No abstract available

Coalbed methane (CBM) is emerging as an important energy resource in Australia. CBM is one of the products of coalification - the process by which peat is transformed into coal during progressive burial. The initial product is biogenic gas, thermogenic gas is produced with increasing pressure and temperature and further biogenic gas may be produced after burial has ceased if the coal becomes exposed to an active groundwater system containing methanogenic bacteria. The storage of CBM within a coalbed reservoir is complex, being a mixture of free gas, dissolved gas and absorbed gas. A number of gas and coal properties govern how much and how fast a coal seam will give up its methane, but the most economically productive seams are naturally fractured or are stimulated to induce and increase fracturing. Unlike conventional gas reservoirs, the continuous production of water from a coalbed reservoir results in a corresponding progressive increase in gas production (up to a certain limit). CBM production in Australia commenced in 1996 and most of Australias coal basins are now covered by production, exploration or application licences. The Cooper Basin contains a huge volume of coal that is recognised to be the source of much of the conventionally trapped gas. No attempt has been made to explore the basin for CBM due to the generally held belief that the coals are too deep. The Weena Trough has been identified as one area in the Cooper Basin in which the Permian coals may be at depths that are economic to exploit. Two wells drilled in the period 1968-70 encountered net coal thicknesses of more than 40m with individual seams up to 18 metres. The fact that elsewhere these coals are known to be the source of much of the basins conventionally trapped gas, combined with the advances made in understanding the nature of CBM generation, storage and production, makes the Weena Trough an ideal target for evaluation

The Ceduna Sub-basin of the deep-water frontier Bight Basin contains a Middle Jurassic-Late Cretaceous sedimentary succession in excess of 15 km thick. Nine offshore exploration wells have been drilled in the basin, mostly clustered around the inboard edge of the Ceduna Sub-basin. As a result, the distal mid-Late Cretaceous strata predicted to contain potential source rock facies, had previously not been sampled. The presence of high quality source rocks in the basin was therefore an open question. 2D seismic data was used to delineate targets for sampling of the pre-Campanian section of the basin. Identified targets included potential source intervals of Albian-Santonian age at locations on the seaward edge of the Ceduna and Eyre Terrace where canyon formation, slumping and faulting have exposed the section. Also, a series of sites were selected to test for potential hydrocarbon seepage in the basin. These sites include areas where recently reactivated deep-seated faults were exposed at the seafloor, basin margin areas where facies thin, and areas where possible seepage was identified from Synthetic Aperture Radar (SAR) data. In February and March 2007, a 3-week marine acquisition programme was carried out on the RV Southern Surveyor. Potential dredge targets were first surveyed with 30 kHz EM300 swath bathymetry and observed with Topaz 3.5 kHz sub-bottom profiler. Near-live swath processing and slope analysis techniques enabled site specific dredge sampling of seafloor terrains where Cretaceous section outcropped or slopes were sufficient to ensure only a thin cover of overlying sediments. Targets include fault scarps and eroded sides of canyons. A better-than-expected number of successful dredges were collected (total of 37) from water depths ranging from 1600-4500m. Geochemical analysis of 259 dredge samples for total organic carbon (TOC) and pyrolysis yields (Rock Eval) identified good to very good organic richness in 13 samples, with TOC values between 2.1% and 6.2%. Of these, seven show liquids potential with Hydrocarbon Index (HI) values ranging between 274 and 479 (mgHC/TOC). The rocks with the best source rock characteristics came from high priority sampling sites in the westernmost Ceduna Sub-basin. Organic geochemical analysis has provided evidence for preservation of organic matter under anoxic conditions close to or at the sediment-water interface. Biostratigraphic analysis of these organic-rich rocks has yielded an age around the Cenomanian-Turonian boundary. Although the dredged rocks are immature for hydrocarbon generation, interpretation of an extensive seismic grid across the basin and petroleum system modelling have shown that this succession occurs with the oil window in the central Ceduna Sub-basin. The results of this study provide the best evidence to date for the presence of good quality liquids-prone source rocks in the basin, successfully addressing a key industry concern in this petroleum exploration frontier.

