VIMP Report 68 - Hydrocarbon prospectivity of areas V01-1, V01-2 and V01-3, offshore Otway Basin: 2001 Acreage Release

Category: Victorian Initiative for Minerals and Petroleum Reports	Product Code: MP-R-34480
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Executive Summary Despite an exploration history dating from 1959, only fourteen exploration wells have been drilled in the Victorian part of the offshore Otway Basin. It was not until 1993 following the gas discoveries at La Bella (GIIP 210 BCF) and Minerva (GIIP 575 BCF) that significant hydrocarbon potential was recognised. The release areas V01-1, V01-2 & V01-3 are all located in the eastern offshore Otway Basin, 250 km southwest of Melbourne. No exploration wells have been drilled in any of the blocks. V01-2 is located in the continental shelf area in water 20 to 500 m deep. V01-1 and V01-3 are deepwater blocks located in depths from 500 to 3000 m.

An extensive database of 2D seismic data covers the blocks, although predominantly located in V01-2. V01-1 has 1119 km of 2D seismic coverage, V01-2 5671 km and V01-3 956 km.

The gazettal release areas are all located in the Voluta Trough, an area of thick, Late Cretaceous sedimentation. The Mussel Platform occurs in the far northeast of V01-2. V01-1 and V01-3 are deep-water blocks that cover the middle to lower parts of the present-day continental slope. V01-2 covers the continental shelf where it overlies the Portland Trough – an area with a significantly thickened Tertiary sequence – and the Bridgewater High which forms the southwestern flank of the trough.

The Voluta Trough has the potential to contain all the elements necessary for successful exploration, including:

The presence of active petroleum systems
Development of regional and intraformational seals
Several prospective reservoir/seal pairs
Untested plays involving structural and stratigraphic traps.

This report presents a review of the petroleum prospectivity of the three permits; specifically, it addresses all the potential plays and source rocks and identifies potential leads in each of the three blocks. Seven potential reservoir plays that constitute discrete fairways in each of the three blocks are described. Two significant source rock sequences have been identified, which are believed to have potential for both oil and gas generation. Principal source rocks belong to the Austral 2 (Eumeralla Formation) and Austral 3 (Sherbrook Group) petroleum systems. These latter source rocks are of the same age as, and belong to, the Austral 3 petroleum system that sourced the giant oil fields in the Gippsland Basin.

The Waarre Formation play, whilst valid in V01-2 over the Bridgewater High, is relatively deep in the Voluta Trough. However, additional plays are described at shallower levels and leads described for each. Plays identified include;

Intra-Paaratte Formation
Top Paaratte Formation/Timboon Formation
Pebble Point Formation
Dilwyn Formation
Mepunga Formation
Oligocene Lowstand Fans

These plays are considered to have significant potential, much of it identified for the first time in this report. The Dilwyn and Mepunga formation plays show many similarities to their age equivalent Latrobe Group 'Coarse Clastics' of the Gippsland Basin, which are prolific oil and gas producers. Additionally, basin modelling of Waarre Formation source rock has identified potential for this oil and gas prone sequence in the area of interest.

Carbon dioxide poses a risk for the economics of gas accumulations in the Otway Basin. Integration of seismic and magnetic data defines a methodology to significantly reduce that risk, assuming the CO₂ is of volcanogenic origin.

Victoria hosts the largest gas market in eastern Australia with a well-established pipeline network linking major population centres. The Port Campbell fields are linked to Melbourne by a pipeline which currently principally services a gas storage project, but which has additional capacity. This network is also linked to the SE Australian markets by two pipelines, one through the north of Victoria and one up the east coast. A pipeline from Port Campbell to Adelaide has also been proposed with first gas in late 2003.

Bibliographic reference Constantine, A.E., Geary, G.C. & Reid, I.S.A, 2001. Hydrocarbon prospectivity of areas V01-1, V01-2 and V01-3, offshore Otway Basin, Victoria, Australia: 2001 Acreage Release. Victorian Initiative for Minerals and Petroleum Report 68. Department of Natural Resources and Environment.