2016 Release Areas

Roebuck Basin

Release Areas W17-4, Offshore Western Australia

Highlights

Bids close on Thursday 19 October 2017

Recent major oil discovery at Phoenix South 1
Liquids-rich gas discoveries at Phoenix South 2, Roc 1 and Roc 2
Adjacent to the proven Northern Carnarvon Basin and Browse Basin hydrocarbon provinces
Shallow to deep water, 150−400 m
Further guidance available, refer to 2017 Special Notices

Release Area W17-4 straddles the boundary between the Rowley and Bedout sub-basins of the Roebuck Basin, offshore Western Australia (Figure 1). The Release Area lies 215 km from the coast in water depths of 150-400 m. The area comprises 78 graticular blocks. Only 16 wells have been drilled in the Roebuck Basin, including discoveries of oil at Phoenix South 1 and liquids-rich gas at Phoenix South 2, Roc 1 and Roc 2.

The Roebuck Basin comprises the Bedout and Rowley sub-basins (Figure 1). The Bedout Sub-basin is filled with approximately 2.5 km of Paleozoic and 7 km of Mesozoic sediments. The Rowley Sub-basin contains about 9 km of Permo-Carboniferous or older strata and up to 6 km of Mesozoic–Holocene sediments. The Rowley and Bedout sub-basins are separated by a structural trend that includes the Bedout High. The anticlinal Bedout High is linked to a late Permian inversion event referred to as the Bedout Movement. The stratigraphy of the Roebuck Basin is summarised in Figure 2.

The only well within the Release Area is East Mermaid 1, located near the northeastern boundary. This well reached TD within strata of Jurassic age. Otherwise, well control is provided by Lagrange 1 (Figure 3) and Bedout 1, both located on the Bedout High to the south of W17-4. These wells intersected strata as old as Triassic (Bedout and upper Keraudren formations) before reaching TD within the Permian Bedout Volcanics. Figure 4 shows the wells and seismic data coverage in the region.

Release Area W17-4 lies over the structural trend that separates the Rowley sub-basin from the Bedout Sub-basin, and includes the northeastern part of the Bedout High (Figure 1). Figure 5 is an interpreted seismic section that depicts the geology of the central part of the Release Area. Structure within the central part of the Release Area is characterised by a series of normal faults that step-down towards the Rowley Sub-basin depocentre. Syn-rift growth is evident in the Permo-Carboniferous succession. In the vicinity of East Mermaid 1, Totterdell et al (2014) have interpreted the presence of large Permo-Carboniferous syn-rift wedges. A pre-Westralian, Carboniferous and older Paleozoic succession is inferred to underlie the Release Area. The conspicuous unconformity at the top-Permian is linked to the Bedout Movement. The Permo-Carboniferous and Triassic intervals both decrease in thickness over the faulted zone. Jurassic and Cretaceous intervals are of essentially uniform thickness across the region, while the Cenozoic succession thickens towards the modern shelf edge located over the inner Rowley Sub-basin.

An active petroleum system in the Bedout Sub-basin was demonstrated by the discoveries at Roc and Phoenix South. The source rocks have been shown to be pre-Jurassic and probably Lower Triassic Locker Shale and Lower to Middle Triassic lower Keraudren Formation (Molyneux et al, 2016). The presence of oil in Phoenix South 1 has challenged the interpretation of a predominantly gas-prone petroleum system in the Roebuck Basin. Petroleum systems modelling indicates that Lower Triassic source rocks are also mature in the Rowley Sub-basin at East Mermaid 1, and between 1500 m and 2500 m water depth in the outer Rowley Sub-basin (Smith et al, 1999; O'Brien et al, 2003).

Other potential source rocks include the fluvio-deltaic Depuch Formation (Jurassic) which includes coaly and algal-rich mudstone and pro-delta marine shales, and Lower Cretaceous marine mudstone. However, these intervals may only be mature where they lie beneath the Cenozoic carbonate wedge in the inner Rowley Sub-basin (Smith et al, 1999). In the absence of well intersections, the presence of Palaeozoic source rocks in the Roebuck Basin, such as those known from the onshore Canning Basin (e.g., Poole Sandstone, Noonkanbah Formation, and marine shales of the Grant Group), is speculative.

