Petroleum source rocks are found at three levels in the Ordovician sectionin the Canning Basin and appear to be at similar stratigraphic levels and ofsimilar organic facies to the source rocks which have produced the gas andgas-condensate fields in the Amadeus Basin. In both basins shallowintersections in drillholes have yielded material at a low level of thermal maturity.Samples have shown that these immature source rocks contain algal-sourcedType 1 kerogens with a high hydrogen index and a large capacity to generate oil(eg Hoffmann et al., 1987). Deeper wells in both basins encountered sourcerocks at higher levels of maturity associated in some cases with oil fluorescenceand shows of live oil. By comparing the results of Rock-Eval pyrolysis analysisfor these more mature source rocks with those of the immature rocks the degreeof kerogen conversion to hydrocarbon (the Transformation Ratio of Espitalie eta)., 1986) can be estimated. The results from 14 wells along the BroomePlatform show a rapid downward increase in transformation ratio (TR) through theOrdovician section which can be correlated to the rapid downward increase in theconodont alteration index (CAI) previously documented by Nicoll & Gorter (1984).This correlation shows that the zone of peak oil generation lies between the endof CAI Zone 1 and the beginning of CAI Zone 2. The Ordovician in the Canning Basin is known mainly from intersectionsin 22 drillholes. It is thickest in two sub-basins: the Willara, bounded to the northby the Admiral Bay Fault, and a larger unnamed sub-basin (roughly coincidentwith the later Fitzroy Trough), bounded to the north by the Oscar Range-Pinnaclefault system. Both fault systems appear to have been active during thedeposition of the Ordovician. The best known source rocks occur along thesouthern side of the northern sub-basin; they appear to be poorly developed, orabsent, in the Willara Sub-basin. Overmature source beds are locally preservedin fault remnants under the Lennard Shelf and may exist at great depth in theFitzroy Trough.

Three economic (1 oil and gas/condensate, 1 gas/condensate, and 1 gas) and fourteen uneconomic (6 oil, 7 gas, and 1 oil/gas) petroleum accumulations have been discovered since 1963 in the Amadeus Basin of central Australia. The petroleum in the Amadeus Basin mainly occupies the structural, fold- related traps within the Upper Proterozoic to Upper Ordovician marine to marginal marine clastic and evaporitic sequences. It is believed to be of algal/bacterial origin. The API gravity ranges from 18 to 54o for crude oils, and from 52 to 64o for condensates; gases are dry and wet. The basin's estimated petroleum resources as at 31 December 1985 comprise 5.74 x 106m3 of oil, 1.53 x 106m3 of natural-gas liquids, and 14.93 x 109m3 of sales gas. Production from Mereenie (oil) and Palm Valley (gas/condensate) accumulations commenced during 1984. Up to 31 December 1985 the cumulative production from the basin stood at 156.3 x 103m3 of oil and condensate, and 44.0 x 106m3 of sales gas. The gas/condensate is transported 146 km to Alice Springs through a 20-cm-diameter pipeline; the oil is transported 269 km to Alice Springs through a 20cm pipeline and from there by rail tankers to Adelaide refinery. As from February 1987 gas from Palm Valley will also be transported to Darwin via a 1537-km pipeline of 35.3 cm diameter.

The Gippsland Basin in southeastern Victoria is Australia's major crude oil and natural gas producing province. To the end of 1986 the basin had supplied 88 per cent of Australia's cumulative crude oil production and 48 per cent of cumulative natural gas production. Crude oil and natural gas were first discovered onshore in 1924, near Lakes Entrance, Victoria. Since then over 125 onshore wells have been drilled, resulting in the discovery of one (1) subeconomic and six (6) uneconomic petroleum accumulations. More than 80 exploration and step-out wells have been drilled offshore, resulting in the discovery of eleven (11) economic, twenty-six (26) subeconomic and six (6) uneconomic petroleum accumulations. The petroleum in the Gippsland Basin mainly occupies structural and structural/stratigraphic traps within the Oligocene, Eocene, Paleocene and Late Cretaceous marine, marginal marine and continental clastic sequences. The petroleum is believed to be of land-plant origin; crude oil results from thermal breakdown of exinite, and natural gas from thermal cracking of vitrinite and exinite. The crude oils are generally very light and paraffinic, ranging from 40 to 60oAPI. Some heavier oils discovered at shallow depths range from 14.6 to 26.5oAPI and are thought to have been biologically degraded. The condensates range from 48 to 63oAPI. The natural gases are generally low in condensate content. Some gas reservoirs contain a high proportion of carbon dioxide. Production of natural gas and oil commenced in 1969 and 1970 respectively. Cumulative production to 31 December 1986 was 344.66 x 106m3 of oil, 9.68 x 106m3 of condensate, 41.75 x 106m3 of LPG and 66.14 x 109m3 of sales gas. The oil and gas produced is transported from the twelve offshore production facilities (platforms) by pipeline to gas and crude oil stabilisation plant at Longford, Victoria for processing, and then to storage and distribution centres. Estimated remaining recoverable petroleum reserves in the Gippsland Basin as at 31 December 1986 are 202.44 x 106m3 of oil, 22.44 x 106m3 of condensate, 44.89 x 106m3 of liquid petroleum gas, and 206.39 x 109m3 of sales gas.

