<p>The Roebuck Basin on Australia’s offshore north-western margin is the focus of a regional hydrocarbon prospectivity assessment being undertaken by the North West Margin Energy Studies Section (NWMES). This offshore program is designed to produce pre-competitive information to assist with the evaluation of the hydrocarbon resource potential of the central North West Shelf and attract exploration investment to Australia. <p>The recent oil and gas discoveries at Phoenix South 1 (2014), Roc 1 (2015-16), Roc 2 (2016), Phoenix South 2 (2016), Phoenix South 3 (2018) and Dorado 1 (2018) in the Bedout Sub-basin demonstrate the presence of a petroleum system in Lower Triassic strata. The current study aims to better understand this new petroleum system and establish its extent. <p>As part of this program, TOC and Rock-Eval pyrolysis analyses were undertaken by Geoscience Australia on selected rock samples from the well Roc 2 to establish their hydrocarbon-generating potential and thermal maturity.

The Roebuck Basin and the adjoining Beagle and Barcoo sub-basins are underexplored areas on Australia’s North West Shelf that are undergoing renewed exploration interest since the discovery of oil at Phoenix South 1 in 2014 and subsequent hydrocarbon discoveries in the Bedout Sub-basin. A well folio of 24 offshore wells across the Beagle, Bedout, Rowley and Barcoo sub-basins has been compiled as part of Geoscience Australia’s hydrocarbon prospectivity assessment across the region. It consists of composite well log plots and well correlations that summarise lithology, lithostratigraphy, Geoscience Australia’s newly acquired biostratigraphic and geochemical data as well as results of petrophysical analysis. A revised sequence-stratigraphic interpretation, key petroleum system elements and drilling results are also documented. The wells dominantly target Triassic shoreward facies (Keraudren Formation) as the primary reservoir objective and Jurassic fluvial-deltaic (Depuch Formation) and/or Lower Cretaceous sandy deltaic facies as the secondary objective. The Keraudren Formation sandstones are sealed intra-formationally either by discontinuous units and/or by the regional Cossigny Member. The Jurassic Depuch Formation sandstones are sealed by regional Lower Cretaceous mudstones. Both charge and structure have been identified as critical issues in the Roebuck Basin. In the Beagle Sub-basin, seal integrity and migration pathways are also considered high risk. Well correlations have identified differences in the basin history and provide insights into the distribution of facies and other characteristics of the Jurassic and Triassic successions. <b>Citation:</b> Nguyen Duy, Rollet Nadege, Grosjean Emmanuelle, Edwards Dianne S., Abbott Steve, Orlov Claire, Bernardel George, Nicholson Chris, Kelman Andrew, Khider Kamal, Buckler Tamara (2019) The Roebuck Basin, Beagle and Barcoo Sub-basin well folio. <i>The APPEA Journal</i><b> 59</b>, 920-927.

The Roebuck Basin on Australia’s offshore north-western margin is the focus of a regional hydrocarbon prospectivity assessment being undertaken by the Offshore Energy Systems Section. This offshore program is designed to produce pre-competitive information to assist with the evaluation of the hydrocarbon resource potential of the central North West Shelf and attract exploration investment to Australia. As part of this program, molecular and isotopic analyses were undertaken by Geoscience Australia on gas samples from the well Dorado 1 and the raw data from these analyses are released in this report.

<div>The Roebuck Basin on Australia’s offshore north-western margin is the focus of regional energy exploration activity. Drilling in the Roebuck Basin resulted in oil and gas discoveries at Phoenix South&nbsp;1 (2014), Roc&nbsp;1 (2015–2016) and Dorado&nbsp;1 (2018) in the Bedout Sub-basin (Figure 1‑2) and demonstrated the presence of a petroleum system in Lower Triassic strata. These discoveries have been evaluated for development and production with infill drilling at Roc&nbsp;2 (2016), Phoenix South&nbsp;2 (2016), Phoenix South&nbsp;3 (2018), Dorado&nbsp;2 (2019), and Dorado&nbsp;3 (2019). Recent drilling by Santos (2022) has resulted in the discovery of oil at Pavo&nbsp;1 (2022) and hydrocarbon shows at Apus&nbsp;1 (2022).</div><div><br></div><div>To complement this industry work, Geoscience Australia’s Offshore Energy Systems program produces pre-competitive information to assist with the evaluation of the energy and resource potential of the central North West Shelf, including both hydrogen and helium resources, and to attract exploration investment to Australia. As part of this program, determination of the molecular and noble gas isotopic composition of natural gases from selected petroleum wells in the Roebuck Basin were undertaken by Smart Gas Sciences, under contract to Geoscience Australia, with results from these analyses being released in this report. This report provides additional gas data to determine the sources of natural gases in the Roebuck Basin and build on previously established gas-gas correlations. Noble gas isotopic data can be used in conjunction with carbon and hydrogen isotopic data to determine the origin of both inorganic and organic (hydrocarbon) gases. This information can be used in future geological programs to determine the source and distribution of hydrogen and helium in natural gases and support acreage releases by the Australian Government.</div><div><br></div>

The Roebuck Basin on Australia’s offshore north-western margin is the focus of a regional hydrocarbon prospectivity assessment being undertaken by the Offshore Energy Systems Section. This offshore program is designed to produce pre-competitive information to assist with the evaluation of the hydrocarbon resource potential of the central North West Shelf and attract exploration investment to Australia. The recent oil and gas discoveries at Phoenix South 1 (2014), Roc 1 (2015-16), Roc 2 (2016), Phoenix South 2 (2016), Phoenix South 3 (2018), Dorado 1 (2018) and Dorado 2–3 (2019) in the Bedout Sub-basin demonstrate the presence of a petroleum system in Lower Triassic strata (Grosjean et al., 2021; Rollet et al., 2019). As part of this program, a range of organic geochemical analyses were acquired on petroleum fluids from the Dorado 1 and Roc 2 wells with these data released in this report.

