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GEOLOGICAL INFORMATION RELEASE AREAS W11-16 AND W11-17, SOUTHERN CARNARVON BASIN WESTERN AUSTRALIA Bids Close – Second Round – 12 April 2012 Poorly explored area immediately to the south of a producing hydrocarbon province. Northeastern part of Release Area W11-16 lies on the same structural trend as Rough Range and Parrot Hill oil discoveries. Proximal to existing pipeline at Carnarvon. Vast majority of the Release Areas lie in water depths from less than 100 m to 1000 m. Structural and stratigraphic plays at multiple stratigraphic levels. Cretaceous regional seal overlies source rocks and quality reservoirs of Paleozoic and Mesozoic age. 2011 Release of Australian Offshore Petroleum Exploration Areas Release Areas W11-16 and W11-17, Southern Carnarvon Basin Western Australia Release Area Geology Page 1 of 22 LOCATION Release Areas W11-16 and W11-17 lie on the continental shelf and slope of the Cuvier margin (Figure 1 and Figure 2) in water depths ranging from 100 m to over 2500 m. They lie to the south of the Mesozoic Northern Carnarvon Basin, the major Australian oil and gas producing basin. The northern part of Release Area W11-16 lies on the same structural trend as the Rough Range anticline, on which an early commercial oil discovery was made in 1953. The Release Areas are located about 100 km to the west and northwest of the township of Carnarvon (Figure 1), which provides access to Western Australian infrastructure. Release Areas W11-16 and W11-17 lie partly within the Paleozoic Bernier Platform and Gascoyne Sub-basin of the Southern Carnarvon Basin and partly on the southernmost Mesozoic Exmouth Sub-basin of the Northern Carnarvon Basin. This is a frontier area with only one well (Pendock 1A, 1969) drilled in the Release Area W11-16 and one (Herdsman 1) about 5 km to the north of it. Pendock 1A, which is located on the Bernier Platform had minor shows in the Paleozoic succession, while Herdsman 1, which was located in the Exmouth Sub-basin, was dry. The area has very limited seismic coverage (>25 km line spacing), except for the northeastern part of Release Area W11-16, where the data coverage is much denser. Release Area W11-16 comprises 264 graticular blocks with a total area of approximately 20,735 km2 and Release Area W11-17 comprises 230 graticular blocks with a total area of approximately 17,925 km2 (Figure 2). 2011 Release of Australian Offshore Petroleum Exploration Areas Release Areas W11-16 and W11-17, Southern Carnarvon Basin Western Australia Release Area Geology Page 2 of 22 RELEASE AREA GEOLOGY Local Tectonic Setting and Structure The Release Areas include three different structural elements: the Gascoyne Sub-basin, Bernier Platform and Exmouth Sub-basin (Figure 3). The northern Release Area (W11-16) overlaps all three elements, whereas the southern Release Area (W11-17) lies almost entirely on the Bernier Platform. Structural architecture of the area is documented only at reconnaissance level. Faults shown on Figure 3 include major faults mapped from seismic data at the Valanginian level combined with some onshore and offshore faults from published structure maps (Hocking et al, 1987, Lockwood and D’Ercole, 2004, Woodside Energy Ltd., 2003b, c). The obvious lack of detail in the southern part of the area is due to sparse seismic data. The Gascoyne Sub-basin and Bernier Platform are also described in the literature as the Gascoyne Platform (Gascoyne Sub-basin and eastern part of the Bernier Platform), the Bernier Ridge and the Bernier Terrace (Figure 3). The Bernier Ridge is an uplifted northerly trending part of the Paleozoic platform separated from the Gascoyne Platform by a series of en echelon faults (Lockwood and D’Ercole, 2004). It coincides with a large scale positive gravity anomaly (Figure 3). Gravity modelling undertaken by Lockwood and D’Ercole (2004) suggests that the ridge corresponds to a faulted crystalline basement high. The area lying between the Bernier Ridge and Mesozoic depocentres of the southern Exmouth and northern Houtman sub-basins (Figure 3) is known as the Bernier Terrace. From the limited seismic data available and regional geological knowledge (Iasky et al, 2003, Mory et al, 2003, Lockwood and D’Ercole, 2004) it appears that it has a similar structure and depositional history to that of the Gascoyne Platform. The Bernier Terrace is separated from the Mesozoic depocentres by a series of large basement-involved faults, which strike northwest-southeast along the boundary with the southern Exmouth Sub-basin and north-northwest-southsoutheast along the boundary with northern Houtman Sub-basin (Figure 3). The Exmouth Sub-basin is the most southerly of the northeast-trending Mesozoic Sub-basins which form part of the Exmouth-Barrow-Dampier intracratonic rift system of the Northern Carnarvon Basin. The southern Exmouth Sub-basin is described as a ramp basin formed by a series of shallowly dipping detachment faults (Partington et al, 2003). It is separated from the Exmouth Plateau by the Kangaroo Syncline and bounded on the southeast by the Rough Range Fault (Figure 3). This fault is a large arcuate normal fault with a throw, locally, of more than 4,000 m (Partington et al., 2003), separating the Gascoyne Sub-basin from the Exmouth Sub-basin. The Rough Range Fault was active throughout the Jurassic, resulting in the deposition of several kilometres of Jurassic sediments in the northern part of Exmouth Subbasin. The architecture of the southernmost part of the Exmouth Sub-basin extending into the Release Areas is poorly known. Geoscience Australia 2011 Release of Australian Offshore Petroleum Exploration Areas Release Areas W11-16 and W11-17, Southern Carnarvon Basin Western Australia Release Area Geology Page 3 of 22 seismic data collected during 2008-09 under the Offshore Energy Security program defines several en-echelon Mesozoic depocentres with complex fault geometries (Figure 4). Steeply dipping normal faults on the boundary between the Paleozoic platform and Mesozoic depocentres are shown in Figure 5. A strike line across one of these depocentres (Figure 6) shows significant faulting and folding within the syn-rift strata as well as a large number of sills and dykes. Maximum thickness of sediments within these depocentres exceeds 3.5 s TWT, which is about 8, 000 m according to Partington et al. (2003). This includes about 2.5 s TWT of syn-rift and 1 s TWT of post-rift strata. Based on interpretation of the regional 2D and Coverack 3D seismic surveys (Figure 7), Partington et al. (2003) suggested that the northeast-southwest trending faults bounding the Mesozoic depocentres, may have originated as Early Paleozoic listric growth faults. These en echelon faults are offset by a series of northwest-southeast