PETROLEUM GEOLOGICAL SUMMARY
RELEASE AREAS W11-4, W11-5 AND W11-6,
ROWLEY SUB-BASIN, ROEBUCK BASIN,
WESTERN AUSTRALIA
Bids Close – 12 April 2012

Under-explored sub-basin.

Offshore extension of the proven Onshore Canning Basin hydrocarbon
province.

Phoenix 1 gas column suggests active petroleum system in area.

Water depths of approximately 80 m to less than 600 m.
2011 Release of Australian Offshore Petroleum Exploration Areas
Release Areas W11-4, W11-5 and W11-6, Rowley Sub-basin, Roebuck Basin,
WA
Release Area Geology
Page 1 of 18
LOCATION
The Rowley Sub-basin Release Areas are located approximately 250 km
north-northeast of Port Hedland, 150 km west of Broome, and 150 km
northwest of the proposed Great Northern Pipeline ( Figure 1). The Release
Areas cover the westernmost inboard region of the Rowley Sub-basin and
extend into the adjacent Bedout Sub-basin, as well as the Broome Platform
and Oobagooma Sub-basin of the offshore Canning Basin. Water depths in
this region range from 80 m in the southeast to 590 m in the west-northwest.
The three Release Areas over the Rowley Sub-basin are, anticlockwise
starting in the northeast, W11-4, W11-5 and W11-6 and comprise
approximately 76, 106 and 100 graticular blocks respectively ( Figure 2.).
While all the Release Areas cover part of the Rowley Sub-basin, a small
portion of W11-4 extends into the western Oobagooma Sub-basin, a small
portion of W11-5 lies within the northern Bedout Sub-basin, and W11-6 also
covers part of the Bedout Sub-basin, Oobagooma Sub-basin and Broome
Platform ( Figure 3). All Release Areas have an interpreted Mesozoic section
with a thickness of 2.2 s (TWT) to greater than 2.8 s (TWT) and contain a
variety of potential structural and stratigraphic plays.
Currently, the petroleum potential of the Rowley Sub-basin is considered poor
due to the perceived absence of a prolific source rock (Smith et al, 1999). The
limited exploration of the sub-basin has made no economic discoveries,
although a tight gas column has been interpreted in Phoenix 1 in the Bedout
Sub-basin ( Figure 1). Evidence of hydrocarbon systems in adjacent subbasins includes the Perindi 1 oil indication in the Oobagooma Sub-basin, and
the Nebo 1 oil discovery in the Beagle Sub-basin.
2011 Release of Australian Offshore Petroleum Exploration Areas
Release Areas W11-4, W11-5 and W11-6, Rowley Sub-basin, Roebuck Basin,
WA
Release Area Geology
Page 2 of 18
RELEASE AREA GEOLOGY
Local Tectonic Setting
The Rowley Sub-basin is a major westward-thickening upper Paleozoic–
Mesozoic depocentre containing about 9 km of Permo-Carboniferous or older
strata and up to 6 km of Mesozoic–Holocene sediments terminated at the
present continental boundary by large rift faults (Smith et al, 1999). The subbasin is separated from the Beagle Sub-basin and Exmouth Plateau of the
Northern Carnarvon Basin to the southwest by the North Turtle Hinge Zone
and Thouin Graben, and from the Bedout and Oobagooma sub-basins by the
Bedout High and Oobagooma High, respectively. The Paleozoic and lower
Mesozoic successions within the Rowley Sub-basin onlap the Broome
Platform, Bedout High and Oobagooma High ( Figure 3).
Structural Evolution and Depositional History of the Sub-basin
The development of the Rowley Sub-basin is largely inferred from what is
known of the geological evolution of the adjacent Bedout Sub-basin and
Canning Basin, including a lower Ordovician–lower Carboniferous section
postulated to underlie the Rowley Sub-basin (Lipski, 1993; Kennard et al,
1994; Smith et al, 1999). The Ordovician–Cenozoic structural and
depositional history of the Rowley Sub-basin can be divided into several
phases (( Figure 4)

