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Nelson Sub-basin

Bids close 21 April 2016

  • Under-explored Mesozoic–Cenozoic basin
  • Adjacent to the gas producing areas of the inner Otway Basin
  • Overlies large areas of the frontier Nelson Sub-basin, a main depocentre within the Otway Basin
  • Sub-basin contains up to 8 km of sediment
  • Potential presence of petroleum systems proven to be productive in adjacent basin
  • Potential good quality reservoirs and seals, oil- and gas-prone source rocks and active petroleum systems
  • Deep to ultra-deep water depths, 250–3400 m
  • Close to Thylacine and Geographe Gas Pipeline
  • Special Notices apply, refer to Guidance Notes

Release Areas V15-1, T15-1 and T15-2 are located on the continental shelf and slope within the Nelson Sub-basin—a frontier exploration province. The areas lie to the south of an established gas producing region in the inner Otway Basin that provides gas for the southeastern Australian energy market. (Figure 1). The greater Melbourne region currently represents Australia’s largest domestic gas market and is supported by a local petroleum refining industry. The Release Areas lie between 20 km and 210 km from the gas pipeline that services the Thylacine and Geographe gas fields. Water depths range from 250 m to 3400 m within V15-1, 260 m to 2400 m in T15-1 and 520 m to 3300 m in T15-2.

The Nelson Sub-basin contains up to 5 s TWT (~8 km) of Cretaceous sediments that are overlain by a thin Cenozoic succession (Figure 2 and Figure 3). The basal section, interpreted to comprise the non-marine, fluvio-lacustrine Lower Cretaceous Crayfish and Eumeralla supersequences (Otway Group), is overlain by a thick, basinward-thickening Upper Cretaceous succession that comprises prodelta and open marine equivalents of the Shipwreck and Sherbrook supersequences (equivalent to the Sherbrook Group). In hydrocarbon producing areas of the Otway Basin, the Waarre and Flaxman formations of the Shipwreck Supersequence, as well as the “Thylacine Sandstone Member” of the Belfast Mudstone, are important petroleum reservoirs.

Although modelling suggests that source rocks within the Lower Cretaceous succession are overmature across much of the deepwater basin, the presence of a thick, predominantly marine Upper Cretaceous succession, and geochemical analyses that suggest input from Upper Cretaceous source rocks in outboard wells, provide encouragement that active petroleum systems are present in the deepwater Otway Basin.

Figure 4 shows the location of seismic and well data within the Release Areas. Numerous 2D and 3D seismic surveys have been acquired. These include the Fugro DS01 and DS02 surveys and the OS02 (Santos), Aragorn (Woodside) and Brandt (Santos) surveys, respectively. The area is also covered by good quality aeromagnetic data. Release Area V15-1 includes the Armit 1 exploration well drilled by Santos in 2004.

Petroleum systems elements

Nelson Sub-basin

Sources
  • Lower Cretaceous distal equivalents of the Otway Group
  • Upper Cretaceous distal equivalents of the Sherbrook Group
Reservoirs
  • Upper Cretaceous distal equivalents of the Waarre Formation, Flaxman formations and the “Thylacine Sandstone Member” at the base of the Belfast Mudstone
  • Upper Cretaceous distal equivalents of the sandstones of the Paaratte Formation
Seals Regional Seals
  • Upper Cretaceous Belfast Mudstone

Intra-formational Seals

  • Upper Cretaceous shales within the distal equivalent of the Flaxman Formation
  • Upper Cretaceous mudstones within the distal equivalent of the Timboon Sandstone
Traps
  • Faulted anticlines, tilted fault blocks with cross-fault seal

Infrastructure and markets

The Nelson Sub-basin is a frontier exploration province and lacks existing infrastructure. The Release Areas, however, lie between 20 and 210 km from the gas pipeline that services the Thylacine and Geographe gas fields in the adjacent Inner Otway Basin.

Critical risks

As this is a frontier area, primary exploration risks relate to the lack of well control and modern, good quality seismic data. The critical exploration risks are associated with the presence and maturity of source rocks, the presence of effective seals and fault seal integrity. Fault-seal integrity may be less of a risk in the Nelson Sub-basin than in other parts of the deepwater Otway Basin, as the area has been less affected by Late Cretaceous and Cenozoic faulting.

Data sets

Wells Data and Seismic Survey listings for the Nelson Sub-basin are available on the Supporting Information page.

Geoscience Australia products

Regional geology and seismic

Stratigraphy

Petroleum systems and accumulations

Search for these and other Geoscience Australia reports and products at www.ga.gov.au/search

Contact Geoscience Australia’s Sales Centre for more information or to order these reports or products, phone +61 (0)2 6249 9966, email sales@ga.gov.au

BLEVIN, J.E. AND CATHRO, D.L., 2008—Australian Southern Margin Synthesis, Project GA707. Client report to Geoscience Australia by FrOG Tech Pty Ltd. https://www.ga.gov.au/products/servlet/controller?event=GEOCAT_DETAILS&catno=68892

BOREHAM, C.J., HOPE, J.M., JACKSON, P., DAVENPORT, R., EARL, K.L., EDWARDS, D.S., LOGAN, G.A. AND KRASSAY, A.A., 2004—Gas–oil–source correlations in the Otway Basin, southern Australia. In: Boult, P.J., Johns, D.R. and Lang, S.C. (eds), Eastern Australasian Basins Symposium II, Petroleum Exploration Society of Australia, Special Publication, 603–627.

