PETROLEUM GEOLOGICAL SUMMARY RELEASE AREAS W11-10 AND W11-11, BEAGLE SUB-BASIN, LAMBERT SHELF AND DAMPIER SUB-BASIN, NORTHERN CARNARVON BASIN WESTERN AUSTRALIA Bids Close – 13 October 2011 Immediately to the east of producing oil and gas fields within one of Australia’s premier offshore petroleum basins. Under-explored area with indications of active petroleum system at Bruce 1. Proximal to established offshore and onshore production infrastructure and major new development projects. A range of possible structural and stratigraphic plays. Water depths mostly less than 100 m. 2011 Release of Australian Offshore Petroleum Exploration Areas Release Areas W11-10 and W11-11,Beagle Sub-basin, Lambert Shelf and Dampier Sub-basin, northern Carnarvon Basin Western Australia Page 1 of 24 LOCATION The Release Areas W11-10 and W11-11 straddle the southern Beagle Subbasin, northeastern Dampier Sub-basin and Lambert Shelf of the Northern Carnarvon Basin. The northeastern corner of Release Area W11-11 extends into the Bedout Sub-basin of the Roebuck Basin. Although the Release Areas are in an under-explored part of the Northern Carnarvon Basin, they are located close to major hydrocarbon accumulations within the Dampier Sub-basin, established petroleum production infrastructure, as well as commercial centres and transport networks along the Western Australian coast (Figure 1). Release Area W11-10 is located immediately to the east of the Legendre, Amulet and Talisman oil accumulations in the Dampier Sub-basin, and is proximal to the gas pipelines connecting the Rankin Platform gas fields to the LNG processing plant at Karratha (Figure 1). Minor oil and gas occurrences have previously been recorded at Bruce 1 (Stirling Petroleum NL, 1979) within Release Area W1111, indicating that an active petroleum system is present in this part of the southern Beagle Sub-basin and the Lambert Shelf. The Release Areas are between 30 and 100 km off the Western Australian coast, near the major regional centres of Dampier, Karratha and Port Hedland (Figure 1), and in 20–130 m of water. Release Area W11-10 comprises 79 graticular blocks with a total area of approximately 6375 km2 and Release Area W11-11 comprises 77 graticular blocks with a total area of approximately 6215 km2 (Figure 2). 2011 Release of Australian Offshore Petroleum Exploration Areas Release Areas W11-10 and W11-11,Beagle Sub-basin, Lambert Shelf and Dampier Sub-basin, northern Carnarvon Basin Western Australia Page 2 of 24 RELEASE AREA GEOLOGY Local Tectonic Setting The Beagle Sub-basin is located in the northeastern part of the Northern Carnarvon Basin. It is bounded to the east by the Bedout and Rowley subbasins of the Roebuck Basin, and to the north and northwest by the Exmouth Plateau. The greater part of the sub-basin consists of a broad transtensional depocentre containing a series of en echelon troughs, fault blocks and anticlines with a general north–south trend (Figure 3). The east-northeasttrending Beagle and Cossigny troughs mark the southern margin of the main depocentre. The North Turtle and Bruce terraces, an east-northeast-trending zone of shallow basement, occur to the south of the Beagle and Cossigny troughs across the North Turtle Fault Zone (Figure 3). The Dampier Sub-basin, to the southwest of the Beagle Sub-basin, comprises subparallel northeast-trending fault-bounded highs and troughs that deepen toward the axial depocentre of the Lewis Trough (Figure 3). The De Grey Nose, a Paleozoic (?Permian) basement fault block cut by north-northwesttrending faults (Blevin et al, 1993), marks the boundary between the Dampier and Beagle sub-basins (Figure 3). The Legendre Trend, a faulted anticline, and the Rosemary Fault System separate the Lewis Trough from the shallowbasement area of the Enderby Terrace to the southeast (Figure 3). The Dampier Sub-basin is bounded to the northwest by the Rankin Platform and to the southwest by the Barrow Sub-basin. The Beagle and Dampier sub-basins are bounded to the southeast by the Lambert Shelf, an offshore extension of the Precambrian Pilbara Block (Figure 3). The shelf consists of a planated basement surface thinly mantled by dominantly Cretaceous–Cenozoic