Interpretation of new aeromagnetic data

The northern marine region of Australia has been selected by the Department of the Environment and Water Resources (DEW; with statutory and policy responsibility for MPAs) and other stakeholders (Commonwealth of Australia, 2007) as a possible location for the establishment of marine parks. This report examines the petroleum prospectivity of the proposed region, with an assessment undertaken by Geoscience Australia. The northern marine assessment region is located offshore on the northern shelf of Australian, extending from the Torres Strait to the NT/WA state boundary. Geologically the region encompasses three provinces; 1) the Timor Sea, 2) the Arafura Sea and 3) the Gulf of Carpentaria. These areas were assessed separately due to different development histories, sedimentary fill and associated prospectivity.

Union-Kern-A.O.G. Middle Creek No. 1 was the fourth wildcat well drilled by Union Oil Development Corporation in the south-eastern part of the Surat Basin. The well, located approximately eight miles north-north-east of Union-Kern-A.O.G. Moonie No. 1, was drilled by Mines Administration Pty Limited for Union Oil Development Corporation to a total depth of 6126 feet. Drilling commenced on 19th May, 1962 and was completed on 8th June, 1962. A full programme of logging, testing, and coring was undertaken. The well penetrated 118 feet of Quaternary-Tertiary sandstone and shale; 2153 feet of Lower Cretaceous Roma Formation; 1053 feet of Lower Cretaceous-Jurassic Blythesdale Formation; 1045 feet of Jurassic Walloon Formation; 639 feet of Hutton Sandstone; 540 feet of Evergreen Shale; and 352 feet of Jurassic-Triassic Precipice Sandstone. Below the unconformity at the base of the Precipice Sandstone at 5912 feet, the test entered volcanic conglomerates and siliceous sandstones of the Permo-Carboniferous Kuttung Formation in which the well bottomed at 6126 feet. No drill stem test was carried out in tile Precipice Sandstone but high resistivity on the electric log suggests freshwater saturation. A 60-minute open hole formation test was made of a sandstone interval (5240-5263 feet) witilin the Evergreen Shale. A net rise of 4790 feet of slightly gassy water (37 gr;/gal.) was recovered on the test. In the absence of any significant shows, cement plugs were set and the well was abandoned on 10til June, 1962. The test drilling operation at Union-Kern-A.O.G. Middle Creek No. 1 was subsidized under tile Petroleum Search Subsidy Act 1959-1961, from surface to total depth.

This report refers to an offshore aeromagnetic survey over the continental shelf of south-eastern Australia, from Gippsland in the east, through Bass Strait, to Encounter Bay and Kangaroo Island in the west. The survey was carried out for Haematite Explorations Proprietary Limited by Aero Service Limited during the period 17th September to 21st December, 1961. A previous reconnaissance aeromagnetic survey carried out by the same contractor over Bass Strait in December, 1960, had indicated the existence of deep Tertiary-Mesozoic sedimentary basins. The objective of the later survey was to delineate these basins and to extend the investigation farther westward with a view to selecting areas for marine seismic surveys. 17,945 miles of aeromagnetic traverse were flown and the results of the operation are presented as contoured maps of total magnetic field intensity and of interpreted basement depth. As a result of the survey, several areas of deep sedimentation were delineated in sufficient detail to allow for the planning of subsequent investigation by marine seismic surveys.