trending relay zones, which were interpreted to have formed in the Permian. These relay zones are intersected by a series of compressional/transpressional northwest-southeast oriented faults inverted during the Santonian and Miocene compressional events (Partington et al, 2003). Santonian inversion structures are widespread both in the Mesozoic depocentres and on the Bernier Platform (Figure 4 and Figure 5). This inversion is coincident with and may have been caused by the major plate reorganisation in the Indian Ocean, when Greater India changed its path from northwest to north (Gibbons et al., 2010). Miocene inversion is even more evident on the seismic (Figure 5). It also affected the whole region and is related to the collision of Australia and Eurasia in the middle Miocene (Partington et al, 2003). A large number of major faults have been inverted and form well defined local anticlines in the post-breakup strata. In the Exmouth Sub-basin, igneous rocks (predominantly sills and dykes) are widespread within the Mesozoic and possibly within the pre-rift upper Paleozoic succession (Figure 6). Most of the igneous activity is associated with the Early Cretaceous breakup on the western Australian margin (Muller et al, 2002).The volume of volcanic rocks noticeably increases to the south, towards the Wallaby Plateau. This part of the margin is described as a volcanic rifted margin characterised by excessive volcanism overprinting all pre-exiting structures (Direen et al, 2008; Symonds et al, 1998) The Wallaby Saddle lies about 80 km to the west of W11-17 and is dominated by seaward dipping reflector sequences (SDRS) interpreted as interbedded lava flows and volcaniclastics, and large intrusive bodies. In the Release Areas, the increased volume of volcanic rock leads to significant difficulties in seismic imaging and consequent difficulties in seismic interpretation. Structural Evolution and Depositional History of the Sub-basin The Paleozoic basinal succession in the region is underlain by the northernmost extension of the Pinjarra Orogen (Lockwood and D’Ercole, 2004). The Gascoyne Sub-basin and Bernier Platform contain an Ordovician 2011 Release of Australian Offshore Petroleum Exploration Areas Release Areas W11-16 and W11-17, Southern Carnarvon Basin Western Australia Release Area Geology Page 4 of 22 to Carboniferous sedimentary succession deposited in the northward-opening intracratonic basin (Mory et al, 2003; Lockwood and D’Ercole, 2004). The Permian to Lower Cretaceous section in this area is largely absent due to erosion. Permian (Lyons Group) sediments are present in the onshore northern part of the Gascoyne Sub-basin (Iasky et al, 2003) and have been interpreted to extend offshore across the northern part of the Bernier Platform, as well as beneath the Mesozoic Exmouth Sub-basin. For a detailed summary of the stratigraphy of the onshore Southern Carnarvon Basin see Regional Geology of the Southern Carnarvon Basin. The stratigraphy of the offshore Southern Carnarvon and the southernmost part of the Exmouth Sub-basin is poorly documented due to lack of wells. Below is an attempt to reconcile current understanding of the main tectonic events in the region with the depositional phases identified from seismic interpretation. Major supersequences in the region have been mapped using existing industry 2D coverage and new seismic data collected by Geoscience Australia in 2008-2009 (survey 310). These supersequences were then correlated to regional tectonic events to define major depositional basin phases (Figure 8). Two Paleozoic supersequences were indentified in the pre-rift succession: Ordovician-Silurian and Devonian-Pennsylvanian: Ordovician-Silurian supersequence (pre-rift 1) Initial formation of the intracratonic basin has been linked to the breakup of Rodinia, which caused uplift of the Pilbara and Northampton Blocks and subsidence of the basement to the west (Lockwood and D’Ercole, 2004). The basin may have stated to form as early as the Late Cambrian with deposition of fluvial and marine sediments. Deposition within this intracratonic basin continued until the Pennsylvanian. The base of the Paleozoic succession is not well imaged on seismic. The Ordovician-Silurian succession is generally characterised by low amplitude, low frequency, continuous to discontinuous reflections (Figure 5). This supersequence has been mapped only within Paleozoic platform areas and it is correlated to coarse grained red beds of the Tumblagooda Sandstone and restricted marine mudstone of the Dirk Hartog Group (Figure 8). Devonian - Pennsylvanian supersequence (pre-rift 2) As a result of Early Devonian tectonism, depocentres shifted to the north with accumulation of mostly shallow marine sediments (Kopke and Sweeney Mia Formations). The formation of an extensive carbonate shelf in the Late Devonian (Frasnian) led to growth of stromatoporoid reefs over parts of the basin. Shallow marine deposition continued into the Mississippian. Supersequence Pre-rift 2 has been mapped on the Paleozoic platform and on the flanks of the Mesozoic depocentres (Figure 5). Lack of seismic resolution in deeper parts of the Mesozoic depocentres (Figure 6) makes it uncertain whether this sequence is present beneath the syn-rift succession. The sequence is characterised by low amplitude, medium to low frequency 2011 Release of Australian Offshore Petroleum Exploration Areas Release Areas W11-16 and W11-17, Southern Carnarvon Basin Western Australia Release Area Geology Page 5 of 22 continuous reflections which are correlated to shallow marine to restricted marine sandstones and carbonate units of the Southern Carnarvon Basin (Figure 8). In the mid Carboniferous the Devonian-Mississippian sequences were folded and faulted along north-trending axes (Mobil, 1994), possibly as a result of the collision of Gondwana with Laurasia. Pennsylvanian/Cisuralian – Base Mesozoic (syn-rift 1/ erosion 1) The southern margin of Tethys evolved by successive shedding of microcontinents, which subsequently drifted and accreted to Southeast Asia. Uplift of central Australia in the middle Carboniferous was followed by initiation of the Westralian Superbasin during Pennsylvanian-Cisuralian extension. This first major rifting event in the region resulted in the formation of north-northeast-south-southwest trending graben on the North West Shelf (Norvick, 2002) and north-south trending graben of the Southern Carnarvon and Perth basins (Mory et al, 2003; Partington et al, 2003). The same event led to the uplift of the Gascoyne Sub-basin and Bernier Platform (Iasky et al, 2003). The Pennsylvanian-Cisuralian succession, intersected in a number of onshore wells (Airey Hill 1, Chargoo 1, Gnaraloo 1 and Warroora 1) is restricted to the northernmost part of the Gascoyne