Numerous play types have been proposed in the Roebuck Basin where Triassic and Jurassic strata thin towards basin highs. Such a geological setting characterises the greater Phoenix area, as well as the southern margin of the Bedout Sub-basin where it onlaps the Broome Platform of the offshore Canning Basin (Figure 6). Release Area W17-4 occupies a similar geological setting in which Mesozoic strata onlap the structural high between the Bedout and Rowley sub-basins. Upper and lower Keraudren Formation stratigraphic, combination stratigraphic-structural, and stratigraphic pinch-out plays are potentially present. The basal Triassic Locker Shale source rock may be overstepped by younger strata towards the structural high.

The Depuch Formation in East Mermaid 1 is dominated by sandstone and numerous coal intervals that may provide source potential. The potential for plays based on Jurassic reservoirs within the Release Area is limited by light structuring, although the presence of the Cenozoic wedge in the Release Area indicates that the source rocks of this age may be buried deeply enough to be mature. The stratigraphy in East Mermaid 1 indicates that the entire Cretaceous interval in the Release Area is likely to be fine-grained.

Plays based on Permian and older reservoirs are poorly constrained because of the absence of Paleozoic well intersections in the Roebuck Basin. Nonetheless, plays may be postulated based on features evident in the Release Area such as tilted fault blocks, syn-rift wedges, and a potential Lower Triassic regional seal over the top-Permian unconformity.

Petroleum systems elements

Bedout Sub-basin

Sources

Permian marine mudstones, siltstones and shales of the Noonkanbah Formation
Triassic transgressive shales of the Locker Shale and lower Keraudren Formation
Jurassic thin coaly and algal-rich mudstones and prodelta marine shales in the Depuch Formation
Lower Cretaceous transgressive marine shales of the Egret Formation, Broome Sandstone and Mermaid Formation

Reservoirs

Possible Upper Permian reefs
Lower Triassic sandstone-prone facies of the Locker Shale and sandstones of the Lower Triassic lower Keraudren Formation and Middle Triassic upper Keraudren Formation
Middle Jurassic fluvio-deltaic sandstones of the Depuch Formation
Jurassic fluvio-deltaic sandstones of the Depuch Formation (including Athol Formation, North Rankin Formation, and Rankin Beds equivalents from the Northern Carnarvon Basin)
Lower Cretaceous deltaic sandstones of the Egret Formation, Broome Sandstone and Mermaid Formation

Seals

Regional seal

Lower Cretaceous claystones of the Baleine and Mermaid formations which overlie the Callovian unconformity.
Intraformational seals
Triassic seals in the upper and lower Keraudren Formation, Cossigny Member and Locker Shale
Upper Triassic transgressive shales and mudstones of the Bedout Formation (North Rankin Formation equivalent)
Jurassic nearshore claystone beds and prodelta shales of the Depuch Formation (Athol Formation equivalent)

Play Types

(see Figure 6)

Upper Permian reef plays (8).
Faulted anticline plays (2).
Lower Triassic lower Keraudren Formation stratigraphic plays (e.g. sandstones, floodplain sandstones, marine incursion sandstones, amalgamated channels and other fluvio-deltaic plays) (3).
Combination structural and stratigraphic plays in the Lower Triassic (e.g. lower Keraudren Formation) (4).
Lower Triassic structural horst plays (5).
Triassic to Lower Jurassic structural (horst) and stratigraphic plays (e.g. 6 & 7)
Upper Triassic faulted anticline and stratigraphic plays (7).
Upper Triassic (upper Keraudren Formation) delta front and nearshore sandstone stratigraphic plays (7).
Lower Jurassic fluvio-deltaic delta front and nearshore sandstone plays (6).
Lower Jurassic Depuch Formation fluvio-deltaics: delta front, barrier island, amalgamated channels, nearshore sandstones and sub-unconformity plays (6).
Rollovers against basin-bounding faults plays (structural plays).
Triassic onlap along the Bedout High (1).