Ordovician–middle Carboniferous

Late Carboniferous–Permian

Triassic–Early Jurassic

Early Jurassic–Early Cretaceous

Early Cretaceous–Holocene
The earliest Ordovician to Carboniferous phase began with the first
extensional event recognised in the region, a northeast–southwest extension
in the Ordovician. This was followed by north–south compression and uplift
(Prices Creek Movement) in the Early Devonian. Three northeast–southwest
extensional events occurred in the Late Devonian to Mississippian (early
Carboniferous). Ordovician to middle Carboniferous sedimentary rocks, as
observed in the onshore Canning Basin, primarily consist of alternating
sequences of marine clastic and carbonate rocks, including the primarily
transgressive Devonian Reef Complex and Fairfield Group (Kennard et al,
1994). The north-northwest–south-southeast oblique-slip reactivation of preexisting structures, termed the Meda Transpression, terminated this phase of
deposition (Kennard et al, 1994; Smith et al, 1999).
2011 Release of Australian Offshore Petroleum Exploration Areas
Release Areas W11-4, W11-5 and W11-6, Rowley Sub-basin, Roebuck Basin,
WA
Release Area Geology
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The next phase began in the Pennsylvanian (late Carboniferous) with a
change to the predominantly northeast-oriented structures of the Roebuck
Basin. This was a period of transition from intracratonic extension to extension
related to terrane separation from Gondwana (Metcalfe, 1988; Smith et al,
1999). In parts of the Canning Basin, syn-rift sedimentation continued along
reactivated intracratonic fractures. Pennsylvanian fluvial deposits are overlain
by a thick succession of Permian glacial deposits (Grant Group), in turn
overlain by Permian marine and fluvio-deltaic clastic rocks (Poole Sandstone,
Noonkanbah Formation, Liveringa Group). The basin fill in the offshore
Canning and Roebuck basins during this initial stage is poorly understood.
Overlying the Paleozoic sequence is a prominent regional unconformity
possibly related to the formation of the Bedout High (Colwell and Stagg,
1994).
The Triassic to the Early Jurassic phase was dominated by thermal sag with
transgressive marine and fluvio-deltaic sedimentation (Locker Shale,
Keraudren and Bedout formations). Separating the lower and upper
Keraudren Formation is the Middle Triassic Cossigny Member, a widespread
limestone unit seismically expressed as a high-amplitude reflector. Triassic to
Early Jurassic deposition was punctuated by multiple northwest–southeast
transpressional events, the Fitzroy Movement, focused along the margins of
the sub-basins in the Ladinian, Norian and Sinemurian (Smith et al, 1999).
The next phase from the Early Jurassic to the Early Cretaceous began after
Sinemurian uplift and erosion with accumulation of a broad prograding wedge
of fluvio-deltaic sediments (Depuch Formation). The deposition occurred
during thermal subsidence across the shelf. Continental breakup in the
Callovian resulted in a second phase of prominent uplift and erosion.
Subsequent thermal subsidence allowed accumulation of condensed marine
mudstones (Baleine and Egret formations) until the Early Cretaceous. An
influx of siliciclastic material (Broome Sandstone) occurred in the Valanginian
with further uplift of the sediment source (Smith 1999, Smith et al, 1999).
The most recent phase began with thermal relaxation of the crust soon after
the Valanginian break-up. This led to the development of a passive-margin
succession of marine mudstones and marls. A major progradational
carbonate wedge developed across the entire North West Shelf in the
Cenozoic. Collision of the Australian and Eurasian plates in the mid-Miocene
led to transpressional inversion of north-northwest-trending Paleozoic faults,
especially in the northeast of the adjacent Oobagooma Sub-basin (Smith et al,
1999).
2011 Release of Australian Offshore Petroleum Exploration Areas
Release Areas W11-4, W11-5 and W11-6, Rowley Sub-basin, Roebuck Basin,
WA
Release Area Geology
Page 4 of 18
EXPLORATION HISTORY
Few wells have been drilled in the Roebuck and offshore Canning basins due
in part to the historical perception that these Basins are not highly
prospective. Almost all of the drilling (12 of the total of 15 wells) in these
offshore basins was undertaken in the Oobagooma and Bedout sub-basins in
the early 70s and early 80s, the other three wells were drilled in the outboard
Rowley Sub-basin; East Mermaid 1 (1973), Whitetail 1 (2003) and
Huntsman 1 (2006).
Drilling in the early 70s was underpinned by several small 2D seismic grids
and a few regional 2D grids. In the late 80s to early 90s, more regional 2D
seismic was acquired and the North West Shelf tie lines were shot by AGSO.
