AAPG ANNUAL CONFERENCE AND EXHIBITION
Making the Next Giant Leap in Geosciences
April 10-13, 2011, Houston, Texas, USA
Petroleum Prospectivity of the Eastern Australian Deepwater Frontier Basins: Insights from the Capel and Faust Basins
(1) Australian Resource Energy and Tourism, Geoscience Australia, Canberra, ACT, Australia.
(2) GNS Science, Lower Hutt, New Zealand.
The Tasman Sea region between Australia, New Zealand and New Caledonia contains a number of deepwater basins that remain to be tested by drilling. A recent geological assessment completed by Geoscience Australia in the Capel and Faust basins has significantly advanced the understanding of region’s petroleum prospectivity. The study formed part of Australian Government’s Offshore Energy Security Program (2006-2011) that delivers pre-competitive information to industry and promote offshore frontier exploration. Parts of this study were carried out in collaboration with GNS Science (New Zealand) and the Geological Survey of New Caledonia.
An integrated workflow based on 3D visualisation and modelling facilitated data synthesis and interpretation in a geologically complex frontier environment. Key data sets used include 2D seismic, gravity, magnetic, multibeam bathymetry and geological samples. Regional tectonic reconstructions and analogue basins (e.g. Maryborough, Gippsland and Taranaki) were used to infer the composition and age of basin sediments, and the likely presence of petroleum system elements. Multi-1D basin modelling tested for hydrocarbon generation and expulsion potential.
Results confirmed the existence of large (over 3000 km2) basin depocentres containing sediments up to 6 km thick. The depocentres formed during two Cretaceous extensional events preceding the final breakup of the eastern Gondwana margin. Syn-rift deposition appears to have been initially dominated by volcaniclastics, then by non-marine to shallow marine clastics. A fining-upward clastic to calcareous bathyal succession was deposited during the post-rift phase. A pre-rift (?Mesozoic) sedimentary succession partially underlies the Cretaceous depocentres.
Potential source rocks (coal or lacustrine) may occur in the pre-rift and syn-rift successions. Basin modelling indicates deeper depocentres are currently within the oil or gas generation window. Reservoirs may be late syn-rift and early post-rift fluvio-deltaic, shoreline and turbiditic sandstones. Potential plays include large anticlinal structures, fault blocks, stratigraphic pinchouts and unconformity traps. The extensive fine-grained post-rift sediments may act as a regional seal. Cenozoic magmatism may have enhanced late-stage hydrocarbon generation, but may have affected the integrity of the regional seal.
The findings will guide future exploration in this vast Tasman Sea frontier region and assist in reducing risk.