PETROLEUM GEOLOGICAL SUMMARY
RELEASE AREAS W11-12, W11-13 AND W11-14,
EXMOUTH PLATEAU, NORTHERN CARNARVON
BASIN,
WESTERN AUSTRALIA
Bids Close – 13 October 2011

Australia’s premier deep-water gas province

Adjacent to multi-Tcf gas fields and numerous recent discoveries

Fault block and structural/stratigraphic traps

Construction and planned expansion of regional LNG facilities

Water depths 900-1400 m
2011 Release of Australian Offshore Petroleum Exploration Areas
Release Areas W11-12, W11-13 and W11-14, Exmouth Plateau, Northern
Carnarvon Basin, Western Australia
Release Area Geology
Page 1 of 21
LOCATION
Release Areas W11-12 to 14 are located in deep water 150-300 km off the
coast of Western Australia on the Exmouth Plateau, within the Northern
Carnarvon Basin (Figure 1). The Release Areas are located to the south and
east of the giant ~8 Tcf Scarborough gas field and to the west and southwest
of the supergiant Io-Jansz field. No wells have been drilled in the Release
Areas. Water depths range from about 900 to 1,400 m.
Release Area W11-12 comprises 13 graticular blocks with a total area of
1,050 km2, W11-13 comprises 11 graticular blocks covering 880 km2 and
W11-14 consists of 10 graticular blocks with an area of 800 km2.
Gas production facilities are currently being developed for the Chevron
operated Gorgon and Io-Jansz fields and the Woodside operated Pluto field.
ExxonMobil and BHP Billiton are currently examining development options for
the Scarborough and Thebe fields, as is Chevron for the Wheatstone field.
Graticular block details for the Release Areas are shown in Figure 2.
2011 Release of Australian Offshore Petroleum Exploration Areas
Release Areas W11-12, W11-13 and W11-14, Exmouth Plateau, Northern
Carnarvon Basin, Western Australia
Release Area Geology
Page 2 of 21
RELEASE AREA GEOLOGY
Local Tectonic Setting
The Exmouth Plateau is a deep-water marginal plateau that represents the
westernmost structural element of the Northern Carnarvon Basin (Figure 3).
Most of the plateau is underlain by 10-15 km of generally flat-lying and tilted,
block-faulted Lower Cretaceous, Jurassic, Triassic and older sedimentary
rocks (Figure 4). This section was deposited during the periods of extension
that preceded breakup of Australia and Argo Land in the Middle Jurassic, and
then Greater India in the Early Cretaceous (Stagg et al, 2004). The dominant
fault trend on the Exmouth Plateau is north-south, swinging to northeastsouthwest near the northern and western margins of the plateau and along
the inner margin adjacent to the Rankin Platform and Exmouth, Barrow and
Dampier sub-basins (Figure 3).
Structural Evolution and Depositional History of the Sub-basin
The Lower Triassic section in the Carnarvon Basin is marked by a regional
marine transgression that represents the sag phase of a previous Paleozoic
rift cycle. The marine Locker Shale (below TD of wells on the Exmouth
Plateau) unconformably overlies the Permian section and grades upwards
into the Middle-Upper Triassic Mungaroo Formation (Figure 4). The
Mungaroo Formation was deposited in a broad, low relief, rapidly subsiding
fluvio-deltaic coastal plain that extended across the Exmouth Plateau. During
marine transgression in the latest Triassic (Rhaetian), carbonate patch reefs
developed on the Wombat Plateau (von Rad et al, 1992a; Williamson et al,
1989) and probably extended across the northern- and western-central parts
of the Exmouth Plateau, while marls, siltstones and thin sandstones (Brigadier
Formation) were deposited elsewhere.
As rifting proceeded between Australia and Greater India, several faulting
episodes occurred in the Jurassic. In the Pliensbachian, rifting inboard of the
Exmouth Plateau formed the Exmouth, Barrow and Dampier sub-basins.
Several kilometres of marine Jurassic sediments, equivalent to condensed
sections on the central Exmouth Plateau (Dingo Claystone equivalents), were
deposited in these troughs. Major rift-fault movement occurred in the
Callovian on the Exmouth Plateau with oceanic crust created in the Argo
Abyssal Plain in the late Oxfordian, and in the Gascoyne and Cuvier abyssal
plains in the Valanginian (Norvick, 2002). Rift and breakup volcanics are
widespread along the outer margins of the Exmouth Plateau and probably
include Upper Triassic, Oxfordian/Callovian and Lower Cretaceous suites
(Stagg et al, 2004).
During the Late Jurassic in the eastern Exmouth Sub-basin, sandy shelfal
facies were deposited within restricted shallow depocentres (including the
Oxfordian Jansz Sandstone reservoir at the supergiant Io-Jansz gas
accumulation). In the Early Cretaceous the Barrow Group delta prograded
2011 Release of Australian Offshore Petroleum Exploration Areas
Release Areas W11-12, W11-13 and W11-14, Exmouth Plateau, Northern
Carnarvon Basin, Western Australia
Release Area Geology
Page 3 of 21
northward across the southern portion of the plateau to form a major sediment
lobe with the shelf edge arced through or near the Investigator 1 and
Zeepard 1 well locations (Boote and Kirk, 1989). A distal claystone equivalent
(Forestier Claystone) was deposited to the north of the delta lobe. Barrow
Group basin floor fans form the reservoir at the Scarborough gas field.
As the newly formed oceanic crust of the Argo, Gascoyne and Cuvier abyssal
plains rapidly subsided, the Exmouth Plateau also foundered and was
progressively transgressed throughout the Cretaceous by shallow marine
mudstone (Muderong Shale) and siltstone (Gearle Siltstone), mid-outer shelf
marl and chalk (Toolonga Calcilutite), and finally Cenozoic bathyal chalk and
ooze.
