The Bonaparte Basin, consisting of the Northern Bonaparte and Southern Bonaparte Basins, is the most northerly sedimentary basin in Western Australia, straddling the border between the Northern Territory and Western Australia. Most of the basin is offshore, covering 250,000 km2 compared to just over 20,000 km2 onshore.
To date, offshore production development has relied on stand-alone infrastructure, such as those established since the 1980s at Challis–Cassini, Jabiru, Laminaria, Corallina, and Blacktip. A combined development plan for the Petrel, Tern and Frigate gasfields has been proposed but is yet to be approved.
Geological setting
The Bonaparte Basin adjoins the Browse Basin to the west and the Money Shoals Basin to the northeast. The Timor Trough defines its northern boundary. The basin developed as a v-shaped, north-opening rift during the Devonian to Early Carboniferous.
Exploration in the area defined a sedimentary succession that dips regionally to the north, with the oldest strata outcropping in the south. The dominant structural element of the basin is the north-northwesterly-oriented Petrel Sub-basin, which preserves up to 17 km of Paleozoic to Cenozoic sedimentary fill. This sub-basin contrasts with the northern sub-basins (the Ashmore and Sahul Platforms, Vulcan Sub-basin, Londonderry High, and Malita Graben), where the predominantly northeasterly fault trends lie orthogonal to those of the Petrel Sub-basin, and the sedimentary fill is dominantly Mesozoic to Cenozoic. This change in orientation is related to the Late Jurassic breakup of Gondwana.
Exploration history
Petroleum exploration of the Bonaparte Basin commenced in the late 1940s, with reconnaissance work in the onshore area. In 1963, Bonaparte 1, the first well in the Western Australian portion of the basin, was spudded by Alliance Oil Developments. Since then, 92 offshore and 12 onshore wells have been drilled in the Western Australian area. Seismic exploration in the Western Australian Bonaparte Basin to date includes more than 200,000 line km of 2D and 19,084 km2 of 3D seismic offshore and 6650 line km of 2D onshore.
| Table 1. Oil and gas discoveries in the Western Australian onshore portion of the Bonaparte Basin | ||||
| YEAR | FIELD/DISCOVERY | OIL/GAS | FORMATION | FORMATION AGE |
| 1963 | Bonaparte | gas | Milligans Formation | Early Carboniferous |
| 1995 | Waggon Creek | gas and oil | Milligans Formation | Early Carboniferous |
| 1998 | Vienta | gas |
Ningbing Group Milligans Formation |
Late Devonian Early Carboniferous |
Petroleum prospectivity
The prospectivity of the Bonaparte Basin is evident from known oilfields and gasfields (Table 1), particularly those in the northwestern Timor Sea. Subcommercial gas accumulations in lower Paleozoic strata indicate that even the older sedimentary rocks have hydrocarbon potential.
Onshore, the units considered mostly likely to generate hydrocarbons are the predominantly shaly Lower Carboniferous Milligans Formation (TOC up to 2.2%, and S1+S2 up to 4.5 mg/g rock) and the Upper Devonian Bonaparte Formation. Vitrinite reflectance measurements suggest that these units are immature to mid-mature in the onshore part of the basin, apart from near the Pincombe Inlier, where Devonian rocks are in the gas generation window, possibly as a result of high heat flow in this area. Gas discoveries in the Western Australian onshore area are Vienta, Waggon Creek and Bonaparte.
Read more about the geology and petroleum prospectivity of the Bonaparte Basin (page 29)