Areas AC07-1, AC07-2, AC07-3, AC07-4 and AC07-5
Ashmore Platform, Bonaparte Basin
Exploration History
Bonaparte Basin Exploration Overview
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, 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 Formation, 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 nine in the Petrel Sub-basin, four on the Sahul Platform, six in the Vulcan Sub-basin, two on the Londonderry High, and two on the Ashmore Platform. Several significant petroleum discoveries were made during this period including Puffin, Troubadour and Sunrise.
Between 1975 and 1982 relatively low levels of exploration drilling were recorded in the offshore Bonaparte Basin (a total of eight wells) due to disputation between Indonesia and Australia over sovereignty of the sea-bed boundary.
The discovery in 1983 of economic oil and gas 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 Challis and Cassini fields is via Floating Production Storage and Offloading Vessels (FPSOs). Production ceased at Skua in 1997.
During the mid 1980s, two non-commercial discoveries of oil were made in stacked reservoirs within the Early Carboniferous Milligans Formation and Late Carboniferous to Early Permian Kuriyippi Formation at Turtle 1 (1984) and Barnett 1 (1985) in the inshore 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 other oil and gas discoveries were made. Further to the north on the Troubadour Terrace, Evans Shoal 1 (1988) identified a significant gas accumulation within the Jurassic Plover Formation, with the appraisal well, Evans Shoal 2, being drilled later in the same year.
Resolution of the territorial dispute between Indonesia and Australia in 1991 established of the Zone of Cooperation (ZOC) and allowed exploration on the Sahul Platform 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, with the discovery of oil at Elang 1 and the identification of a new oil play on the Flamingo and Laminaria highs.
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. In that year, only one exploration well (Jura 1) was drilled in the former ZOC Area A. Since that time, Coleraine 1 (2000) and Kuda Tasi 1 (2001) have been drilled within ZOC Area A. These wells were followed by oil recoveries at Kuda Tasi 2 (2003) in what is now known as the Joint Petroleum Development Area (JPDA).
Exploration drilling on the Londonderry High in 2000 identified numerous gas accumulations within the Hyland Bay Formation at Prometheus 1, Rubicon 1, Ascalon 1A and Saratoga 1.
In the Petrel Sub-basin, two wells (Sandbar 1 and Blacktip 1) were drilled during 2001 in the inshore portion of the basin. No hydrocarbons were encountered in Sandbar 1, but Blacktip 1 was completed as a gas discovery. This well encountered a 20 m gross gas column within the Triassic Mount Goodwin Formation, and a 339 m gross gas column from several high quality, stacked reservoir zones within the Early Permian Keyling Formation. Further drilling in the Petrel Sub-basin met with limited success, with Shakespeare 1 and Weasel 1 having minor oil and gas indications. Polkadot 1 (2004) encountered non-commercial gas in the Hyland Bay Formation, but the recently drilled well Blacktip North 1 (2006), which also targeted gas in this formation, was dry.
Although drilling continued in the Vulcan Sub-basin throughout 2002–2003,
no new commercial discoveries were made. However, from June 2005 to mid-2006,
there has been a revival in exploration success with the wildcat wells Katandra
1, 1A and Vesta 1 discovering both oil and gas. The development wells Puffin
7 and 9 recovered oil, and the extension/appraisal wells to the Montara
field by Coogee Resources successfully discovered more oil at Swift North
1, ST1 and Swallow 1.
During 2002–2003, drilling on the Laminaria High and Flamingo High
has been 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.
Drilling has been active in the Malita and Calder graben area since mid-2005, with gas discoveries been made at Caldita 1 (2005), Evans Shoal South 1 (2006) and Barossa 1, ST1 (2006), with appraisal drilling continuing at Caldita 2 (2007).
Ashmore Platform Exploration History
Drilling on the Ashmore Platform commenced in 1968 with the Ashmore Reef 1 stratigraphic well drilled by BOC of Australia Limited to a total depth (TD) of 3915 m in 39 m of water.
Only one well has been drilled in Area AC07-1, Cromwell 1A, which was drilled by OMV Australia Pty Ltd in 2001. It tested the Early–Middle Jurassic Plover Formation on a horst structure, but no significant shows were observed. No effective top seal was intersected and this is postulated to be the primary reason for the absence of hydrocarbons.
Four wells have been drilled in Area AC07-2; all on the Ashmore Platform.
Sahul Shoals 1 (1969–70) was drilled by BOC of Australia Limited with a TD of 3802 m in 28 m of water. It was drilled as a subsidised well and tested what was mapped as a large anticlinal structure. The well reached Permian limestones, but no significant shows were encountered.
