Five wells have been drilled in the release areas. Three of these wells are located within NT03-3 and one each in areas NT03-5 and NT03-6 (Figure 1).
Newby-1 (in area NT03-5) was drilled in 1969 to test a stratigraphic pinch-out feature with upper Palaeozoic and Mesozoic reservoirs. No significant hydrocarbon shows were encountered. This well is not regarded as a valid test because of the absence of suitable trapping geometry at its location.
Flat Top-1 (in area NT03-6) was drilled in 1970 to test a stratigraphic pinch-out play of Permian sands at the basin margin. Shows of bitumen and biodegraded oil were observed on cuttings from the Lower Permian Fossil Head Formation. A small quantity of gas with air contamination, recovered by FIT from the Upper Permian Hyland Bay Formation, is interpreted as dissolved gas in formation water. The failure of this well is attributed to the absence of an effective stratigraphic trap.
Heron-1 (in area NT03-3) was drilled in 1971/72 by Arco to test a northeast trending anticline (Figure 3). Closure was subtle and fault dependent with some evidence of intrusive salt structuring. At the target horizons the well intersected thick Flamingo shales resting on the Plover Formation. The validity of the trap is in doubt. Numerous gas shows were recorded in the Jurassic/Cretaceous sections, however no testing was carried out.
Shearwater-1 (in area NT03-3) was drilled in 1974 by Arco to test a northeast trending faulted anticline located along a hingeline between the Sahul Platform and the Malita Graben. The well intersected the Bathurst Island Group unconformably overlying the Plover Formation. The Plover was silicified and tight. There is no doubt surrounding the validity of the trap. The Plover Formation did record residual oil staining over a 10 m interval, but there were no other recorded shows.
Jacaranda-1 was drilled in 1984 by Tricentrol in adjacent permit NT/P63 to test a fault dependent structure flanking the Malita Graben. Flamingo Formation siltstones, shales and sandstones recorded large gas shows. A thin Oxfordian section comprising mainly tight sandstones overlies silicified Plover Formation. There may be some tight gas pay in the Flamingo Formation but the validity of the trap is in doubt. Target reservoirs were of poor quality.
Curlew-1 was drilled in 1974 in the adjacent permit NT/P64 by Arco to test a domal closure over a salt piercement structure. Minor gas shows were encountered in the Flamingo and Plover formations but there was no testing. The validity of the trap is in doubt.
Wonarah-1 (in area NT03-3) was drilled by Shell Development in 1998 targeting a stratigraphic play in the Middle Cretaceous. The well was a dry hole and was plugged and abandoned.
In the last 5 years there has been extensive seismic acquired (25,000 line km) over the release areas. The northern and eastern portions of area NT03-3 are covered by a 2 x 5 km grid. The western portion is covered by a 5 x 5 km grid.
The NT03-4 release area has a 4 x 2 km grid in the east and a 4 x 5 km grid in the west. A 5 km grid, and in places a 4 x 2 km grid, occurs over most of release area NT03-5. Seismic coverage for areas NT03-6 and NT03-7 is not as extensive.
The quality of seismic survey data obtained before 1980 is poor to fair and between 1981 and 1991 is fair to good. The quality of data acquired since 1997 is good.
Situated near NT03-7, the Petrel gas accumulation is a significant discovery made in the Petrel Sub-basin. The Tern gas accumulation lies further to the southwest.
A recent dry gas discovery in WA waters, Blacktip-1, encountered gas pay in five separate intervals; the Permian Mt Goodwin Formation, Hyland Bay Formation, Keyling Formation and Treachery Formation. The gross column is 188 m. The trap at Blacktip-1 is anticlinal and contains reserves of up to 1.2 TCF of sweet, dry gas. Two out of three drill stem tests flowed gas at potentially commercial rates; the total combined flow rate of production tests 1,2 and 3 was 89.4 mmscf/day. The discovery is 300 km from Darwin and occurs in 55m of water. The high productivity of the well in what is a proven gas province and the proximity of the Petrel and Tern fields, together with a strong likelihood of further discoveries, all offer encouragement for future commercial development.