The Architecture and Petroleum Potential of Australia's Onshore Sedimentary Basins from Deep Seismic Reflection Data and Petroleum Maturation Systems Modelling; the Arrowie, Georgina and Darling Basins

Many of the onshore sedimentary basins in Australia are underexplored with respect to hydrocarbons. The Onshore Energy Security Program was funded by the Australian Government over five years (2006-2011) for Geoscience Australia to provide precompetitive geoscience data and assessments of the potential of some frontier onshore sedimentary basins for energy resources, including hydrocarbons, uranium, thorium and geothermal energy. The basins studied in this project include the Burke River Structural Zone of the Georgina Basin (northwest Queensland), the Yathong Trough in the eastern Darling Basin (western New South Wales), and the Arrowie Basin (South Australia). The interpretation of deep seismic reflection profiles and petroleum systems maturation modelling was undertaken in these basins to increase the understanding of their petroleum potential. 

The Arrowie Basin seismic data shows an asymmetrical basin architecture, with the basin fill being
~3800 m at its thickest. Several sequence boundaries are mapped in this seismic section, and are
correlated with the sequence boundaries between the major Neoproterozoic stratigraphic groups in
the Adelaide Rift System. In the easternmost part of the seismic section, a series of east-dipping
thrust faults disrupt the stratigraphic section. The petroleum systems maturation modelling shows
that potential Cambrian source rocks are likely immature to mature for oil generation. In contrast,
potential Neoproterozoic source rocks are likely to be mature to overmature for oil generation, and
immature to mature for gas generation. With hydrocarbon systems clearly present in the Arrowie
Basin as shown by bitumen in shallow exploration wells drilled in the 1950's, future work, possibly
with a focus on unconventional hydrocarbons, would be warranted.

The Burke River Structural Zone of the Georgina Basin seismic data shows the basin is ~65 km
wide, with a half-graben geometry, being bounded in the west by a rift border fault. The succession in the basin has a maximum thickness of ~2800 m, with the stratigraphy being relatively flat lying, and thickening towards the west. The petroleum systems maturation modelling shows potential Cambrian source rocks are likely to be oil mature. Significant generation and expulsion probably occurred early in the burial history, in response to Cambrian-Ordovician loading. Expulsion occurred after trap formation in the Neoproterozoic-Cambrian, but before later trap formation in the Devonian. The required long preservation time and unroofing are the major risk factors within the basin.

The Yathong Trough of the Darling Basin seismic data interpretation shows that the basin fill consists of a thick succession characterised by alternating high and low amplitude seismic reflections, interpreted to represent the expected Devonian succession mudstones and sandstones. 

The basement units below the Yathong Trough are interpreted to be Ordovician turbidites and
Ordovician-Silurian granites, considered to be part of the Lachlan Orogen. The petroleum systems
maturation modelling shows that potential Lower and Middle Devonian source rocks are likely to be
overmature for oil generation and mature for gas generation. Generation and expulsion from Lower
and Middle Devonian potential marine source rocks occurred early during their burial history, prior
to Carboniferous uplift and erosion, and thus, major trap formation. Later burial during the Permian
and/or Cretaceous may have resulted in minor gas generation and expulsion from a Middle Devonian
potential source rock.

Tags: Earth Sciences, GA Publication, Published_External, Record, petroleum exploration, seismic reflection
Organization: Australian Ocean Data Network