Print this pageStructural History and the Pre-Salt Play of the Officer Basin, South Australia
The Neoproterozoic-Devonian Officer Basin in South Australia may contain a similar petroleum system to those of Oman and Siberia as it was located between these at the time of their formation and contains similar rocks. It thus has the potential to hold several very large oil fields capped by thick in-situ salt. However, the prospective area, which lies under one of the most remote areas of Australia, remains completely untested. Oil shows are common in shallow mineral wells and several have been correlated to pre-salt source rocks. Excellent quality reservoirs are proven in nearby wells (>20% phi, > 1 Darcy) and abundant salt implies long-term preservation is feasible. Source rocks up to 21% TOC (Western Mining NJD1)have been reported from equivalent strata in Western Australia. Target depths are 1800-3000 m and source rocks are currently at their maximum burial depth within the oil window.
Over 2000 kms of 2D seismic, recorded in 2007 to 2009, has allowed the recognition of 7 stages of deformation in the Officer Basin. Understanding timing of hydrocarbon migration in relation to these tectonic episodes will be a key factor in finding commercial oil here.
Stages are:
1. Late Willouran-Torrensian (~780-760 Ma) extension causing the formation of horsts and deep water deposition
2. Sturtian / Marinoan (760-650 Ma) glaciogenic uplift and erosion
3. Salt movement and shelf collapse, possibly triggered by the Acraman impact (580 Ma).
4. Massive apparent uplift and deep incision by canyons (575 Ma), possibly caused by True Polar Wandering
5. Petermann Ranges compression (545 Ma) causing thrusting beneath and into stage 4 canyons, and showing syn-sedimentary canyon fill-growth with decollement on the Callanna salt layers.
6. Post-Cambrian mild compression (Delamerian or Rodingan Orogenies 510Ma - 435 Ma) which set up anticlines similar to the large Mereenie oil field in the Amadeus Basin.
7. Alice Springs Orogeny (355 Ma), which is confined to the far north and east of the Officer Basin.
Examples of all periods of deformation and the attendant structural styles are shown in the recent 2D seismic.
Peak hydrocarbon generation and migration from the deep Munyarai Trough occurred in the Cambro-Ordovician. Thus any traps formed during the Alice Springs Orogeny are higher risk compared with those formed during the Rodingan/Delamerian, Petermann Ranges compressional events and Late Willouran extension.
AAPG Search and Discover Article #90100©2009 AAPG International Conference and Exhibition 15-18 November 2009, Rio de Janeiro, Brazil