Sub-basin. It consists predominantly of shale and sandstone deposited in a glacio-marine environment (Lyons Group; Hocking et al, 1987; Figure 8). The rest of the Gascoyne Sub-basin and Bernier Platform remained relative structural highs with no deposition until the earliest Cretaceous. It is estimated that up to 6 km of section may have been removed by erosion between the Permian and Early Cretaceous (Mory et al., 2003). Only a thin cover of Cretaceous and Cenozoic strata overlies the Paleozoic succession in these areas. The Top Permian has been mapped in the southern Exmouth Sub-basin on Coverack 3D survey by Partington et al. (2003). Current assessment has used only 2D data. Multiple faulting and folding of the basin fill makes it impossible to reliably identify the early syn-rift package. The presence of the syn-rift 1 unit is assumed beneath the Mesozoic succession (Figure 4) and is tentatively interpreted as Cisuralian. This unit is characterised by high amplitude, low frequency reflections of high to medium continuity. Base Mesozoic – Lower Jurassic (erosion 2/subsidence 2) From at least the Early Triassic, deposition continued within the ExmouthBarrow-Dampier intra-cratonic rift system (Figure 8). The Gascoyne Platform, which remained an elevated horst complex, diverted sediments to the north and the south. The Exmouth Sub-basin became the major depocentre for Triassic and Jurassic sediments. The Locker Shale was deposited in shallow shelf environment during a widespread Early Triassic marine transgression which is recognised along the whole western Australian margin from the Bonaparte Basin to the Perth Basin (Figure 8). It is generally a uniform shale sequence, with local sandy horizons and the carbonate Cunaloo Member near 2011 Release of Australian Offshore Petroleum Exploration Areas Release Areas W11-16 and W11-17, Southern Carnarvon Basin Western Australia Release Area Geology Page 6 of 22 the base (Hocking et al, 1987). The Locker Shale is overlain by a thick succession of mainly fluvio-deltaic to marginal marine sediments of the Mungaroo Formation. The reservoir units of the Mungaroo Formation host giant gas accumulations on the Rankin Platform in the Northern Carnarvon Basin. The sand percentage in this formation is variable, which significantly affects the economic viability of hydrocarbon accumulations (Hocking et al, 1987). Shaly intervals of the Mungaroo Formation are considered as potential source rocks. The interpreted Base Mesozoic to Upper Jurassic succession (Figure 4 and Figure 6) is characterised by medium to high amplitude, medium frequency, variable continuity reflections. Seismic data shows a large number of igneous features, mostly sills and dykes, especially in the lower part of this succession. In the central parts of the depocentres the thickness of this unit exceeds 2 s TWT (two way time). Lower Jurassic - Lower Cretaceous (syn-rift 2) Two units mapped within the Jurassic succession correspond to two different extensional episodes (Figure 8): the Early Jurassic and the Middle to Late Jurassic. The first extensional phase is associated with breakup of Argoland (Norvick, 2002). The second extensional phase starting in the Middle Jurassic preceded the breakup between Australia and Greater India. The Jurassic supersequence within the Exmouth Sub-basin includes the Brigadier Formation and Dingo Claystone, as well as the Learmonth Formation, the deposition of which was restricted to the basin margin (Partington et al, 2003). The Brigadier Formation is a paralic to shallow-marine deposit characterised by siltstone with claystone, shale and fine sandstone. The overlying Dingo Claystone is a thick unit with a very consistent lithology dominated by grey argillaceous siltstone (Hocking et al, 1987). The Dingo Claystone is considered to be the source rock for most of the hydrocarbon discoveries in the Exmouth Sub-Basin (Hocking et al, 1987). The distribution of the Learmonth Formation was controlled by major faults which were active at the time of the deposition. It is an alluvial to shallow-marine fan complex formed at the foot of elevated fault blocks (Hocking et al, 1987). The Berriassian uplift of the Gascoyne Sub-basin and Bernier Platform prior to the breakup provided the sediment source for the Barrow Delta which prograded northward over the Exmouth Sub-basin, however there is no evidence that the Barrow Group is present in the southernmost part of the Exmouth Sub-basin (Partington et al, 2003, Figure 8). The Lower Jurassic to Lower Cretaceous succession (Figure 4 and Figure 6) is characterised by medium to high amplitude, high frequency and high continuity seismic facies. The supersequence is highly faulted and includes a number of unconformities of limited spatial extent. 2011 Release of Australian Offshore Petroleum Exploration Areas Release Areas W11-16 and W11-17, Southern Carnarvon Basin Western Australia Release Area Geology Page 7 of 22 Valanginian to Barremian (Post-rift 1) Valanginian breakup was accompanied by a major structural inversion which resulted in the uplift of the Ningaloo Arch and erosion of the Barrow Group and older Jurassic sediments across much of the Exmouth Sub-basin (Tindale et al, 1998). The delta sediments were reworked and re-deposited as the Birdrong Sandstone, which overlies the breakup unconformity (Figure 8). The Birdrong Sandstone is primarily a coastal to near-shore deposit which formed at the onset of the post-breakup subsidence. It is the reservoir for the Rough Range oil accumulation and it has been the primary target for exploration in the Southern Carnarvon Basin. The regional marine transgression during the Hauterivian resulted in the deposition of the Muderong Shale (Figure 8), which is the main regional seal in the Exmouth Sub-basin. Although named the Muderong Shale, the unit is dominantly an argillaceous siltstone with thin lenses of siltstone and fine sandstone (Hocking et al, 1987). This supersequence is fairly thin (less than 100 ms). It fills lows in the Valanginian surface and is often absent over the highs (Figure 4 and Figure 5 and Figure 6). It is a highly reflective seismic unit with high amplitude, medium frequency and high continuity reflections. Aptian to Turonian (Post-rift 2) In the Aptian, shallow marine conditions spread to current onshore areas of the Gascoyne Sub-basin. At the same time in the offshore areas an open marine environment resulted in the onset of widespread carbonate sedimentation. The onshore Aptian-Albian Windalia Radiolarite is a uniform white radiolarian siltstone. It is overlain by argillaceous Gearle Siltstone deposited in a low energy, restricted marine environment (Hocking et al, 1987), possibly inner shelf for the Gascoyne Sub-basin and outer shelf for the Exmouth Sub-basin. There is a prominent