Well control for W17-4

Bedout 1 (1971)

Bedout 1 was drilled by BOC of Australia Ltd to test the seismically delineated, unfaulted anticlinal dome of the Bedout High. The well reached a total depth of 3073 mRT. The well penetrated Upper Cretaceous claystones and carbonates (465 m thick), Lower Cretaceous clastic sediments (450 m thick), and a thick Jurassic succession (1113 m) of deltaic sandstones with interbedded claystone and coal, including potential source rocks. A thin section (52 m) of Triassic sandstone and claystone overlies volcanic conglomerate in the base of the well. Volcanic rocks were unexpected. Good reservoirs were confirmed in the Lower Cretaceous, Jurassic and Upper Triassic intervals, but no hydrocarbon shows were encountered.

East Mermaid 1 (1973)

East Mermaid 1 was drilled by Shell Development Australia Pty Ltd to test a northeast-southwest-oriented series of low relief anticlinal highs that were mapped in the southeastern part of the Rowley Sub-basin and which display closure in the Middle Jurassic and throughout the Cretaceous. East Mermaid ST1 reached a total depth of 4068 mRT, and intersected a predominantly fine-grained Cretaceous succession and a thick (1184 m) Jurassic succession of sandstone, siltstone and coal. The well confirmed the predicted structural configuration and identified the primary target of Jurassic sandstones as terrestrial in nature. No hydrocarbons were encountered, which was attributed to the lack of a proximal source rock. An AGSO marine survey in 2006 (Jones et al, 2007) indicated that the tested anticlinal structures are associated with the 'Mermaid Fault Zone', in which faults extend to or near the seabed, and are currently active. Trap integrity is accordingly also a high risk at this prospect.

Lagrange 1 (1983)

Lagrange 1 was drilled by BP Petroleum Development Australia Pty Ltd to test Upper Triassic sandstones on the anticlinal crest of the Bedout High, with secondary targets in the Lower to Middle Jurassic and Paleozoic sediments. The well reached a total depth of 3260 mRT and penetrated a succession that is similar to that in Bedout 1 (Figure 3). Palaeozoic targets were not reached because an unexpectedly thick interval of Permian volcanics. Lagrange 1 was plugged and abandoned as a dry hole.

Infrastructure and markets

No infrastructure is present or currently planned within the Roebuck Basin. Given recent exploration successes, future development is under consideration. The nearest oil infrastructure is approximately 260 km to the southwest of W17-4 where the Mutineer-Exeter oil accumulation (Northern Carnarvon Basin) is serviced by the Modec Venture 11 floating production, storage and offloading (FPSO) facility. Fletcher-Finucane is also tied back to the Mutineer-Exeter FPSO. Gas pipelines are in operation approximately 275 km to the southwest of W17-4, servicing the Angel gas accumulation.

Critical risks

Until the recent discoveries at Phoenix South and Roc, the lack of a proven petroleum system was the major risk. The lack of discoveries in the Roebuck Basin was originally attributed to the lack of valid traps caused by the relatively gentle structuring, rather than a lack of hydrocarbon charge. A poor understanding of the petroleum systems, migration pathways and play types across the broader Roebuck Basin is due to the paucity of exploration wells.

The Bedout Sub-basin was initially thought to be gas-prone due to the misinterpreted gas discovery at Phoenix 1 (which is now believed to possess a significant oil column). However, evidence of palaeo-oil columns exist within the basin and the recent discoveries indicate that the Roebuck Basin is both oil- and gas-prone.

Well control within Release Area W17-4 is limited to Mermaid 1, located near the northeastern boundary. Weathered or altered igneous lithologies, such as the Permian Bedout Volcanics (Lagrange 1, Bedout 1), and the Triassic volcanics recently intersected in several Rowley Sub-basin wells (Anhalt 1, Hannover South 1, Steel Dragon 1), are an exploration risk in the Release Area.

