The Neoproterozoic to Late Paleozoic-aged Amadeus Basin is a large (~170 000 km2) east–west-trending basin, bounded to the south by the Musgrave Province and to the north by the Arunta Block of the Northern Territory. Commercial oil and gas production is established in the northern part of the basin but the southern part is still a frontier exploration area. Vintage and new seismic reflection data have been used with well data along the south-eastern Amadeus Basin to construct a new structural and depositional model. Three major phases of deformation controlling deposition have been identified. The first phase is characterised by a SW–NE trending structural fabric and is thought to be older than the deposition of the first sediments identified above basement (Heavitree and Bitter Springs formations). The second phase corresponds to the Petermann Orogeny (580–540 Ma) and trends in a NW–SE orientation. The third phase is the Alice Springs Orogeny (450–300 Ma) and is oriented W–E to WNW–ESE in this part of the basin. This tectono-stratigraphic model involving three distinct phases of deformation potentially explains several critical observations: the lack of Heavitree reservoir at Mt Kitty-1, limited salt movements before the Petermann Orogeny (~300 Ma after its deposition) and salt-involved structures that can be either capped by the Petermann Unconformity and overlying Cambrian to Devonian sediments, or can reach the present day surface. Finally, this model, along with availability of good quality seismic data, opens new perspectives for the hydrocarbon exploration of the Amadeus Basin. Each of the tectonic phases impacts the primary petroleum system and underpins play-based exploration.
Regional seismic and sequence stratigraphic analysis of the Browse Basin identified a new Late Cretaceous play fairway involving ponded turbidite systems deposited within confined basins. This work highlighted the potential for isolated sandstone reservoirs in the Middle Campanian sequence of the Caswell Sub-basin. Extensional faults were expected to provide vertical conduits for charge from underlying Early Cretaceous source rocks.The play concept was tested by the drilling of two exploration wells in 2001. The Carbine prospect was a potential stratigraphic trap involving deposition of turbidite sandstones within a localised basin set up by slumping in an intra-slope setting. Carbine–1 penetrated a 77 m thick section of high quality, 100% net-to-gross sandstone but failed to encounter hydrocarbons.A similar ponded turbidite model was invoked for the Marabou prospect although in this case the confined basin was controlled by pre-existing topography at the toe of the slope. The trapping mechanism for Marabou was largely stratigraphic although a small area of anticlinal closure was present. Marabou–1 penetrated 102 m of good quality sandstone with elevated gas readings over the uppermost 22 m. Borehole problems prevented the acquisition of wireline logs or testing but it appears likely that the well penetrated a sub-commercial hydrocarbon column restricted to the four-way dip closure.The well results confirmed the presence of ponded turbidite systems with excellent reservoir characteristics. Further work is required, however, to address the critical risks associated with hydrocarbon migration and updip seal. Nevertheless, ponded turbidite systems remain attractive exploration targets particularly in basins where updip seal is assisted by structuring and where the reservoirs are intercalated with prolific source rocks.
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