unconformity within this supersequence. It is tentatively correlated with the middle Albian and is more pronounced in the deeper water parts of the area. Overall the supersequence is characterised by medium amplitude, medium to high frequency, high continuity reflections Turonian to Base Cenozoic (Post-rift 3) In the early Santonian regional uplift and fault reactivation largely overprinted previously formed structures in the Northern Carnarvon Basin (Tindale et al, 1998). In the Release Areas, Santonian tectonism caused inversion on a number of major faults and formation of anticlinal structures in the pre-existing post-rift succession (Figure 4 and Figure 5). Following a brief depositional hiatus, carbonate deposition recommenced with the onset of full ocean circulation in the Turonian and deposition of the Toolonga Calcilutite. The Toolonga Calcilutite disconformably overlies the Winning Group (Figure 8) and consists of fossiliferous calcilutite and calcisiltite deposited in a lowenergy, middle-shelf marine environment. In the northern Gascoyne Platform 2011 Release of Australian Offshore Petroleum Exploration Areas Release Areas W11-16 and W11-17, Southern Carnarvon Basin Western Australia Release Area Geology Page 8 of 22 the Toolonga Calcilutite grades up into the overlying Korojon Calcarenite, which consists of silty calcarenite and calcisiltite deposited in a moderateenergy marine environment. In the Release Areas, the post-rift 3 supersequence is highly variable in thickness. It is very thin in shallow water areas and increases up to 500 ms in deeper areas of the slope, where the basal part of the unit develops bright chaotic reflections possibly suggesting turbidite origin. The rest of the unit is characterised by medium to low amplitude, high frequency and generally continuous reflections. Base Cenozoic to Miocene (Post-rift 4) The Cenozoic succession in the Southern Carnarvon Basin is predominantly flat lying and consists of shallow-marine carbonates (Cardabia and Giralia Calcarenites and Trealla Limestone). Offshore, thick prograding carbonates were deposited throughout most of the Cenozoic (Hocking et al., 1987). Progradational succession is clearly imaged on the seismic (Figure 4) in the inboard part of the continental slope. It is bounded by Base Cen and Olig seismic horizons (Figure 8). In deeper parts of the area this sequence is highly disrupted by buried channels and .slump deposits. It is characterised by medium to high amplitude, high frequency, high continuity reflections, which become less continuous in its upper part. Miocene to Holocene (Post-rift 5) The Miocene collision between Australia and Eurasia reactivated major preexisting faults and led to the formation of widespread compressional structures (Iasky et al, 2003). Miocene inversion anticlines are widespread both over Paleozoic and Mesozoic parts of the basin (Figure 4 and Figure 5). This sequence is generally thin (less than 150 ms) and is characterised by low to high amplitude, high frequency, high continuity reflections. 2011 Release of Australian Offshore Petroleum Exploration Areas Release Areas W11-16 and W11-17, Southern Carnarvon Basin Western Australia Release Area Geology Page 9 of 22 EXPLORATION HISTORY Release Areas W11-16 and W11-17 lie within frontier under-explored part of the Carnarvon Basin. Over most of the area, seismic coverage has more than 25 km line spacing (Figure 7) with only one well (Pendock 1A) drilled in the shallow water eastern part of Release Area W11-16. Northern and eastern parts of the Release Areas have the best seismic coverage with 1-5 km line spacing and a 3D grid in the northernmost part of W11-16. In the last 20 years, permits have existed only over parts of the Release Area W11-16. Between 1991 and 1995 Mobil Oil Australia Ltd held a permit on the southern inboard part of W11-16, and between 2000 and 2003 Shell Development (Australia) Pty Ltd had two permits covering the northern part of W11-16 and extending further north into the Exmouth Sub-basin. The work program within these permits was focused on seismic acquisition with only one well (Herdsman 1) drilled in the southern Exmouth Sub-basin. Current permits WA-284P and WA-385P, held by Shell, lie immediately to the north of the Release Area W11-16 (Figure 1). Lack of exploration activity in the area could be partly attributed to focus on hugely successful exploration in the adjacent Northern Carnarvon Basin. To view image of seismic coverage follow this link: http://www.ga.gov.au/energy/projects/acreage-release-andpromotion/2011.html#data-packages 2011 Release of Australian Offshore Petroleum Exploration Areas Release Areas W11-16 and W11-17, Southern Carnarvon Basin Western Australia Release Area Geology Page 10 of 22 Well Control Only one well was drilled within the Release Areas, Pendock 1A (1969). A more recent well (Herdsman 1, 2003) was drilled just to the north of W11-16. Both wells were dry, however minor shows are noted in the Silurian and Devonian section in Pendock 1A. The lack of success in both wells is attributed to poor understanding of source rock distribution and their maturity. Herdsman 1 (2003) Herdsman 1 was drilled in 2003 by Woodside Energy Ltd within the Exmouth Sub-basin in the Northern Carnarvon Basin, in a water depth of 556.7 m (Figure 1), approximately 227 km north of Carnarvon and 46 km north of Pendock 1. Herdsman 1 is the southernmost well in the Exmouth Sub-basin (Woodside Energy Ltd, 2003a). The well tested a structural closure over a tilted fault block with the primary targets in the Lower Cretaceous Birdrong Sandstone and Middle Jurassic Learmonth Formation. The well reached a total depth of 2010 mRT intersecting Cenozoic, Cretaceous and Jurassic sections. The deepest units intersected were the Jurassic Athol (1397.7-1462.7 mRT) and Learmonth (1462.7 mRT to TD) formations (Woodside Energy Ltd, 2003a). The Jurassic section was thinner and sandier than anticipated. The Learmonth Formation penetrated in this well comprises a lower non-marine medium-grained sandstone package (>80 m) and a locally carbonaceous claystone interval (115 m) that grades upwards into a non-marine medium-grained sandstone package (352 m). The overlying Athol Formation comprises 65 m of silty claystone grading into argillaceous siltstone deposited in a non-marine to marginal marine environment. The Cretaceous breakup unconformity separates the Athol Formation from the overlying Birdrong Sandstone (1367.7-1397.7 mRT), a non-marine to near-shore sandstone containing minor silt. The Birdrong Sandstone is in turn overlain by the 57.5 m of Muderong Shale, 51.5 m of Windalia Radiolarite, 285 m of Gearle Siltstone followed by undifferentiated Upper Cretaceous and Cenozoic carbonates. No indications of hydrocarbons were seen in