The molecular composition of fluid inclusion (FI) oils from Leander Reef-1, Houtman 1 and Gage Roads-2 provide evidence of the origin of palaeo-oil accumulations in the offshore Perth Basin. These data are complemented by compound specific isotope (CSI) profiles of n-alkanes for the Leander Reef-1 and Houtman-1 samples, which were acquired on purified n-alkane fractions gained by micro-fractionation of lean FI oil samples, showing the technical feasibility of this technique. The Leander Reef-1 FI oil from the top Carynginia Formation shares many biomarker similarities with oils from the Dongara and Yardarino oilfields, which have been correlated with the Early Triassic Kockatea Shale. However, the heavier isotopic values for the C15-C25 n-alkanes in the Leander Reef-1 FI oil indicate that it is a mixture, and suggest that the main part of this oil (~90%) was sourced from the more terrestrial and isotopically heavier Early Permian Carynginia Formation or Irwin River Coal Measures. This insight would have been precluded when looking at molecular evidence alone. The Houtman-1 FI oil from the top Cattamarra Coal Measures (Middle Jurassic) was sourced from a clay-rich, low sulphur source rock with a significant input of terrestrial organic matter, deposited under oxic to suboxic conditions. Biomarkers suggest sourcing from a more prokaryotic-dominated facies than for the other FI oils, possibly a saline lagoon. The Houtman-1 FI oil ?13C CSI data are similar to data acquired on the Walyering-2 oil. Possible lacustrine sources include the Early Jurassic Eneabba Formation or the Late Jurassic Yarragadee Formation. The low maturity Gage Roads-2 FI oil from the Carnac Formation (Early Cretaceous) was derived from a strongly terrestrial, non-marine source rock containing a high proportion of Araucariacean-type conifer organic matter. It has some geochemical differences to the presently reservoired oil in Gage Roads-1, and was probably sourced from the Early Cretaceous Parmelia Formation.

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.

A prospectivity assessment of the offshore northern Perth Basin, Western Australia, was undertaken as part of the Australian Goverment's Offshore Energy Security Program.

The Oil Identification Reference Kit (OIRK) is a subset of the oils registered in Australia's National Oil-on-the-Sea Identification Database (NOSID). It's purpose is to provide laboratories engaged in oil fingerprinting with a series of well characterised reference oils and the materials, methods and reference data to support quantitative analysis of petroleum biomarkers. Biomarker methods are rapidly being incorporated in oil identification protocols as they offer several advantages over traditional methods. There is a lack of commercially available reference materials, especially those suitable for quantitative determination. The NOSID database and the OIRK are the products of collaboration between the Australian Geological Survey Organisation (AGSO), the Australian Government Analytical Laboratories (AGAL) and the Australian Maritime Safety Authority (AMSA).

Harold Raggatt Award for Distinguished Lecturer Series: "Offshore Australian oil families and petroleum systems" by Dr Dianne Edwards presented as a powerepoint presentation on 1 August 2001.

AOGC 2012 conference abstract

The Exploring for the Future program is an initiative by the Australian Government dedicated to boosting investment in resource exploration in Australia. As part of the Exploring for the Future program, this study aims to improve our understanding of the petroleum resource potential of northern Australia. This data release presents new field emission scanning electron microscopy (FE-SEM) of broad ion beam- polished samples (BIB-SEM) to visualise mineral and organic matter (OM) porosity on 15 Proterozoic aged shales. Samples were selected from the Velkerri and Barney Creek formations in the McArthur Basin and the Mullera Formation, Riversleigh Siltstone, Lawn Hill and Termite Range formations in the South Nicholson region. Qualitative maceral analysis of the 15 samples are described in addition to bitumen reflectance measurements. These samples were analysed at the Montanuniversität Leoben, Austria in June 2020. The results of this study can be used to improve our understanding of porosity, microstructures, seal capacity and hydrocarbon prospectivity of Proterozoic aged sedimentary basins in northern Australia.