NOPIMS data

Data relating to the Release Areas can be downloaded from the National Offshore Petroleum Information Management System (NOPIMS), an online data discovery and delivery system for all Australian offshore petroleum wells and seismic surveys. http://www.ga.gov.au/nopims

Marine and environmental information

Release Area W17-4 characteristics

Release Area W17-4 is located over continental slope, ridge and terrace geomorphic features in water depths of approximately 150-400 m, and is 166 km northwest of the nearest coast at Eighty Mile Beach. Imperieuse Reef is located 4 km to the north, Clerke Reef is 5.5 km to the north and Mermaid Reef Commonwealth Marine Reserve is 3.5 km to the north.
Seabed sediment comprises mainly calcareous tubes and pelagic foraminiferal mud (James et al, 2004). Sediment texture is described as poorly sorted gravel, sand and aragonite carbonate mud (James et al, 2004).
Potential hazards include tropical cyclones. Shallow fluid expulsion structures identified in the release area are unlikely to be caused by hydrocarbon seepage. Sand waves have also been identified (Nicholas et al, 2016).

Commonwealth marine reserves

A portion of Release Area W17-4 overlaps the Argo-Rowley Terrace Commonwealth Marine Reserve (CMR), currently zoned multiple use IUCN VI, and is located 3.5 km south of the Mermaid Reef CMR, 125 km south west of Kimberley CMR and 166 km north of Eighty Mile Beach CMR.

Key ecological features

Release Area W17-4 overlaps the Mermaid Reef and Commonwealth waters surrounding Rowley Shoals key ecological feature. The area is also located 14 km north of the ancient coastline at the 125 m depth contour and 97 km to the south west of the continental slope demersal fish communities (National Conservation Values Atlas, 2017).

Biologically important areas

Release Area W17-4 overlaps or is close to the following biologically important areas (National Conservation Values Atlas, 2017). The Area:

Overlaps the foraging and breeding area for the Little Tern, White-tailed Tropicbird, resident and migrant populations. The Lesser Frigatebird, Brown Booby, Lesser Crested Tern, Roseate Tern and Wedge-tail Shearwater breeding and foraging areas are to the south with breeding sites on the Kimberley and Pilbara coast and islands.
Overlaps with the Pygmy Blue Whale known distribution area and migration corridor to the north of Rowley Shoals along the shelf edge at depths 500–1000 m.
Lies to the north of the Humpback Whale northern migration corridor.
Lies to the north of the summer Flatback Turtle internesting area, offshore of 80 Mile Beach.
Overlaps with the Whale Shark foraging area and northern migration along the 200 m isobath.

Table 1 Breeding periods (b) for key seabirds whose foraging areas are adjacent or overlapping to the Release Area.

	Jan	Feb	Mar	Apr	May	Jun	Jul	Aug	Sept	Oct	Nov	Dec
Brown Booby		b	b	b	b	b	b	b	b	b
Lesser Crested Tern			b	b	b	b
Little Tern							b	b	b	b
Roseate Tern			b	b	b	b	b
Wedge-tailed Shearwater	b	b	b	b				b	b	b	b	b
White-tailed Tropicbird					b	b	b	b	b	b

The Atlas of Living Australia (http://www.ala.org.au/) and the North-West Atlas (http://www.northwestatlas.org) provide further information and visualisations on animals and plants recorded from the release area, including Threatened or Listed Species.

Heritage

No shipwrecks are listed in the area. The wreck of the Lively is located near Mermaid Reef.

