As part of Queensland Government’s Strategic Resources Exploration Program, in conjunction with the Australian Government’s Exploring for the Future program, a study to improve the subsurface knowledge of Proterozoic basins in northwest Queensland (NWQ) is underway. Proterozoic sedimentary basins are prevalent across central and western Australia. Several of these basins have proven petroleum systems, with the best discoveries to date being in the Greater McArthur Basin, Northern Territory. Recent exploration and appraisal in the Beetaloo Sub-basin of the Greater McArthur Basin has identified large volumes of gas resources contained within unconventional shale reservoirs. In NWQ, the Isa Superbasin and overlying South Nicholson Basin are related in both age and likely deposition to the Greater McArthur Basin. The thick, extensive shale units of the Isa Superbasin are excellent source rocks, while the Mullera Formation in the South Nicholson Basin also has potential but has not been investigated in detail. There are several potential reservoirs within the Proterozoic section and younger units of the overlying Georgina and Carpentaria basins, including clastic and carbonate types. Exploration in the Isa Superbasin identified an estimated 22.1 trillion cubic feet of prospective resources (Armour Energy 2015) in unconventional shale reservoirs of the Lawn Hill Formation and Riversleigh Siltstone. This paper will discuss the stratigraphy, depositional and structural history of these Proterozoic basins and characterise their source and reservoir units using existing and recently acquired geophysical, geochemical, petrographic and petrophysical datasets. From this, several plays or play concepts will be identified and described to help understand the region’s potential for both conventional and unconventional petroleum resources.
At Huizui, a major centre of ground stone tool manufacture, five main lithologies were used, each for a particular purpose: oolitic dolomite for spades; diabase for axes, adzes and chisels; fine micaceous sandstone for knives and sickles; other sandstone for grinding slabs; and fine limestone for lime. This reflects the functional properties of these lithologies. Diabase, oolitic dolomite and fine micaceous sandstone are tough and take sharp edges, which for diabase are particularly sharp and easily resharpened. All five rock types are probably available within 8 km of the site. Ground stone tool production may have been located at Huizui because of its proximity to the adjacent sandstone hills, which provided abundant abrasive material. Overall, raw materials are dominated by oolitic dolomite, which was quarried from a single thin-bedded layer that outcrops as flat pavements. Diabase was sourced from river cobbles, and micaceous sandstone was quarried. All three of these lithologies were extracted as raw material that required minimal shaping to make tools. This factor was probably responsible for the choice of oolitic dolomite over fine-grained dolomite, which is more common and occurs closer to Huizui, but cannot be easily quarried. The small amounts of probably exotic lithologies (including red rhyolite, marble, turquoise, ?jade) may have been used for elite items.
A project to improve the understanding of petroleum source rocks across Queensland’s basins was proposed through the Industry Priorities Initiative. The study has identified new source rocks, improved characterisation of known source rocks, and examined their potential as unconventional reservoirs. Round 2 of the project sampled known source rock formations in the Adavale, Bowen, Cooper and Eromanga basins, all with proven petroleum potential. Forty-eight samples from these basins were screened through Rock-Eval and total organic carbon by LECO to determine candidates for further analysis. Pyrolysis gas chromatography was conducted on selected samples (n = 15) to understand the bulk chemical signatures of kerogens with fluids extracted to derive isotopic and biomarker signatures. Organic petrology (n = 11) examined kerogen components and reflectance. Immature samples were analysed for bulk kinetics (n = 10) to determine the stability of kerogens while some were sent for compositional kinetics (n = 7), to predict the gas to oil ratio (GOR) and saturation pressure. Some more mature samples were sent for late gas analysis (n = 6) to understand hydrocarbon generation at later stages of thermal maturation. The results indicate that the marls in the Bury Limestone may have promising potential, that the Permian coals are the principal source rocks in the Cooper and Bowen basins and that the coals and mudstones of the Birkhead Formation have potential to generate. High production index values were noted in the Bury Limestone, as well as coal and mudstone samples from the Cooper and Bowen basins, suggesting that some of these source rocks also have good retention capabilities.
SUMMARYThe plays of the Bowen and Surat basins consist of conventional structural plays along major regional structures and depositional platforms, most of which have some stratigraphic component. These can be subdivided into three main regions: the eastern and western flanks of the Taroom Trough, and the Denison Trough. Coal seam gas is found in fairway zones within the Permian coals of the Bowen Basin, which can be subdivided into two main fairways: structurally associated plays in the southern Bowen Basin, and a tighter play in the northern Bowen Basin. Coal seam gas is also found along a broad fairway in the Walloon Coal Measures of the Surat Basin. Recent exploration for new targets has highlighted potential for tight gas in the deeper sections of the Bowen Basin, though further evaluation is required. More speculative plays within the region include tight gas within potential, but untested targets in the deeper sections of the Denison Trough.
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