2011 Release of Australian Offshore Petroleum Exploration Areas
Release Areas W11-12, W11-13 and W11-14, Exmouth Plateau, Northern
Carnarvon Basin, Western Australia
Release Area Geology
Page 4 of 21
EXPLORATION HISTORY
Two major exploration campaigns have focused on the deep-water Exmouth
Plateau, the first in 1979 to 1980 for oil targets, and the second, currently
underway, searching for gas. The initial exploration programs were
undertaken by Esso and Phillips (Barber, 1988) and eleven deep-water (740–
1375 m) wells were drilled (Walker, 2007), targeting oil charge from the
Jurassic Dingo Claystone. Two wells were gas discoveries: Jupiter 1, a
Triassic horst trap; and Scarborough 1, an inverted Lower Cretaceous Barrow
Group basin floor fan. At the time of the Scarborough 1 discovery (1979), the
available technology and the undeveloped LNG market, made the remote,
deep-water gas accumulation uneconomic to develop. All other wells drilled
during this period had significant gas shows, but there were no oil discoveries.
The second phase of exploration commenced in the mid 1990s with the
drilling of the Scarborough 2 appraisal well in 1996. This second phase
focused on the established Triassic fault-block play along the eastern margin
of the Exmouth Plateau. Acreage on the northern and western Exmouth
Plateau was released in 2000, but failed to attract successful bids.
The supergiant Io-Jansz gas field was discovered by Jansz 1 (2000) and Io 1
(2001) and represented a new Oxfordian play type on the Exmouth Plateau
(Jenkins et al, 2003). Following this discovery, gas became the primary
exploration target and extensive new acreage was awarded on the central,
northern and western Exmouth Plateau.
In 2007, BHP Billiton drilled Thebe 1 in Permit WA-346-P and discovered 23 Tcf (57-85 Bcm) of gas in a Triassic fault block (BHP Billiton, 2007;
Anonymous, 2007). Thebe 2 (2008) was drilled 16 km to the north of the initial
discovery and confirmed expectations of the size and quality of the Thebe
resource (BHP Billiton, 2008a).
Market conditions have changed markedly since exploration in the 1970s with
major gas trade established with Japan, contracts to supply LNG to China,
production facilities under construction for Pluto, and development proposals
for Wheatstone, Scarborough and Thebe. In 2007, Hess was awarded the
deep-water petroleum exploration permit WA-390-P, located southwest of the
supergiant Io-Jansz field, with an aggressive bid including a 16 well drilling
commitment. In 2008, four wells were drilled with three gas discoveries
(Glencoe 1, Briseis 1 and Nimblefoot 1) and the fourth containing noncommercial gas (Warrior 1). In all three discoveries, accumulations occur
within the post-Callovian interval, with Briseis 1 also encountering additional
pay in the Triassic Mungaroo Formation (Smallwood et al, 2010). The
Oxfordian (W. spectabilis) sandstones encountered in Glencoe 1 are
analogous to those encountered at Io-Jansz. In contrast, Nimblefoot 1 and
Briseis 1 both encountered gas pay within deep-water Berriasian delta-front
turbidite sandstones sourced from the Barrow delta to the south, analogous to
2011 Release of Australian Offshore Petroleum Exploration Areas
Release Areas W11-12, W11-13 and W11-14, Exmouth Plateau, Northern
Carnarvon Basin, Western Australia
Release Area Geology
Page 5 of 21
the Scarborough gas field. In 2009 seven wells were drilled (Toporoa 1,
Dunlop 1, Lightfinger 1, Bravo 1, Rimfire 1, Mentorc 1 and Hijinx 1) with six
gas discoveries (Jonasson, 2010). A twelfth well, Glenloth 1, was completed
in 2010 by Hess, and was also a gas discovery (Jonasson and Mack, 2010).
Other recent gas finds have been made at Achilles 1 (2009), Yellowglen 1
(2009), Satyr 1 (2009) and Sappho 1 (2010) to the east; Chandon 1 (2006),
Martell 1 (2009), Noblige 1 (2010), Larsen 1 (2010) and Larsen Deep 1 (2010)
to the northeast; and Kentish Knock 1 (2009), Guardian 1 (2009), Brederode 1
(2010) and Alaric 1 (2010) to the west (Figure 1). The discovery of gas at
Brederode 1 (Chevron permit WA-264-P) and Alaric 1 (Woodside permit WA434-P) significantly extend the western extent of known gas resources on the
Exmouth Plateau (Woodside, 2010a).
Well Control
No wells occur within the Release Areas, but several occur in close proximity
(Jupiter 1, Mercury 1, Scarborough 1 and Jacala 1) and others provide
important stratigraphic control or nearby gas discoveries (Figure 1).
Zeewulf 1 (1979)
Zeewulf 1 was the first well drilled on the southern Exmouth Plateau. It was
drilled by Esso Australia Ltd in 1194 m water depth and reached a TD of
3500 mKB. The well tested a tilted Triassic fault block and intersected 2443 m
of Cenozoic to Lower Cretaceous claystone, foraminiferal ooze, marl, siltstone
and glauconitic sandstone which overlies 643 m of basinal to prodelta and
delta front claystone, siltstone and sandstone of the Barrow Group. The
Barrow Group was underlain by a 5 m section of Upper Jurassic siltstone,
shale and dolomite and 409 m of Upper Triassic sandstone, siltstone,
claystone and minor coal of the Mungaroo Formation to TD. Reservoir quality
sandstones were encountered in the Lower Cretaceous Barrow Group (2026% porosity) and Upper Triassic Mungaroo Formation (11-21% porosity).
Minor gas and condensate were recovered from the Mungaroo Formation and
probably came from an overmature source in the Triassic sedimentary
section. The lack of hydrocarbons in Zeewulf 1 was attributed to reduced
vertical trap closure, partial leakage of hydrocarbons upwards along southeast
bounding fault and inability of hydrocarbons generated in surrounding graben
to migrate into the structure (Esso Australia Ltd, 1979).
Investigator 1 (1979)
Investigator 1 was drilled by Esso Australia Ltd to test the delta front
sandstones of the Lower Cretaceous Barrow Group in a large closure formed
by a combination of northward depositional dip on the delta front, regional
south to southeast tilting of the Exmouth Plateau and gentle Cenozoic arching
about a northeast-trending axis (Figure 5); Esso Australia Ltd, 1980a). The
well was drilled in 841 m water depth and reached a TD of 3,745 mKB. It
penetrated and sampled an Albian-Barremian succession of claystone, marl
and siltstone to 1,492 mKB, overlying a 1,748 m thick section of basinal to
prodelta and delta front claystone, siltstone and sandstone of the target
2011 Release of Australian Offshore Petroleum Exploration Areas
Release Areas W11-12, W11-13 and W11-14, Exmouth Plateau, Northern
Carnarvon Basin, Western Australia
Release Area Geology
Page 6 of 21
Barrow Group. The Barrow Group was underlain by a 15 m section of Upper
Jurassic claystone, Middle-Lower Jurassic marl (44 m), Upper Triassic
(Rhaetian) marl (65 m) and Upper Triassic (Norian) interbedded sandstone,
siltstone, claystone and minor coal of the Mungaroo Formation (382 m thick to
TD). Sandstones of good reservoir quality occur within the Barrow Group (13–
30% porosity), but those within the Upper Triassic Mungaroo Formation were
generally poor (5–16% porosity).
