Abstract
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.
Highlights
In 2014, the surprise discovery of oil in Phoenix South 1 on Australia’s North West Shelf (NWS) heralded the Bedout Subbasin as a new oil province in Australia (Fig. 1a)
The Dorado oil field, discovered in 2018 and located about 40 km south of Phoenix South 1, is one of the largest oil resources found in Australia in decades (Weller and Amiribesheli 2018; Cockerill 2020) and confirms the magnitude of the resources in the Bedout Sub-basin
Whether these discoveries represent a new oil province is challenged by the presence of gas in the Greater Phoenix area wells, Roc 1–2, Phoenix South 2–3 and Dorado 1–3
Summary
In 2014, the surprise discovery of oil in Phoenix South 1 on Australia’s North West Shelf (NWS) heralded the Bedout Subbasin as a new oil province in Australia (Fig. 1a). The Dorado oil field, discovered in 2018 and located about 40 km south of Phoenix South 1, is one of the largest oil resources found in Australia in decades (Weller and Amiribesheli 2018; Cockerill 2020) and confirms the magnitude of the resources in the Bedout Sub-basin. Whether these discoveries represent a new oil province is challenged by the presence of gas in the Greater Phoenix area wells, Roc 1–2, Phoenix South 2–3 and Dorado 1–3. Oil field Gas field Basin outline Sub-basin outline Major fault Minor fault Petroleum well Oil discovery Gas discovery Oil and gas discovery Gas discovery and oil show Oil show Gas show Dry hole (b)
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