ABSTRACT

The Permo-Triassic Cooper and Jura-Cretaceous Eromanga basins, together with the Surat/Bowen basins of similar age, form two of the most prolific hydrocarbon-bearing successor basins in Queensland, Australia. Recent renewed exploration in these basins has been highly successful, following the discovery of the Jackson oilfield in 1982, and subsequent widespread application of high resolution regional seismic coverage to identify structural and subtle traps.

Natural gas has been discovered in 29 fields in the Central Eromanga and Cooper basins of southwestern Queensland with total reserves in excess of 1.5 TCF. Fluvial sandstones of the Lower Permian Patchawarra and Upper Permian Toolachee formations contain most of the reserves. Considerable gas-liquid reserves are also found in these reservoirs.

Existing reserves are located primarily in extensional structural traps. Additional gas potential is identified in flank areas of the more prominent structural axes in fault-bounded, pinchout and subunconformity trapping configurations. Numerous untested prospects and leads are identified with the potential to contain approximately 1.5 TCF of gas.

In contrast, the more thoroughly explored Surat/Bowen basins do not contain large untested structural traps. However, detailed grids of high resolution seismic have refined the settings of various plays and lead to the identification of subtle combination traps in this important hydrocarbon province. Despite over 650 exploration wells drilled in the region, it is still relatively unexplored. There is a 50 per cent probability that 80 BCF will be found and a 20 per cent probability that 290 BCF will be discovered in the portion of the basin making up the Roma Shelf.

Future exploration and development will be constrained by the relatively small domestic gas markets. Historically this has been the case for these gasprone terrigenously filled basins, despite low exploration risk.

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