An additional episode of seismic acquisition occurred between 1998 and
2002, and included the first 3D grids used to determine objectives drilled in
2003 and 2006 by Whitetail 1 and Huntsman 1 respectively. Currently, two
seismic grids are being acquired by Petroleum Geo-Services (PGS) across
the Release Areas, and other 2D and 3D seismic has recently been acquired
to the south of W11-5. Recent data acquisition in the area conducted by
Geoscience Australia includes a hydrocarbon seepage survey in 2006 over
the Roebuck and offshore Canning Basins and an aeromagnetic survey in the
Oobagooma Sub-basin in 2007.
Within the Roebuck Basin, results to date have been limited to gas shows and
discoveries in the Triassic Sandstones of Phoenix 1 and 2. In the Oobagooma
Sub-basin, Perindi 1 intersected several intervals in Paleozoic clastics and
carbonates with oil indication. In the more intensively explored Beagle Subbasin to the southwest, oil was discovered in the Callovian Calypso Formation
sandstones at Nebo 1 (Osborne, 1994), but no economic discoveries in any of
these offshore basins have been made.
From the 2007 and 2008 acreage release permits immediately to the east and
south of the Release Areas have been awarded ( Figure 1). Woodside
Energy Ltd has WA-415-P and WA-416-P abutting W11-4 and W11-6
respectively. In 2010 Woodside Energy completed a 4,100 km 2D seismic
survey (Koolama 2D) mostly over WA-415-P and WA-416-P (Woodside
Petroleum Ltd, 2010, p.7). The blocks adjacent to W11 and W11-6 are
operated/held by Finder Exploration (WA-435-P and WA-436-P) and
Carnarvon Petroleum Ltd (WA-443-P). Finder Exploration conducted a 15,856
km2 aeromagnetic survey over the entirety of WA-436-P and a portion of WA443-P (Carnarvon Petroleum Ltd, 2010, p. 6), with further plans for 2D and 3D
seismic surveys across WA-435-P and WA-436-P, including a significant
portion of the 1,100 km2 Phoenix 3D survey that should lie within WA-435-P.
Well Control
Nine wells have been drilled in the Roebuck Basin and six in the offshore
Canning Basin; none with commercial success ( Figure 1). Three wells (East
2011 Release of Australian Offshore Petroleum Exploration Areas
Release Areas W11-4, W11-5 and W11-6, Rowley Sub-basin, Roebuck Basin,
WA
Release Area Geology
Page 5 of 18
Mermaid 1, Huntsman 1 and Whitetail 1) have unsuccessfully tested the
potential of the Rowley Sub-basin, including deep-water prospects. East
Mermaid 1 lies within Release Area W11-5, only 10s of meters from Release
Area W11-4 and approximately 1 km west of Release Area W11-6. Six wells
have been drilled in the adjacent Bedout Sub-basin (Bedout 1, Keraudren 1,
Lagrange 1, Minilya 1 and Phoenix 1 and 2), with the only significant
hydrocarbon indications being the tight gas column discovery in Phoenix 1
and gas shows in Phoenix 2. Of the six wells drilled in the offshore Canning
Basin (Kambara 1, Lacepede 1, Minjin 1, Pearl 1, Perindi 1 and Wamac 1) all
are within the Oobagooma Sub-basin. Ten wells have been drilled in the
eastern part of the Beagle Sub-basin, southwest of the Release Areas
(Bruce 1, Cimba 1, Darwin 1, Depuch 1, Halo 1, Huascaran 1, Nebo 1,
North Turtle 1, Picard 1 and Poissonnier 1). The only significant discovery in
the Beagle Sub-basin is a small oil pool at Nebo 1. The following summaries
of key wells are based on the relevant well completion reports.
Lacepede 1 and 1A (1970)
Lacepede 1 and 1A were drilled by BOC of Australia Ltd approximately 129
km northwest of Broome in the central Oobagooma Sub-basin. Lacepede 1
was abandoned at 224 m due to technical difficulties and Lacepede 1A
reached a total depth (TD) of 2,286 mRT. The wells were drilled to test an
elongate east–west-trending anticlinal structure. Lacepede 1A penetrated
Miocene sediments unconformably overlying an Early Cretaceous to
Pennsylvanian (upper Carboniferous) sedimentary succession (originally
interpreted to be upper Permian; Helby and Partridge, 1982). Lacepede 1A
penetrated the most complete Jurassic section in the Canning Basin at that
time, with rocks of Early Jurassic age being recorded for the first time. The
entire Triassic and most of the Permian section is absent, such that Jurassic
(Tithonian–Toarcian) sediments unconformably overlie lower Permian
(Asselian) to upper Carboniferous sediments. No significant hydrocarbons
shows were encountered in the wells. Slight increases in the background gas
readings occurred in the Jurassic and Permian sections and gas prone Middle
to Upper Jurassic shales were identified with TOC of up to 2.3% (Conoco,
1992). However, no fluorescence was observed and wireline logs indicated
100% water saturation throughout the well. Lacepede 1A confirmed the
