The hydrocarbon generative potential and the thermal maturity of source rocks in the offshore northern Perth Basin was reassessed based on existing and new geochemical data to get a better understanding of the basin's prospectivity. The study establishes for the first time that the main source of onshore accumulations, the Late Permian-Early Triassic Hovea Member, is well developed offshore and contains organic-rich sediments of oil-prone character. This finding shatters the long-held view that the Hovea Member was either absent or of poor quality offshore and provides a new perspective on the basin's prospectivity. The source potential of the Hovea Member varies spatially with best source rocks observed in the Beagle Ridge and Central Abrolhos Sub-basin. The Late Permian Irwin River Sequence and several Jurassic Sequences are also identified as prime potential source rocks offshore, mostly for their gas-generative potential. Oil-generative potential was identified in the Middle to Late Jurassic Yarragadee Sequence and possibly in the Middle Jurassic Cadda Sequence.

<div>Throughout geological history, marine organic-rich shales show variable but appreciable enrichment in uranium (U), < 5 to > 500 ppm. Here we report the results of high-energy resolution fluorescence detection (HERFD) x-ray absorption spectroscopy at U L3 and M4 edges to characterize U speciation in marine sediments.</div><div><br></div><div>We characterised U oxidation state in samples from the Cretaceous Toolebuc Formation of the Eromanga Basin, Australia. Nine samples were carbonaceous shales with high total organic carbon (TOC) content of 5.9 to 13.4 wt&nbsp;% and with low maturity organic matter. Two samples of coquinite were selected for comparison (TOC 0.3 and 2.4 wt %).</div><div><br></div><div>Our results suggest that a significant proportion of U in marine black shales (~20 to 30%) exists as U(VI) (Figures 1-2), despite the extremely reducing (anoxic to euxinic) conditions during sediment precipitation and diagenesis. Within individual samples, spot analyses indicate variation in the estimated oxidation state within a range of ~20% of U(VI). Uranium is unevenly distributed at mm to nanoscale. Nanoscale secondary ion mass spectrometry (NanoSIMS) reveals different associations that often coexist in single samples; nano-particulate uranium is associated with organic matter matrix or sulphide minerals, whereas phosphate minerals display diffuse uranium enrichment. The coquinite has a higher proportion of U(VI), consistent with the dysoxic depositional environment (Boreham and Powell, 1987).</div><div><br></div><div>The unexpectedly enhanced proportion of U(VI) relative to U(IV) within marine organic-rich shales implies that U might not be immediately fixed by reduction processes during sedimentation, but adsorbed by accumulating organic matter, at least in part as U(VI). This is consistent with the behaviour of uranium reported within the water column of the anoxic Black Sea (Anderson, 1989), experiments on U(VI) sorption by organic matter (e.g., Bhat et al., 2008), and previously documented redox state of U from continental organic-rich Eocene (56-34 Ma) sediments of paleochannel and lacustrine origin (Cumberland et al., 2018).</div><div><br></div><div>The results are significant for improving hydrocarbon exploration in known fields (covering the gap to a carbon-free economy without development of new greenfield oil provinces); economic geology (uranium, base-metal, and critical-metal deposits); and environmental management (evaluating potential mobilization of U by groundwaters).</div><div><br></div>This Abstract was submitted and presented to the 2023 Goldschmidt Conference Lyon, France (https://conf.goldschmidt.info/goldschmidt/2023/meetingapp.cgi)

Geoscience Australia currently uses two commercial petroleum system modelling software packages, PetroMod https://www.software.slb.com/products/petromod and Zetaware http://www.zetaware.com, to undertake burial and thermal history modelling on wells in Australian sedimentary basins. From the integration of geological (age-based sedimentary packages, uplift and erosional events), petrophysical (porosity, permeability, and thermal conductivity) and thermal (downhole temperature, heat flow, vitrinite reflectance, and Tmax) input data, to name the most significant, a best-fit model of the time-temperature history is generated. Since the transformation of sedimentary organic matter (kerogen) into petroleum (oil and gas) is a chemical reaction, it is governed by chemical kinetics i.e. time and temperature (in the geological setting, pressure is of secondary importance). Thus, the use of chemical kinetics associated with a formation-specific, immature potential source rock (where available) from the basin of interest is considered a better practical approach rather than relying on software kinetic defaults, which are generally based on the chemical kinetics determined experimentally on Northern Hemisphere organic matter types. As part of the Offshore Energy Systems program hydrocarbons from the Lower Cretaceous Eumeralla Formation were selected where available from onshore wells; compositional kinetics (1-, 2-, 4- and 14-component (phase) kinetics) were undertaken by GeoS4, Germany. The phase kinetics approach is outlined in Appendix 1. This report provides the compositional kinetics for potential source rocks from the Lower Cretaceous Otway Group, Otway Basin, Australia. The kinetic data were used in the offshore petroleum system modelling reported in Schenk et al. (2021).

