Offshore exploration of the Bonaparte Basin commenced in 1965 when regional aeromagnetic data were acquired. This was supplemented by regional seismic coverage acquired between 1965 and 1974. The first offshore exploration wells in the basin, Ashmore Reef 1 and Sahul Shoals 1, located on the Ashmore Platform, were drilled as stratigraphic tests. Although these wells failed to encounter hydrocarbons, they indicated that the Jurassic section is either thin or absent and that Triassic sandstones form potential petroleum reservoirs over much of the Ashmore Platform.
Between 1969 and 1971, seven wells were drilled in the offshore Petrel Sub-basin. This drilling campaign resulted in the discovery of the Petrel and Tern gas accumulations reservoired within the Late Permian Hyland Bay Subgroup, which constitutes a primary exploration target in the outboard Petrel Sub-basin.
In the early 1970s, exploration expanded beyond the limits of the Petrel Basin into the Vulcan Sub-basin and onto the Londonderry High and Sahul Platform. Between 1971 and 1975, 24 wells were drilled; a further five in the Petrel Sub-basin, two on the Sahul Platform, seven in the Vulcan Sub-basin, five on the Londonderry High, three on the Ashmore Platform and two in the Malita Graben. Several significant petroleum discoveries were made during this period including the Puffin (oil), Troubadour (gas) and Sunrise (gas) accumulations.
Between 1975 and 1982 relatively low levels of exploration drilling took place in the offshore Bonaparte Basin (a total of eight wells) due to a dispute over sovereignty of the sea-bed boundary.
The discovery in 1983 of economic oil in Jabiru 1A (which tested a Jurassic horst block in the Vulcan Sub-basin) stimulated further exploration in the offshore part of the Bonaparte Basin, and 21 exploration wells were drilled in the next three years (1984 to 1986). Of these wells, 12 were located in the Vulcan Sub-basin and on the western flank of the Londonderry High. This phase of exploration resulted in the discovery of a further three commercial oil accumulations in the Vulcan Sub-basin (Cassini, Challis and Skua). Oil production from the Jabiru, Skua, Challis and Cassini fields is via Floating Production Storage and Offloading facilities (FPSOs). Production ceased at Skua in 1997.
During the mid 1980s, two non-commercial discoveries of oil were made in stacked reservoirs within the Milligans and Kuriyippi formations at Turtle 1 (1984) and Barnett 1 (1985) in the inboard Petrel Sub-basin.
After a brief downturn in 1987, levels of offshore exploration drilling in the Bonaparte Basin accelerated. Between 1988 and 1990, 31 exploration wells were drilled in the Vulcan Sub-basin. Drilling results from these wells proved disappointing, although several oil and gas discoveries were made. In the northern Bonaparte Basin, Evans Shoal 1 (1988) intersected a significant gas accumulation within the Jurassic Plover Formation. However, it was 10 years before this discovery was appraised with the Evans Shoal 2 well (1998).
Resolution of the territorial dispute between Indonesia and Australia in 1991 established the Zone of Cooperation (ZOC) and allowed exploration on the Sahul Platform and adjacent areas to resume. Between 1992 and 1998, the focus of exploration in the offshore Bonaparte Basin shifted to this area. Of the 73 exploration wells drilled here during this period, 43 were located either on or adjacent to the Sahul Platform, Laminaria High and Flamingo High. The first commercial petroleum success in the area resulting from this phase of exploration occurred in 1994, when Elang 1 discovered liquid hydrocarbons and identified a new oil play on the Flamingo and Laminaria highs. Shell and Woodside carried out appraisal drilling of the Troubadour (Bard 1) and Sunrise (Loxton Shoals 1, Sunrise 2, Sunset 1, Sunset West 1) discoveries. Elsewhere at this time, the only significant oil discovery was at Tenacious 1 (1997) in the Vulcan Sub-basin (Woods and Maxwell, 2004).
In 1999, Timor-Leste was granted independence by Indonesia . This created a climate of uncertainty with regard to petroleum exploration in the Zone of Cooperation (ZOC). In that year, only one exploration well (Jura 1) was drilled in the former ZOC Area A; now known as part of the Joint Petroleum Development Area (JPDA). During 2002-2003, drilling on the Laminaria High and Flamingo High was focussed on the development of the accumulations at Buffalo, Kuda Tasi, Laminaria and Bayu/Undan. Of the few recent exploration wells that have been drilled in this area, Firebird 1 (2005) discovered gas and Kitan 1 (2008) discovered oil.
Exploration drilling on the Londonderry High in 2000 identified numerous gas accumulations within the Hyland Bay Subgroup at Prometheus 1, Rubicon 1, Ascalon 1A and Saratoga 1.
Two wells (Sandbar 1 and Blacktip 1) were drilled during 2001 in the inboard portion of the Petrel Sub-basin. No hydrocarbons were encountered in Sandbar 1, but Blacktip 1 was completed as a gas discovery (Leonard et al, 2004). Further drilling in the Petrel Sub-basin resulted in limited success, with Shakespeare 1 and Weasel 1 recording only minor oil and gas indications. Polkadot 1 (2004) encountered non-commercial gas in the Hyland Bay Subgroup, but the recently drilled well Blacktip North 1 (2006), which also targeted gas in this formation, was dry. Appraisal drilling of the Blacktip structure was carried out by Blacktip 2 (2009). The latest exploration wells to have been drilled in this sub-basin were Marina 1 (2007) and Sidestep 1 (2008).
In January 2001 oil in was discovered in Audacious 1 in the Vulcan Sub-basin (Maxwell et al, 2004). Although drilling continued in the Vulcan Sub-basin throughout 2001-2003, no further commercial discoveries were made. From 2004 to 2005, there was a revival in exploration success in this sub-basin with Katandra 1A and Vesta 1 discovering both oil and gas (Woods, 2004). Development and extension drilling at Puffin continued (Puffin 7-12; 2006-2008), and production via FPSO commenced in October 2007. Extension/appraisal wells successfully discovered more oil at Swift North 1 ST1 and Swallow 1, with the results of Swift 2 to be released. Development drilling of the Montara-Skua-Swift/Swallow oil accumulations has commenced with production to be via FPSO.
Exploration has been active in the northern Sahul Platform and Malita and Calder graben region since the mid-2005, with the gas discovery at Caldita 1 (2005) and appraisal drilling at Evans Shoal South 1 (2006), Barossa 1 ST1 (2006), Caldita 2 (2007) and Heron 2. The most recent well drilled was Blackwood 1 ST1 (2008) by MEO Australia Ltd. This revival of exploration in the northern Bonaparte Basin is partly due to gas now becoming an economically exploitable commodity and also the commissioning of the Wickham Point LNG plant near Darwin.
In summary, 282 exploration wells and 100 extension/appraisal wells have been drilled in the Bonaparte Basin, of these wells, 64 are hydrocarbon discoveries, giving a technical success of 23%.
Updated information on drilling successes, permit histories and reserves can be found in'Oil and Gas Resources of Australia, 2005' (Geoscience Australia, 2005) and from Western Australia's Department of Mines and Petroleum web site (www.dmp.wa.gov.au/371.aspx) and the Northern Territory Department of Regional Development, Primary Industry, Fisheries and Resources web site (www.nt.gov.au/d/Minerals_Energy/) and publications (NT DPIFM, 2007).