Areas NT07-3, NT07-4, NT07-5 and W07-4

Petrel Sub-basin, 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.

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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).


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Petrel Sub-basin Exploration History

In 1839, the crew of HMS Beagle found bitumen in water wells sunk on the banks of the Victoria River in the southern Petrel Sub-basin. This is one of the earliest oil shows documented in Australia. Since initial petroleum exploration began in the early 1950s, a significant number of accumulations have been discovered including: offshore - Barnett, Blacktip, Fishburn, Lesueur, Penguin, Petrel, Tern and Turtle; and onshore - Bonaparte, Garimala, Keep River, Vienta, Waggon Creek and Weaber. To date, there has been no commercial hydrocarbon production from these discoveries. However, Blacktip is currently being developed for domestic gas to Darwin. The petroleum-bearing reservoirs are found in numerous Carboniferous and Permian formations.

There is good seismic coverage over all of the release areas. Areas NT07-3, NT07-4, NT07-5 and W07-4 have data coverage with a range of survey vintages from 1964 onwards, the most recent being the East Petrel survey shot by NOPEC in 1997, who acquired almost 2000 km of data. Geoscience Australia acquired approximately 2200 km of deep seismic data, AGSO 100, in the region during the 1990s.

Relevant wells

The release areas are in close vicinity to a number of hydrocarbon discoveries. Area NT07-3 is located adjacent to the Petrel gas discovery and in proximity to the Tern and Blacktip gas fields. Area NT07-4 contains the exploration well Billawock 1 (1992), which has oil indications. Area NT07-5 is in proximity to the Blacktip gas field and contains the Shakespeare 1 (2003) and Kinmore 1 (1971) exploration wells. Shakespeare 1 contains oil indications, and Kinmore 1 contains oil and gas indications. Area W07-4 is in the vicinity of the Blacktip gas discovery and contains the Matilda 1 (1985) exploration well. This well has oil and gas indications.

Petrel Gas Field - Petrel 1 (1969), Petrel 1A (1970), Petrel 2 (1971), Petrel 3 (1982), Petrel 4 (1988), Petrel 5 (1994), and Petrel 6 (1996).

The Petrel gas field was discovered in 1969 and since then a total of six wells have drilled the structure. The accumulation lies 270 km west of Darwin and is currently held under the retention leases NT/RL1 and WA-6-R. The accumulation is hosted within the Hyland Bay Formation and trapped within a domal feature, the Petrel Anticline (Figure 6). Initial gas reserves are estimated to be 535 BCF (NTDBRID, 1997). The gas at Petrel is moderately dry, with condensate to gas ratios of between 2.8 and 50.5 cubic metres of condensate per million cubic metres of gas (0.5 and 9 bbls/MMscf, respectively).

Tern Gas Field - Tern 1 (1971), Tern 2 (1982), Tern 3 (1982), Tern 4 (1994), and Tern 5 (1998).

The Tern gas field was discovered in 1971, with a total of five wells drilling the structure. This accumulation is situated 300 km west of Darwin and approximately 50 km to the southwest of the Petrel gas accumulation, which is situated within the exploration permit WA-18-P. The accumulation is hosted in the Hyland Bay Formation within a salt-related faulted anticline (Figure 7). Initial gas reserves are estimated to be 415 BCF with 5.7 MMbbls of oil/condensate (DIR, WA, 2002).

Penguin 1 (1972) was drilled by Arco and is located between Petrel and Tern. A thick sequence of sedimentary rocks ranging from Lower Permian to Recent was penetrated and the well reached a total depth (TD) of 2757 m. Several gas shows were recorded near the base of the Late Permian Hyland Bay Formation, and two FIT's at 2540 m and 2535 m recovered 3.6 and 3.5 m3, respectively, of methane.

Kinmore 1 (1974) was drilled by Australian Aquitaine Petroleum Pty Ltd in permit NT/P17 targeting the Kulshill Group on the southeastern flank of a salt diapir on the northwest-plunging Bougainville/Kinmore anticlinal ridge. The well reached a TD of 3250 mKB, with oil and gas indications intersected in the Kulshill Group.

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Turtle and Barnett Oil and Gas Discovery - Turtle 1 (1984), Turtle 2 (1989), Barnett 1 (1985), Barnett 2 (1989), and Barnett 3 (1990).

The Turtle and Barnett accumulations were discovered on the Turtle-Barnett High in 1984 and 1985, respectively. The discoveries are located approximately 320 km southeast of Darwin in permit WA-318-P. The oil is reservoired in sandstones of the Keyling Formation, Treachery Shale, Kuriyippi Formation, Tanmurra Formation and Milligans Formation, and gas is reservoired in sandstones of the Langfield Group. The reservoirs are located in a large domal drape closure. Initial oil reserves are estimated to be 7.7 MMbbls for Turtle and 9.6 MMbbls for Barnett (DIR, WA, 2002).

In two drill stem tests (DSTs) carried out in Barnett 2, 39°API oil flowed to the surface on jet pump at rates of 120 and 146 m3/d (752 and 921 bbls/d, respectively) from the Kuriyippi Formation. A DST undertaken within the Langford Group flowed gas to the surface at a rate of 2550 m3/d (0.09 MMscf/d), with a trace of 44°API condensate. Medium to light (33 to 36°API) oil was recovered (but did not flow) from the Treachery Shale during two DST's carried out in Turtle 1, and from the Tanmurra and Milligans formations during two DSTs carried out in Turtle 2. Oil was also recovered by wireline formation tests carried out in Barnett 1, Turtle 1 and Turtle 2 (Durrant et al, 1990).