<div>Geoscience Australia (GA) has produced a folio of 32 wells across the central and southeast regions. This folio covers the areas from Normanby 1 on the Normanby Terrace, through the Shipwreck Trough and Nelson Sub-basin, to Whelk 1 in the southeast. Composite logs for each well in the folio include wireline logs, petrophysical analysis, interpreted lithology, organic geochemical data, organic petrology data, and sequence stratigraphic markers. This folio also includes core-based depositional environment (DE) and gross depositional environment (GDE) interval interpretations which were used to constrain wireline interpretation of DE/GDE away from core control. The folio includes the digital data package used to construct each well composite. The new folio complements a recently published folio of northeast offshore Otway Basin wells, and both were designed as resource for exploration in the offshore Otway Basin.</div>

<div>This study was commissioned by Geoscience Australia (GA) as part of the Exploring for the Future program to produce a report on the organic petrology for rock samples from drill holes of the Birrindudu Basin, Northern Territory, Australia. A suite of 130 drill core samples from 6 drill holes was analysed using standard organic petrological methods to identify the types of organic matter present, assess their relative abundances and determine the levels of thermal maturity attained by the sedimentary organic matter using the reflectance of organoclasts present. </div>

Geoscience Australia and its predecessors have analysed the hydrochemistry of water sampled from bores, surface features, rainwater and core samples (pore water). Samples have been collected during drilling or monitoring projects, including Exploring for the Future (EFTF). The hydrochemistry database includes physical-chemical parameters (EC, pH, redox potential, dissolved oxygen), major and minor ions, trace elements, isotopes and nutrients. The resource is accessible via the Geoscience Australia Portal <a href="https://portal.ga.gov.au/">(https://portal.ga.gov.au/)</a>

