The Late Carboniferous-Cainozoic Browse Basin is a large, offshore basin on the northwestern Australian poly-phased margin. 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 identified reserves at the end of 2000 were 0.48 GL of oil, 94.3 GL of condensate and 858.96 BCM of gas.
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 Early 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 sedimentary section and lie in 100 to 1500 metres water depth. The outer Browse Basin underlies the deep-water Scott Plateau (1500- 4000 metres water depth).
The Carboniferous section is predominantly fluvio-deltaic and the Permian-Early Triassic section is marine. Middle-Late Triassic rocks include fluvial and shallow marine clastics and minor carbonates. Early-Middle Jurassic syn-rift sediments comprise deltaic and coastal-plain clastics and coal. Widespread erosion occurred in the Callovian and Upper Jurassic sandstones and shales onlap, drape and provide 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-Tertiary section records a major progradational clastic-to-carbonate cycle.
The Early Cretaceous claystones provide a thick regional seal and contain potential oil-prone source rocks. Potential source rocks also occur in the Late Jurassic, Middle-Early Jurassic, Triassic and syn-rift Palaeozoic sections. Reservoir facies are best developed within the fluvio-deltaic Middle-Early Jurassic section and submarine fans of Berriasian, Barremian, Campanian and Maastrichtian age.