Legacy dataset from the NABRE Project, comprising multi-spectral gamma logs obtained on different drill core in the Mount Isa Province to McArthur Basin regions (Northern Territory and Queensland).

This report highlights results of petroleum systems analysis undertaken on the northern Lawn Hill Platform area of the Isa Superbasin, specifically focusing on burial and thermal history modelling. A second report will highlight the results of the source rock analysis and maturity modelling.

The Geological and Bioregional Assessments (GBA) Program is a series of independent scientific studies undertaken by Geoscience Australia and the CSIRO, supported by the Bureau of Meteorology, and managed by the Department of Agriculture, Water and the Environment. The Program consists of three stages across three regions with potential to deliver gas to the East Coast Gas Market. Stage 1 was a rapid regional prioritisation conducted by Geoscience Australia, to identify those sedimentary basins with the greatest potential to deliver shale and/or tight gas to the East Coast Gas Market within the next five to ten years. This prioritisation process assessed 27 onshore eastern and northern Australian basins with shale and/or tight gas potential. Further screening reduced this to a shortlist of nine basins where exploration was underway. The shortlisted basins were ranked on a number of criteria. The Cooper Basin, the Beetaloo Sub-basin and the Isa Superbasin were selected for more detailed assessment. Stage 2 of the program involved establishing a baseline understanding of the identified regions. Geoscience Australia produced regional geological evaluations and conceptualisations that inform the assessment of shale and/or tight gas prospectivity, ground- and surface-water impacts, and hydraulic fracturing models. Geoscience Australia’s relative prospectivity assessments provide an indication of where viable petroleum plays are most likely to be present. These data indicate areal and stratigraphic constraints that support the program’s further work in Stage 3, on understanding likely development scenarios, impact assessments, and causal pathways. <b>Citation:</b> Hall Lisa S., Orr Meredith L., Lech Megan E., Lewis Steven, Bailey Adam H. E., Owens Ryan, Bradshaw Barry E., Bernardel George (2021) Geological and Bioregional Assessments: assessing the prospectivity for tight, shale and deep-coal resources in the Cooper Basin, Beetaloo Subbasin and Isa Superbasin. <i>The APPEA Journal</i><b> 61</b>, 477-484. https://doi.org/10.1071/AJ20035

The energy component of Geoscience Australia’s Exploring for the Future (EFTF) program aimed to improve our understanding of the petroleum resource potential of northern Australia. The sediments of the Mesoproterozoic South Nicholson Basin and the Paleoproterozoic Isa Superbasin on the northern Lawn Hill Platfrom (nLHP) are primary targets of the EFTF program, as they are known to contain highly prospective organic-rich units with the potential to host unconventional gas plays. A defining feature of shale gas plays is that they require technological intervention to increase bulk rock permeability and achieve commercial flow rates. The Egilabria prospect, intersecting nLHP sediments in northwest Queensland, flowed gas to surface from a fracture-stimulated lateral well, demonstrating a technical success. Elsewhere in the region, shale gas prospectivity is limited by a lack of well data. Shale rock brittleness in the nLHP part of the Isa Superbasin was analysed in two studies under the EFTF program. These studies showed that shale brittleness ranges from ductile to brittle; zones of brittle shales were present in all supersequences. Shale brittleness is controlled by increasing quartz and decreasing clay content, with carbonate content proving insignificant. Organic-rich target zones in the Lawn and River supersequences are demonstrated to be brittle and favourable for fracture stimulation. <b>Citation:</b> Bailey, A.H.E., Jarrett, A.J.M., Wang, L., Champion, D.C., Hall, L.S. and Henson, P., 2020. Shale brittleness in the Isa Superbasin on the northern Lawn Hill Platform. In: Czarnota, K., Roach, I., Abbott, S., Haynes, M., Kositcin, N., Ray, A. and Slatter, E. (eds.) Exploring for the Future: Extended Abstracts, Geoscience Australia, Canberra, 1–4.