No significant hydrocarbon shows were recorded in the target Barrow Group
reservoir, but elevated mud gas levels and small amounts of wet gas and
questionable oil films in wireline tests were recorded in low permeability
sandstones of the Mungaroo Formation. Log analysis indicates 48–86% water
saturation in these sandstones. The lack of hydrocarbons in the Barrow Group
sands was attributed to the absence of effective migration pathways for any
hydrocarbons generated within the deeper Mungaroo section.
Jupiter 1 (1979)
Jupiter 1 was drilled by Phillips Australian Oil Company in water depths of
960 m to test a tilted Triassic horst block. The well reached a TD of 4946 mRT
in a thick section of interbedded Triassic siltstone, claystones, sandstone and
minor coal and dolomite (A. reducta to S. quadrifidus spore/pollen zones) of
the Mungaroo Formation (Phillips Australian Oil Company, 1980a). The well
penetrated 466 m of inferred calcareous ooze and marl of Holocene to Late
Cretaceous age without returns, and sampled Cretaceous chalk, calcareous
claystone and siltstone to 1,857 mRT, and a 15 m section of Upper Jurassic
claystone to 1,872 mRT. This Jurassic claystone was unconformably
underlain by 23 m of Upper Triassic (Rhaetian) carbonate and claystone,
39 m of transgressive marine siltstone and sandstone (ascribed to the
Brigadier Formation by Crostella and Barter, 1980) and a thick section of
Upper-Middle Triassic deltaic sediments of the Mungaroo Formation (1,8954,946 mRT). This is the maximum known drilled thickness of Triassic section
on the Exmouth Plateau.
A 22.5 m gas column was discovered in Upper Triassic sandstones (1,9111,933 mRT; Brigadier Formation) with reserves of about 0.15 Tcf (4 Bcm;
Walker, 2007). This accumulation has a strong flat-spot DHI on seismic data,
which indicates the spill-point of the gas into the bounding fault, and venting
through to a gas-chimney is also evident on seismic (Barber, 1988).
Scarborough 1 (1979)
Scarborough 1 was drilled by Esso Australia Ltd to test a large, low relief
anticline within the Barrow Group delta that displayed a prominent flat-lying
bright spot conforming to the crest of the structure (Esso Australia Ltd,
1980b). The well was drilled in a water depth of 912 m and was abandoned at
a TD of 2364 mKB due to mechanical problems. It penetrated an upper
Campanian-Hauterivian marl and claystone succession overlying pro-delta
claystone (Upper Delta sequence) and prograding submarine fan sandstone
(Lower Delta sequence) of the Lower Cretaceous Barrow Group (total 683 m
2011 Release of Australian Offshore Petroleum Exploration Areas
Release Areas W11-12, W11-13 and W11-14, Exmouth Plateau, Northern
Carnarvon Basin, Western Australia
Release Area Geology
Page 7 of 21
thick). Drilling was abandoned within the Barrow Group, and the underlying
Triassic section was not reached.
Scarborough 1 discovered a 59 m gas column within good quality sands
(average 23% porosity) of the lower Barrow Group basin floor fan sealed by
prodelta claystone. Formation testing at 1,904.5 mKB recovered 5.2 m3 of
methane with only 0.12% ethane and no fractions heavier than propane.
Additional appraisal wells Scarborough 2 (1996-1997) and Scarborough 3, 4
and 5 (2004-2005) have since been drilled. Scarborough 2 was drilled to a TD
of 2,068 mKB to appraise the southeast limit of the lower delta fan reservoir
discovery, and to confirm the presence of higher gas-bearing sands in the
upper delta fan with seismic amplitude anomalies (Esso Australia Ltd, 1997).
A total of 84 m of conventional core were cut in the upper and lower fans, and
both successions were confirmed to be gas bearing from log analysis, MDT
samples and production testing. The upper fan reservoir contained a 39 m
gross gas interval with lower than expected porosity (20%), permeability (<1–
10 mD) and gas saturation (49%). The lower fan reservoir contained a 28 m
gross gas interval with excellent porosity (26%), permeability (1,000–
5,000 mD) and gas saturation (70%). Cores indicate that the upper fan
consists mostly of thin-bedded pelagic mudstone and debris-flow sands,
whereas the lower fan comprises amalgamated channel sands. Pressure
gradients and gas compositions suggest that the upper and lower fans are in
communication, with the same gas-water contact as Scarborough 1.
Scarborough 3 was located on the southwest flank of the structure to appraise
the upper fan complex of the Barrow Group. It encountered a 53 m gross gas
column and demonstrated that high-quality, amalgamated turbidite sands
were developed in the upper fan (Gorter, 2005). Scarborough 4 and
Scarborough 5 were drilled to further appraise the turbidite sandstones of the
lower fan with the upper fan sandstones a secondary objective.
Scarborough 4 intersected 10.5 m of net gas pay in the upper fan complex
and 34.1 m in the lower fan complex while Scarborough 5 encountered 6.2 m
and 36 m of net gas pay in these same units, respectively.
The Scarborough domal anticline, which was generated by structural
inversion in the Campanian, is approximately 350 km2 in area and contains
reserves of about 8 Tcf (226 Bcm) of gas (BHP Billiton, 2008b). ExxonMobil
and BHP Billiton are currently assessing development options, including a
floating LNG facility.