Pollard 1 (1984) was the next well drilled by BHP Petroleum Pty Ltd. The well reached at TD of 2702 m in 303 m of water. It was designed to test Triassic sands mapped within a Base Cretaceous closure; however, no significant hydrocarbon shows were observed.
Pokolbin 1 (1990) was drilled by TCPL Resources to a depth of 2271 m in 208 m of water. The well targeted the Triassic Upper Pollard and Challis formations on a horst block structure. Good quality reservoirs were encountered, but no significant hydrocarbon shows were observed. Post-drill, the structure is considered valid; however, significant faults to the surface present a leakage risk.
Warb 1A (1992) was drilled by WMC to a TD of 2583 m in 329 m of water. The objective of the well was to test an interpreted sand build-up that was considered to comprise stacked submarine fans. However, drilling showed this was not the case. No significant shows were observed in the target, but residual oil shows were observed in cuttings and sidewall cores from the Miocene Oliver Formation.
Five wells have been drilled in Area AC07-3.
Rainbow 1 (1985) was drilled by BHP Petroleum Pty Ltd to a TD of 2700 m in 135 m of water. The well tested prognosed Late Triassic sands within a Base Cretaceous closure on a horst block structure. The well intersected a thick Triassic carbonate section. However, the lack of shows was attributed to faults on the structure creating poor seal capacity and possibly unfavourable hydrocarbon migration pathways.
Pascal 1 (1990) was also drilled by BHP Petroleum Pty Ltd, with the well reaching a TD of 2850 m in 100 m of water. The primary objectives of the well were an areally large low relief structure, interpreted to be a Late Cretaceous Puffin Formation submarine fan and Late Triassic Nome Formation sands below the Base Cretaceous Unconformity. Good quality Puffin Formation sands were intersected, but were water wet. The Nome Formation was absent, with the well intersecting Challis Formation sands below the unconformity. No hydrocarbons were encountered.
TCPL then drilled the next three wells in relatively rapid succession. Rothbury 1 (1991) was drilled to a TD of 3027 m in 115 m of water. The well targeted interpreted Late Jurassic Upper Swan Formation; however, this formation was absent and Lower Swan Formation was intersected. Minor shows were absent, but no reservoir quality units were intersected.
Great Eastern 1 (1991) followed immediately after Rothbury 1 and reached a TD of 2800 m in 114 m of water. The well targeted a four-way dip closure mapped at both Cretaceous and Eocene levels. The primary target was the Puffin Formation with the Grebe Member of the Hibernia Formation the secondary target. The primary target proved to be tight and post-drill analysis suggests that the well was drilled outside closure.
Caversham 1 (1992) was drilled to a TD of 3048 m in 115 m of water. The objective of the well was the Upper Swan Formation and, while geochemical analysis suggests that hydrocarbons could have migrated through the structure, no reservoir quality sandstones were intersected.
Mount Ashmore 1B (1980) was drilled by Woodside Petroleum Development Pty Ltd to a TD of 2655 m in 623 m of water, and is the only well drilled to date in Area AC07-4. The well targeted Middle to Early Jurassic and Triassic reservoirs in a large dome shaped structure; however, no significant shows were observed.
Two wells have been drilled in Area AC07-5.
Delta 1 (1988) was drilled by Elf Aquitaine Exploration Australia Pty Ltd to a TD of 2900 m in 205 m of water. The well targeted Maastrichtian sands draped over a horst block structure, and it terminated in the Cretaceous section. No significant shows were encountered.
Lucas 1 (1990) was drilled by Santos Limited to a TD of 2800 m in 90 m of water, and targeted sandstones in the Late Cretaceous Puffin Formation and Late Triassic Nome Formation on a east-northeast to west-southwest-trending faulted anticline on the eastern edge of the Ashmore Platform, 19 km west of the Puffin Field. While good quality reservoirs were encountered, no significant shows were observed. The lack of hydrocarbons may be attributed to discontinuous migration pathways from potential source areas in the Vulcan Sub-Basin.
Cartier 1 (1988) was drilled immediately to the north of Area AC07-5 by Santos Limited and targeted Middle to Late Triassic sandstones in a tilted fault block structure, but the targets were water wet. Cretaceous sands overlying the structure were intersected, although they had not been interpreted. These could contribute to poor sealing properties for the structure.
Figure 1 shows that numerous other wells have been drilled in the vicinity of the release areas.
