Sandra Menpes
Principal Geologist
Essential Petroleum Resources Limited

Essential Petroleum Resources Limited (Essential) has significant interests in acreage over the highly prospective Late Cretaceous Discovery Bay High in the central Otway Basin (Figure 1).
The Discovery Bay High separates the sandier Late Cretaceous section of the Morum Sub-basin from the shale-prone Late Cretaceous section of the Nelson Sub-basin and provides a focus for regional hydrocarbon migration.

The Bernoulli and Fermat prospects lie on the western side of the Discovery Bay High where Waarre Formation Unit C sands are expected. A 3D seismic survey to resolve the complex Bernoulli structure is planned for April 2007 followed by a well to test either Fermat or Bernoulli in the second quarter of 2008.

Recent mapping of depth processed (PSDM) seismic data acquired over the shelf margin has defined two exciting deep water Waarre leads in VIC/P50 (Figures 2 and 3). The Oliphant Lead is a rollover into a Late Cretaceous growth fault and the Bragg Lead is a tilted fault block sealed vertically and laterally by thick marine shales. The leads are of large areal extent and structural relief. A 500 line kilometre 2D seismic survey would be sufficient to mature one or both of these leads to drillable prospect status.

The Discovery Bay High

Two major offsets in Late Cretaceous extension influence basin fill in the Otway Basin.

The first offset in Late Cretaceous extension occurs between the Tartwaup Fault and the Mussel Fault in the central Otway Basin (Figure 4). The offset is coincident with, and is attributed to, the Miakite Creek basement fault. The Discovery Bay High is a zone of thinned Sherbrook Group between the Morum and Nelson sub-basins, coincident with the Late Cretaceous offset.

The offset in Late Cretaceous extension caused by the Miakite Creek Fault has influenced sand distribution in the eastern part of the Morum Sub-basin. Waarre C and Flaxman C sands were confined to the Morum Sub-basin and the western side of the Discovery Bay High during the Turonian. During the Campanian, Paaratte Formation river systems were focused west of the offset.
The second major offset in Late Cretaceous extension occurs between the Mussel Fault and the Sorell Fault. This offset is coincident with, and is attributed to, the Moyston basement fault. All of the currently known Late Cretaceous gas fields of the Otway Basin occur in this area known as the Shipwreck Trough and the Port Campbell Embayment. In contrast the analogous area associated with the Miakite Creek basement fault, referred to as the Discovery Bay High, is as yet only very lightly explored.

Leads and Prospects

The Late Cretaceous leads and prospects on the Discovery Bay High are intimately related to the Miakite Creek basement fault and its influence on Late Cretaceous basin fill. The Bernoulli and Fermat prospects in VIC/P46, and the Oliphant and Bragg leads in VIC/P50, lie on the western side of the Discovery Bay High where Waarre Formation Unit C sands are interpreted. The Curie Prospect is an interpreted Lower Campanian basin floor fan associated with the Paaratte Formation delta building west of the Miakite Creek Fault.

Preliminary interpretation of the recently processed OEP06 survey in VIC/P50 has revealed a dramatic thickening of the Upper Campanian section (Timboon Sandstone equivalent) east of the Miakite Creek Fault into the deepwater Nelson Sub-basin. There is evidence to suggest the fault became extensional at this time in response to a change in extension direction.

It is likely that the Miakite Creek Fault continued to influence basin fill through the Tertiary. A digital elevation image over part of southern Australia shows that the proto-Murray River fed sediments west of the fault into VIC/P46 and VIC/P50. The Oligocene Descartes turbidite fan complex is believed to have been fed by drainage similarly constrained by basement architecture.

In summary the Miakite Creek Fault influenced structure and basin fill in the vicinity of the Discovery Bay High, impacting key petroleum system elements and providing opportunities for hydrocarbon discovery.

For more information contact:
Essential Petroleum Resources Limited
Tel: +61 3 9699 3009
Fax: +61 3 9699 3110
Web: www.essentialpetroleum.com.au

References:

PALMOWSKI, D., HILL, K.C. and HOFFMAN, N., 2004: Structural-stratigraphic styles and evaluation of the offshore Otway Basin – a structural seismic analysis. In: Boult, P.J., Johns, D.R. and Lang, S.C. (Eds), Eastern Australian Basins Symposium II, Petroleum Exploration Society of Australia, Special Publication, 75-96.

WOOLLANDS, M.A. and WONG, D., (Eds), 2001. Petroleum Atlas of Victoria, Australia