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.

Exploring for the Future (EFTF) is a four-year $100.5 million initiative by the Australian Government conducted by Geoscience Australia in partnership with state and Northern Territory government agencies, CSIRO and universities to provide new geoscientific datasets for frontier regions. As part of this program, Geoscience Australia acquired two new seismic surveys that collectively extend across the South Nicholson Basin (L120 South Nicholson seismic line) and into the Beetaloo Sub-basin of the McArthur Basin (L212 Barkly seismic line). Interpretation of the seismic has resulted in the discovery of new basins that both contain a significant section of presumed Proterozoic strata. Integration of the seismic results with petroleum and mineral systems geochemistry, structural analyses, geochronology, rock properties and a petroleum systems model has expanded the knowledge of the region for energy and mineral resources exploration. These datasets are available through Geoscience Australia’s newly developed Data Discovery Portal, an online platform delivering digital geoscientific information, including seismic locations and cross-section images, and field site and well-based sample data. Specifically for the EFTF Energy project, a petroleum systems framework with supporting organic geochemical data has been built to access source rock, crude oil and natural gas datasets via interactive maps, graphs and analytical tools that enable the user to gain a better and faster understanding of a basin’s petroleum prospectivity. <b>Citation:</b> Henson Paul, Robinson David, Carr Lidena, Edwards Dianne S., MacFarlane Susannah K., Jarrett Amber J. M., Bailey Adam H. E. (2020) Exploring for the Future—a new oil and gas frontier in northern Australia. <i>The APPEA Journal</i><b> 60</b>, 703-711. https://doi.org/10.1071/AJ19080

<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.

Presentation from the Exploring for the Future Roadshow on the Energy prospectivity of the South Nicholson region, regional geochemical data acquisition and shale gas prospectivity analysis.

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 the bulk kerogen kinetics of 21 potential source rocks from the McArthur Basin and the Lawn Hill Platform to understand the rate of hydrocarbon conversion. Kerogen was isolated from bulk rock, and analysed by a Rock-Eval 6 (Vinci Technologies, France) using four different temperature ramps. All sample preparation and analyses were carried out in Geoscience Australia’s in-house laboratories. The results of this study can be used to improve our understanding of the hydrocarbon generative potential of Proterozoic aged source rocks in northern Australia.

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 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.

The Exploring for the Future program is an initiative by the Australian Government dedicated to boosting investment in resource exploration in Australia. The initial phase of this program led by Geoscience Australia focussed on northern Australia to gather new data and information about the potential mineral, energy and groundwater resources concealed beneath the surface. The northern Lawn Hill Platform is an intracratonic poly-phased history region of Paleoproterozoic to Mesoproterozic age consisting of mixed carbonates, siliciclastics and volcanics. It is considered a frontier basin with very little petroleum exploration to date, but with renewed interest in shale and tight gas, that may present new exploration opportunities. An understanding of the geochemistry of the sedimentary units, including the organic richness, hydrocarbon-generating potential and thermal maturity, is therefore an important characteristic needed to understand the resource potential of the region. As part of this program, Rock-Eval pyrolysis analyses were undertaken by Geoscience Australia on selected rock samples from 2 wells of the northern Lawn Hill Platform.

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 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. The physical properties of organic matter in sedimentary rocks changes composition in an irreversible and often sequential manner after burial, diagenesis, catagenesis and metagenesis with increasing thermal maturity. Characterising these changes and identifying the thermal maturity of sedimentary rocks is essential for calculating thermal models needed in a petroleum systems analysis. This study presents organic petrology on 15 Proterozoic aged shales 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 the thermal maturity and hydrocarbon prospectivity of Proterozoic aged sedimentary basins in northern Australia.