First Published: GEO ExPro, December 2015

 

Abstract

The 2014 Phoenix South-1 well drilled offshore Western Australia has confirmed at least four discrete oil columns in the Triassic Lower Keraudren Formation. The discovery of exceptionally good quality light oil with a high API gravity and favourable mobility represents one of the most significant developments in the region in recent times. The discovery, made whilst searching for the extension of discovered gas, represents a new oil province for Australia.
Polarcus’ Capreolus multi-client 3D survey offshore Western Australia covers an area of 22,130 km2, the largest single 3D survey ever acquired off Australia. The new data spans parts of the North Carnarvon and Roebuck Basins, providing exploration companies with an extensive regional high quality broadband 3D seismic dataset over this underexplored frontier. The Phoenix South discovery opens up the potential for a new oil province across an area historically only considered prospective for gas, with the oils derived from a Lower Triassic source interval clearly imaged on the new seismic. The new 3D data covers the Phoenix structure and allows investigation of the extent of the new oil province across the region.

A New Oil Province Offshore the North West Shelf

The Australian North West Shelf is comprised of four areas, namely the Carnarvon, Roebuck/Offshore Canning, Browse and Bonaparte Basins. These are filled with a thick sequence of late Palaeozoic, Mesozoic and Cenozoic successions. The area formed part of the Gondwana Supercontinent during the Palaeozoic, but by the Permian rift development had initiated in response to regional extension. Continental break-up began in the early Jurassic, resulting in deposition of syn and post-rift Jurassic to Cenozoic successions.

Figure: Incoherency plot showing the extent of faulting affecting the Jurassic sequence at 3.5 sec TWT in the Northern Carnarvon Basin.

The northernmost part of this basin consists of the Beagle Sub-basin and the Exmouth Plateau. Depositional environments consisted of siliciclastic deltaic to marine sequences throughout the Triassic to the Cretaceous. Early to Middle Jurassic rifting occurred followed by deposition of Late Cretaceous to Cenozoic carbonates during post-rift thermal sag.

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