Browse Basin

The Browse Basin covers about 223 000 km² and lies entirely offshore, north of Broome. It contains an upper Paleozoic to Cenozoic sedimentary section up to 15 km thick. About 1600 km² surrounding Scott and Seringapatum Reefs is under State jurisdiction and includes part of the Torosa gasfield and the Zephyros 1 gas discovery.

Geological setting

The basin borders Phanerozoic basins to the south (Roebuck and Canning) and northeast (Bonaparte), and onlaps onto the Paleoproterozoic Kimberley Basin to the southeast. The oldest known successions in the basin are Upper Carboniferous to Lower Permian near the southeastern basin margin, which represent erosional remnants whereas the only other sections older than Late Permian known in the basin are within salt diapirs.

The sedimentary succession of the Browse Basin spans a regional late Middle Jurassic unconformity. The strata below are deeply buried and extensively block-faulted. Overlying the breakup unconformity are up to 4000 m of relatively undisturbed Upper Jurassic to Cenozoic marine facies with small faults and anticlines that developed during the Late Cenozoic collision of the Australasian and Eurasian plates.

Exploration commenced in the Browse Basin in 1967 when the first seismic data was acquired. Within the area surrounding Scott Reef there have been about 3100 line-km of 2D seismic data recorded, and about half of the area is covered by six partially overlapping 3D surveys. The third well drilled in the basin, Scott Reef 1 (completed in 1971), discovered one of Australia’s largest gasfields (renamed Torosa) within the Lower to Middle Jurassic Plover Formation.

Since then, over 140 wells have been drilled across the basin yielding over 25 hydrocarbon discoveries including the Ichthys (2003) and Prelude (2006) gasfields. Discoveries since 2011 include the Bassett West 1, Boreas 1, Crown 1, Lasseter 1, Pharos 1, Poseidon North 1, Proteus 1 and Zephyros 1.

Although the combined gas reserves of the fields in the basin total over 900 Gm³ (33.4 thousand cubic feet), only two have been developed, mainly due to their isolated location in deep waters. Production from Ichthys (operated by Inpex), which commenced in 2018, is sent to Darwin via the 890 km-long Ichthys Gas Export Pipeline. Prelude (operated by Shell) commenced production in 2018 via a floating liquefied natural gas (FLNG) facility. Development of Woodside’s Brecknock, Calliance and Torosa fields has been delayed.

Prospectivity

A surge in exploration between 2007 and 2014 yielded a highly encouraging hydrocarbon discovery rate. Reservoirs generally lie at depths between 4000 and 5000 m, or between 3000 and 3500 m towards the basin’s margin where stratigraphic plays may be effective. Several structures and potential stratigraphic plays remain undrilled in the basin.