presence of thick, porous and permeable reservoirs in the Lower Cretaceous
and Jurassic sections and is thought to have adequately tested the
Cretaceous, Jurassic and uppermost Permian sections of the Lacepede
structure.
Bedout 1 (1971)
Bedout 1 was drilled by BOC of Australia Ltd to test the seismicallydelineated, unfaulted, anticlinal dome of the Bedout High. The well reached a
total depth of 3,073 mRT, and penetrated 465 m of Upper Cretaceous
claystone and carbonate, 450 m of Lower Cretaceous clastic sediments, and
a 1,113 m thick Jurassic succession of deltaic sandstone with interbedded
claystone and coal, including potential source rocks. A thin section (52 m) of
Triassic sandstone and claystone overlies volcaniclastic conglomerate in the
bottom of the well. The latter were not anticipated and were interpreted as
2011 Release of Australian Offshore Petroleum Exploration Areas
Release Areas W11-4, W11-5 and W11-6, Rowley Sub-basin, Roebuck Basin,
WA
Release Area Geology
Page 6 of 18
basement. Good reservoirs were confirmed in the Upper Cretaceous, Jurassic
and Upper Triassic intervals, but no hydrocarbon shows were encountered in
the well.
Wamac 1 (1973)
Wamac 1 was drilled by Amax Petroleum (Australia) Inc. to a TD of
2,764 mRT and is located 110 km northwest of Broome in the central
Oobagooma Sub-basin ( Figure 5). The well tested the Paleozoic
sedimentary succession in an east–west elongated structural feature. Seismic
mapping indicated an areal closure of >250 km2 in the Devonian and also
possible closure in the Lower Permian. Wamac 1 penetrated a Quaternary to
Carboniferous sedimentary succession similar to that in Lacepede 1A. The
Paleozoic sediments are intruded by Permian to Lower Triassic dolerite.
Difficulties encountered while drilling one of these sills led to termination of the
well ~900 m above planned TD. Absence of hydrocarbon shows may have
been due to lack of structural closure in the Mesozoic and upper Paleozoic or
low porosity and negligible permeability throughout the Paleozoic, although
logs and lithologic analysis indicate good reservoir quality through the Lower
Cretaceous and Jurassic. Immature source rock intervals in the Jurassic
indicate potential for oil and gas in deeper parts of the basin.
East Mermaid 1 (1973)
East Mermaid 1 lies within Acreage Release Block W11-5 in the southeastern
part of the Rowley Sub-basin, and was drilled by Shell Development Australia
Pty Ltd. It was drilled to test a series of northeast–southwest oriented, low
relief, anticlinal highs mapped and displaying closure in the Middle Jurassic
and throughout the Cretaceous. East Mermaid 1 ST1 reached a total depth of
4,068 mRT, intersecting a predominantly fine-grained Cretaceous succession
and a thick (1,184 m) Jurassic succession of sandstone, siltstone and coal.
The well confirmed the predicted structural configuration and identified the
primary target Jurassic sandstones as terrestrial in nature. No hydrocarbons
were encountered in the well, which was attributed to the lack of a proximal
source rock. Recent research suggests that the tested anticlinal structures are
associated with the 'Mermaid Fault Zone', in which faults extend to or near to
the seabed, and are currently active (Jones et al, 2007). Therefore, trap
integrity is a major risk at this site ( Figure 6).
Minilya 1 (1974)
Minilya 1 was drilled by BOC of Australia Ltd to test an interpreted faultcontrolled positive feature located in the outboard part of the Bedout Subbasin. The well reached a total depth of 2,400 mRT and intersected
Cretaceous claystone, sandstone and carbonates terminating in a succession
of Middle Jurassic sandstone and claystone with minor coal. These
sandstones, the primary objective, showed variable but good porosity.
Sandstones with effective porosity were also intersected in the Upper
Cretaceous succession. No significant hydrocarbon shows were recorded in
the well. Interpretation of seismic data acquired over the area in 1992 (C92A)
suggests that there is no closure on the Minilya 1 structure (Esso, 1994).
2011 Release of Australian Offshore Petroleum Exploration Areas
Release Areas W11-4, W11-5 and W11-6, Rowley Sub-basin, Roebuck Basin,
WA
Release Area Geology
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Phoenix 1 (1980)
Phoenix 1 was drilled by BP Petroleum Development Australia Pty Ltd to test
an interpreted large northeast–southwest trending, elongate anticline
transected by a series of north-northeast to south-southwest trending faults in
the Bedout Sub-basin. These faults were interpreted to have formed four main
culminations, with Phoenix 1 located on the most central of these. More
recent seismic data suggest, however, that structuring in the area is more
complex (Apache, 1995). The primary objective of the well was Middle to
