BLEVIN, JANE E., and * PAUL E. WILLIAMSON, Petroleum Resource Assessment Branch, Bureau of Resource Sciences (formerly in the Bureau of Mineral Resources), Parkes, ACT, Australia

ABSTRACT: Triassic to Early Cretaceous Exploration Targets in the Beagle Sub-basin, North West Shelf, Australia

The Beagle sub-basin is situated in the northern Carnarvon basin on Australia's hydrocarbon-rich North West Shelf. The sub-basin is presently considered under-explored with only 10 wells drilled since exploration began in 1967. Drilling in shallow waters along the southern basin margin has confirmed excellent reservoirs exist in Middle to Late Triassic sandstones. Potential reservoirs could be sourced directly by the underlying Locker Shale, a well-documented regional marine sequence deposited in the Carnarvon basin during Early Triassic time. Drilling has also confirmed the presence of thick Triassic age claystones that could act as an effective intraformational seals. Structuring of traps occurred during periods of tectonic activity associated with rift onset and continental breakup in the Late Triassic to Middle Jurassic.

Seaward of the basin margin fault system is a series of north-northeasterly trending intra-basin highs separated by deep intervening troughs. On seismic data, the troughs shows a strongly developed synclinal geometry with sediments reaching a maximum thickness in the central trough and thinning to onlap and drape the surrounding trough margins. During the late stages of continental rifting in the late Middle Jurassic, potential reservoirscomposed of fluvial and paralic sandstones were deposited along the trough margins. Following breakup in the Callovian, marine conditions were rapidly established and persisted virtually uninterrupted until the early Aptian. The Late Jurassic marine sequence is an important and proven source interval in the Dampier Sub-basin to the south. Plays associ ted with the intra-basin highs include pre-breakup Jurassic reservoirs in rotated fault blocks and Neocomian submarine fans which are locally well developed along the horst margins.

AAPG Search and Discovery Article #90987©1993 AAPG Annual Convention, New Orleans, Louisiana, April 25-28, 1993.