the Birdrong Sandstone and it was evaluated as water-bearing. Reservoir quality was good with an average porosity of 28% and a net-to-gross ratio of 87%. The secondary objective, the Learmonth Formation sandstones, were penetrated about 390 metres shallower than expected, due to more extensive erosion at the breakup unconformity. The Learmonth Formation is also evaluated as water bearing with good reservoir properties (average porosity of 26% and a net-to-gross ratio of 86%). The Herdsman trap was interpreted to be valid. The lack of hydrocarbon charge was thought to be due to the absence of Jurassic source rocks at this location and extensive erosion during the Valanginian. It has been suggested that if Jurassic source rocks are present, they are small in volume and are insufficiently buried to have matured (Woodside Energy Ltd, 2003a). Low 2011 Release of Australian Offshore Petroleum Exploration Areas Release Areas W11-16 and W11-17, Southern Carnarvon Basin Western Australia Release Area Geology Page 11 of 22 reservoir temperatures (40 to 60°C) were also confirmed. However, spore colouration indicated the section is marginally mature for oil at the base of the Cretaceous interval and is mature for both oil and gas generation in the Jurassic interval. This is confirmed by the vitrinite reflectance analysis which found the lower part of the section to be quite mature (Woodside Energy Ltd, 2003a). Geochemical analyses were performed by Geotech on four sidewall core samples from 1,428 to 1,920 mRT and cuttings from 1,950 to 1,955 mRT (Woodside Energy Ltd, 2003a). The sidewall cores yielded 0.64 to 3.10% Total Organic Carbon (TOC), the maximum occurring at 1,895 mRT. The Hydrocarbon Indices (HI) are very poor ranging from 47 to 157, with the lowest at 1,895 mRT, suggesting gas source potential only. Fluid Inclusion Stratigraphy (FIS) was performed on cuttings from 1090 to 2010 mRT by Fluid Inclusion Technologies Inc (Woodside Energy Ltd, 2003a, Appendix 3). Results of this work suggest that very poor Lower Jurassic or Upper Triassic source rocks were mature some time before the Valanginian breakup. The migrated compounds were limited in volume and consisted of wet gas and possibly other liquids. Very high net-to-gross ratio in the Learmonth Formation strata provides effective pathways for migration but is unfavourable for trap formation. Any traps that might have existed were disrupted by the Valanginian tectonism. The remaining traces of hydrocarbons have been biologically altered due to temperatures less than 80°C (Woodside Energy Ltd, 2003a). Pendock 1A (1969) Pendock 1 and Pendock 1A were drilled in 1969 by the Canadian Superior Oil (Aust.) Pty Ltd. Both wells were located approximately 181 km north of the town of Carnarvon within the Gascoyne Sub-Basin of the Southern Carnarvon Basin. Pendock 1 was drilled in a water depth of 132.6 m (10.4 mKB) and reached a TD of 242.6 mKB. Indications of excessive deviation and drill string hang-ups led to abandoning the well and spudding of Pendock 1A approximate 12 m away from the original location (Canadian Superior Oil (Aust.) Pty Ltd, 1970). Pendock 1A was drilled in 131.1 m water depth and reached a TD of 2,501 mKB. The well tested a large anticlinal structure beneath the breakup unconformity interpreted from seismic data. The primary target was the Lower Cretaceous Birdrong Sandstone and the secondary targets were possible Triassic to Jurassic sandstone intervals. The lower 651 m of Pendock 1A penetrated the Upper Ordovician to Silurian Dirk Hartog Formation. Above the Dirk Hartog Group the well intersected 184.7 m of the Lower Devonian Nannyarra Formation., 558.1 m of Devonian Gneudna Formation, and 77.1 m of the Mississippian Moogooree Limestone. Within the Devonian Gneudna Formation the well encountered a dense dolomite unit containing abundant stromatoporoids and corals, which was interpreted to represent a reef or a carbonate bank deposit. The breakup unconformity at the top of the Moogooree Limestone suggests erosion or non-deposition from Cisuralian to lowest Cretaceous. The presence 2011 Release of Australian Offshore Petroleum Exploration Areas Release Areas W11-16 and W11-17, Southern Carnarvon Basin Western Australia Release Area Geology Page 12 of 22 of Mesozoic strata has been incorrectly inferred from the aeromagnetic data, which indicated over 5,000 m of sediments at this location. Above the breakup unconformity, the well intersected 202 m of the Aptian to Cenomanian Winning Group, including only 7.3 m of the Birdrong Sandstone. The upper part of the well intersected 685 m of Upper Cretaceous to Holocene carbonates. Minor shows of oil were found in the Devonian and Silurian section (GENOA Oil N.L., 1970: Canadian Superior Oil (Aust.) Pty Ltd, 1970). Oil stains were detected in the Nannyarra (1718 mKB) Formation and the overlying Point Maud Member of the Gneudna Formation (1,409 and 1,413 mKB). Oil staining and fluorescence were also detected within the Coburn Formation of the Dirk Hartog Group (e.g. 2,201 mKB). Methane gas shows occurred throughout the Paleozoic with the maximum readings in the interval 2,121-2,124 mKB. Hydrocarbon shows in the Paleozoic imply this interval is prospective elsewhere in the basin. Rock-Eval of a limited number of samples from the Silurian/Devonian source interval indicated that these rocks are thermally immature. More recently work has shown that the Gneudna Formation is currently mature at Pendock 1A (Ghori et al, 2005). Although Pendock 1A failed to intersect anticipated Triassic and Jurassic strata, minor shows encountered in the Devonian and Silurian succession provide important information about a possible Paleozoic petroleum system in this region. 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_sthcarnvarvon_AR11.xls 2011 Release of Australian Offshore Petroleum Exploration Areas Release Areas W11-16 and W11-17, Southern Carnarvon Basin Western Australia Release Area Geology Page 13 of 22 Data Coverage Seismic Data Between 1966 and 1973, nine surveys acquired seismic data over this region. Most of these surveys acquired only a few widely spaced lines of limited quality in the Release Areas. The exceptions are the Carnarvon Basin West (1966) and Gnaraloo West (1967) surveys, both of which provide a tight grid with a line spacing of about 5 km. This data imaged a large pre-breakup anticline tested by Pendock 1A (1969). From 1979 to 1982, four surveys acquired seismic data over the Release Areas. These were small local grids on the inboard edge of Release Area W11-16 (From 1992 to 1994, four surveys collected seismic data in the region: AGSO surveys 135 (1994) and 136 (1994), the Carnarvon Terrace Detail (1992) and the Cuvier (1992) surveys. These surveys acquired seismic in the southeast corner and