Upper Triassic sandstone of the Keraudren Formation, while Middle Jurassic
sandstone units directly below the Callovian breakup unconformity were a
secondary target. However, seismic data indicated a lack of closure at the
upper objective. The well reached a total depth of 4,880 mRT, exceeding the
planned total depth of 4,450 m after gas-bearing Middle Triassic sandstones
were intersected. Reservoirs in the Keraudren Formation provided good
hydrocarbon indications. Despite good reservoir characteristics in the upper
Keraudren Formation sandstones (average porosity of 14%, ranging from 19–
12%, decreasing with depth), detected hydrocarbons were limited to oil
staining and cut fluorescence. The lower Keraudren Formation sandstone
reservoirs exhibited gas and fluorescence (all sandstones below 4,223 mRT
are gas-bearing; net gas pay is estimated to be 110.5 m over seven zones),
but logs and core analysis indicate very low porosity (average porosity of 9%,
ranging from 4–15%).
Hydrocarbon types in the lower Keraudren Formation sandstones show
fractionation with depth, which suggests intra-formational sourcing of gas and
existence of discrete reservoirs that are not in communication due to
intercalated sealing shales. Drilling was terminated without testing when it
was deemed unsafe to continue with the available pressure-control
equipment. The well was abandoned in January 1983.
Phoenix 2 (1982)
Phoenix 2 was drilled by BP Petroleum Development Australia Pty Ltd to test
Triassic sandstones in a fault block forming part of the 'Phoenix structure' in
the Bedout Sub-basin. The well reached a total depth of 4,967 mRT. The
sedimentary succession intersected is very similar to that in Phoenix 1, but
the basal 591 m of Lower to Middle Triassic Locker Shale is interpreted as the
outboard facies equivalent of the lower Keraudren Formation interpreted in
Phoenix 1. Gas shows are interpreted at low saturations in thin zones within
the Triassic sandstones, which have extremely low permeabilities and
generally poor reservoir qualities. Oil indications, such as natural fluorescence
and possible staining, were also identified. The targeted reservoirs showed
significantly lower permeabilities compared to Phoenix 1, and therefore had
lower hydrocarbon saturations. Calculations based on the low permeabilities,
indicated that commercial hydrocarbon flows could not be obtained from the
reservoir sandstones. Therefore, no production testing was carried out.
Modelling by Lisk et al (2000) suggests the Triassic Keraudren Formation is
mature for gas/condensate and minor oil generation in more deeply buried
sections of the Bedout Sub-basin. This unit is mature in Phoenix 1 and
2011 Release of Australian Offshore Petroleum Exploration Areas
Release Areas W11-4, W11-5 and W11-6, Rowley Sub-basin, Roebuck Basin,
WA
Release Area Geology
Page 8 of 18
predominantly gas prone, with fluorescence and oil staining likley sourced
from thin shales within the unit (Forth and Jourdan, 1982). The Keraudren
Formation at Phoenix 2 is early mature for oil and predominantly gas prone,
but one thin zone is modelled to be capable of generating light oil.
Lagrange 1 (1983)
Lagrange 1 was drilled by BP Petroleum Development Australia Pty Ltd to test
Upper Triassic sandstones on the irregular anticlinal crest of the Bedout High,
with secondary targets in the Lower to Middle Jurassic and, more
speculatively, in Paleozoic sediments. The well reached a total depth of
3,260 mRT and penetrated a sedimentary succession very similar to that in
Bedout 1. Paleozoic targets were not reached because an unexpectedly thick
succession of volcanics (<391 m) was encountered. Lagrange 1 was plugged
and abandoned as a dry hole.
Whitetail 1 (2003)
Whitetail 1 was drilled by Woodside Energy Limited in 953 m of water in the
Rowley Sub-basin. It tested the gas potential of a large tilted fault block
intersected by a series of north–south trending faults. Lower and Upper
Cretaceous regional seals were shown to be present over the structure and
micro-permeability tests indicate effective sealing capacity. The target
reservoir (Depuch Formation) showed average log porosity of 27%, but was
interpreted as water wet to total depth (2,504 mRT). No hydrocarbon shows
were evident. Vitrinite reflectance indicates the sequence penetrated is
immature for hydrocarbon generation, although spore colouration within the
Depuch Formation indicate marginal maturity for oil generation. Analysis of
cuttings, sidewall cores and well logs suggest there was no effective
hydrocarbon charge. Two potential reasons for charge failure are an
ineffective source kitchen and a lack of fault seal to the northwest of the