Mercury 1 (1979)
Mercury 1 was drilled by Phillips Australian Oil Company on the eastern flank
of the Exmouth Plateau bathymetric arch to test Upper Triassic fluvio-deltaic
reservoirs within a tilted fault block sealed by drape closure of Lower
Cretaceous claystones. The structure is bounded to the west by a major
north-south trending normal fault with a throw of about 900 m (Phillips
Australian Oil Company, 1980b). It was envisaged that deeply buried Lower
Cretaceous claystone within the Kangaroo Syncline to the east would provide
2011 Release of Australian Offshore Petroleum Exploration Areas
Release Areas W11-12, W11-13 and W11-14, Exmouth Plateau, Northern
Carnarvon Basin, Western Australia
Release Area Geology
Page 8 of 21
a hydrocarbon charge. The well was drilled in a water depth of 1,142 m and
reached a TD of 3812 mKB within the Upper Triassic Mungaroo Formation. It
penetrated and sampled a thin upper Paleocene marl overlying Upper
Cretaceous marl and chalk to 2,032 mKB and Lower Cretaceous marl, chalk,
siltstone and claystone to 2,399 mKB. The Cretaceous section unconformably
overlies basal Jurassic marl and claystone to 2416 mKB, Upper Triassic marl
and limestone to 2,467 mKB, and Upper Triassic sandstone, siltstone and
claystone with abundant coal to TD. No Barrow Group sandstones were
encountered.
High quality reservoirs were encountered in the deeper parts of the Mungaroo
Formation, but only poor quality reservoirs (thin argillaceous sandstones and
interbedded siltstone and shale) occur in the uppermost part of the tilted fault
blocks that are in the zone of potential drape closure entrapment. Only minor
hydrocarbon indications were reported in this interval and wireline logs
indicated no productive hydrocarbon zones and high water saturations. High
mud gas readings (generally 5,000–10,000 ppm, mainly methane but with
minor ethane and propane) were recorded while drilling the Albian to Rhaetian
interval (2,140–2,467 mKB).
Eendracht 1 (1980)
Eendracht 1 was drilled by Esso Australia Ltd to test Upper Triassic (preRhaetian) reservoirs within an elongate tilted horst block bounded to the west
by a major normal fault (Esso Australia Ltd, 1981a). The well was drilled in a
water depth of 1,354 m and reached a TD of 3,410 mKB within the Mungaroo
Formation. It penetrated Paleocene to Albian calcilutites to 2,184.5 mKB, a
thin Barremian-Hauterivian claystone (Muderong Shale equivalent) to
2,195 mKB, Lower Cretaceous prodelta siltstone and claystone (Barrow
Group) to 2,344.5 mKB, a condensed section of Upper to Lower Jurassic
claystone (Dingo Claystone equivalent), Upper Triassic (Rhaetian) marl to
2,419 mKB, and Upper Triassic shallow marine to deltaic siltstone, claystone
and sandstone of the Mungaroo Formation.
Four gas-bearing sandstones in the Triassic Mungaroo Formation were
intersected over the interval 2,467-2,652 mKB, with a total net gas pay of
25.5 m. The maximum observed gas column was 44 m in a thin sandstone at
2,467 m; the three deeper gas sands were recognised pre-drill as seismic
amplitude anomalies.
Sirius 1 (1980)
Sirius 1 was drilled by Esso Australia Ltd in 1,173.9 m water depth and
reached a TD of 3,500 mKB. The well tested a large, low-relief anticline within
the Lower Cretaceous Barrow Group (Esso Australia Ltd, 1981b). The
Triassic sandstones of the Mungaroo Formation were a secondary target. No
samples were collected down to 1,573.6 mKB and the well intersected Lower
Cretaceous claystone, calcareous ooze, marl and siltstone to 1,675 mKB
(Toolonga Calcilutite, Gearle Siltstone and Muderong Shale equivalents)
overlying 1,213 m of deltaic Barrow Group sandstone and siltstone. The
Barrow Group was underlain by a 109 m thick section of Lower to Upper
2011 Release of Australian Offshore Petroleum Exploration Areas
Release Areas W11-12, W11-13 and W11-14, Exmouth Plateau, Northern
Carnarvon Basin, Western Australia
Release Area Geology
Page 9 of 21
Jurassic marl, biomicrite and siltstone (Dingo Claystone equivalent), 11 m of
Upper Triassic (Rhaetian) marl, sandstone and claystone and 492 m of Upper
Triassic Mungaroo Formation siltstone and sandstone. Reservoir quality
sandstones were encountered in the Lower Cretaceous Barrow Group (2535% porosity) and Upper Triassic Mungaroo Formation (10-25% porosity)
although fewer reservoir quality sandstones were encountered in the
Mungaroo Formation than expected.
Gas shows were recorded in the Barrow Group (2,740-2,850 mKB) and
Mungaroo Formation (3,015-3,500 mKB). The Barrow Group test failed due to
the lack of intra-Barrow Group seals within the sandy Lower Cretaceous
section.
Leyden 1B ST (1996)
Leyden 1B ST was drilled by BHP Petroleum Pty Ltd in 1025 m water depth
on the southern edge of the Exmouth Plateau at the boundary with the
Exmouth Sub-basin. The well reached a TD of 4,300 mRT and tested a large
northeast-southwest trending, eroded and tilted Triassic horst block with
Upper Triassic Mungaroo Formation sandstones the primary objective (BHP
Petroleum Pty Ltd, 1997). No samples were collected down to 1,640 mRT and
the well intersected Cenozoic to Upper Cretaceous calcareous claystone and
siltstone to 1,743 mRT, Albian to Turonian Gearle Siltstone to 2,482 mRT,
Upper Aptian Basal Gearle Member claystone (Windalia Radiolarite
equivalent) to 2,562 mRT, Aptian to Barremian Muderong Shale to
2,642 mRT, Barremian to Valanginian Mardie Greensand to 2660 mRT and
Barremian Birdrong Sandstone to 2,688 mRT. The Birdrong Sandstone (see
stratigraphic column for Exmouth Sub-basin) was underlain by Berriasian
Barrow Group from 2,688-3,801 mRT and Upper Triassic Mungaroo
Formation from 3,801 mRT to TD. Reservoir quality varies across the
Mungaroo Formation but is generally good (8-18% porosity) in three thick
channel sandstones at 3,920-3,964 mRT, 4,135-4,198 mRT and 4,2594,290 mRT.
Elevated gas levels were observed across the entire Mungaroo Formation.
