The Georgina Basin is the most prospective undeveloped onshore petroleum province in the Northern Territory, particularly in the southern part of the basin, south of latitude 21°S, where the thickest basinal successions have developed, as well as strong folding related to distal effects of the Alice Springs Orogeny. Most previous petroleum exploration has focused on depocentres on the southern margin, now marked by the Dulcie and Toko Synclines. These depocentres contain regionally extensive, organically rich, oil-mature source rocks, with siliciclastic lenses and some phosphorite-rich layers. The Cambrian succession is the most prospective and is marked at the base by coarse siliciclastic rocks overlain by platform carbonate rocks of Early to Middle Cambrian age. The Middle Cambrian carbonate succession, comprising the Thorntonia Limestone and Arthur Creek Formation, provides a reservoir-source/seal couplet extending over 80 000 km2. Both formations include excellent microbial source rocks, which are mature over wide areas; subordinate reservoir rocks relate to secondary porosity formed in shoal and shoreline deposits. Similar plays occur in the Late Cambrian Chabalowe Formation (Hagen Member), where peritidal carbonate mud and sand are sealed by evaporite. Sediment loading during the Ordovician initiated hydrocarbon generation over wide areas of this very sparsely explored basin, which includes subtle structural traps and large stratigraphic plays.
Georgina Basin (6 CABS papers):
• Extremely rich, oil-prone microbial source rocks in the Middle Cambrian Arthur Creek Formation/Thorntonia Limestone section are pivotal to the exploration effort and there is evidence of widespread oil migration. • The facies architecture of the overlying Steamboat Sandstone comprises recently recognised tidal channel and deltaic facies well represented on seismic, but lacking well control. The potential reservoirs are up to 150 m thick. The basin has been unroofed to some degree leading to shallow target depths of 300 – 1000 m and stratigraphic/structural entrapment could be large (> 50 MMbbl oil-in- place). • Other large stratigraphic plays are Arthur Creek shoals and sandy debris flows, and also Hagen Member shoreline plays, all of which have potential in the tens of millions of barrels.
LANDER TROUGH
Wiso Basin
The Wiso Basin is an extensive Palaeozoic basin (160,000km2) lying west of the Tennant Region, east of the Tanami Region and north of the Arunta Region. The basin has strong similarities with the georgina basin in terms of its stratigraphy and architecture. The major structural feature of the basin is a major fault-conrolled depositional trough on its southern margin, the Lander Trough. The remainder of the basin comprises a Palaeozoic platform succession generally less than 300 m thick. Very little drilling has occurred in the basin and the best well control lies immediately north of the Lander Trough. Seismic and gravity survey data suggest 2000-3000 m of Cambrian to Devonian sediment within the Trough.
The Wiso Basin is largely unexplored for minerals and petroleum. The Lander Trough has potential for hydrocarbons, although little data exists regarding source rock potential or maturity. Based on similarities and correlations with the Georgina Basin, the Wiso Basin has potential base metal mineralisation, particularly MVT-style lead -zinc, along with sedimentary phosphate. There is also significant potential for mineralisation in Palaeoproterozoic basement that underlies the shallow central and northern parts of the Basin.
Wiso Basin:
• This basin has many analogies with the Georgina Basin but a basinal stratigraphic test is required to assess available petroleum systems. • Any success in the Georgina Basin will stimulate exploration in this western counterpart. Amadeus Basin ( 7 CABS papers): • This is a significant producing basin but exploration methodologies lag by 15-20 years. • Recent studies by NTGS and others show the Neoproterozoic in the Amadeus Basin is an attractive gas target, particularly in the southern portion of the basin where large structural and combination plays could provide a major gas resource via fractured reservoirs (Heavitree Quartzite). • Exploration is in its infancy but there is potential for large reserves. • There is also an impetus for gas exploration given the current gas supply contracts for Darwin expire in early 2009 and additional supply for other resource/industrial projects should arise in the next five to 10 years.
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