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Surprisingly few natural hydrocarbon seeps have been identified in Australia's offshore basins despite studies spanning thirty years. Initial studies of natural hydrocarbon seepage around the Australian margin were generally based around the geochemical analysis of stranded bitumens, water column geochemical `sniffer' sampling, synthetic aperture radar or airborne laser fluorsensor. Later studies involved the integration of these remote sensing and geochemical techniques with mutli-channel and shallow seismic. A review of these earlier studies indicates that many seepage interpretations need to be re-evaluated and that previous data sets, when set in a global context, often represent normal background hydrocarbon levels. Relatively few sites of proven natural hydrocarbon seepage in Australia's offshore sedimentary basins can be reconciled with the dominantly passive margin setting and low recent sedimentation rates, which are not favourable for high rates of seepage, and difficulties in proving seepage on high energy, shallow carbonate shelves, where seabed features may be rapidly reworked and modern marine signatures are overprinted on authigenic seep carbonates. Active thermogenic methane seepage on the Yampi Shelf, the only proven documented occurrence in Australia, is driven by deposition of a thick Late Tertiary carbonate succession and Late Miocene tectonic reactivation. Therefore, to increase the success of detecting and correctly interpreting natural hydrocarbon seepage, data need to be analysed and integrated within the context of the local geological setting, and with an understanding of what is observed globally.

A recent Geoscience Australia sampling survey in the Bight Basin recovered hundreds of dredge samples of Early Cenomanian to Late Maastrichtian age. Given the location of these samples near the updip northern edge of the Ceduna Sub-basin, they are all immature for hydrocarbon generation with vitrinite reflectance - 0.5% RVmax, Tmax < 440oC and PI < 0.1. Excellent hydrocarbon generative potential is seen for marine, outer shelf, black shales and mudstones with TOC to 6.9% and HI up to 479 mg hydrocarbons/g TOC. These sediments are exclusively of Late Cenomanian-Early Turonian (C/T) in age. The high hydrocarbon potential of the C/T dredge samples is further supported by a dominance of the hydrogen-rich exinite maceral group (liptinite, lamalginite and telalginite macerals), where samples with the highest HI (> 200 mg hydrocarbons/g TOC) contain > 70% of the exinite maceral group. Pyrolysis-gas chromatography and pyrolysis-gas chromatography mass spectrometry of the C/T kerogens reveal moderate levels of sulphur compounds and the relative abundances of aliphatic and aromatic hydrocarbons predict the generation of a paraffinic-naphthenic-aromatic low wax oil in nature. Not enough oom for rest of Abstract

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The North West Margin Transects Cruise is part of a program being undertaken by AGSO to determine the structural architecture of the north-western margin of Australia and the influence of structuring on the location, migration and trapping ofhydrocarbons in the region. An important aspect of this program is the acquisition ofa series of full margin 'dip' transects extending from unrifted cratonic basement tobeyond the continent-ocean boundary, and at least two 'strike' transects that willextend along the full length of the shelf from the eastern Timor Sea to North WestCape. The major objective of the proposed cruise is to extend previous AGSO deepseismic surveys across the Browse (Survey 119), offshore Canning (SNOWS-3/Survey 120) and northern Carnarvon Basins (SNOWS-/Survey 101, SNOWS-2/Survey 110) to complete these margin transects. Specific objectives of theproposed survey are: *Determine the regional structural framework of the Scott Plateau area and itsrelationship to adjacent features such as the Argo Abyssal Plain, the BrowseBasin and the Rowley Sub-Basin of the offshore Canning Basin; *Determine the regional structural framework of the Exmouth Plateau and itsrelationship to adjacent features such as the Barrow-Dampier Sub-basin, and theArgo and Gascoyne Abyssal Plains. *Define the broad deep-crustal structure of the region and develop a modelexplaining the tectonic, subsidence and thermal history of the Scott Plateau andthe Exmouth Plateau in relation to the development of the continental margin andadjacent ocean basins. *Assess the effects of the deep crustal structures and their reactivation phases onthe development of known petroleum accumulations. To address these objectives it is proposed that RV Rig Seismic be used to acquireabout 3276 km of deep crustal (16 second record length) multichannel seismic andother geophysical data along 9 transects across the outer margins of the Browse,offshore Canning and northern Carnarvon Basins. The survey will tie into the 1991SNOWS-1 (101), 1992 SNOWS-2 (110), 1993 Browse Basin (119) and SNOWS-3(120) surveys.

