HYDROCARBON SIGNIFICANCE OF UPPER PALAEOZOIC SEDIMENTS ASSOCIATED WITH THE KOBURRA TROUGH, GALILEE BASIN

Abstract

The Koburra Trough is a major tectonic feature in the northeastern Galilee Basin of Queensland. The oldest rocks identified in exploratory drilling were Devonian sandstone, shale and siltstone, possibly representing a northern extension of the Adavale Basin. These rocks contain a fossil microflora and may be prospective for hydrocarbons. Overlying them are a maximum of 1979 m of Upper Palaeozoic sediments, and a maximum of 1180 m of Triassic sediments, together comprising the Galilee Basin succession. The lithofacies of the Late Palaeozoic is dominantly sandstone-shale; the lower beds show evidence of glacial derivation, and the upper beds contain coal measures. Shows of oil and gas have been recorded from the basal part of the sequence in the two deep wells (ENL Lake Galilee −1 and FPN Koburra −1) drilled in the trough. Structural and stratigraphic factors favour the existence of hydrocarbon traps on the south-western flank. "Large" inferred reserves of Upper Permian sub-bituminous coal have been discovered in Geological Survey exploration near outcrop at the southeastern end. Preference in the use of this coal is to be given to manufacture in Queensland of synthetic fuels and petrochemicals. The geological survey petroleum statigraphic drilling campaign is providing invaluable new data on the Galilee Basin.