northeast corner of W11-16. The more recent seismic data include the tight grid of the 1998 Western Geco Carnarvon Terrace 2D Speculative Survey and the 2002 2D and 3D Coverack surveys (Woodside Energy Ltd, 2003b, c). Shell Development (Australia) also collected aeromagnetic data over the same region which partially covers Release Area W11-16. Analysis of these data resulted in identification of a number of prospects, one of which was tested by Herdsman 1. In 2008-09 under the Offshore Energy Security Program, Geoscience Australia acquired regional seismic data in frontier areas of the western Australian margin (survey GA-310), including parts of the Southern Carnarvon Basin (Figure 7). Seismic lines targeted potential depocentres delineated by gravity lows and cover mostly north-western deep-water parts of the Release Areas. These datasets, together with open file industry data were used in the current hydrocarbon prospectivity assessment. In November 2009, Searcher Sesimic (2010) shot the non-exclusive 2D Acheron seismic survey with line spacing of 25 km across the both Release Areas (Figure 7). These data provide a regional grid over the Paleozoic Bernier Platform and have not been interpreted. To view image of seismic coverage follow this link: http://www.ga.gov.au/energy/projects/acreage-release-andpromotion/2011.html#data-packages Swath bathymetry, gravity, magnetic data and dredge samples In 2008-09, Geoscience Australia conducted a marine reconnaissance survey over vast areas of the continental slope on the Western Australian margin. This survey acquired high resolution bathymetry, gravity and magnetic data, as well as a number of dredge samples in the region (Figure 7). Dredge samples were collected from the walls of the deeply incised canyons, the aim being to sample the pre-breakup succession. All sampling sites are located in deep water to the west of the Release Areas. Unfortunately, many samples 2011 Release of Australian Offshore Petroleum Exploration Areas Release Areas W11-16 and W11-17, Southern Carnarvon Basin Western Australia Release Area Geology Page 14 of 22 lacked microfossils and their age could not be determined. The oldest dated samples are of Berriasian age. Detailed sample descriptions are given by Daniell et al (2010). Satellite data Satellite hydrocarbon slick detection in the region was undertaken by Shell in 2000. Datasets collected included ALF, SAR, Landsat 1, Spot, IRS, IKONOS and Earth Resources satellite scenes. Analysis of these data resulted in identifying two medium confidence slicks; one within the Release Area W1116 and one further to the east, close to the coastline (see Figure 3 in Partington et al, 2003). 2011 Release of Australian Offshore Petroleum Exploration Areas Release Areas W11-16 and W11-17, Southern Carnarvon Basin Western Australia Release Area Geology Page 15 of 22 PETROLEUM SYSTEMS AND HYDROCARBON POTENTIAL Petroleum systems The region has potentially two active petroleum systems: Paleozoic and Mesozoic. So far no commercial discoveries from Paleozoic petroleum systems have been found in the Southern Carnarvon Basin, however oil and gas shows were detected in a number of wells. Within the Paleozoic Gascoyne Sub-basin and Bernier Platform, source rocks are present in the Silurian and Upper Devonian. Effective reservoirs and seals are present both in the Paleozoic and the post-breakup Cretaceous succession. The Mesozoic petroleum system of the southern Exmouth Sub-basin of the Northern Carnarvon Basin includes potential source rocks in the Triassic Mungaroo Formation and Jurassic Dingo Formation with multiple reservoir and seal units in the Triassic, Jurassic and Cretaceous. The potential of the Mesozoic petroleum system in the southernmost part of the Exmouth Sub-basin has not been proven. A test of a valid structure at Herdsman 1 suggests that the thickness of the Mesozoic succession is a critical factor for hydrocarbon generation in this part of the basin. Source Rocks The best Paleozoic source rocks are within the Silurian Coburn Formation, and Devonian Gneudna Formation (Ghori et al, 2005; Figure 9). Silurian– Devonian source rocks have been shown to have good potential for both oil and gas generation. Silurian source beds have organic richness of over 7% TOC, potential yield (S1 + S2) of up to 38 mg/g, and hydrogen index of up to 505 mgHC/gTOC. The main source rocks in the Gascoyne Sub-basin are organic rich and oil-prone laminated mudstones within carbonate facies of the Devonian Gneudna Formation. Devonian source beds have organic richness of up to 13.5% TOC, potential yield of up to 40 mg/g, and hydrogen index of up to 267 mgHC/gTOC. However, all of these source rocks are thin and probably of limited extent. Maturity and petroleum generation modelling of the Paleozoic succession (Ghori et al., 2005) showed that the maturity of these units progressively increases from immature in the south-southeast to mature in the north-northwest, commensurate with increasing depth of burial. The presence of Triassic and Jurassic source rocks is inferred from the northern part of the Exmouth Sub-basin, where they charge a number of commercial accumulations. These may include organic-rich units of the Lower Triassic Locker Shale and deltaic Upper Triassic Mungaroo Formation. The Upper Jurassic Dingo Claystone is the principal source for oil in the Exmouth Sub-basin (Tindale et al, 1998), however it is not clear how far south it extends and whether it is present within the Release Areas, as this unit is missing at Herdsman 1. Reservoirs and seals The Paleozoic succession contains a number of potential reservoir and seal units (Figure 9). The Ordovician red beds (Tumblagooda Sandstone) has variable porosity and permeability, although even at depths greater than 1,000 m porosity is typically good, with an average of 13%. The Gneudna 2011 Release of Australian Offshore Petroleum Exploration Areas Release Areas W11-16 and W11-17, Southern Carnarvon Basin Western Australia Release Area Geology Page 16 of 22 Formation provides the prime reservoir potential, with the reefal Point Maud Member demonstrating favourable reservoir properties. Seal is inferred to be provided by thick marine shales and marls of the upper Gneudna Formation overlying the Point Maud Member. The Triassic Mungaroo Formation and Lower Cretaceous Birdrong Sandstone are the main reservoir units in the Mesozoic succession (Figure 9). The Birdrong Sandstone overlies the breakup unconformity, has excellent reservoir characteristics and hosts a number of oil and gas accumulations both onshore and offshore in the Northern Carnarvon Basin. The Birdrong sandstone has been the prime exploration target in the area. The Dingo Claystone, Muderong Shale, Windalia Radiolarite and Gearle Siltstone are possible seals