<b>Organic Geochemistry (ORGCHEM) Schema. Australian Source Rock and Fluid Atlas</b> The databases tables held within Geoscience Australia's Oracle Organic Geochemistry (ORGCHEM) Schema, together with other supporting Oracle databases (e.g., Borehole database (BOREHOLE), Australian Stratigraphic Units Database (ASUD), and the Reservoir, Facies and Shows (RESFACS) database), underpin the Australian Source Rock and Fluid Atlas web services and publications. These products provide information in an Australia-wide geological context on organic geochemistry, organic petrology and stable isotope data related primarily to sedimentary rocks and energy (petroleum and hydrogen) sample-based datasets used for the discovery and evaluation of sediment-hosted resources. The sample data provide the spatial distribution of source rocks and their derived petroleum fluids (natural gas and crude oil) taken from boreholes and field sites in onshore and offshore Australian provinces. Sample depth, stratigraphy, analytical methods, and other relevant metadata are also supplied with the analytical results. Sedimentary rocks that contain organic matter are referred to as source rocks (e.g., organic-rich shale, oil shale and coal) and the organic matter within the rock matrix that is insoluble in organic solvents is named kerogen. The data in the ORGCHEM schema are produced by a wide range of destructive analytical techniques conducted on samples submitted by industry under legislative requirements, as well as on samples collected by research projects undertaken by Geoscience Australia, state and territory geological organisations and scientific institutions including the Commonwealth Scientific and Industrial Research Organisation (CSIRO) and universities. Data entered into the database tables are commonly sourced from both the basic and interpretive volumes of well completion reports (WCR) provided by the petroleum well operator to either the state and territory governments or, for offshore wells, to the Commonwealth Government under the Offshore Petroleum and Greenhouse Gas Storage Act (OPGGSA) 2006 and previous Petroleum (submerged Lands) Act (PSLA) 1967. Data are also sourced from analyses conducted by Geoscience Australia’s laboratory and its predecessor organisations, the Australian Geological Survey Organisation (AGSO) and the Bureau of Mineral Resources (BMR). Other open file data from company announcements and reports, scientific publications and university theses are captured. The ORGCHEM database was created in 1990 by the BMR in response to industry requests for organic geochemistry data, featuring pyrolysis, vitrinite reflectance and carbon isotopic data (Boreham, 1990). Funding from the Australian Petroleum Cooperative Research Centre (1991–2003) enabled the organic geochemical data to be made publicly available at no cost via the petroleum wells web page from 2002 and included BOREHOLE, ORGCHEM and the Reservoir, Facies and Shows (RESFACS) databases. Investment by the Australian Government in Geoscience Australia’s Exploring for the Future (EFTF) program facilitated technological upgrades and established the current web services (Edwards et al., 2020). The extensive scope of the ORGCHEM schema has led to the development of numerous database tables and web services tailored to visualise the various datasets related to sedimentary rocks, in particular source rocks, crude oils and natural gases within the petroleum systems framework. These web services offer pathways to access the wealth of information contained within the ORGCHEM schema. Web services that facilitate the characterisation of source rocks (and kerogen) comprise data generated from programmed pyrolysis (e.g., Hawk, Rock-Eval, Source Rock Analyser), pyrolysis-gas chromatography (Py-GC) and kinetics analyses, and organic petrological studies (e.g., quantitation of maceral groups and organoclasts, vitrinite reflectance measurements) using reflected light microscopy. Collectively, these data are used to establish the occurrence of source rocks and the post-burial thermal history of sedimentary basins to evaluate the potential for hydrocarbon generation. Other web services provide data to characterise source rock extracts (i.e., solvent extracted organic matter), fluid inclusions and petroleum (e.g., natural gas, crude oil, bitumen) through the reporting of their bulk properties (e.g., API gravity, elemental composition) and molecular composition using gas chromatography (GC) and gas chromatography-mass spectrometry (GC-MS). Also reported are the stable isotope ratios of carbon, hydrogen, nitrogen, oxygen and sulfur using gas chromatography-isotope ratio mass spectrometry (GC-IRMS) and noble gas isotope abundances using ultimate high-resolution variable multicollection mass spectrometry. The stable isotopes of carbon, oxygen and strontium are also reported for sedimentary rocks containing carbonate either within the mineral matrix or in cements. Interpretation of these data enables the characterisation of petroleum source rocks and identification of their derived petroleum fluids, which comprise two key elements of petroleum systems analysis. Understanding a fluid’s physical properties and molecular composition are prerequisites for field development. The composition of petroleum determines its economic value and hence why the concentration of hydrocarbons (methane, wet gases, light and heavy oil) and hydrogen, helium and argon are important relative to those of nitrogen, carbon dioxide and hydrogen sulfide for gases, and heterocyclic compounds (nitrogen, oxygen or sulfur) found in the asphaltene, resin and polar fractions of crude oils. The web services and tools in the Geoscience Australia Data Discovery Portal (https://portal.ga.gov.au/), and specifically in the Source Rock and Fluid Atlas Persona (https://portal.ga.gov.au/persona/sra), allow the users to search, filter and select data based on various criteria, such as basin, formation, sample type, analysis type, and specific geochemical parameters. The web map services (WMS) and web feature services (WFS) enable the user to download data in a variety of formats (csv, Json, kml and shape file). The Source Rock and Fluid Atlas supports national resource assessments. The focus of the atlas is on the exploration and development of energy resources (i.e., petroleum and hydrogen) and the evaluation of resource commodities (i.e., helium and graphite). Some data held in the ORGCHEM tables are used for enhanced oil recovery and carbon capture, storage and utilisation projects. The objective of the atlas is to empower people to deliver Earth science excellence through data and digital capability. It benefits users who are interested in the exploration and development of Australia's energy resources by: • Providing a comprehensive and reliable source of information on the organic geochemistry of Australian source rocks • Enhancing the understanding of the spatial distribution, quality, and maturity of petroleum source rocks. • Facilitating the mapping of total petroleum and hydrogen systems and the assessment of the petroleum and hydrogen resource potential and prospectivity of Australian basins. • Facilitating the mapping of gases (e.g., methane, helium, carbon dioxide) within the geosphere as part of the transition to clean energy. • Enabling the integration and comparison of data from diverse sources and various acquisition methods, such as geological, geochemical, geophysical and geospatial data. • Providing data for integration into enhanced oil recovery and carbon capture, storage and utilisation projects. • Improving the accessibility and usability of data through user-friendly and interactive web-based interfaces. • Promoting the dissemination and sharing of data among Government, industry and community stakeholders. <b>References</b> Australian Petroleum Cooperative Research Centre (APCRC) 1991-2003. Australian Petroleum CRC (1991 - 2003), viewed 6 May 2024, https://www.eoas.info/bib/ASBS00862.htm and https://www.eoas.info/biogs/A001918b.htm#pub-resources Boreham, C. 1990. ORGCHEM Organic geochemical database. BMR Research Newsletter 13. Record 13:10-10. Geoscience Australia, Canberra. https://pid.geoscience.gov.au/dataset/ga/90326 Edwards, D.S., MacFarlane, S., Grosjean, E., Buckler, T., Boreham, C.J., Henson, P., Cherukoori, R., Tracey-Patte, T., van der Wielen, S.E., Ray, J., Raymond, O. 2020. Australian source rocks, fluids and petroleum systems – a new integrated geoscience data discovery portal for maximising data potential. Geoscience Australia, Canberra. http://dx.doi.org/10.11636/133751. <b>Citation</b> Edwards, D., Buckler, T. 2024. Organic Geochemistry (ORGCHEM) Schema. Australian Source Rock and Fluid Atlas. Geoscience Australia, Canberra. https://pid.geoscience.gov.au/dataset/ga/149422