Conventional cores were cut in the silty sandstone reservoirs at Barnett 1, 2 and 3, and at Turtle 1 and 2. The reservoir sandstones contained residual oil, and had an average core-plug porosity of 17 % and an average permeability of 10 mD. These sandstones exhibit poor reservoir characteristics due to the presence of a calcareous matrix and authigenic clays. However, these units often show extensive fracturing. Drilling problems encountered at Turtle 2 are attributable to an extensive network of fractures developed in the oil-bearing reservoirs.

Matilda 1 (1985) was drilled by Western Mining Corporation Ltd in permit WA-128-P targeting the Kulshill Formation in the basinward flank of a salt-induced structure. The well reached TD at 2313 mRT, with oil and gas indications intersected in the Kulshill Group and Fossil Head Formation. The Matilda structure relied on fault seal of the Kulshill Formation against an intrusive salt. The lack of hydrocarbon shows in the well may be due to leakage along the fault planes.

Billawock 1 (1992) was drilled by BHP Petroleum in permit NT/P43 targeting deltaic sandstones of the Treachery Shale in a roll-over anticline on the down-thrown side of a major basin-margin fault. The well reached a TD of 1734 mRT and confirmed the high quality of the target reservoirs. Oil indications were intersected in the Hyland Bay, Fossil Head, Keyling, Treachery and Kuriyippi formations. These are believed to be sourced in situ from immature–early mature source material. Post-drill analysis concluded that the Billawock structure probably does not have access to mature source rocks.

Blacktip 1 (2001) was the discovery well for the Blacktip gas field. The accumulation is situated approximately 300 km southwest of Darwin, within permit WA-279-P. The gas is hosted in the Keyling Formation in a four-way-dip closure. Initial gas reserves are estimated to be 1139 BCF with 1.9 MMbbls of condensate (DIR, WA, 2002). Blacktip North 1 was drilled by ENI in October–December 2006; however, this well was dry. Further information for this well is not currently available.

Sandbar 1 (2001) was drilled by Woodside Energy Ltd in the western portion of the Cambridge Trough and targeted a basin-floor fan, but failed to intersect significant hydrocarbons.

Shakespeare 1 (2003) was drilled by Woodside in permit NT/P57. The well reached a TD of 2182 m with oil indications. The well is still confidential and further information is unavailable at this time.

Polkadot 1 (2004) was drilled by Woodside in permit WA-313-P, near Penguin 1. Gas was encountered but this well is still confidential and further information is unavailable at this time.


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Relevant Wells Listing

Well Operator Year Total Depth (m) Hydrocarbons
Barnett 1 Australian Aquitaine Petroleum Pty. Ltd. 1985 2350 Oil & gas indications
Barnett 2 Elf Aquitaine Exploration Australia Pty Ltd 1989 2817.6 Oil recovered, gas indication
Barnett 3 Santos Limited 1990 1700 Oil & gas indications
Billawock 1 BHP Petroleum 1992 1734 Oil indication
Blacktip 1 Woodside Energy Ltd 2001 3181 Proven gas zone, oil indications
Blacktip North 1 Woodside Energy Ltd 2006 N/A Drilling at time of publication
Bougainville 1 Australian Aquitaine Petroleum Pty. Ltd. 1972 2676 Gas indications
Cambridge 1 Western Mining Corporation Limited 1984 2228 Oil & gas indications
Kingfisher 1 Teikoku Oil (Bonaparte Gulf) Co., Ltd. 1994 3257 Oil & gas indications
Kinmore 1 Australian Aquitaine Petroleum Pty Ltd 1974 3250 Oil & gas indications
Kulshill 1 Aust Aquitaine Petroleum 1966 4394 Oil & gas indications
Kulshill 2 Aust Aquitaine Petroleum 1966 1961 Oil & gas indications
Lacrosse 1 Arco Limited 1969 3054 Oil & gas indications
Matilda 1 Western Mining Corporation Limited 1985 2313 Oil & gas indications
Moyle 1 Aust Aquitaine Petroleum 1966 539 No shows
Penguin 1 Arco Australia Limited 1972 2756.9 Potential oil zone, oil indications
Petrel 1 Arco Ltd 1969 3979.8 Oil & gas indications
Petrel 1A Arco Australia Limited 1970 4089.8 Gas indications
Petrel 2 Arco Australia Limited 1971 4724.7 Potential oil zone, oil indications
Petrel 3 Australian Aquitaine Petroleum Pty. Ltd. 1982 3970 Proven gas zone, oil indications
Petrel 4 Elf Aquitaine Exploration Australia Pty. Ltd. 1988 3975 Proven gas zone, oil indications
Petrel 5 Santos Limited 1994 3935 Proven gas zone
Petrel 6 Santos Limited 1996 3915 Oil & gas indications
Polkadot 1 Woodside Energy Ltd. 2004 3791 Gas indications
Sandbar 1 Woodside Energy Ltd 2001 2950 Oil & gas indications
Shakespeare 1 Woodside Energy Ltd 2003 2182 Oil indication
Sunbird 1 Teikoku Oil (Bonaparte Gulf) Co., Ltd. 1994 3324 Oil & gas indications
Tern 1 Arco Australia Limited 1971 4351.9 Gas indications
Tern 2 Australian Aquitaine Petroleum Pty Ltd 1982 3140 Proven gas zone
Tern 3 Australian Aquitaine Petroleum Pty Limited 1982 2683 Gas indications
Tern 4 Santos Limited 1994 2700 Proven gas zone
Tern 5 Santos Limited 1998 2702 Proven gas zone
Turtle 1 Western Mining Corporation Limited 1984 2700 Proven oil zone, potential gas zone
Turtle 2 Western Mining Corporation Ltd 1989 2760 Oil recovered, gas indication
Weasel 1 Woodside Energy Ltd. 2003 1776 Oil indication

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