However, they are probably residual hydrocarbons in the form of gascondensate. Residual gas was also encountered in the basal Barrow Group at
3,650 mRT (BHP Petroleum Pty Ltd, 1997).
Jacala 1 (2006)
Jacala 1 was drilled by BHP Billiton Petroleum Pty Ltd in 1,062 m water depth
to a TD of 2,217 mRT. This high risk well targeted oil in a large simple 4-way
dip structure with Lower Cretaceous Barrow Group sandstones the primary
objective (TapOil Ltd, 2006). The well did not encounter hydrocarbons (ROC
Oil Ltd, 2010) and detailed results have not yet been released.
Chandon 1 (2006)
Chandon 1 was drilled by Chevron Australia Pty Ltd in 1,200 m water depth to
a TD of 3,100 m, and is located 31 km northwest of the Jansz 2 well. Unlike
the Io-Jansz accumulation, the objective was a Triassic fault block, and a
2011 Release of Australian Offshore Petroleum Exploration Areas
Release Areas W11-12, W11-13 and W11-14, Exmouth Plateau, Northern
Carnarvon Basin, Western Australia
Release Area Geology
Page 10 of 21
197 m gross gas column was intersected in high quality Mungaroo Formation
sandstones (Jonasson, 2007). The Chandon accumulation has been
estimated to contain up to 4 Tcf (113 Bcm) gas (Blevin, 2007). Detailed
results of the well have not yet been released.
Thebe 1 (2007) and Thebe 2 (2008)
Thebe 1 was drilled by BHP Billiton about 50 km north of the Scarborough gas
field in 1,173 m water depth. The well discovered a 73 m gas column (BHP
Billiton, 2007) in a Triassic fault block that may contain 2-3 Tcf (57–85 Bcm) of
gas (Anonymous, 2007). Thebe 2 was drilled 16 km to the north of the initial
discovery and confirmed expectations of the size and quality of the Thebe
resource (BHP Billiton, 2008a). Detailed results of the wells have not yet been
released.
Belicoso 1 (2007)
Belicoso 1, the most northerly exploration well on the Exmouth Plateau (about
81 km north of Mercury 1), was drilled by Woodside Petroleum Ltd in over
1400 m water depth to test a north-northeast trending Triassic horst block
(Woodside, 2007a). The well did not encounter hydrocarbons, but intersected
thick, high-quality reservoirs (Woodside, 2007b). Detailed results of the well
have not yet been released.
Martell 1 (2009)
Martell 1 was drilled by Woodside Petroleum Ltd in 1,290 m water depth
about 27 km northeast of Chandon 1. Pressure testing of sandstones over an
interval 2,778 to 3,201 mRT confirmed a gross gas column of about 110 m
and the presence of a gas-water contact (Woodside, 2009a). The
accumulation occurs within a top Triassic horst block (Woodside, 2009b).
Detailed results of the well have not yet been released
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_exmouthplt_AR11.xls
.
2011 Release of Australian Offshore Petroleum Exploration Areas
Release Areas W11-12, W11-13 and W11-14, Exmouth Plateau, Northern
Carnarvon Basin, Western Australia
Release Area Geology
Page 11 of 21
Seismic Coverage
The Release Areas are covered by regional 2D seismic grids acquired in the
late 1970s (approximate 5 km line spacings) and 1991-1997 (line spacings of
about 10–20 km). Deep seismic data was acquired by Geoscience Australia in
1991–1995 across the central and northern Exmouth Plateau (Surveys 101,
110, 128; Geoscience Australia 2001), and across the outer margins of the
Plateau (Surveys 135, 162; Stagg et al, 2004).
WesternGeco acquired two multi-client 3D surveys in 2008: Keystone and
Aragon. The Keystone survey was acquired across several blocks including
much of Release Area WA11-12 (WesternGeco, 2010a). The Aragon survey
was acquired in WA-251-P and covers most of Release Areas WA11-13 to 14
(WesternGeco, 2010b). Fugro is acquiring the Eendracht 3D multi-client
survey in 2009-10 across several blocks directly south of W11-13 to 14 and
including the bottom part of W11-13 (Fugro Multiclient Services, 2010). In
2008, a new multi-client survey (PGS New Dawn) was acquired across the
Exmouth Plateau including a few lines over the Release Areas (Petroleum
Geo-Services, 2009).
Seismic data are generally of high quality across the Exmouth Plateau, and
indications of gas charge and gas-water contacts can commonly be imaged
directly as amplitude anomalies and flat-spots.
To view image of seismic coverage follow this link:
http://www.ga.gov.au/energy/projects/acreage-release-andpromotion/2011.html#data-packages
Other data
In addition to commercial petroleum exploration wells, scientific Ocean Drilling
Program (ODP) wells have also been drilled on the Exmouth Plateau. In 1988,
ODP Leg 122 (Haq et al, 1990; von Rad et al, 1992b) drilled two wells on the
western Exmouth Plateau (Figure 1) and four wells on the northern Exmouth
Plateau (Wombat Plateau). Detailed descriptions of the fully cored holes and
interpretation of the results are given by von Rad et al (1992b).
2011 Release of Australian Offshore Petroleum Exploration Areas
Release Areas W11-12, W11-13 and W11-14, Exmouth Plateau, Northern
Carnarvon Basin, Western Australia
Release Area Geology
Page 12 of 21
PETROLEUM SYSTEMS AND HYDROCARBON POTENTIAL
Table 1: Petroleum Systems Elements Summary
Sources
Triassic Mungaroo Formation (gas-prone)
Lower Cretaceous Barrow Group (basin floor fans, turbidites)
Oxfordian Jansz Sandstone (upper-lower shoreface)
Upper Triassic (Rhaetian) reefs (no discoveries to date)
Reservoirs
Upper Triassic Brigadier Formation (shallow marine-deltaic)
Top Triassic Mungaroo Formation (fluvio-deltaic)
Intra-Triassic Mungaroo Formation (fluvio-deltaic)
Lower Cretaceous marine Muderong Shale (regional seal)
Lower Cretaceous distal condensed claystones, Barrow Group
(Forestier Claystone equivalents)
Seals
Jurassic condensed marls/claystones (Dingo Claystone
equivalents)
Intra-formational Mungaroo Formation claystones (cross-fault)
Tilted Triassic fault blocks and associated drapes
Oxfordian shoreface sandstone stratigraphic traps
Play Types
Lower Cretaceous basin floor fan stratigraphic traps
Upper Triassic (Rhaetian) pinnacle reefs
The supergiant Io-Jansz gas field, giant Scarborough gas field, and the
Jupiter 1 and Eendracht 1 gas discoveries, together with the recent gas
discoveries in the Chandon 1, Thebe 1 and 2, Martell 1, Glencoe 1,
Nimblefoot 1, Briseis 1, Kentish Knock 1, Brederode 1 and Alaric 1 wells,
demonstrate that the deep-water Exmouth Plateau is prospective for large gas
discoveries. All these discoveries are attributed to a widespread regional gas
system sourced from the Triassic succession.
