Geology and Exploration in Southwest Pacific Australian Region: Western and Northwestern Margin Basins
of Australia
WOOLLANDS, MICHAEL ALAN, BHP Petroleum Pty Ltd., Melbourne, Victoria, Australia
The Marginal basins
of Western and Northwestern Australia extend approximately 3800 km along the coast and comprise both continental shelf and adjacent deepwater plateau areas. From north to south, the principal
basins
are the Sahul/Malita, Browse, Carnarvon, and Perth
basins
.
Their overall development
and tectonic history are related primarily to rifting associated with the
Mesozoic
break-up of the Australian continental margin.
The stratigraphic sequence within each basin is broadly similar, with initial widespread Triassic-Early Jurassic deposition in broad regional pre-rift sags. Middle
Jurassic to Late Jurassic rifting on the Northwest Shelf and early Cretaceous rifting in the Perth basin varies in intensity across the region, and provides the primary control of hydrocarbon distribution through trap type, reservoir, and
source
rock quality. The best-developed oil
source
rocks
of the region are found in these Jurassic rifted sequences. A post-rift passive margin sequence developed from the early Cretaceous-Recent, with most hydrocarbon discoveries being found beneath the regional base Cretaceous (Valanginian) post-rift unconformity.
Although drilling to date has been generally sparse, with only some 824 wells throughout the entire area, significant accumulations of gas and oil have been found in the offshore Carnarvon basin and the Vulcan Graben area of the Browse basin.
Recent discoveries of commercial oil at Jabiru in the Vulcan graben and Griffin in the Carnarvon basin have again focused activity on the area's oil potential. Many structural traps remain to be drilled and the potential for stratigraphic trapping has been only slightly explored.
Large, poorly explored frontier areas, between the established producing areas and in the Perth basin, as well as adjacent deepwater, are available. However, present data suggest that not all key success factors, notably mature oil source
rocks
and good
reservoirs
, may be present in these areas.
AAPG Search and Discovery Article #91004 © 1991 AAPG Annual Convention Dallas, Texas, April 7-10, 1991 (2009)