W15-6 to W15-8: bids close 21 April 2016
W15-9 to W15-12: cash bids close 15 October 2015 (pre-qualification), 4 February 2016 (auction)
- Within one of Australia’s premier offshore producing basins
- Close to numerous oil and gas accumulations including Stag, Wandoo, Reindeer, Legendre, Wanaea and Fletcher-Finucane,
- Cash Bid Release Areas include the Chamois oil and Elk gas accumulations
- Shallow water depths (<40–200 m)
- Oil-prone Upper Jurassic and gas-prone Triassic to Middle Jurassic source rocks
- Stacked structural and stratigraphic targets at Triassic, Jurassic and Lower Cretaceous levels
- Special Notices apply; refer to Guidance Notes
W15-6 and W15-7 are small (2 and 1 graticular blocks, respectively) Release Areas in the Beagle Sub-basin, close to the common boundary with the Dampier Sub-basin (Figure 1). They are within a short distance of the Fletcher-Finucane, Talisman and Amulet oil accumulations and approximately 150 km north of the town of Dampier. Release Area W15-8 comprises 15 graticular blocks, is located approximately 45 km north of Dampier and is close to the Wandoo, Jalfrezi and Legendre oil and the Gungurru oil and gas accumulations. The Release Area includes the Hampton 1 and Morrel 1 gas discoveries and the Bloodwood 1 oil show.
Release Areas W15-9 to W15-12 range in size from 1 to 6 graticular blocks, are considered mature in exploration terms and are available for cash bidding. Release Area W15-11 includes the Elk gas accumulation and Release Area W15-12 includes the Chamois oil accumulation. The areas are located between 65 and 150 km northeast of Barrow Island (Figure 1).
The Dampier and Beagle sub-basins contain Paleozoic to Cenozoic sedimentary successions of up to 10‑20 km in thickness (Figure 2). The Dampier Sub-basin hosts proven petroleum systems. Late Triassic, Early–Middle and Late Jurassic source rocks have expelled hydrocarbons that are now reservoired in both structural and stratigraphic traps. Gas is predominantly sourced from Triassic to Middle Jurassic fluvio-deltaic sediments of the Mungaroo and Brigadier formations, the Murat Siltstone, and the Athol and Legendre formations. Oil is predominantly sourced from the Upper Jurassic Dingo Claystone. Structural trap styles in the sub-basin include tilted fault blocks, fault dependent rollovers, anticlines, drape features and horsts (Figure 3).
Although only oils generated from Early–Middle Jurassic source rocks are known in the Beagle Sub-basin, there is the potential for gas and liquids generation from older source rocks. The recent success of Phoenix South 1 in the neighbouring Roebuck Basin has highlighted the possibility that older sedimentary units in the sub-basin may have sourced hydrocarbons. In addition to structural traps, there is the potential for stratigraphic targets within the release areas. These include stratigraphic pinch-outs, unconformity sub-crops and transgressive sandstone packages at the base of the Locker Shale.
Although well coverage is not dense within the northern Dampier and southern Beagle sub-basins, the 2015 release areas are almost entirely covered by 3D seismic data (Figure 4). The release areas are close to established infrastructure that could facilitate the development of commercial discoveries (Figure 1).
Petroleum systems elements
Dampier and Beagle sub-basins
|Sources||Dampier and Beagle sub-basins
|Reservoirs||Dampier and Beagle sub-basins
Infrastructure and markets
The Beagle Sub-basin Release Areas are close to the Fletcher-Finucane oil fields. The production wells at Fletcher-Finucane are tied back to the Mutineer-Exeter FPSO. The Dampier Sub-basin Release Areas are close to the Legendre, Wanaea/Cossack, Stag and Wandoo developments and to several gas pipelines (the Devil Creek Pipeline, the North Rankin to Withnell Bay Pipeline, the Pluto LNG Export Pipeline and the Northwest Shelf 42” Trunkline to Karratha). These pipelines connect producing offshore gas fields to onshore processing facilities and provide domestic gas to the Western Australian market and LNG to international markets.
In parts of the Dampier Sub-basin, trap integrity and reservoir preservation constitute significant exploration risks. In the northwest part of the sub-basin, diagenesis of Jurassic sandstones as a result of increased burial depth may adversely impact on reservoir porosity and permeability. Variable sandstone distribution/porosity within fine-grained, deep-water sediments can also be problematic. Exploration risks associated with the in-board areas of the Dampier Sub-basin include hydrocarbon migration distance, biodegradation of oil in shallow reservoirs and the potential absence of a competent seal.
The source of oil in the Beagle Sub-basin is unproven. In the absence of an oil charge from the Late Jurassic Dingo Claystone, it is possible that Early to Middle Jurassic source rocks in the Victoria Syncline could have generated oil.
While Early Cretaceous to Late Jurassic sandstones intersected by wells drilled in the Talisman oil field are hydrocarbon-bearing, wells drilled within the release areas (Sable 1 and Aurora 1) are water-wet. In some areas, late gas flushing of oil reservoirs is also considered to constitute an exploration risk.
Wells Data and Seismic Survey listings for the Beagle and Dampier sub-basins are available on the Supporting Information page.
Geoscience Australia products
Regional geology and seismic
Line Drawings of AGSO-Geoscience Australia’s Regional Seismic Profiles, Offshore Northern and Northwestern Australia, Australian Geological Survey Organisation Record 2001/36 by Colwell and Kennard 2001.
1994 Barrow and Dampier Sub-basins Airborne Laser Fluorosensor (Mk III) Survey Interpretation Report. Australian Geological Survey Organisation Record 2001/16 by Cowley, 2001.
Barrow/Dampier, WA, 1993 (P597). Airborne Digital dataset by Richardson, 1993.
Survey 97: Operations Report for the Joint BMR/Woodside Petroleum High Resolution Seismic Program in the Dampier Sub-basin, October 1990. Bureau of Mineralogical Resources Record 1991/67 by O’Brien and Bickford, 1991.
Interpreted Horizons and Faults for Seismic Survey 101. Carnarvon Basin. Dataset by Kennard et al, 2003.
Interpreted Horizons and Faults for Seismic Survey 110. Carnarvon Basin. Dataset by Kennard et al, 2003.
Carnarvon Cretaceous-Tertiary Tie Report. Australian Geological Survey Organisation Record 1996/36 by Romine and Durrant, 1996.
Northern Carnarvon Basin Biozonation and Stratigraphy Chart 36. Chart by Kelman et al, 2013.
Petroleum systems and accumulations
Source Rock Time-slice Maps: Offshore Northwest Australia, 2004. Dataset by West et al, 2004.
Australian Petroleum Systems: Dampier Sub-basin Module. Australian Geological Survey Organisation Record 1993/31 by Spencer et al, 1993.
Australian Petroleum Systems: Roebuck and Offshore Canning Basins – Beagle Sub-basin Module, Australian Geological Survey Organisation Record 1995/03 by Sayers et al, 1995.
The Oils of Western Australia II. Report by Edwards and Zumberge, 2005.
Australian Petroleum Accumulations Report, Carnarvon Basin, Western Australia. Australian Geological Survey Organisation Report by Felton et al, 1993.
Characterisation of Natural Gases from West Australian Basins. AGSO and Geotechnical Services Non-Exclusive Study, 2000.
Light Hydrocarbon Geochemistry of the WA-28-P Area, Dampier Sub-basin, Western Australia: Rig Seismic Survey 97: Project 121.19. Bureau of Mineral Resources Record1992/61 by O’Brien, 1992.
Search for these and other Geoscience Australia reports and products at www.ga.gov.au/search
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