Sub-Salt Structures and Tectonic Evolution of the Officer Basin, South Australia

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

The Officer Basin is located in south central Australia straddling the WA /SA state boundary. The basin started to form in Neoproterozoic times about 800 MYA. Three subsequent orogenic periods developed punctuated by three periods of substantial sedimentation. Basin sediments are Neoproterozoic, Cambrian, Paleozoic, Permian and Tertiary in age.

At least 3 complete petroleum systems have been identified in the basin. The oldest system represents Neoproterozoic syn-rift deposition and includes evaporites and interbedded source rocks of the Alynia Formation. Younger petroleum systems are related to Early Cambrian orogenics and also contain evaporites in part. Tectonic 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.

At least two intervals of evaporite deposition are evident from seismic and wellbore records. Salt cored diapiric structures are seen 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. 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. Based on recent gravity and seismic work, the current interpretation favours one large basin with a shallow ridge (Nason Ridge?) running north /south through it near the state boundary.

The recent acquisition of over 1200km of high definition seismic data in South Australia, and over 15,000 km of airborne gravity and magnetic (Falcon system) by Officer Basin Energy PL will be used to demonstrate the large number of new sub-salt structures in the Officer Basin, the basin’s tectonic development and evolution, and its hydrocarbon potential.

AAPG International Conference and Exhibition, Cape Town, South Africa 2008 © AAPG Search and Discovery