The Proterozoic was an important eon which saw profound changes in the geochemistry of the oceans and the first appearance and proliferation of complex life [1]. In this study we examine the relationships between organic matter and ocean geochemistry in sedimentary sequences in Northern Australia. The geobiology of the McArthur Basin has been comprehensively studied and characterised. The ca. 1.3 Ga Velkerri Formation within the Roper Superbasin is predominantly ferruginous with episodes of euxinia coupled to enhanced primary productivity [2]. In contrast, black carbonaceous shales of the ca. 1.6 Ga Fraynes and Barney Creek Formations are pervasively anoxic and euxinic [3]. The latter formation is dominated by aromatic isoprenoids, biomarkers for green and purple sulfur bacteria commonly associated with photic zone euxinia [4]. In contrast, little attention has been given to the likely coeval South Nicholson Basin and Lawn Hill Platform located directly south of the McArthur Basin, straddling the Queensland and Northern Territory border. Here we provide new insights into the paleo-environments of Paleoproterozoic and Mesoproterozoic sedimentary successions in the Lawn Hill Platform and South Nicholson Basin based on multi-proxy sedimentary geochemical analyses including biomarkers, isotopes (?13C, ?15N and ?34S) and trace metals. The results in this study while preliminary at present, demonstrate redox heterogeneity with oscillations between ferruginous and euxinic conditions broadly correlating with increases in total organic carbon content. Complexities in the data remain including potential influences of hydrothermal alteration on the thermal evolution, and mobility and abundances of trace metals in some sections of the basins. Abstract submitted to/presented at the 2018 Australian Geoscience Council Convention (AGCC)

Shale gas plays require technology such as fracture stimulation to increase rock permeability and achieve commercial rates of flow. The brittleness of shales are a major control on the ease of fracture stimulation. The Brittleness Index (BI) is a proxy for rock strength, based on geomechanical parameters, and/or rock mineralogy, and provides an indication of hydraulic stimulation effectiveness. Legacy drill core does not always have the geophysical logs needed for assessment of shale brittleness, therefore mineralogical and geochemical derived proxies for shale brittlenesss are often used with varying success. Shales from the Paleoproterozoic Lawn Hill Platform of north-west Queensland and the Northern Territory are known to contain organic-rich sedimentary units with the potential to host shale-gas plays. The Egilabria 2 DW1 well demonstrated a technical success in flowing gas from the Lawn Supersequence and recent geomechanical logging in the Egilabria prospect have demonstrated the presence of brittle rocks favourable for fracture stimulation with similarities between logged geophysics and X-Ray Diffraction (XRD) derived brittleness (Bailey et al., 2019). In this study we assess the brittleness of shales from twelve wells across the Isa Superbasin that do not have geophysical log data using XRD, major elemental analyses from X-Ray Fluorescence (XRF) and mineral carbon (MinC) techniques. The results of this study demonstrate highly variable mineral components between all analysed supersequences. The brittleness index (BI) of the shales derived from XRD ranges from ductile to brittle with zones of brittle shales present in all supersequences. Shale brittleness is controlled by increasing quartz and decreasing clay content with little influence from carbonates. Major elements based on XRF showed moderate to poor correlations to mineral type and the brittleness index was significantly higher than the results calculated by XRD. XRF analyses are not recommended as a proxy for shale brittleness in the Isa Superbasin region. The MinC parameter was highly effective as a proxy for carbonate based on comparisons with XRD derived carbonate concentrations. An important finding in this study is the variations in BI and TOC between supersequences, and within supersequences. This is evident down-hole and spatially across the area sampled. Future work is needed to investigate sweet spots for shale gas production.

The main aim of this study is to use petroleum systems analysis to improve the understanding of the petroleum systems present on the Lawn Hill Platform of the Isa Superbasin. Part A of this report series reported the results of burial and thermal modelling of two wells (Desert Creek 1 and Egilabria 1). Results from the 1-D modelling help other aspects of interest such as the hydrocarbon generation potential and distribution of hydrocarbons by source rock which this publication presents. Modelling uncertainties are reported and described, highlighting knowledge gaps and areas for further work.

