Sub-Salt Structures in the Officer Basin, Australia

Paul J. Bennett¹, Jim F. Allender², and Peter Boult^3
1Officer Basin Energy, Inc., Alberta, AB, Canada
²Allender Exploration, Unley, SA, Australia
³PIRSA, Adelaide, WA, Australia

The Officer Basin straddles the southern WA /SA state boundary. Up to 15 km of sediments above crystalline basement are recorded on the northern edge of the basin adjacent to the Musgrave metamorphic complex. Basin sediments are Neoproterozoic, Cambrian, Paleozoic, Permian and Tertiary in age.

At least 3 complete petroleum systems have been identified. The oldest represents Neoproterozoic syn-rift deposition and includes evaporites and source rocks of the Alynia Formation. Beneath the Alynia are course detrital clastics eroded from the Precambrian surface (Pyndian Sandstone).

Structuring that juxtapositions source and reservoir with a cover of evaporitic beds is evident on regional seismic lines and has been recognized for several years.

Salt cored diapiric structures exist at the extreme east and west ends of the basin. Also present are salt walls, ridges and collapse structures with most of these features associated with sub-salt faulting. The central part of the basin is marked by a large area of “stable salt” having numerous sub-salt and post salt structures that modify the Neoproterozoic and Cambrian sedimentary assemblages.

Gravity interpretation shows the thickest section of sediments to be located from just west of the state boundary eastward to where the basin narrows and thrusts upwards near Marla in South Australia. The current interpretation has one large basin with a shallow ridge (Nason Ridge?) running north /south through it near the state boundary.

AAPG Search and Discovery Article #90078©2008 AAPG Annual Convention, San Antonio, Texas