prospect. Neither were able to be assessed from well results.
Huntsman (2006)
Huntsman 1 was drilled by Woodside Energy Limited as a rank wildcat in the
western Rowley Sub-basin in a water depth of 1,469 m. The well reached a
total depth of 4,375 mRT, and tested Middle and Lower Jurassic reservoir
targets. Quality reservoir sandstones were encountered, but proved to be
water wet with no significant hydrocarbon shows acknowledged (Woodside
Petroleum Ltd, 2006, p. 7). Lack of charge is deemed to be the cause of
failure. Detailed interpretative results had not been released at the time of
writing.
For further details regarding wells and available data follow this link:
http://www.ret.gov.au/Documents/par/data/documents/Data%20list/data%20li
st_rowley_AR11.xls
2011 Release of Australian Offshore Petroleum Exploration Areas
Release Areas W11-4, W11-5 and W11-6, Rowley Sub-basin, Roebuck Basin,
WA
Release Area Geology
Page 9 of 18
Data Coverage
While only one well has been drilled within the Acreage Release Areas (East
Mermaid 1) more than 25 seismic surveys cover these areas. These seismic
surveys are of variable quality and vintage. One of the earlier and more
regional seismic surveys, Mermaid Cartier, acquired in 1973 by the Burmah
Oil Company of Australia Ltd., crosses the Browse, offshore Canning and
Roebuck basins. This survey covers the eastern portion of W11-4 and a few
lines cross into W11-6. During a later stage of regional exploration the Japan
National Oil Company ran two regional surveys, the Offshore Canning Basin
Marine Geophyscial Survey in 1987 and the Offshore Fitzroy Graben in 1988,
providing coverage over the three Release Areas. In 1990 and 1993, AGSO
acquired seismic lines providing regional ties to wells in adjacent basins (
Figure 5 Figure 6 and Figure 7). Several surveys during 1998 and 1999
provide grids with line spacing around 10 km over a large portion of the
Rowley Sub-basin, including half of W11-4 and part of W11-5. The Tarantula
survey, shot by Woodside Energy Ltd in 2000, provides good high resolution
coverage over the western part of W11-5, and the Veritas Browse 2001
MC2D survey provides a grid with 6 to 10 km line spacing over most of W11-4
and some of W11-6. The Tarantula 2D survey is currently being reprocessed
by CGGVeritas and Multiclient Geophysical (MCG). In 2010, PGS acquired
additional regional tie lines crossing the Release Areas including the
Deepwater Canning (Golden Orb) multi-client survey and the New Dawn
survey. No 3D seismic has been obtained within the Release Areas.
Significant gaps in the closely spaced seismic coverage lie along the
boundary between the Rowley and adjacent Sub-basins, and include large
areas of W11-5 and W11-6.
To view image of seismic coverage follow this link:
http://www.ga.gov.au/energy/projects/acreage-release-andpromotion/2011.html#data-packages
Other notable datasets gathered in or near the Release Areas includes the
Geoscience Australia hydrocarbon seepage survey conducted in the Roebuck
and offshore Canning Basins in June 2006; several survey locations are
within W11-4 and W11-5 (Survey SS06/06; Jones et al, 2007). No definitive
evidence of natural hydrocarbon seepage was detected. Head space gas
analyses of gravity core sub-samples, and biomarker screening of sediments
and carbonate concretions, revealed no thermogenic hydrocarbons or
biomarkers diagnostic of methane oxidation. Additionally, two aeromagnetic
surveys have been conducted adjacent to the Release Areas; a Geoscience
Australia survey in 2007 to the east of W11-4 and W11-6 and a Carnarvon
Petroleum and Finder Exploration survey in 2010 to the south of W11-5. The
two surveys cover an area of more than 47,500 km2.
2011 Release of Australian Offshore Petroleum Exploration Areas
Release Areas W11-4, W11-5 and W11-6, Rowley Sub-basin, Roebuck Basin,
WA
Release Area Geology
Page 10 of 18
PETROLEUM SYSTEMS AND HYDROCARBON POTENTIAL
The petroleum potential of the offshore Canning and Roebuck Basins is
currently considered to be poor compared to other areas along the North
West Shelf, because of the perceived absence of a prolific source rock (Smith
et al, 1999). Interpreted mild structural deformation in the Late Jurassic and
Early Cretaceous suggests that restricted depocentres did not exist, thus
claystone source rocks typical of the adjacent Carnarvon and Browse basins
could not accumulate in the Roebuck Basin. Several alternative source rock
intervals have been proposed for the Roebuck Basin (Kennard et al, 1994;
Smith, 1999; Geoscience Australia and Geomark Research, 2005). Table 1
lists these potential source rock intervals along with proposed reservoirs,
seals and play types.
Table 2: Potential Petroleum Systems Elements Summary
Sources
Reservoirs
Seals