Source Rocks
The thick Triassic and older sedimentary section on the Exmouth Plateau has
the greatest potential for mature source facies, with possible organic-rich units
2011 Release of Australian Offshore Petroleum Exploration Areas
Release Areas W11-12, W11-13 and W11-14, Exmouth Plateau, Northern
Carnarvon Basin, Western Australia
Release Area Geology
Page 13 of 21
in the Lower Triassic (marine Locker Shale equivalents) and Upper Triassic
(deltaic Mungaroo Formation facies and marine equivalents). Recent
exploration activities on the Exmouth Plateau are based on a model that
invokes gas charge from the deeply buried coal and carbonaceous claystone
of the Mungaroo Formation. Peak gas generation from these Triassic source
rocks is interpreted to occur now at depths greater than 5 km subsea (Bussell
et al, 2001).
Organic-rich sediments may also be present within the condensed Jurassic
and Upper Cretaceous succession, but these are immature.
Reservoirs
Fluvio-deltaic sandstones of the Upper Triassic Mungaroo Formation (eg
Eendracht, Thebe, Martell and Chandon) and basin-floor fan and turbidite
sandstones of the Lower Cretaceous Barrow Group (eg Scarborough,
Nimblefoot and Brieseis shallow) provide good quality reservoirs across the
Exmouth Plateau and are likely to represent the main reservoir target within
the Release Areas. Transgressive marine sandstones of the Brigadier
Formation (eg Jupiter) and Rhaetian reefal carbonates provide additional
potential reservoir targets.
Seals
Fine-grained deep-water Cretaceous sediments (Muderong Shale and distal
facies of the Barrow Group) provide a regional seal across the Exmouth
Plateau. There are also intra-formational seals within the deltaic sequences of
the Upper Triassic Mungaroo Formation. The Rhaetian marl and Jurassic
condensed marls/claystones (Dingo Claystone equivalents), where preserved,
can also provide a top seal to Triassic reservoirs.
Play Types
High relief top Triassic fault blocks together with associated drape features
and deeper intra-Triassic cross-fault traps provide numerous potential
structural traps on the Exmouth Plateau (Figure 5 and Figure 6). Upper
Triassic (Rhaetian) pinnacle and patch reefs (such as those intersected in
ODP holes on the Wombat Plateau; Williamson et al, 1989) have been
identified as potential new plays across parts of the central Exmouth Plateau.
Woodside unsuccessfully tested one of these plays with Tiberius 1 drilled in
WA-434-P in 2010 (Woodside, 2010b). Other proven stratigraphic traps in the
region include Lower Cretaceous basin floor fans (eg Scarborough) and
Upper Jurassic shoreface sandstones (eg Io-Jansz, Glencoe).
Critical Risks
Given that a proven hydrocarbon system has already been established across
the central Exmouth Plateau, continued success relies on the identification of
additional valid traps with access to charge from the gas-prone Mungaroo
source. 3D seismic and AVO technology are thus key exploration tools that
are likely to contribute to continued exploration success on the deep-water
2011 Release of Australian Offshore Petroleum Exploration Areas
Release Areas W11-12, W11-13 and W11-14, Exmouth Plateau, Northern
Carnarvon Basin, Western Australia
Release Area Geology
Page 14 of 21
Exmouth Plateau (Longley et al, 2002; Korn et al, 2003; Williamson and Kroh,
2007).
2011 Release of Australian Offshore Petroleum Exploration Areas
Release Areas W11-12, W11-13 and W11-14, Exmouth Plateau, Northern
Carnarvon Basin, Western Australia
Release Area Geology
Page 15 of 21
FIGURES
Figure 1:
Location map of Release Areas W11-12, W11-13 and W11-14,
on the Exmouth Plateau, Northern Carnarvon Basin.
Figure 2:
Graticular block map and graticular block listings for Release
Areas W11-12, W11-13 and W11-4, on the Exmouth Plateau,
Northern Carnarvon Basin.
Figure 3:
Structural elements of the Exmouth Plateau showing the 2011
Release Areas and location of seismic section shown in
Figure 5.
Figure 4:
Generalised stratigraphy of the Exmouth Plateau, based on the
Northern Carnarvon Biozonation and Stratigraphy Chart (Nicoll
et al 2009). Geologic Time Scale after Gradstein et al (2004)
and Ogg et al (2008). Seismic horizons after Kennard and
Colwell (2001).
Figure 5:
AGSO seismic line 110-12 across the southern Exmouth
Plateau.
Figure 6:
Play types on the Exmouth Plateau (modified from Woodside,
2009b). Lower Cretaceous Barrow Group basin floor fan and
turbidite plays (eg Scarborough, Nimblefoot and Briseis
shallow) not shown.
2011 Release of Australian Offshore Petroleum Exploration Areas
Release Areas W11-12, W11-13 and W11-14, Exmouth Plateau, Northern
Carnarvon Basin, Western Australia
Release Area Geology
Page 16 of 21
REFERENCES
ANONYMOUS, 2007—Regional Update, Australia. Journal of Petroleum
Technology, 59 (11), November 2007, page 10.
BARBER, P., 1988—The Exmouth Plateau deepwater frontier: a case study.
In: Purcell, P.G. and Purcell, R.R. (eds), The North West Shelf, Australia:
Proceedings of the Petroleum Exploration Society of Australia Symposium,
Perth, 173–187.
