-evaluation of overlooked petroleum potential in the Powell Depression, southern Galilee Basin

Troup, Alison1,2, Esterle, Joan1, Rodrigues, Sandra1, Guerer, Derya1

1 School of Earth and Environmental Sciences, University of Queensland, Brisbane, Australia; 2 Queensland Department of Natural Resources, Mines and Energy, Brisbane, Australia

 Extensive sedimentary basin development occurred in eastern Australia during the late Carboniferous to Triassic. The Cooper and Bowen basins are both part of productive petroleum systems, with source rocks and reservoirs found in late Permian and Triassic units, as well as Jurassic and Cretaceous units in the overlying Surat and Eromanga basins. No corresponding discovery has been made in the Galilee Basin. Partially as a result of perceived prospectivity, the Galilee Basin is under-studied and under-explored.

The Galilee Basin is a large late Carboniferous to Triassic aged sedimentary basin in central Queensland, extending across an area of approximately 247,000 km2, though most of this extent is under the cover of the Triassic to Cretaceous Eromanga Basin. It is divided into four main regions: the Lovelle Depression in the north west, the Koburra Trough in the north east, the Springsure Shelf in the south east and the Powell Depression in the south west. It overlies metasedimentary rocks and remnant sedimentary basins of the Thompson Orogen, including the early to middle Carboniferous Drummond Basin in the north east, underlying the Koburra Trough and the Devonian Adavale Basin in the southwest, underlying the Powell Depression.

Recent projects have re-evaluated the late Permian units of the Koburra Trough, which examined the sequence stratigraphy, palaeogeography, age dates, provenance and lithostratigraphic correlation with the Bowen Basin and past projects have evaluated the petroleum potential of the Lovelle Depression. However, the Powell Depression has been overlooked in previous regional studies, potentially due to the effect of perceived prospectivity or a relatively lower number of wells available for interpretation.

By proxy to the Cooper Basin and Bowen Basin, the Galilee Basin should be expected to have a late Carboniferous to Permian sourced petroleum system. Age-equivalent rocks of the major source rock bearing units in the Cooper and Bowen basins are present in the southern Powell Depression, though controls on the source rock quality and maturity in the Powell Depression are scarce. Coal seams are present in the late Permian Bandanna Formation, though the coal seam distribution in the Powell Depression is uncertain. For a conventional petroleum system, reservoirs and traps are likely to be channel sandstones associated with late Carboniferous to early Permian glacial outflow channels or late Permian fluvial channels. The major regional seals in the Bowen and Cooper basins are a thick Triassic aged sequence of terrestrial mudstones in the Moolayember and Tinchoo formations. Thus the Moolayember Formation should also provide a regional seal in the Powell Depression

Historical exploration in the Powell Depression region primarily targeted structures in the Adavale Basin. As these structures form basement highs to the Galilee Basin, a thinner sequence was drilled, which has formed the perception of limited exploration potential. Seismic reflection survey data show thickening of the Galilee Basin sequence off these basement structures, which suggests potential in this region may have been overlooked.


Biography

Alison has more than ten years worth of experience working with the Queensland Government examining the petroleum potential of Queensland’s sedimentary basins. She is still working full time, but has also started studying for her PhD at the University of Queensland.

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