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.

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Shell was attracted to the potential of the northern Drummond Basin by large anticlinal structures, already evident from patchy outcrop and limited seismic data. An exploration strategy was developed to assess, in the most cost effective manner, the principal uncertainties associated with the play over a two- year period.Initially a regional seismic program of 270 km was acquired. This provided sub- surface control essential for the subsequent corehole drilling program, and an outline of the regional structural framework. The drilling program of six 500 m coreholes, each overlapping slightly in terms of stratigraphy, was sited along one of Shell's seismic lines. A total of 2569 m of core was recovered, providing 2083 m of true stratigraphic coverage, thus facilitating detailed stratigraphic, reservoir, seal and geochemical studies.The new seismic data have led to a revision of the tectonic model of the basin, which, despite a complex uplift history, remains at maturity levels compatible with hydrocarbon occurrence. Core studies have highlighted the major exploration risks as relatively poor reservoir quality, limited source- rock development and thin intra- formational seals.Despite the disappointing outcome in terms of hydrocarbon prospectivity, significant advances have been made in the understanding of the geology of central Queensland, particularly relating to tectonics and burial history, which may be of regional significance.

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.