BHP BILLITON, 2007—[Web page] BHP Billiton announces gas discovery at
Thebe 1 offshore Australia, 13 August 2007.
http://www.bhpbilliton.com/bb/investorsMedia/news/2007/bhpBillitonAnnounce
sGasDiscoveryAtThebe1OffshoreAustralia.jsp (last accessed 14 October
2010).
BHP BILLITON 2008a—[Web page] Defining our future, 20 October 2008.
http://www.bhpbilliton.cbom/bbContentRepository/docs/definingOurFuture.pdf
(last accessed 14 October 2010).
BHP BILLITON, 2008b—[Web page] Investment presentation, Australian
Analysts’ Tour, 27 October 2008, Petroleum Australia presentation.
http://www.bhpbilliton.com/bbContentRepository/docs/petroleumSitePresentat
ion08.pdf (last accessed 14 October 2010).
BHP PETROLEUM PTY LTD, 1997—Leyden 1, 1A, 1B & 1B/ST1 Well
Completion Report, unpublished.
BLEVIN, J.E., 2007—PESA industry review: Exploration highlights for 2006.
The APPEA Journal, 47, 2, 631-648.
BOOTE, R.D. AND KIRK, R.B., 1989—Depositional wedge cycles on an
evolving plate margin, Western and northwestern Australia. American
Association of Petroleum Geologists Bulletin, 73, 216-243.
BUSSELL, M.R., JABLONSKI, D., ENMAN, T., WILSON, M.J. AND BINT,
A.N., 2001—Deepwater exploration: northern Western Australia compared
with Gulf of Mexico and Mauritania. The APPEA Journal, 41(1), 289–319.
CROSTELLA AND BARTER, 1980—Triassic-Jurassic depositional history of
the Dampier and Beagle Sub-basins, Northwest Shelf of Australia. APEA
Journal, 20 (1), 25-33.
ESSO AUSTRALIA LTD, 1979—Zeewulf 1 Well Completion Report,
unpublished.
ESSO AUSTRALIA LTD, 1980a—Investigator 1 Well Completion Report,
unpublished.
2011 Release of Australian Offshore Petroleum Exploration Areas
Release Areas W11-12, W11-13 and W11-14, Exmouth Plateau, Northern
Carnarvon Basin, Western Australia
Release Area Geology
Page 17 of 21
ESSO AUSTRALIA LTD, 1980b—Scarborough 1 Well Completion Report,
unpublished.
ESSO AUSTRALIA LTD, 1981a—Eendracht 1 Well Completion Report,
unpublished.
ESSO AUSTRALIA LTD, 1981b—Sirius 1 Well Completion Report,
unpublished.
ESSO AUSTRALIA LTD, 1997—Scarborough 2 Well Completion Report,
unpublished.
FUGRO MULTICLIENT SERVICES, 2010—[Web page] Australia-Eendracht
3D New Non-Exclusive Seismic Survey.
http://www.fugromcs.com.au/Australia/3D_Eendracht3D.htm (last accessed 7
October 2010).
GEOSCIENCE AUSTRALIA, 2001—Line drawings of Geoscience Australia’s
regional seismic profiles, offshore northern and northwestern Australia.
Geoscience Australia Record 2001/36, GeoCat 36352, unpublished.
GORTER, J.D., 2005—2004 Exploration Review. The APPEA Journal, 45 (2),
129-144.
HAQ, B.U., von RAD, U., O’CONNELL, S. AND OTHERS, 1990—
Proceedings of Ocean Drilling Program, Initial Reports, 122. Ocean Drilling
Program, College Station, Texas, 862 pp.
JENKINS, C.C., MAUGHAN, D.M., ACTON, J.H., DUCKETT, A., KORN, B.E.
AND TEAKLE, R.P., 2003—The Jansz gas field, Carnarvon Basin, Australia.
The APPEA Journal, 43 (1), 303–324.
JONASSON, K., 2007—[Web page] Review of exploration activities in 2006.
Petroleum in Western Australia, April 2007. Department of Industry and
Resources, Western Australia, page 14.
http://www.dmp.wa.gov.au/documents/PWA_April_2007.pdf (last accessed 13
October 2010).
JONASSON, K., 2010—[Web page] Petroleum exploration, production and
development activity in Western Australia in 2009. Petroleum in Western
Australia, April 2010. Department of Industry and Resources, Western
Australia, page 12.
http://www.dmp.wa.gov.au/documents/Petroleum_WA_April_2010.pdf (last
accessed 14 October 2010).
JONASSON, K. AND MACK, C., 2010—[Web page] Petroleum exploration,
production and development activity in Western Australia-Highlights from
January to June 2010. Petroleum in Western Australia, September 2010.
Department of Industry and Resources, Western Australia, page 12.
2011 Release of Australian Offshore Petroleum Exploration Areas
Release Areas W11-12, W11-13 and W11-14, Exmouth Plateau, Northern
Carnarvon Basin, Western Australia
Release Area Geology
Page 18 of 21
http://www.dmp.wa.gov.au/documents/Petroleum_in_WA_magazine_09_10.p
df (last accessed 14 October 2010).
KENNARD, J.M. AND COLWELL, J.B., 2001—Line drawings of AGSO –
Geoscience Australia’s regional seismic profiles, offshore northern and
northwestern Australia. AGSO Record 2001/36, AGSOCAT 36353.
KORN, B.E., TEAKLE, R.P., MAUGHAN, D.M. AND SIFFLEET, P.B., 2003—
The Geryon, Orthrus, Maenad and Urania gas fields, Carnarvon Basin,
Western Australia. The APPEA Journal, 43 (1), 285-301.
LONGLEY, I.M., BUESSENSCHUETT, C., CLYDSDALE, L., CUBITT, C.J.,
DAVIS, R.C., JOHNSON, M.K., MARSHALL, N.M., MURRAY, A.P.,
SOMERVILLE, R., SPRY, T.B. AND THOMPSON, N.B., 2002—The North
West Shelf of Australia – a Woodside perspective. In: Keep, M. and Moss,
S.J. (eds), The Sedimentary Basins of Western Australia 3: Proceedings of
the Petroleum Exploration Society of Australia Symposium, Perth, WA, 2002,
27–88.
NICOLL R.S, G. BERNADEL, T. HASHIMOTO, A.T. JONES, A.P. KELMAN,
J.M. KENNARD, S. LE POIDEVIN, D.J. MANTLE, N. ROLLET AND P.R.
