Browse Basin
The Browse Basin lies entirely offshore north of Broome and covers approximately 140 000 km2. The basin is bounded by the Leveque Shelf in the south, the Kimberley Block to the east, and the Ashmore Platform and Scott Plateau in the north, and grades into the offshore Canning Basin to the southwest. The area can be serviced from Broome, which has adequate port and air facilities.
Geological Setting
The Late Ordovician to Recent Browse Basin is a large, offshore basin on the northwestern Australian poly-phased margin (Figure 26). The basin is a proven hydrocarbon province, with major undeveloped gas/condensate fields in the outer and central basin, and minor oil discoveries on the basin’s eastern margin.
The Browse Basin developed during six major tectonic phases: Late Carboniferous to Early Permian extension; Late Permian to Triassic thermal subsidence; Late Triassic to Early Jurassic inversion; Early to Middle Jurassic extension; Late Jurassic to mid-Tertiary thermal subsidence; and Late Miocene inversion. Initial extension resulted in half-graben geometries and the formation of two distinct depocentres, the Caswell and Barcoo Sub-basins. These depocentres contain in excess of 15 km of sedimentary section, and lie in 100 to 1500 m water depth.
The outer Browse Basin underlies the deepwater Scott Plateau (1500 to 5000 m water depth). The Carboniferous section is predominantly fluviodeltaic, and the Permian to Lower Triassic section is mostly marine. Middle to Upper Triassic rocks include fluvial and shallow marine clastics and minor carbonates. Lower to Middle Jurassic syn-rift sediments comprise deltaic and coastal-plain clastics and coal.
Widespread erosion occurred in the Callovian, with onlapping Upper Jurassic sandstones and shales providing a thin regional seal across most pre-Callovian structures. Widespread transgression commenced in the Valanginian and peaked in the Turonian, and resulted in the deposition of thick open marine claystones. The Turonian to Tertiary section records a major progradational clastic-to-carbonate cycle.
The Lower Cretaceous claystones provide a thick regional seal and contain potential oil-prone source rocks. Potential source rocks also occur in the Upper Jurassic, Middle to Lower Jurassic, Triassic and syn-rift Paleozoic sections. Reservoir facies are best developed in sandstones of the fluviodeltaic Middle to Lower Jurassic section, and in Cretaceous submarine fans of Berriasian, Barremian, Campanian and Maastrichtian age.
Exploration History
Exploration commenced in the Browse Basin in 1967, when Burmah Oil Company Australia Ltd (BOCAL) (Woodside) acquired 1600 km of regional seismic. To date, over 71 000 km of seismic data has been acquired, the majority of which is now on open–file.
BROWSE BASIN Scott Reef 1 (1971), was the fourth well drilled in the basin, discovering potentially Australia’s largest gasfield. Since then there have been a further eleven hydrocarbon discoveries. Although the combined gas reserves of these fields are over 700 Gm3, they have yet to be developed.
The main obstacle to their development is isolation, being almost 300 km from the mainland and in 300–500 m of water.
Petroleum Prospectivity
The Browse Basin is one of Australia’s most hydrocarbon-rich basins. The most significant hydrocarbon fields of the Browse Basin occur in the Caswell Sub-basin;
- Scott Reef (Torosa) 325 Gm3 (11.5 Tcf) gas, 19 GL (119 MMbbl) condensate (DMP, 2006),
- Brecknock 150 Gm3 (5.3 Tcf) gas, 17 GL (107 MMbbl) condensate (DMP, 2006),
- Brecknock South (Calliance) 150 Gm3 (5.3 Tcf) gas, 13.8 GL (87 MMbbl) condensate (DMP, 2006),
- Brewster area, Ichthys 198 Gm3 (7 Tcf) gas, 44 GL (276 MMbbl) condensate (DMP, 2006), and
- Crux 37 Gm3 (1.3 Tcf) gas, 7.6 GL (48 MMbbl) condensate (Nexus investor update, March 2006).