References and Information Resources

National Conservation Values Atlas http://www.environment.gov.au/webgis-framework/apps/ncva/ncva.jsf

Atlas of Living Australia http://www.ala.org.au/

Argo-Rowley Terrace Commonwealth Marine Reserve https://www.environment.gov.au/topics/marine/marine-reserves/north-west/argo-rowley-terrace

Mermaid Reef Marine Reserve http://www.environment.gov.au/topics/marine/marine-reserves/north-west/mermaid-overview

Eighty Mile Beach Commonwealth Marine Reserve http://www.environment.gov.au/topics/marine/marine-reserves/north-west

Commonwealth Fisheries http://www.afma.gov.au/fisheries/

North-West Atlas (www.northwestatlas.org)

Western Australian Fisheries http://www.fish.wa.gov.au/Fishing-and-Aquaculture/Commercial-Fishing/

Shipwrecks http://www.environment.gov.au/heritage/historic-shipwrecks/australian-national-shipwreck-database

Geoscience Australia products

Regional geology and seismic

Petroleum geology inventory of Australia’s offshore frontier basins. Geoscience Australia Record 2014/09 by Totterdell et al (2014). http://dx.doi.org/10.11636/Record.2014.009
Line Drawings of AGSO – Geoscience Australia’s Regional Seismic Profiles, Offshore Northern and Northwestern Australia. Geoscience Australia Record 2001/36 by Colwell and Kennard 2001. http://www.ga.gov.au/metadata-gateway/metadata/record/gcat_a05f7892-b56a-7506-e044-00144fdd4fa6/Line+Drawings+of+AGSO-Geoscience+Australia%27s+Regional+Seismic+Profiles%2C+Offshore+Northern+and+Northwestern+Australia

Stratigraphy

Roebuck and Offshore Canning Basin Biozonation and Stratigraphy Chart No.14, by Martinez et al (1998) https://d28rz98at9flks.cloudfront.net/24221/Roebuck_Basin1994.pdf

Petroleum systems and accumulations

Geoscience Australia marine survey SS06/2006 post-survey report: natural hydrocarbon seepage survey on the central North West Shelf, by Jones et al (2007). http://www.ga.gov.au/metadata-gateway/metadata/record/65453/

References

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CARNARVON PETROLEUM LTD, 2016a—[Web page] Roc / Phoenix area volumetric update 14 November 2016 http://www.carnarvon.com.au/wp-content/uploads/2016/11/Roc-Phoenix-volumes.pdf (last accessed 10 April, 2017).

CARNARVON PETROLEUM LTD, 2015—[Web page] Investor Presentation February/March 2017 http://www.carnarvon.com.au/wp-content/uploads/2017/02/1648231.pdf (last accessed 10 April, 2017).

COLLINS, L.B., 2011—Geological setting, marine geomorphology, sediments and Oceanic Shoals growth history of the Kimberley region. Journal of the Royal Society of Western Australia, 94, 89-105.

COLLINS, L.B., JAMES, N.P. AND BONE, Y., 2014—Carbonate shelf sediments of the western continental margin of Australia. In: Chiocci, F.L. & Chivas, A.R. (Eds) Continental Shelves of the World: Their evolution during the last Glacio-eustatic cycle. Geological Society, London.

COLWELL, J.B. AND STAGG, H.M.J., 1994—Structure of the Offshore Canning Basin: first impressions from the new regional seep-seismic data set. In: Purcell, P.G. and Purcell, R.R. (Eds), The Sedimentary Basins of Western Australia: Proceedings of Petroleum Exploration Society Australia Symposium, Perth, 1994, 757–768.

GORTER, J.D., 1996—Speculation on the origin of the Bedout High – a large, circular structure of pre-Mesozoic age in the offshore Canning Basin, Western Australia. PESA News, October/November, 32–33.

JAMES, N.P., BONE, Y., KYSER, T.K., DIX, G.R. AND COLLINS, L.B., 2004—The importance of changing oceanography in controlling late Quaternary carbonate sedimentation on a high-energy, tropical, ocenic ramp: north-western Australia. Sedimentology, 51, 1179-1205.

JONES, A.T., KENNARD, J.M., RYAN, G.J., BERNARDEL, G., EARL, K.L., ROLLEY, N., GORSJEAN, E., AND LOGAN, G.A., 2007 —Geoscience Australia marine survey SS06/2006 post-survey report: natural hydrocarbon seepage survey on the central North West Shelf. Geoscience Australia, Record 2007/21, 693. http://www.ga.gov.au/metadata-gateway/metadata/record/65453/ (last accessed 19 April, 2017).