The Otway Basin is a northwest-southeast trending rift basin which spans from onshore Victoria and South Australia into the deep-water offshore. The prospective supersequences within the basin are largely of Cretaceous age which host three possible petroleum systems (Austral 1, 2 and 3). While there is production from onshore depocentres, and the inboard Shipwreck Trough, the majority of the offshore basin remains underexplored. Recent regional studies have highlighted the need for further work across the underexplored parts of the basin and here we focus on the offshore northwest Otway Basin, integrating reinterpreted historical well data, newly acquired and recently reprocessed seismic data. This new Well Folio consists of composite logs and supporting data which includes interpreted lithologies, petrophysical analyses, the analysis of historic organic geochemistry and organic petrology. In addition, updated well markers are provided based on seismic interpretation and new biostratigraphy in key wells. This integrated study provides the basis for renewed prospectivity assessment in the northwest offshore portion of the Otway Basin.

<div>The Proterozoic basins of northern Australia have been the focus of regional hydrocarbon prospectivity studies undertaken by the Exploring for the Future&nbsp;program dedicated to increasing investment in resource exploration in northern Australia. As part of this program, a compilation of the compound-specific isotopic compositions of linear alkanes in source extracts, oils and oil stains from 21 boreholes&nbsp;of the greater McArthur Basin has been completed. The samples were analysed in Geoscience Australia’s Isotope and Organic Geochemistry Laboratory and the stable carbon and hydrogen isotopic data of individual alkanes are released in this report. </div>

The Cooper Basin is Australia's premier onshore hydrocarbon producing province and hosts a range of conventional and unconventional gas play types. This study investigates the petroleum generation potential of the basin's major Permian source rocks, to improve regional understanding of the basin's hydrocarbon prospectivity. Source rock distribution, thickness, present-day amount of total organic carbon (TOC), quality (Hydrogen Index) and maturity were mapped across the basin, together with original source quality maps prior to the on-set of generation. Results of the source rock property mapping and basin-specific kinetics were integrated with 1D burial and thermal history models and a 3D basin model to create a regional pseudo-3D petroleum system model for the basin. The modelling outputs quantify the spatial distribution of both the maximum possible hydrocarbon yield, as well as the oil/ gas expelled and retained, for ten Permian source rocks. Monte Carlo simulations were used to quantify the uncertainty associated with hydrocarbon yields and to highlight the sensitivity of results to each input parameter. The principal source rocks are the Permian coal and coaly shales of the Gidgealpa Group, with highest potential yields from the Patchawarra Formation coals and coaly shales. The broad extent of the Cooper Basin's Permian source kitchen and its large total generation potential (P50 scenario >2000 bboe) highlights the basin¿s significance as a world-class hydrocarbon province. The difference between the P90 (~800 bboe) and P10 (>4000 bboe) scenarios demonstrate the range of uncertainties inherent in this modelling.