This publication is the sucessor to Oil and Gas Resources 2000 and continues as the definitive reference on exploration, development and production of Australia's petroleum resources. It covers exploration, reserves, undiscovered resources, development, production and supporting information and statistics. It includes a forecast of Australia's crude oil and condensate production from 2001 to 2015, and sustainability indicators for petroleum resources. Information on Australia's petroleum data availability is also included. A revised estimate of Australia's undiscovered resources is included. The Appendices describe wells drilled and seismic surveys carried out in 2001. There is also a chronological listing of offshore and onshore oil and gas discoveries to 2001, listings of all petroleum platforms and pipelines, and a map showing all Australian petroleum exploration and development titles, with a key of title holders and interests as at March 2001. OGRA 2001 provides the background for much of the advice on petroleum resources given to the Australian government and is a key source for petroleum exploration, production and service companies, petroleum engineers and geologists, energy analysts, stockbrokers and share investors.

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The processing, interpretation and mapping of slicks offshore of the South West Margins using ten ERS satellite radar scenes and four Radarsat scenes has been completed successfully. All slick interpretations have been attributed with a hydrocarbon likelihood Level ranging from Level 2 to Level 4 with Level 2 being the most likely. Given the absence of actual field data, no Level 1 slicks have been mapped (see Glossary of Slick and Other Interpretations, p3 below). For all the fourteen scenes interpreted and mapped, there is only one Level 2 slick. This significant slick is located on the western edge of scene ERS 2 WO 01907-01 Orbit 5883. No locations have been provided of the sources of mapped slicks. Although an approximate point source would normally be provided for Level 2 slicks, the only Level 2 slick mapped (as above) is not complete as it is on the edge of the image (and presumably would continue on to an adjacent image acquired at the same time if it were available) and given the depth to sea floor of between 2,500m to 3,000m, it is not possible to provide a point source. Likewise, while an approximate point source would normally be provided for Level 3 slicks, given the depth to sea floor in the locations of the two Level 3 slicks mapped (same scene as for the Level 2 slick) of between 2,500m to 5,500m, it is not possible to provide a point sources. As per normal, Level 4 slicks are not provided with a source point. Many of the Level 4 slicks are located along the coastline in or near to the surf break zone (some possibly adjacent to rocky outcrops) and as such are regarded as false slicks as they most likely relate to differences in sea surface conditions and not to the formation of hydrocarbons.

This study undertook geochemical and isotopic analyses on a wide selection of oil stains from the Thorntonia Limestone, Arthur Creek Formation and the Arrinthrunga Formation and its lower Hagen Member in order to define geochemical inter-relationships between the oils, characterize their source facies and to determine the extent of post-emplacement alteration. Oil stains were collected from BHD-4 and -9, Elkedra-2 and -7A, Hacking-1, MacIntyre-1, M13 PD, NTGS99/1, Owen-2, Randall-1 and Ross-1 over a depth range from 91 to 1065 m and were analysed for bulk, molecular (biomarkers) and carbon isotopic compositions. Gas chromatograph of the saturated hydrocarbon fraction clearly showed biodegradation as the main alteration process in the shallow reservoirs. Unaltered oil stains show a dominance of medium weight n-alkanes with a maximum at n-C15. Biodegradation results in a progressive loss of the lighter hydrocarbons and an accompanying shift in n-alkane maximum to C27, to finally a complete loss of n-alkanes and a large unresolved complex mixture (UCM). The absence of 25-norhopanes suggests a mild level of biodegradation. The low ratio of saturated hydrocarbons/aromatic hydrocarbons (<1, down to 0.42) compared to high ratios (up to 4.35) for oils with abundant lower molecular weight n-alkanes is consistent with biodegradation. However, low ratios are also seen for otherwise pristine oils, suggesting a complex charge history of initial biodegraded and subsequent re-charge with n-alkane-laden oil. The level of biodegradation is not too severe as to overtly affect the distribution of the biomarkers C19 - C26 tricyclic terpanes, C24 tetracyclic terpane, C27 - C35 hopanes, C30 triterpane (gammacerane) and C27- C29 desmethylsteranes, enabling their use in oil-oil correlation and definition of oil populations. To clarify the inter-relationships among the Georgina Basin oil stains multivariate statistical analysis was used involving a wide range of biomarker ratios that are source-specific and environmental indicators. Resulting oil populations showed a strong correlation with their reservoir unit across the basin, suggesting juxtaposition of source and reservoir within the same stratigraphic unit. Oil-source correlation based on biomarker, bulk carbon isotopes of saturated and aromatic hydrocarbons and n-alkane-specific carbon isotopes identified Thorntonia(!), Arthur Creek(!) and Hagen(.) Petroleum Systems. The latter petroleum system is characterised by relatively high gammacerane, indicating an evaporitic depositional environment. Alternatively, an evaporatic organic facies from an Arthur Creek Formation source may have sourced the Hagen Member oil stains, considering that other oil stains reservoired within the Arrinthrunga Formation show a close affinity with oil stains from the Arthur Creek(!) Petroleum System, suggesting an inter-formational Arthur Creek-Hagen Petroleum System at Elkedra-2. An Arthur Creek-Hagen(!) petroleum system is evident at Elkedra-7A while there is a mixed Thorntonia Limestone and Arthur Creek source contribute to the oil stain at Ross-1.