LIPSKI, P., 1993—Tectonic setting, stratigraphy and hydrocarbon potential of the Bedout Sub-basin, North West Shelf. The APEA Journal, 33(1), 138–150.

LIPSKI, P., 1994—Structural framework and depositional history of the Bedout and Rowley sub-basins. In: Purcell, P.G. and Purcell, R.R. (Eds), The Sedimentary Basins of Western Australia. Proceedings of the West Australian Basins Symposium, Petroleum Exploration Society of Australia, Perth, 769–777.

LISK, M., OSTBY, J., RUSSEL, N.J. AND O’BRIEN, G.W., 2000—Oil migration history of the offshore Canning Basin. The APPEA Journal, 40(2), 133–151.

MARSHALL, N.G., AND LANGM S.C., 2013—A new sequence stratigraphic framework for the North West Shelf, Australia. In: Keep, M. and Moss, S.J. (Eds) The Sedimentary Basins of Western Australia 4: Proceedings of Petroleum Exploration Society of Australia Symposium. Petroleum Exploration Society of Australia, Perth. 1-32.

MARTINEX, J.I., TOTTERDELL, J.M., EDWARDS. D.S., SHAFIK, S., AND GLEN, K.S. 1998—Roebuck and Offshore Canning Basin Biozonation and Stratigraphy Chart No.14. Australian Geological Survey Organisation, Canberra. https://d28rz98at9flks.cloudfront.net/24221/Roebuck_Basin1994.pdf (last accessed April 21, 2017).

MCLOUGHLIN, R.J., DAVIS, T.L.O. AND WARD, T.J., 1988—Sedimentary provinces, and associated bedforms and benthos on the Scott Reef-Rowley Shoals platform off North-West Australia. Australian Journal of Marine and Freshwater Research, 39, 133-144.

MOLYNEUX, S., GOODALL, J., MCGEE, R., MILLS, G., AND HARTUNG-KAGI, B.,—Observations on the Lower Triassic petroleum prospectivity of the offshore Carnarvon and Roebuck basins. APPEA Journal, 2016, 173-201.

NICHOLAS, W.A., CARROLL, A.G., RADKE, L., TRAN, M., HOWARD, F.J.F., PRZESLAWSKI, R., CHEN, J., SIWABESSY, P.J.W. AND NICHOL, S.L. 2016—Seabed Environments and Shallow Geology of the Leveque Shelf, Browse Basin, Western Australia: GA0340 – Interpretive report. Geoscience Australia, Record 2016/18.

O’BRIEN, G.W., COWLEY, R., LAWRENCE, G., WILLIAMS, A.K., WEBSTER, M., TINGATE, P. AND BURNS, S., 2003—Migration, leakage and seepage characteristics of the offshore Canning Basin and northern Carnarvon Basin: implications for hydrocarbon prospectivity. The APPEA Journal, 43(1), 149–166.

OGG, J.G., OGG, G.M. AND GRADSTEIN, F.M., 2016—A Concise Geologic Time Scale: 2016. Elsevier BV, 250 pp.

SMITH, S.A., 1999—The Phanerozoic basin-fill history of the Roebuck Basin. PhD Thesis, University of Adelaide, unpublished.

SMITH, S.A., TINGATE, P.R., GRIFFITHS, C.M. AND HULL, J.N.F., 1999—The structural development and petroleum potential of the Roebuck Basin. The APPEA Journal, 39(1), 364–385.

SMITH, T.E., EDWARDS, D.S., KELMAN, A.P. LAURIE, J.R., LE POIDEVIN, S., NICOLL, R.S., MORY, A.J., HAINES, P.W. AND HOCKING, R.M., 2013—[web page] Canning Basin Biozonation and Stratigraphy Chart 31. Geoscience Australia. http://www.ga.gov.au/metadata-gateway/metadata/record/gcat_e2f14025-512e-3cac-e044-00144fdd4fa6/Canning+Basin+Biozonation+and+Stratigraphy%2C+2013%2C+Chart+31 (last accessed 14 April, 2017).

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