Results of geochemical investigations by the Bureau of Mineral Resources (BMR) and the Commonwealth Scientific and Industrial Research Organisation (CSIRO) indicate significant potential for hydrocarbon source throughout the Permian sequence with the Cattle Creek Formation (shallow shelf mudstone and shale facies, and prodelta mudstone facies) and the Reids Dome Beds (fluvial flood basin facies) constituting the most favourable source rock facies. The source rock facies comprise dominantly humic organic matter indicating that the Permian source is mainly gas-prone. The existing mature organic zone within the trough encompasses much of the Cattle Creek Formation and a section of the Reids Dome Beds; this suggests that present-day hydrocarbon generation may be taking place within these source rocks.A complementary regional facies analysis by the Geological Survey of Queensland (GSQ) demonstrated a relationship between hydrocarbon-bearing reservoirs and facies types. Clearly distributary channel, tidal, beach and barrier bar facies constitute the most favourable reservoir facies. Within the interval covered by the Cattle Creek Formation and Aldebaran Sandstone, juxtaposition of source and reservoir facies has been recognised and could present favourable stratigraphic traps. Three zones are recognised:an area extending from Rolleston to Westgrove;within the Kildare area; andan area extending from GSQ Taroom 10 to AAO Kia Ora 1.These zones deserve further consideration. Results of this integrated investigation lends optimism to further exploration.

In the Bothamsall Oilfield, sandstone reservoirs at the base of the Lower Coal Measures comprise distributary-channel and barrier-bar facies. Diagenetic modifications were achieved principally by chemical processes, with mixed-layer illite/montmorillonite clay, ferroandolomite and ferroancalcite widespread in the barrier-bar facies; quartz, ferroandolomite, and kaolinite important in the channel facies; and quartz, ferroandolomite and siderite prevalent in the overbank facies. Porosity retention is greatest in coarse-grained sandstone located in the axial region of channel facies, and least in fine-grained sandstone where quartz cementation predominates. Early oil emplacement in coarse-grained sandstone of the channel facies arrested quartz diagenesis and inhibited further diagenetic reactions, whereas in barren water-filled zones diagenesis proceeded unimpeded.

Exploration activity in the northern Galilee Basin has been sporadic and is still at an immature stage. Recent geological investigations by the Queensland Department of Resource Industries have brought about a better understanding of the geological setting and stratigraphic evolution of the basin. These investigations also identified key source and reservoir units, determined maturation trends and delineated areas with hydrocarbon potential. The geological results indicate that the Aramac Coal Measures and Betts Creek beds contain the most favourable source and reservoir rocks. Thermal modelling of vitrinite reflectance data suggests that various parts of the basin reached maturity for hydrocarbon generation at different times. Integration of the geological results and thermal modelling has enabled exploration concepts to be developed for the basin. Application of these concepts has highlighted areas along the western margin of the Koburra Trough and eastern Maneroo Platform, and areas adjacent to the Cork Fault and the Wetherby Structure in the Lovelle Depression that warrant further exploration.

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The Galilee Basin in central Queensland is an extensive intracratonic basin containing up to 2 800 m of Late Carboniferous to Middle Triassic strata deposited under predominantly fluviatile conditions in two depocentres, the Lovelle Depression and the Koburra Trough.The exploration criteria of petroleum geochemistry, reservoir rock quality, structural and trapping style have been assessed.The source potential is generally poor with the Aramac Coal Measures, basal Jericho Formation, and the underlying Devonian rating best for possible hydrocarbon generation. Organic maturation is generally not reached until the Late Carboniferous Jochus Formation. The predominant organic maceral type for the Late Carboniferous and the Permian is vitrinite, suggesting gas-prone source.The potential for reservoir rock is best developed in the Aramac Coal Measures and Colinlea Sandstone correlative units within a fluvial channel sandstone facies. Structural and stratigraphic traps formed in the Late Carboniferous and the Early Permian are thought to be most prospective. The presence of oil and gas in ENL Lake Galilee 1 does imply that hydrocarbons have been generated in the basin or possibly from the underlying Devonian. The application of oil/source rock correlation data suggests the basal Jericho Formation or the underlying Devonian as the oil source. The Aramac Coal Measures, with a combination of reservoir and source facies even though only marginally mature, are thought to offer the best play.Lack of success to date may well reflect deficiencies in one or more of the exploration criteria. However, examination of drilling locations suggests that many wells were poorly sited owing to the difficulty in seismic mapping below the Late Permian coal seams.