Larapintine 2 (Goldwyer Fm, Nambeet Fm)

Larapintine 3 (Pillara and Nullara reef complexes,
Fairfield Grp)

Larapintine 4 (Laurel Fm, Anderson Fm)

Gondwana 1 (Poole Ss, Noonkanbah Fm)

Gondwana 2 (Locker Sh, Keraudren Fm)

Westralian 1 (Depuch Fm)

Westralian 3 (Baleine Fm)

Larapintine 3 and 4 (Tandalgoo Fm Poulton Fm)

Larapintine 3 and 4 (Anderson Fm)

Gondwana 1 (Grant Gp)

Gondwana 2 (Locker Sh, Keraudren Fm)

Westralian 1 (Depuch Fm)

Westralian 3 (Egret Fm, Broome Sdstn, Mermaid Fm)

Gondwana 2 (Locker Sh, Keraudren Fm, Cossigny Mbr)

Westralian 1 (Bedout Fm, Depuch Fm)

Westralian 3 (Baleine Fm, Broome Ss, Mermaid Fm)
2011 Release of Australian Offshore Petroleum Exploration Areas
Release Areas W11-4, W11-5 and W11-6, Rowley Sub-basin, Roebuck Basin,
WA
Release Area Geology
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
Lower–Upper Triassic Locker Sh, Keraudren Fm,
Cossigny Mbr; Onlap