Legacy product - no abstract available

No abstract available

Sampling, prior to CO2 injection at the CO2CRC Otway Project, southeastern Victoria at the end of 2007 early 2008, provided a stocktake of the molecular and isotopic (carbon and hydrogen) compositions of the subsurface hydrocarbon and non-hydrocarbon gases (and heavier hydrocarbons) at, and in close proximity to, the injection site. This baseline study is also fundamental to the assessment of present sub-surface petroleum components as natural tracers for injected gases arriving at the monitoring well. The CO2CRC Otway Project will use the CO2-rich natural gas (containing 79% CO2 and 20% methane) from the Buttress-1 well; totalling 100,000 tons of gas injected over 2 years. This gas mixture will be injected supercritically into sandstones of the CRC-1 well below the original gas-water contact at ~2000 m in the Waarre Formation. The depleted natural gas well at Naylor-1 is the monitoring well, situated 300 m updip of the injection well. Gas from the Waarre Formation in Naylor-1 observation well contains <1% CO2, which is isotopically depleted in 13C (13C -15.8) by 9 compared to CO2 (13C -6.8) in Buttress-1. Thus the carbon isotopes of CO2 can act as a primary natural tracer for monitoring purposes. Isotopically, the minimum detection limit would result from an increase of ~20 % in the CO2 concentration at Naylor-1 from the Buttress-derived CO2. On the other hand, the carbon and hydrogen isotopes of methane, wet gases and higher hydrocarbons are very similar between Buttress-1, CRC-1 and Naylor-1, requiring addition of external conservative tracers (Boreham et al., 2007) for the monitoring of hydrocarbon components. Although the content of liquid hydrocarbons in the gases is very low (<1%), there is the potential for supercritical CO2 extraction of these high molecular weight components (e.g. black oil in the Caroline-1 CO2 gas field and solid wax at the Boggy Creek CO2 production plant) that can be either advantageous (lubrication) or detrimental (clogging) to monitoring equipment at Naylor-1. The CRC-1 well provided an opportunity to collect downhole mud gases over many formations. Maximum total hydrocarbon concentration of 0.97 % occurred in the Waarre Formation Unit C. Surprisingly, a free gas zone in the overlying Flaxmans Formation had a lower maximum concentration (0.17 %). Carbon isotopes for the hydrocarbon gases from 1907 to 2249 mRT showed little downhole variation, while the 13C CO2 averaged -16, identical to CO2 at Naylor-1. Interestingly, the condensate recovered from a MDT in the Flaxmans Formation showed depletions in 13C for the C11 to C20 n-alkanes of up to 6 for n-C15 compared to n-alkanes of oils and condensates sourced from the Eumeralla Formation of the eastern Otway Basin (Boreham et al., 2004). Water washing is suspected at CRC-1 but is not expected to be a major factor affecting hydrocarbon compositions in the short term. The results of this subsurface petroleum audit have been pivotal in demonstrating the need for the addition of external tracers, especially for the hydrocarbon components, and provide an integral part of the near-surface, soil gas and atmospheric monitoring activities of the CO2CRC Otway Project. References Boreham, C.J., Hope, J.M., Jackson, P., Davenport, R., Earl, K.L., Edwards, D.S., Logan, G.A., Krassay, A.A., 2004. Gas-oil-source correlations in the Otway Basin, southern Australia. In: Boult, P.J., Johns, D.R., Lang, S.C. (Eds.), Eastern Australasian Basins Symposium II, Petroleum Exploration Society of Australia, Special Publication, pp. 603-627. Boreham, C.J., Underschultz, J., Stalker, L., Freifeld, B., Volk, H., Perkins, E., 2007. Perdeuterated methane as a novel tracer in CO2 geosequestration. In: Farrimond, P. et al. (Eds.), The 23rd International Meeting on Organic Geochemistry, Torquay, England 9th-14th September 2007, Book of Abstracts, 713-714.