CLIFF, D.C.B., TYE, S.C. AND TAYLOR, R., 2004—The Thylacine and Geographe gas discoveries, offshore eastern Otway Basin. The APPEA Journal 44(1), 441–462.

DUDDY, I.R., EROUT, B., GREEN, P.F., CROWHURST, P.V. AND BOULT, P.J., 2003.—Timing constraints on the structural history of the western Otway Basin and implications for hydrocarbon prospectivity around the Morum High, South Australia. The APPEA Journal, 43(1), 59–83.

GEOLOGICAL SURVEY OF VICTORIA, 1995—The stratigraphy, structure, geophysics and hydrocarbon potential of the Eastern Otway Basin. Geological Survey of Victoria, Report 103, 241 pp.

GIBSON, G.M., MORSE, M.P., IRELAND, T.R. AND NAYAK, G.K., 2011—Arc-continent collision and orogenesis in western Tasmanides: Insights from reactivated basement structures and formation of an ocean-continent transform boundary off western Tasmania. Gondwana Research, 19, 608–627.

GIBSON, G. M., TOTTERDELL, J.M., MORSE, M. P., GONCHAROV, A., MITCHELL, C.H. AND STACEY, A.R., 2012—Basement structure and its influence on the pattern and geometry of continental rifting and breakup along Australia’s southern rift margin. Geoscience Australia, Record, 2012/47.

GRADSTEIN, F.M., OGG, J.G. SCHMITZ, M.D. AND OGG, G.M. (eds), 2012—The Geologic Time Scale 2012: Volumes 1 & 2. Elsevier BV, 1144 pp.

HALL, M. and KEATLEY, J. 2009—Otway Basin, stratigraphic and tectonic framework. GeoScience Victoria 3D Victoria Report 2, Department of Primary Industries.

KRASSAY, A.A., CATHRO, D.L. AND RYAN, D.J., 2004—A regional tectonostratigraphic framework for the Otway Basin. In: Boult, P.J., Johns, D.R. and Lang, S.C. (eds), Eastern Australasian Basins Symposium II, Petroleum Exploration Society of Australia, Special Publication, 97–116.

LUXTON, C.W., HORAN, S.T., PICKAVANCE, D.L. AND DURHAM, M.S., 1995—The La Bella and Minerva gas discoveries, offshore Otway Basin. The APEA Journal, 35, 405–417.

MANTLE, D.J., BERNECKER, T., KELMAN, A.P. AND PATRIDGE, A.D., 2009—Otway Basin Biozonation and Stratigraphy, 2009 Chart 34. In: Smith, T.E., Kelman, A.P., Nicoll, R.S., Laurie, J.R. and Le Poidevin, S.R., 2013. Geoscience Australia's Basin Biozonation and Stratigraphy Chart Series. Basin Biozonation and Stratigraphy Chart Series.

O’BRIEN, G.W., BERNECKER, T., THOMAS, J.H., DRISCOLL, J.P. AND RIKUS, L., 2006—An assessment of the hydrocarbon prospectivity of Areas VIC/O-06(1), VIC/O-06(2), VIC/O-06(3) and V06-1, eastern onshore and offshore Otway Basin, Victoria, Australia. Victorian Initiative for Minerals and Petroleum Report 90, Department of Primary Industries.

O’BRIEN, G.W., BOREHAM, C.J., THOMAS, H.J. AND TINGATE, P.R., 2009—Understanding the critical success factors determining prospectivity—Otway Basin, Victoria. The APPEA Journal, 49(1), 129–170.

PARTRIDGE, A.D., 2001—Revised stratigraphy of the Sherbrook Group, Otway Basin. In: Hill, K.C. and Bernecker, T. (eds), Eastern Australian Basins Symposium, A Refocused Energy Perspective for the Future, Petroleum Exploration Society of Australia, Special Publication, 455–464.

STACEY, A.R., MITCHELL, C.H., STRUCKMEYER, H.I.M. AND TOTTERDELL, J.M., 2013—Geology and hydrocarbon prospectivity of the deepwater Otway and Sorell basins, offshore southeastern Australia. Geoscience Australia, Record, 2013/02.

TOTTERDELL, J., HALL, L., HASHIMOTO, T., OWEN, K. AND BRADSHAW, M., 2014—Petroleum geology inventory of Australia's offshore frontier basins. Geoscience Australia, Record, 2014/009.

Figures

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Figure 1

 Otway Basin-Nelson Sub-basin-figure-1 image map
Location map of the 2015 Release Areas within the Nelson Sub-basin of the Otway Basin, showing exploration wells, petroleum accumulations and the location of the seismic section in Figure 3. Release Areas shown by outline only are discussed elsewhere.
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Figure 2

 Otway Basin-Nelson Sub-basin-figure-2 image map
Stratigraphy and hydrocarbon shows of the Otway Basin. Based on the Otway Basin Biozonation and Stratigraphy Chart 34 (Mantle et al, 2009). Geologic Time Scale after Gradstein et al (2012).
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Figure 3

 Otway Basin-Nelson Sub-basin-figure-3 image map
Seismic line ds02/219 across the Nelson Sub-basin of the Otway Basin. Interpretation by Stacey et al (2013). Location of the seismic line is shown in Figure 1.
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Figure 4

 Otway Basin-Nelson Sub-basin-figure-4 image map
Seismic and well data coverage in the vicinity of the Release Areas in the Nelson Sub-basin of the Otway Basin. Release Areas shown by outline only are discussed elsewhere.
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