TEMPLE (2010) Northern Carnarvon Basin, Biozonation and Biostratigraphy,
2010, Chart 36. On CD: Basin Biozonation and Stratigraphy Charts, 2010.
Geoscience Australia.
NORVICK, M.S., 2002—Palaeogeographic Maps of the Northern Margins of
the Australian Plate: Final Report. Unpublished report for Geoscience
Australia.
PETROLEUM GEO-SERVICES, 2009—[Web page]
http://www.pgs.com/Data_Library/Asia-Pacific/Australia/New-Dawn-2D/ (last
accessed 14 October 2010).
PHILLIPS AUSTRALIAN OIL COMPANY, 1980a—Jupiter 1 Well Completion
Report, unpublished.
PHILLIPS AUSTRALIAN OIL COMPANY, 1980b—Mercury 1 Well Completion
Report, unpublished.
ROC OIL LTD, 2010—[Web page] Drilling Program.
http://www.rocoil.com.au/Public/Activities/Drilling_Programme.aspx (last
accessed 14 October 2010).
SMALLWOOD, J.R., BANFIELD, J., COX, P., GRIFFIN, D.,
KUSUMANEGARA, Y., OWEN, P.B., PRESCOTT, E., SANTONI, S AND
SMITH, J.G., 2010—Extending the Exmouth Plateau post-Callovian fairway:
WA-390-P Phase I exploration. Extended abstract in APPEA 2010 conference
proceedings.
2011 Release of Australian Offshore Petroleum Exploration Areas
Release Areas W11-12, W11-13 and W11-14, Exmouth Plateau, Northern
Carnarvon Basin, Western Australia
Release Area Geology
Page 19 of 21
STAGG, H.M.J., ALCOCK, M.B., BERNARDEL, G., MOORE, A.M.G.,
SYMONDS, P.A. AND EXON, N.F., 2004—Geological framework of the outer
Exmouth Plateau and adjacent ocean basins. Geoscience Australia Record,
2004/13, unpublished.
TAPOIL LTD, 2006—[Web page] Jacala 1 Exploration Well Update, March
2006. http://www.tapoil.com.au/investor-archive.aspx?ContentID=4591 (last
accessed 13 October 2010).
von RAD, U., EXON, N.F. AND HAQ, B.U., 1992a—Rift to drift history of the
Wombat Plateau, northwest Australia: Triassic to Tertiary Leg 122 results. In
von Rad, U., Haq, B.U., ET AL, Proceedings of Ocean Drilling Program, Initial
Reports, 122. Ocean Drilling Program, College Station, Texas, 765-800.
von RAD, U., HAQ, B.U., ET AL, 1992b—Proceedings of Ocean Drilling
Program, Initial Reports, 122. Ocean Drilling Program, College Station, Texas,
934 pp.
WALKER, T.R., 2007—Deepwater and frontier exploration in Australia –
historical perspectives, present environment and likely future trends. The
APPEA Journal 47(1), 15-38.
WESTERNGECO, 2010a—[Web page] Keystone 3D.
http://www.multiclient.westerngeco.com/Default.cfm?id=4970 (last accessed
14 October 2010).
WESTERNGECO, 2010b—[Web page] Aragon 3D.
http://www.multiclient.westerngeco.com/Default.cfm?id=4969 (last accessed
14 October 2010).
WILLIAMSON, P.E., EXON, N.F., HAQ, B.U., AND von RAD, U., 1989—A
North West Shelf Triassic Reef Play: results from ODP Leg 122. The APEA
Journal, 29 (1), 328-344.
WILLIAMSON, P.E. AND KROH, F., 2007—The role of amplitude versus
offset technology in promoting offshore petroleum exploration in Australia.
The APPEA Journal, 47 (1), 161-174.
WOODSIDE, 2007a—[Web page] Woodside investor briefing 2007, Sydney,
15 November 2007; Sustaining growth and value presentations.
http://www.woodside.com.au/NR/rdonlyres/7A7B410A-7F01-4A15-BB828A505B090078/0/ASX070aWoodsideInvestorBriefingSustainingGrowthandVa
luePresentations.pdf (last accessed 14 October 2010).
WOODSIDE, 2007b—[Web page] ASX announcement 21 November 2007,
Belicoso well clarification.
http://www.woodside.com.au/NR/rdonlyres/CD92F449-2274-4E68-AE0D7176198AA49F/0/BelicosaWellClarification.pdf (last accessed 14 October
2010).
2011 Release of Australian Offshore Petroleum Exploration Areas
Release Areas W11-12, W11-13 and W11-14, Exmouth Plateau, Northern
Carnarvon Basin, Western Australia
Release Area Geology
Page 20 of 21
WOODSIDE, 2009a—[Web page] Martell gas discovery update, 25 February
2009. http://www.woodside.com.au/NR/rdonlyres/ECC18A32-9C7A-497190C4-96FABA6306FE/0/MartellGasDiscoveryUpdate.pdf (last accessed 18
October 2010).
WOODSIDE, 2009b—[Web page] Half year results briefing, 19 August 2009
http://www.woodside.com.au/NR/rdonlyres/783AD8C4-AF6D-4B23-9BA51A635FF82291/0/ASX0402009HalfYearResultsBriefingpresentationbyCEOan
dCFO.pdf (last accessed 15 October 2010).
WOODSIDE, 2010a—Gas discovery at Alaric, ASX Announcement, 16
August 2010 http://www.woodside.com.au/NR/rdonlyres/79013843-477641C0-B31B-920630672289/0/ASX036GasDiscoveryatAlaric.pdf (last
accessed 9 November 2010).
WOODSIDE, 2010b—[Web page] Pluto expansion – outer hubs encouraging,
p34. Half year results briefing, 18 August 2009
http://www.woodside.com.au/NR/rdonlyres/0D78CDCE-626B-4547-9170DB0DF64AD818/0/ASX0422010HalfYearResultsBriefingSpeakerNotesandSli
des.pdf (last accessed 18 October 2010).
Front page image courtesy of Petroleum Geo-Services.
2011 Release of Australian Offshore Petroleum Exploration Areas
Release Areas W11-12, W11-13 and W11-14, Exmouth Plateau, Northern
Carnarvon Basin, Western Australia
Release Area Geology
Page 21 of 21