Union-Kern-A.O.G. Flinton No. 1 Well was drilled by Union Oil Development Corporation in the south-western part of the Surat Basin, Queensland. The well, located approximately eight miles east-south-east of Flinton and 44 miles south-west of U.K.A. Cabawin No. I, was drilled by Oil Drilling and Exploration Limited for Union Oil Development Corporation to a total depth of 9123 feet. Drilling commenced on 10th August, 1963 and was completed on 11th September, 1963. A full programme of logging, testing, and coring was undertaken. The well penetrated 2685 feet of shales with minor sands of the Lower Cretaceous Roma Formation; 2384 feet of sandstone with interbedded siltstone, claystone, and shale of the Jurassic Blythesdale Formation; 668 feet of the Walloon Formation; 565 feet of the Hutton Sandstone; 888 feet of Evergreen Shale and Precipice Sandstone equivalents; 718 feet of the Triassic Wandoan Formation equivalent; 392 feet of the Triassic Cabawin Formation; 563 feet of the Permian Kianga Formation; 167 feet of the Permian Back Creek Formation; and 93 feet of Permo-Carboniferous Kuttung Formation in which the well bottomed at 9123 feet. Flinton No. 1 was drilled to test the hydrocarbon potential of a closed seismic structure. At the location of the well, the "G" Horizon structure map, which represents the structure on a stratigraphic level approximately at the top of the Precipice Sandstone, indicates a closure of about 100 feet over an area of about eleven square miles. No significant oil or gas shows were recorded. A drillstem test of the interval 7817 to 7845 feet was abortive because of packer failure. The well was then plugged below 4490 feet and leased for conversion to a water well. The stratigraphic drilling operation at Union-Kern-A.O.G. Flinton No. 1 was subsidized under the Petroleum Search Subsidy Act 1959-1961, from surface to total depth.

Flaxmans No. 1 Well was located within the south-eastern part of the Otway Basin, approximately 20 miles south-east of Warrnambool, on the Victorian coast. The well was drilled by Oil Drilling and Exploration Limited for Frome-Broken Hill Company Proprietary Limited, to a total depth of 11,528 feet. Drilling commenced on 3rd May, 1961 and was completed on 25th August, 1961. A full programme of logging, testing, and coring was undertaken. The well penetrated Miocene-Oligocene sediments to a depth of 2008 feet, Eocene-Upper Cretaceous to 4833 feet, Upper Cretaceous to 6490 feet, Middle Cretaceous to 6876 feet, Lower Cretaceous to 7330 feet, and Lower Cretaceous - (?) Jurassic otway Group sediments to total depth of 11,528 feet. Flaxmans No. 1 was drilled to test the hydrocarbon potential of the Tertiary and Mesozoic sediments in a closed seismic structure. Sixteen drillstem tests and ten production tests were undertaken but the maximum yield of 250 Mcf/D of gas from the interval 10,842 to 11,528 feet could not be maintained and the well was plugged and abandoned. Other possible reservoirs tested in the well yielded only small amounts of petroliferous gas, probably from solution in formation water. The stratigraphic drilling operation at Flaxmans No. 1 was subsidized under the Petroleum Search Subsidy Act 1959, from 4833 feet to total depth.

Wongela GeoIilysical Pty Ltd conducted a helicopter gravity survey for the French Petroleum Company (Australia) Pty Limited in northern South Australia during the period 22nd August to 21st November, 1963, and established 2204 new gravity stations. The area surveyed is in Oil Exploration Licences Nos 20 and 21, and originally covered 34,000 square miles. This area was increased to 35,500 square miles to fill in a gap between the subject survey and the Delhi Alton Downs survey farther east. The work is tied to previous reconnaissance gravity surveys in Central Australia and completes the gravity coverage of the Simpson Desert. The survey was carried out to determine the extent of Palaeozoic sedimentation in the area and in particular to determine whether Amadeus Basin sediments extend into the survey area. These sediments are masked in the area by relatively flat-lying Mesozoic and more recent sediments. The younger sediments have much the same thickness and density throughout the survey area, and for this reason their contribution to variations in the anomaly field is small. Hence the variations in the anomaly field are thought to be due mainly to density contrasts in the basement and between the basement and pre-Mesozoic sediments. The survey results have defined some major geological structural units. These are described and discussed individually in the text of the report. Of particular interest is the Dalhousie Gravity Depression which probably represents a large area of pre-Permian sedimentation, about 8000 feet in thickness. To the east of this feature is a platform area which was probably fairly stable and high standing dUring pre-Permian time in which period it received only a thin cover of sediments. It is probable that since early Permian times the area has been depressed relative to the area of the Dalhousie Gravity Depression and the area farther west, and has received extensive Permian and Mesozoic sedimentation, the sediments thickening towards the east.