in the Mesozoic succession (Figure 9). The Muderong Shale and Gearle Siltstone are proven effective seals in the northern Exmouth Subbasin (Iasky et al., 2003). Generation, expulsion and migration Burial, thermal and erosional histories are complex and poorly constrained in the Gascoyne Sub-basin (Iasky et al., 2003). Geohistory modelling by Ghori et al. (2005) indicated that petroleum generation and migration from Silurian and Devonian source rocks peaked during the Permian, whereas generation from Permian source rocks peaked during the Triassic. Therefore, in the Gascoyne Sub-basin, mid-Carboniferous to Cisuralian structures are the most prospective, although there is the risk of breaching during later tectonic events. On the Bernier Platform there is some controversy as to how much of the Triassic and Jurassic section was eroded during the uplift preceding the Valanginian breakup (Lockwood and D’Ercole, 2004). Maturity of the source rocks would depend on the thickness of the eroded section. In the model with major erosion during the Permian, the maximum rate of hydrocarbon generation from Silurian and Devonian source rocks occurs at the end of the Permian (Iasky et al, 2003). For the model with major erosion during the Early Cretaceous the peak of hydrocarbon generation for these units extends from the Permian to Middle Jurassic. If no deposition occurred between the Permian and Cretaceous, peak hydrocarbon expulsion may have occurred more recently which would result in filling of Miocene structures only. In the Exmouth Sub-basin, the thickness of the Mesozoic synrift succession and the presence of good source rocks in the area are the main risk. Maximum thickness of the Jurassic rocks is interpreted to be up to 5-6 km in the northeastern part of Release Area W11-16. These rocks are buried deep enough to have generated oil before the breakup (Partington et al, 2003). However, across the basin, thickness of the interpreted Jurassic succession is highly variable, which suggests that some of the Jurassic source rocks would have generated much later. The inferred Triassic succession is buried up to 8 km below the breakup unconformity and is also likely to have generated hydrocarbons (Partington et al, 2003), whereas the underlying Paleozoic section is likely to be mostly overmature. 2011 Release of Australian Offshore Petroleum Exploration Areas Release Areas W11-16 and W11-17, Southern Carnarvon Basin Western Australia Release Area Geology Page 17 of 22 Plays The Paleozoic Gascoyne Sub-basin hosts a number of structural and stratigraphic plays. Structural plays include fault block and Miocene reactivation anticline plays (Figure 10). Paleozoic traps include Ordovician, Silurian and Devonian reservoir rocks in rotated fault blocks created by midto Lopingian and Late Jurassic rifting. Such traps may be effective if sealed by intraformational shales. Low dips and small fault displacements imply that such traps may be quite large (Mory et al, 2003). In the northern part of the sub-basin, east of Pendock 1A, there are a few untested faulted anticlines, in which reefal carbonate facies of the Point Maud Member of the Gneudna Formation may be sealed intraformationally (Iasky et al., 2003). In the southwestern offshore Bernier Platform, there are fault block plays in which the Kockatea Shale seals the Tumblagooda Sandstone. These traps could have been charged by hydrocarbons that migrated updip from more deeply buried sections of the Kockatea Shale in the Abrolhos Sub-basin (Mory et al, 2003). The main objective for petroleum exploration in the Gascoyne Sub-basin has been the Birdrong Sandstone, sealed by the Muderong Shale in Miocene anticlinal structures formed as a result of normal fault inversion. A few untested Miocene structures have been identified by Iasky et al (2003) in the northern part of the area surrounding Pendock 1A. A likely problem with the Birdrong Sandstone is that a strong artesian flow could flush hydrocarbons from all but the most robust traps (Mory et al, 2003). Possible stratigraphic plays in the Gascoyne Sub-basin include incised channels filled by Birdrong Sandstone and sealed by the Muderong Shale. In the northern part of the sub-basin there may be additional traps in which the Birdrong Sandstone is missing, thereby allowing the Muderong Shale to seal dipping Paleozoic reservoir rocks (Iasky et al., 2003). Mobil (1994) suggested some of the stratigraphic traps may be charged by long-distance migration from the Mesozoic source rocks in the adjacent Exmouth Sub-basin. The prime risks for Paleozoic plays are the volume of available source rock, trap integrity because of the long period of preservation required, and relative timing of generation versus trap formation (Ghori et al, 2005). Some of the trapped hydrocarbons from Silurian-Lower Devonian sources are likely to have been lost during Permian and Valanginian rifting and Miocene inversion (Partington et al., 2003) In the Exmouth Sub-basin several types of structural and stratigraphic plays are present. Within the synrift succession, the main structural plays are fault blocks and faulted anticlines (Figure 10). They could include Upper Triassic fluvio-deltaic sandstones sealed by Lower to Middle Jurassic claystone, or Upper Jurassic transgressive sandstone (Oxfordian to Tithonian) sealed by Muderong Shale (Partington et al., 2003). In the post-rift succession, structural traps include Santonian and Miocene anticlines (Figure 10) formed as a result of inversion on normal faults during major tectonic reactivation events. These traps may be present at the Birdrong Sandstone or Windalia 2011 Release of Australian Offshore Petroleum Exploration Areas Release Areas W11-16 and W11-17, Southern Carnarvon Basin Western Australia Release Area Geology Page 18 of 22 Sand Member level and charged from underlying Jurassic source rocks or through secondary migration along the reactivated faults from deeper stratigraphic levels (e.g. Triassic source rocks). The main risk for these plays is breach of trap integrity in the Pliocene to Holocene. Seismic data suggest that some of the faults extend to the sea floor. Stratigraphic plays are associated with pinchouts of the Birdrong Sandstone onto the Valanginian unconformity highs, or drapes over these highs (Figure 10). These plays may be charged by Jurassic or Triassic source rocks and sealed by the Muderong Shale. Risks Overall, the main risks for plays in the Release Areas are: The presence of mature source rocks in the syn-rift succession (Exmouth Sub-basin) The volume of available source rock (Paleozoic section) breached seals artesian flow (Birdrong Sandstone) biodegradation 2011 Release of Australian Offshore Petroleum Exploration Areas Release Areas W11-16 and W11-17, Southern Carnarvon Basin