In 2014, the surprise discovery of oil in the well Phoenix South 1 on Australia’s North West Shelf (NWS) heralded the Bedout Sub-basin as Australia’s new petroleum province. The well had initially targeted gas in Triassic reservoirs of the Keraudren Formation and Locker Shale but unexpectedly encountered oil instead. This has fuelled a revival of exploration in the area with subsequent wells Roc 1, Roc 2, Phoenix South 2 and Dorado 1 all successful in penetrating hydrocarbon columns. The Phoenix South 1 accumulation is significant as it demonstrates the occurrence of an effective oil-prone source rock within the Lower–Middle Triassic for the first time on the NWS. It also raised the possibility that a source rock analogue to the Hovea Member of the Lopingian–Lower Triassic Kockatea Shale, a well-established source of oil and gas in the northern Perth Basin, may also be effective on the NWS. In order to understand the origin of the Phoenix South 1 accumulation, its geochemical composition was compared to those of Triassic-sourced oils from the Perth Basin and petroleum fluids from the neighbouring Browse Basin, and Beagle and Dampier sub-basins.

The Roebuck Basin on Australia’s offshore north-western margin is the focus of a regional hydrocarbon prospectivity assessment being undertaken by the Offshore Energy Studies section. This offshore program is designed to produce pre-competitive information to assist with the evaluation of the hydrocarbon resource potential of the central North West Shelf and facilitate exploration investment in Australia. The recent oil and gas discoveries at Phoenix South 1 (2014), Roc 1 (2015-16), Roc 2 (2016), Phoenix South 2 (2016), Phoenix South 3 (2018), Dorado 1 (2018), Dorado 2 (2019) and Dorado 3 (2019) wells in the Bedout Sub-basin demonstrate the presence of a petroleum system in Lower Triassic strata (Thompson, 2020; Thompson et al., 2015 and 2018). The current study aims to better understand this new petroleum system and establish its extent. As part of this program, a range of organic geochemical analyses were acquired on source rocks from the Roc 2 well with these data released in this report.

<p>The Roebuck Basin on Australia’s offshore north-western margin is the focus of a regional hydrocarbon prospectivity assessment being undertaken by the North West Margin Energy Studies Section (NWMES). This offshore program is designed to produce pre-competitive information to assist with the evaluation of the hydrocarbon resource potential of the central North West Shelf and attract exploration investment to Australia. <p>The recent oil and gas discoveries at Phoenix South 1 (2014), Roc 1 (2015-16), Roc 2 (2016), Phoenix South 2 (2016), Phoenix South 3 (2018) and Dorado 1 (2018) in the Bedout Sub-basin demonstrate the presence of a petroleum system in Lower Triassic strata. The current study aims to better understand this new petroleum system and establish its extent. <p>As part of this program, compositional and isotopic analyses were undertaken by Geoscience Australia on gas samples from the wells Roc 1 and Roc 2 and data from these analyses are released in this dataset.

<p>The Roebuck Basin and adjoining Beagle Sub-basin are underexplored areas on Australia’s North West Shelf and are undergoing renewed exploration interest since the discovery of oil at Phoenix South 1 and gas at Roc 1, 2 in the Bedout Sub-basin. A well folio of 24 offshore wells across the Beagle, Bedout, Rowley and Barcoo sub-basins was completed as part of Geoscience Australia’s assessment of hydrocarbon prospectivity across the region. The study consists of composite well log plots summarising lithology, stratigraphy, GA’s newly acquired biostratigraphic and geochemical data and petrophysical analysis, in conjunction with revised sequence interpretations. <p>The wells included in the well folio package are: <p>Anhalt 1, Barcoo 1 ST2, Bedout 1, Bruce 1, Cossigny 1, De Grey 1A ST1, Delambre 1, Depuch 1, East Mermaid 1B ST1, Hanover South 1, Huntsman 1, Keraudren 1. Lagrange 1, Minilya 1, Nebo 1, Omar 1, Phoenix 1, Phoenix 2, Phoenix South 1 ST1 ST2, Picard 1, Poissonnier 1, Roc 1, Steel Dragon 1 and Wigmore 1

The unexpected discovery of oil in Triassic sedimentary rocks of the Phoenix South 1 well on Australia’s North West Shelf (NWS) has catalysed exploration interest in pre-Jurassic plays in the region. Subsequent neighbouring wells Roc 1–2, Phoenix South 2–3 and Dorado 1–3 drilled between 2015 and 2019 penetrated gas and/or oil columns, with the Dorado field containing one of the largest oil resources found in Australia in three decades. This study aims to understand the source of the oils and gases of the greater Phoenix area, Bedout Sub-basin using a multiparameter geochemical approach. Isotopic analyses combined with biomarker data confirm that these fluids represent a new Triassic petroleum system on the NWS unrelated to the Lower Triassic Hovea Member petroleum system of the Perth Basin. The Bedout Sub-basin fluids were generated from source rocks deposited in paralic environments with mixed type II/III kerogen, with lagoonal organofacies exhibiting excellent liquids potential. The Roc 1–2 gases and the Phoenix South 1 oil are likely sourced proximally by Lower–Middle Triassic TR10–TR15 sequences. Loss of gas within the Phoenix South 1 fluid due to potential trap breach has resulted in the formation of in-place oil. These discoveries are testament to new hydrocarbon plays within the Lower–Middle Triassic succession on the NWS.