Relevant Wells Listing
| Well | Operator | Year | Total Depth (m) | Hydrocarbon |
|---|---|---|---|---|
| Cartier 1 | Santos Limited | 1988 | 2635 | |
| Cash 1 | Coastal Oil and Gas Australia 20 Pty Ltd | 2002 | 2172 | |
| Caversham 1 | TCPL Resources Ltd | 1992 | 3080 | Oil indication |
| Cromwell 1 | OMV Australia Pty. Ltd. | 2001 | 397 | |
| Cromwell 1A | OMV Australia Pty. Ltd. | 2001 | 2032 | Oil indication |
| Delta 1 | Elf Aquitaine Exploration Australia Pty Limited | 1988 | 2900 | Gas indications |
| Great Eastern 1 | TCPL Resources Ltd | 1991 | 2800 | |
| Gryphaea 1 | BHP Petroleum Pty Ltd | 1987 | 3950 | Oil & gas indications |
| Langhorne 1 | TCPL Resources Ltd | 1991 | 2600 | |
| Lucas 1 | Santos Ltd | 1990 | 2800 | No shows |
| Maple 1 | BHP Petroleum | 1990 | 4230 | Proven gas zone, oil shows |
| Mount Ashmore 1 | Woodside/Burmah Oil NL | 1980 | 664 | |
| Mount Ashmore 1A | Woodside/Burmah Oil NL | 1980 | 1058 | |
| Mount Ashmore 1B | Woodside Petroleum Development Pty Ltd | 1980 | 1680 | |
| Mount Ashmore 1B ST1 | Woodside Petroleum Ltd | 1980 | 2655 | Oil indication |
| Paqualin 1 | BHP Petroleum | 1989 | 4242 | Oil & gas indications |
| Parry 1 | BHP Petroleum | 1988 | 2469 | Oil indication |
| Pascal 1 | BHP Petroleum | 1990 | 2850 | No shows |
| Pituri 1 | BHP Petroleum Pty. Ltd. | 1994 | 2124 | Proven oil zone, gas indication |
| Pokolbin 1 | TCPL Resources Ltd | 1990 | 2271 | |
| Pollard 1 | BHP Petroleum Pty. Ltd. | 1984 | 2702 | Oil & gas indications |
| Prion 1 | Arco Australia Limited | 1974 | 2960.5 | Gas indications |
| Puffin 1 | Arco Australia Limited | 1972 | 2961.1 | Potential oil & gas zones |
| Puffin 2 | Arco Australia Limited | 1974 | 2560 | Proven oil & gas zones |
| Puffin 3 | Arco Australia Limited | 1975 | 2470 | Proven oil zone, gas indication |
| Puffin 4 | BHP Petroleum | 1988 | 2456 | Strong oil indication |
| Puffin 5 | AEC International (Australia) Pty Ltd | 2000 | 2414 | Gas flowed on test, oil shows |
| Puffin 6 | AEC International (Australia) Pty Ltd | 2001 | 2326 | Oil indication |
| Puffin 7 | AED Oil Limited | |||
| Puffin 9 | AED Oil Limited | 2006 | 2388 | |
| Rainbow 1 | BHP Petroleum Pty. Ltd. | 1985 | 2700 | |
| Rothbury 1 | TCPL Resources Pty Ltd | 1991 | 3027 | Oil indication |
| Sahul Shoals 1 | B.O.C. of Australia Limited | 1970 | 3802.4 | Oil & gas indications |
| Swan 1 | Arco Australia Limited | 1973 | 3284.2 | Proven gas zone |
| Swan 2 | Citco Australia Petroleum Limited | 1980 | 4063.6 | Oil & gas indications |
| Swan 3 | BHP Petroleum | 1991 | 2461 | Proven gas zone, oil shows |
| Swan 3 ST1 | BHP Petroleum | 1991 | 2530 | Proven gas zone, oil shows |
| Tenacious 1 | Cultus Timor Sea Ltd | 1997 | 3205 | Potential oil zone |
| Tenacious 1 DW 1 | Cultus Timor Sea Ltd | 1997 | 3010 | Proven oil zone, gas indication |
| Tenacious 2 | Woodside Offshore Petroleum | 1998 | ||
| Tenacious West 1 | Woodside Offshore Petroleum Pty. Ltd. | 1998 | 3060 | Oil indication |
| Tenacious West 1 ST1 | Woodside Offshore Petroleum Pty Ltd | 1998 | 3030 | Potential oil & gas zones |
| Turbo 1 | Japex AC Ltd | 2000 | 3900 | |
| Warb 1 | Western Mining Corporation Limited | 1992 | 627 | |
| Warb 1A | Western Mining Corporation Limited | 1992 | 2583 | Oil recovered |
| Yarra 1 | TCPL Resources Ltd | 1990 | 3248 | No shows |