Lower–Middle Jurassic Depuch Fm; Prodelta, Barrier
Island, Channels

Mesozoic to Cretaceous rift related structural traps

Miocene collision structural traps
Play Types
Potential Source Rocks
Although organic-rich marine shales are well documented within the
Ordovician succession of the onshore Canning Basin, it is likely that this
Ordovician Larapintine 2 Petroleum system is not well developed across the
Roebuck Basin and therefore not highly prospective (Taylor, 1992; Kennard et
al, 1994). These sources are characterised by the occurrence of the oil-prone
alga Gloeocapsomorpha prisca, and are particularly well developed on the
terraces along the northern flank of the Broome Platform (Kennard et al,
1994). If source rock intervals do exist they may be generating hydrocarbons
for Mesozoic reservoirs along basin margins (Kennard et al, 1994; Lisk et al,
2000). In the onshore Canning Basin there are several potential Devonian and
Carboniferous source rock intervals (Larapintine 3 and 4), but whether these
intervals are present in the Rowley Sub-basin is unknown (Kennard et al,
1994; Nicoll et al, 2009).
Transgressive Early Permian, Gondwana 1, marine shales of the Poole
Sandstone and Noonkanbah Formation are organic-rich in the Fitzroy Trough
(Kennard et al, 1994), and form part of a global Pennsylvanian (upper
Carboniferous)-Early Permian source unit (Warris, 1993). These sources may
also be present, and are likely to be mature in the more deeply buried portions
of the Roebuck and offshore Canning basins. Marine shales of the underlying
upper Grant Group are also locally organic-rich, but generally have poor
generative potential.
The most prospective petroleum source rock is part of the Gondwana 2
system and was identified by Smith et al (1999) as Tr1 and Tr2 ( Figure 8).
These comprise transgressive shale and minor coal intervals within the
Locker Shale and Keraudren Formation (Esso, 1994; Smith et al, 1999;
Woodside Energy Limited, 2001). The gas discovery in Phoenix 1 and the gas
show in Phoenix 2 are attributed to these source intervals. In the outer Rowley
Sub-basin, middle mature Tr1 and Tr2 could be presently expelling liquids
(Smith et al, 1999; O’Brien et al, 2003).
Belonging to the Westralian 1 system are several thin coaly and alga-rich
layers and correlative pro-delta marine shales of the Depuch Formation.
These have been identified through geochemical studies of well cuttings and
2011 Release of Australian Offshore Petroleum Exploration Areas
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sequence stratigraphic interpretations, and may be early to late mature
beneath the Oligocene carbonate wedge (Conoco, 1992; Smith et al, 1999).
Post-dating the Callovian breakup are potential source rocks of the
Westralian 3 system including the Baleine Formation ( Figure 4). These
transgressive marine deposits occur in large volumes but are only likely to be
mature beneath the Oligocene carbonate wedge (Smith et al, 1999).
Potential Reservoirs
In the Rowley Sub-basin potential sandstone reservoirs occur at several
stratigraphic levels. These include sandstones within the Permian Grant
Group, shoreward depositional facies of the Keraudren Formation and Locker
Shale, and Lower Cretaceous deltaic sands (Lipski, 1993; Kennard et al,
1994; Smith et al, 1999). The Keraudren Formation and Locker Shale are
likely to have higher porosity and permeability in the more shallowly buried
areas where there is less potential for secondary carbonate and silica
precipitation (Lipski, 1993). The Jurassic Depuch Formation offers a variety of
potential reservoir sands within the fluvio-deltaic complex, including channel,
coastal and potential barrier-bar sand bodies (Smith et al, 1999). The
youngest possible reservoirs proposed are deltaic sand bodies developed in
the Lower Cretaceous succession on the inner axis of the Rowley Sub-basin
during breakup of Australia’s western margin (Smith et al, 1999).
Potential Seals
The proposed seals for the Rowley Sub-basin include intraformational shales
in the Keraudren Formation (effective in Phoenix 1), the Cossigny Member of
the Keraudren Formation and the Locker Shale (Lipski, 1993). Additional
seals could include the transgressive shales of the Bedout Formation,
nearshore claystone beds and prodelta shales in the Depuch Formation, and
the Lower Cretaceous regional claystone overlying the Callovian unconformity
(Lipski, 1993; Smith et al, 1999).
Potential Play Types
Onlap plays of Triassic age, and subtle fluvio-deltaic complex plays in the
Jurassic have been proposed for the Rowley Sub-basin. The Triassic onlap
plays along the Bedout High could be charged from Larapintine or Gondwana
source rocks and sealed by the Cossigny Member of the Keraudren
Formation. Potential stratigraphic plays in the Jurassic Depuch Formation
consist of a variety of sand bodies within the fluvio-deltaic complex, charged
either intraformationally or from underlying source rocks (Lipski, 1993; Smith
et al, 1999). In addition to stratigraphic plays, there is potential for various
structural traps to be present along several largely untested fault trends within
the Roebuck Basin, including widespread structuring at the top Cossigny
Member and base Cretaceous levels as suggested by seismic data acquired
subsequent to the drilling of Phoenix 1 and 2 (Apache, 1995).
2011 Release of Australian Offshore Petroleum Exploration Areas
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Critical Risks
Effective hydrocarbon generation in the Rowley Sub-basin is a major risk,
because of the lack of significant hydrocarbon discoveries. However, the
interpreted gas column at Phoenix 1 is evidence of generation within the
Rowley Sub-basin, and widespread grains with oil inclusions (GOITM)
discovered in wells across the Roebuck and offshore Canning Basins may be
indicative of widespread migration. Therefore, the lack of significant
discoveries could be in part due to a lack of valid traps, or due to breaching by
recent movement on faults, rather than a lack of oil charge (Lisk et al, 2000;
Jones et al, 2007). Other risks include timing of trap and seal development
and late gas flushing (Lisk et al, 2000).
2011 Release of Australian Offshore Petroleum Exploration Areas
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FIGURES
Figure 1:
Location map of Release Areas W11-4, W11-5 and W11-6, in
the Rowley Sub-basin, Roebuck Basin, showing existing
exploration permits, wells and proposed Great Northern
Pipeline.
Figure 2:
Graticular block map and graticular block listings for Release
Areas W11-4, W11-5 and W11-6, in the Rowley Sub-basin,
Roebuck Basin.
Figure 3:
Structural elements of the Roebuck Basin and adjacent basins
(after Smith et al, 1999).
Figure 4:
Generalised stratigraphy of the Roebuck Basin and the
adjacent Canning Basin regions, based on the Northern
Carnarvon Basin Biozonation and Stratigraphy Chart (Nicoll et
al, 2010), Smith et al (1999). Geologic Time Scale after
Gradstein et al (2004) and Ogg et al (2008).
Figure 5:
AGSO seismic line 120/11 through Release Area W11-4 and
Wamac 1 well (see Figure 3 for location).
Figure 6:
AGSO seismic line 120/03 through Release Areas W11-4,
W11-5, W11-6 and East Mermaid 1 well (see Figure 3 for
location).
Figure 7:
AGSO seismic line 120/09 through Release Areas W11-5 and
W11-6 (see Figure 3 for location).
Figure 8:
Petroleum systems of the Roebuck Basin (modified after Smith,
1999 and Smith et al, 1999).
2011 Release of Australian Offshore Petroleum Exploration Areas
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REFERENCES
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2011 Release of Australian Offshore Petroleum Exploration Areas
Release Areas W11-4, W11-5 and W11-6, Rowley Sub-basin, Roebuck Basin,
WA
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LIPSKI, P., 1993—Tectonic setting, stratigraphy and hydrocarbon potential of
the Bedout Sub-basin, North West Shelf. The APEA Journal, 33(1), 138–150.
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seepage characteristics of the offshore Canning Basin and northern
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OGG, J. G., OGG, G. AND GRADSTEIN, F. M., 2008—The Concise Geologic
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OSBORNE, D.G., 1994—Nebo Oil discovery, Beagle Sub-basin. In: Purcell,
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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—
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TAYLOR, D., 1992—A Review of Ordovician Source Rocks, Canning Basin,
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WARRIS, B.J., 1993—The hydrocarbon potential of the Palaeozoic basins of
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2 November 2010).
2011 Release of Australian Offshore Petroleum Exploration Areas
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WA
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WOODSIDE PETROLEUM LIMITED, 23 July 2010—[Web page] Second
Quarter Activities Report,
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November 2010).
Front page image courtesy of Petroleum Geo-Services.
2011 Release of Australian Offshore Petroleum Exploration Areas
Release Areas W11-4, W11-5 and W11-6, Rowley Sub-basin, Roebuck Basin,
WA
Release Area Geology
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