The Browse basin lies entirely offshore beneath the remote northwestern continental shelf of Australia. It occupies an area of approximately 39,000 mi² (100,000 km²), most of which lies in water depths exceeding 650 ft (200 m). The basin originated during the Paleozoic as a broad, intracratonic downwarp, which was considerably modified by tectonism association with continental break up during the Jurassic. After passing through restricted rift-basin and rim-basin phases during Early-Middle Jurassic and Late Jurassic-Early Cretaceous times the basin was opened to oceanic circulation in the Late Cretaceous, when its western margin subsided. Prograding Tertiary shelf carbonates subsequently covered the old basin and formed the present continental shelf. /P>

Exploration of the basin and environs began in 1964 when license areas totaling some 63,000 mi² (164,000 km²) were awarded to the "Northwest Shelf Joint Venture," a consortium of companies presently comprising the Woodside Group, together with Hematite Petroleum, Shell Development Australia, California Asiatic and BP Petroleum Development Australia. During the 11-year period to 1975, some 13,700 mi (22,000 km) of seismic were shot and 11 exploration wells drilled, resulting in the discovery of gas at Scott reef. At the end of the initial permit period some 62% of the total area was relinquished. The remaining permit areas, totaling 24,162 mi² (62,579 km²) were renewed for the first renewal period of 5 years. During this renewal period a furt er 4,100 mi (6,700 km) of seismic were acquired and 8 wells drilled, resulting in 2 additional gas discoveries (Brecknock and Brewster) and one encouraging oil show (Caswell). In 1980, following statutory relinquishment, remaining permit areas, totaling 10,842 mi² (28,083 km²), were renewed for a further 5-year period.

Initial obstacles to exploration were water depth and the considerable thickness of multiple-generating Tertiary carbonates covering much of the basin. These have been largely overcome by advances in drilling technology and seismic data processing. Lost circulation zones and geopressured claystone intervals continue to cause problems with drilling.

Geochemical and maturation studies indicate that mature source rocks are present in the central basin, parts of which have been generative since the Late Cretaceous. Structural analysis suggests that the timing of trap formation is favorable with respect to likely hydrocarbon migration throughout much of the central basin, but is less favorable in the north, where a very late phase of structural growth is evident.

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