Western Australia Release Area Geology Page 19 of 22 FIGURES Figure 1: Location of Release Areas W11-16 and W11-17, showing wells, permits and bathymetry. Figure 2: Graticular block map and graticular block listings for Release Area W11-16 and W11-17 Southern Carnarvon Basin, Western Australia. Figure 3: Tectonic elements of the Southern Carnarvon Basin based on GA interpretation and compilation from Hocking et al (1987), Lockwood and D’Ercole (2004) and Woodside Energy Ltd (2003b, c). Also shown is the location of the seismic sections in (Figure 4 and Figure 5 and Figure 6). Figure 4: Interpretation of GA seismic line 310-42 intersecting three enechelon Mesozoic depocentres separated by relay zones. See location of the line of the line in Figure 3. Figure 5: Dip line (gpctr-93-0405) across the northern part of the Gascoyne Platform, intersecting Pendock 1A. See location of the line in Figure 3. Figure 6: Strike line (wg98ct-4) intersecting northern part of the Bernier Platform and the Mesozoic depocentre of the southern Exmouth Sub-basin. See location of line in Figure 3. Figure 7: Recently acquired seismic data, extent of GA Marine Reconnaissance Survey 2476 and geological sampling sites. Figure 8: Generalised stratigraphy of the Gascoyne and Exmouth subbasins, showing regional tectonic events, basin phases and seismic horizons, based on the Northern Carnarvon Basin Biozonation and Stratigraphy Chart (Nicoll et al, 2010). Geologic Time Scale after Gradstein et al (2004) and Ogg et al (2008). Figure 9: Petroleum systems elements and possible play types for the Release Areas. Geologic Time Scale from Gradstein et al, 2004 and Ogg et al, 2008. Figure 10: Conceptual play diagram for the Release Areas. Source rock intervals: SR1 – Coburn Formation; SR2 – Gneudna Formation; SR3 – Locker Shale; SR4 – lacustrine shale of the Mungaroo Formation; SR5 – Dingo Formation. 2011 Release of Australian Offshore Petroleum Exploration Areas Release Areas W11-16 and W11-17, Southern Carnarvon Basin Western Australia Release Area Geology Page 20 of 22 REFERENCES CANADIAN SUPERIOR OIL (AUST) PTY LTD, 1970—Well completion report, Pendock 1A, Unpublished report, 111p. DANIELL, J., JORGENSEN, D.C., ANDERSON, T., BORISSOVA, I., BURQ, S., HEAP, A.D., HUGHES, M., MANTLE, D., NELSON, G., NICHOL, S., NICHOLSON, C., PAYNE, D., PRZESLAWSKI, R., RADKE, L., SIWABESSY, J., SMITH, C. AND SHIPBOARD PARTY, 2010—Frontier Basins of the West Australian Continental Margin: Post‐ survey Report of Marine Reconnaissance and Geological Sampling Survey GA2476. Geoscience Australia, Record 2009/38, 229pp DIREEN, N.G., STAGG, H.M.J., SYMONDS, P.A. AND COLWELL, J.B., 2008— Architecture of volcanic rifted margins: new insights from the Exmouth - Gascoyne margin, Western Australia. Australian Journal of Earth Sciences, 55 (3). pp. 341-363. GENOA OIL N.L., 1970—Final report on Pendock N 1 well, Western Australia. Unpublished report, 151p. GHORI, K.A.R., MORY, A.J. AND IASKY, R.P., 2005—Modeling petroleum generation in the Paleozoic of the Carnarvon Basin, Western Australia: Implications for prospectivity. AAPG Bulletin, v. 89, no. 1 (January 2005), pp. 27–40. GIBBONS A., WHITTAKER J. , MÜLLER M.R., 2010—Revised plate tectonic history of the west Australian margin reveals how the Gascoyne Terrane docked at West Burma, ASEG Extended Abstracts 2010, 1–4. GRADSTEIN, F., OGG, J. AND SMITH, A. (EDITORS), 2004—A Geologic Time Scale 2004. Cambridge: Cambridge University Press, 589p. HOCKING R.M., MOORS H.T. AND VAN DE GRAAFF . J.E., 1987— Carnarvon Basin: diagrammatic cross-sections and palaeogeographic reconstructions, GSWA Bulletin 133 p3. IASKY, R.P., D’ERCOLE, C., GHORI, K.A.R., MORY, A.J. AND LOCKWOOD, A.M., 2003—Structure and petroleum prospectivity of the Gascoyne Platform, Western Australia: Western Australia Geological Survey, Report 87, 56p. LOCKWOOD, A.M. AND D’ERCOLE, C., 2004—The evolution of the Bernier Ridge, southern Carnarvon Basin, Western Australia: implications for petroleum prospectivity. The APPEA Journal, 44 (1), 241–67. MOBIL, 1994—WA-229-P Cuvier seismic survey interpretation report, Unpublished report, 25p. MORY, A.J., IASKY, R.P. AND GHORI, K.A.R., 2003—A summary of the geological evolution and petroleum potential of the Southern Carnarvon Basin, Western Australia: Western Australia Geological Survey, Report 86, 26p. 2011 Release of Australian Offshore Petroleum Exploration Areas Release Areas W11-16 and W11-17, Southern Carnarvon Basin Western Australia Release Area Geology Page 21 of 22 MÜLLER, R.D., MIHUT, D., HEINE, C., O'NEILL, C. AND RUSSELL, I., 2002—Tectonic and volcanic history of the Carnarvon Terrace: Constraints from seismic interpretation and geodynamic modelling, In: The Sedimentary Basins of Western Australia 3, ed: Gorter, J., Petroleum Exploration Society of Australia, Perth, 719-740. NORVICK, M.S., 2002—Palaeogeographic Maps of the Northern Margins of the Australian Plate: Final Report. Unpublished report for Geoscience Australia. OGG, J.G., OGG, G. AND GRADSTEIN, F.M., 2008—The Concise Geologic Time Scale. Cambridge: Cambridge University Press, 177p. PARTINGTON, P.A., AURISCH, K., CLARK, W., NEWLANDS, I., PHELPS, S., SENYCIA, P., SIFFLEET, P. AND WALKER, T., 2003—The hydrocarbon potential of exploration permits WA-299-P and WA-300-P, Carnarvon Basin: a case study. The APPEA Journal, 43 (1), 339–61. SEARCHER SEISMIC, 2010—[Web page] Acheron 2D Non-Exclusive Seismic Survey, Carnarvon Basin, Australia, http://www.searcherseismic.com/projects/australia/carnarvon_basin/Acheron. aspx (last accessed 26 November 2010) SYMONDS P.A., PLANKE, S., FREY, Ø. AND SKOGSEID, J., 1998— Volcanic development of the Western Australian continental margin and its implications for basin development. The Sedimentary Basins of Western Australia 2: Proceedings of Petroleum Exploration Society of Australia Symposium, edited by P.G. and R.R. Purcell, Perth, 33-54. TINDALE, K., NEWELL, N., KEALL, J. AND SMITH, N., 1998—Structural evolution and charge history of the Exmouth Sub-basin, Northern Carnarvon Basin, Western Australia. In: Purcell, P.G. and Purcell, R.R. (eds), The Sedimentary Basins of Western Australia 2: Proceedings of the Petroleum Exploration Society of Australia Symposium, Perth, 1998, 447–472. WOODSIDE ENERGY LTD., 2003a—WELL COMPLETION REPORT Herdsman-1 Interpretive Data (WA-299-P, Carnarvon Basin) WOODSIDE ENERGY LTD., 2003b— Coverack 2001/2 3D, Seismic Interpretation Report, WA-299-P, Exmouth Sub-Basin, Unpublished report, 20p. WOODSIDE ENERGY LTD., 2003c— Coverack 2001/2 3D, Seismic Interpretation Report, WA-300-P, Exmouth Sub-Basin, Unpublished report, 19p. 2011 Release of Australian Offshore Petroleum Exploration Areas Release Areas W11-16 and W11-17, Southern Carnarvon Basin Western Australia Release Area Geology Page 22 of 22