As at 31 December 1989 the Otway Basin, which is located along the southeast margin of the Australian mainland, was known to contain a total of seven economic and six subeconomic petroleum and non-petroleum gas accumulations. All have been discovered since the late 1950s as a result of petroleum exploration drilling. Three accumulations have been or could be used as a source of petroleum natural gas or carbon dioxide: the North Paaratte gas accumulation in Victoria and the Caroline carbon dioxide accumulation in South Australia, both of which are currently being exploited, and the Wallaby Creek gas accumulation in Victoria, which has been identified by permit holders as an accumulation likely to be developed in the future (1992-1994). In addition, the Katnook and Ladbroke Grove gas accumulations in South Australia are being considered for development in the near future. The initial petroleum reserves of the Otway Basin as at 31 December 1988 are estimated to be 0.483 billion cubic metres of sales gas and 0.002 million kilolitres of condensate (not including the reserves of the Katnook and Ladbroke Grove accumulations). Production from the Caroline carbon dioxide accumulation commenced in 1968, and this field continues to supply this commodity much of the South Australian and Victorian markets. Production of natural gas from the North Paaratte accumulation commenced in August 1986. This field supplies domestic and industrial users in Warrnambool, Victoria.

As at January 1993, nineteen hydrocarbon accumulations, six of which are commercial, have been discovered in the Canning Basin. The commercial accumulations occur in Permian to Devonian reservoirs on an area of relatively shallow basement (Lennard Shelf) flanking the northern margin of the Fitzroy Trough. Oil is produced from Famennian reefs, associated drape structures, and four-way dip closures in Permo-carboniferous, Grant Group and Anderson Formation sandstones. The most likely sources of these hydrocarbons are Late Devonian and Carboniferous marine shales in the Fitzroy Trough kitchen area. The small size of the accumulations in the Canning basin (less than 0.5 million barrels of recoverable oil) precludes the development of large infrastructure projects. Oil is trucked to the storage and shiploading facilities at Broome and then shipped to the Kwinana oil refinery in Western Australia. On the southern margin of the Fitzroy Trough, oil and gas have been recovered from a transgressive Ordovician sequence of sandstones shales and carbonates. Although the Ordovician has yet to yield a commercial discovery, Devonian reef plays in the overlying section may enhance the attractiveness of Ordovician objectives in this area. To date, exploration effort in the basin has been largely directed to the northern, onshore Canning Basin. The offshore Canning and the Kidson Sub-basin remain underexplored. Higher risk plays in these areas have yet to be adequately tested.

The Onshore Energy Security Program, funded by the Australian Government, Geoscience Australia has acquired deep seismic reflection data across several frontier sedimentary basins to stimulate interest in petroleum exploration in onshore Australia. Detailed interpretation of deep seismic reflection profiles from four onshore basins, focusing on overall basin geometry and internal sequence stratigraphy will be presented here, with the aim of assessing the petroleum potential of the basins. At the Southern end of the exposed part of the Mt Isa Province, northwest Queensland, a deep seismic line (06GA-M6) crosses the Burke River Structural Zone of the Georgina Basin. The basin here is >50 km wide, with a half graben geometry, and bound in the west by a rift border fault. The Millungera Basin in northwest Queensland is completely covered by the thin Eromanga basin and was unknown prior to being detected on two seismic lines (06GA-M4 and 06GA-M5) acquired in 2006. Following this, seismic line 07GA-IG1 imaged a 65 km wide section of the basin. The geometry of internal stratigraphic sequences and post-depositional thrust margin indicate that the original succession was much thicker than preserved today. The Yathong Trough in the southeast part of the Darling Basin in NSW has been imaged in seismic line 08GA-RS2 and interpreted in detail using sequence stratigraphic principles, with several sequences being mapped. The upper part of this basin contains Devonian sediments, with potential source rocks at depth.

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This year, the Commonwealth Government is offering 6 large exploration areas in the frontier Bight Basin. The release areas (Figure 1) are situated in the central Great Australian Bight off southern Australia, approximately 415 to 655 km west of Port Lincoln, South Australia and 250 to 530 km southwest of Ceduna, South Australia. The areas are located within the Ceduna Sub-basin, in the eastern part of the Bight Basin, in water depths ranging from 130 to 4600 m. At present, no permits are held in this part of the basin. The release areas range in size from 85 to 90 graticular blocks (6000 to 6395 km2), and bids for all 6 areas close on 29 April 2010. Most exploration drilling in the Bight Basin has focused on the margins of the Ceduna Sub-basin and the Duntroon Sub-basin to the southeast of the current release areas. Gnarlyknots 1A, drilled by Woodside Energy and partners in 2003, is the only well to have attempted to test the thick, prospective Ceduna Sub-basin succession away from the margins of the sub-basin. Unfortunately the well was not an exploration success, as it had to be abandoned due to deteriorating weather and ocean conditions without reaching all planned target horizons. In 2007, Geoscience Australia conducted a marine sampling survey in the Bight Basin that dredged a suite of organic-rich rocks of Cenomanian-Turonian age from the northwestern exposed edge of the Ceduna Sub-basin. Geochemical analyses have characterised these samples as world-class, oil-prone, marine potential source rocks. Seismic interpretation indicates that this interval can be mapped throughout most of the basin and is mature for oil and gas generation across much of the Ceduna Sub-basin.

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