Seismic reflection mapping, geochemical analyses and petroleum systems modelling have increased our understanding of the highly prospective Mesoproterozoic and Paleoproterozoic source rocks across northern Australia, expanding the repertoire of exploration targets currently being exploited in Proterozoic petroleum systems. Data collected during the Exploring for the Future program have enabled us to redefine and increase the extent of regional petroleum systems, which will encourage additional interest and exploration activity in frontier regions. Here, we present a review of the Paleoproterozoic McArthur and Mesoproterozoic Urapungan petroleum supersystems, and the most up-to-date interpretation of burial and thermal history modelling in the greater McArthur Basin (including the Beetaloo Sub-basin), South Nicholson Basin and Isa Superbasin. We also present potential direct hydrocarbon indicators imaged in the 2017 South Nicholson Deep Crustal Seismic Survey that increase the attractiveness of this frontier region for hydrocarbon exploration activities. <b>Citation:</b> MacFarlane, S.K., Jarrett, A.J.M., Hall, L.S., Edwards, D., Palu, T.J., Close, D., Troup, A. and Henson, P., 2020. A regional perspective of the Paleo- and Mesoproterozoic petroleum systems of northern Australia. In: Czarnota, K., Roach, I., Abbott, S., Haynes, M., Kositcin, N., Ray, A. and Slatter, E. (eds.) Exploring for the Future: Extended Abstracts, Geoscience Australia, Canberra, 1–4.

<p>The Isa Superbasin is a Paleoproterozoic to Mesoproterozoic succession (approximately 1670-1575 Ma), primarily described in north-west Queensland. Despite the basin’s frontier status, recent exploration in the northern Lawn Hill Platform has demonstrated shale gas potential in the Lawn and River supersequences. Here, we characterise the unconventional reservoir properties of these supersequences, providing new insights into regional shale gas prospectivity. <p>The depths, thicknesses and mappable extents of the Lawn and River supersequences are based on the 3D geological model of Bradshaw et al. (2018). Source rock net thickness, total organic carbon (TOC), kerogen type and maturity are characterised based on new and existing Rock-Eval and organic petrology data, integrated with petroleum systems modelling. Petrophysical properties, including porosity, permeability and gas saturation, are evaluated based on well logs. Mineralogy is used to calculate brittleness (see also Jarrett et al., 2019, this volume). Regional stress and pressure regimes are also reviewed. <p>Abundant source rocks are present in the Isa Superbasin succession. Overall, shale rock characteristics were found to be favourable for both sequences assessed; both the Lawn and River supersequences host thick, extensive, and organically rich source rocks with up to 7.1 wt% total organic carbon (TOC) in the Lawn Supersequence and up to 11.3 wt% TOC in the River Supersequence. Net shale thicknesses demonstrate an abundance of potential shale gas reservoir units across the Lawn Hill Platform. <p>With average brittleness indices of greater than 0.5, both the Lawn and River supersequences are interpreted as likely to be favourable for fracture stimulation. As-received total gas content from air-dried samples is favourable, with average values of 0.909 scc/g for the Lawn Supersequence and 1.143 scc/g for the River Supersequence <p>The stress regime in the Isa Superbasin and the surrounding region is poorly defined; however, it is likely dominated by strike-slip faulting. Modelling demonstrates limited stress variations based on both lithology and the thickness of the overlying Phanerozoic basins, resulting in likely inter- and intra-formational controls over fracture propagation. No evidence of overpressure has been observed to date, however, it is possible that overpressures may exist deeper in the basin where less permeable sediments exist. <p>This review of the shale reservoir properties of the Lawn and River supersequences of the Isa Superbasin significantly improves our understanding of the distribution of potentially prospective shale gas plays across the Lawn Hill Platform and more broadly across this region of northern Australia.

The Energy component of Geoscience Australia’s Exploring for the Future (EFTF) Programme is aimed at improving our understanding of the petroleum resource potential of northern Australia, in partnership with the state and territory geological surveys. The sediments of the Mesoproterozoic South Nicholson Basin and the underlying Paleoproterozoic Isa Superbasin in the Northern Territory and Queensland are amongst the primary targets of the EFTF Energy program as they are known to contain organic rich sedimentary units with the potential to host unconventional gas plays, although their subsurface extent under the cover of the Georgina Basin is presently unknown. In order to economically produce from unconventional reservoirs, the petrophysical rock properties and in-situ stresses must be conducive to the creation of secondary permeability networks that connect a wellbore to as large a reservoir volume as possible. This study utilises data from the recently drilled Armour Energy wells Egilabria 2, Egilabria 2-DW1, and Egilabria 4 to constrain rock properties and in-situ stresses for the Isa Superbasin sequence where intersected on the Lawn Hill Platform of northwest Queensland. These results have implications for petroleum prospectivity in an area with proven gas potential, which are discussed here in the context of the rock properties and in-situ stresses desired for a viable shale gas play. In addition, this has relevance to potential future exploration across the broader Isa Superbasin sequence.