sediments (Figure 4). Extensional faulting has created fault blocks and small half-graben in places, especially in the outboard areas. The Beagle and Dampier sub-basins contain a Paleozoic to Cenozoic sedimentary succession with a maximum thickness of 10–12 km. The sediments are dominantly Triassic to Middle Jurassic in the Beagle Sub-basin (Figure 4), and Triassic to Lower Cretaceous in the Dampier Sub-basin. The deeper depocentres of the Dampier Sub-basin contain thick successions of Jurassic oil-prone sediments that are underlain by faulted gas-prone Triassic sediments. Most of the succession underlying the North Turtle, Bruce and Enderby terraces comprises faulted, landward-thinning Triassic sediments (Figure 4). These sediments are thinly covered by Lower to Middle Jurassic sediments that are unconformably overlain by Cretaceous sediments (Figure 4). Over the Lambert Shelf, Triassic to Jurassic sediments are preserved only in the outboard areas, and the Cretaceous–Cenozoic succession onlaps the Precambrian basement in the inshore areas (Figure 4). 2011 Release of Australian Offshore Petroleum Exploration Areas Release Areas W11-10 and W11-11,Beagle Sub-basin, Lambert Shelf and Dampier Sub-basin, northern Carnarvon Basin Western Australia Page 3 of 24 Structural Evolution and Depositional History of the Sub-basin During the Silurian to Permian, the Northern Carnarvon Basin experienced continental to shallow marine deposition, as intracratonic rift and sag basins developed in the initial stages of the Gondwana breakup (Hocking, 1990). By the late Permian, narrow northeast-trending depocentres were starting to form (Hill, 1994), accompanied by shallow marine deposition (Hocking, 1990). Permian and older sediments are missing, however, from most of the inshore parts of the Dampier and Beagle sub-basins and the Lambert Shelf. In these areas, which include Release Areas W11-10 and W11-11, the Triassic succession directly overlies the Precambrian basement. During the Early Triassic, a regional marine transgression deposited marine claystone and siltstone of the Locker Shale (Figure 5). On the Lambert Shelf and Enderby Terrace, the Locker Shale commonly overlies a transgressive basal sandstone and grades upwards into the thick Middle to Upper Triassic fluvio-deltaic sandstone, siltstone, claystone and coal of the Mungaroo Formation (Figure 5). The Middle Triassic Cossigny Member of the Mungaroo Formation in the Beagle Sub-basin (Figure 5) comprises paralic to marine siltstone, claystone, limestone and dolomite, and forms an important regional seismic marker within the sub-basin. Thickness of the Triassic succession ranges from less than 200 m over parts of the Enderby Terrace, to an estimated 5–6 km in the deeper parts of the Dampier Sub-basin (Stagg and Colwell, 1994). Rapid subsidence and transgression from the end of Triassic to Sinemurian resulted in deposition of the fluvio-deltaic to shallow marine Brigadier Formation and Murat Siltstone (Figure 5), which comprise thinly bedded sandstone, siltstone, claystone and marl. Reservoir-quality shallow marine sandstone overlying the Brigadier Formation is known as the North Rankin Formation (Figure 5; Seggie et al, 2007). In the Beagle Sub-basin and over the Lambert Shelf, a major Late Triassic transpressional event (Fitzroy Movement II; Smith et al, 1999) formed a series of topographic highs, leading to the isolation of the Beagle Sub-basin from the Dampier Sub-basin and exposure of the Lambert Shelf (Blevin et al, 1994; Stephenson et al, 1998). As a result, the Brigadier and North Rankin formations are thin or absent over structural highs in these areas. A major rifting phase during the Toarcian–Bathonian resulted in further structural compartmentalisation of the Northern Carnarvon Basin, forming the en echelon depocentres of the Beagle, Dampier, Barrow and Exmouth subbasins (Kopsen and McGann, 1985; Boote and Kirk, 1989; Hocking, 1990; Hill, 1994; Romine et al, 1997). Marine siltstone and claystone of the Athol Formation were extensively deposited over the JP1 rift-onset unconformity (Figure 5; previously known as the ‘Pliensbachian unconformity’). Fluviodeltaic and shallow marine sandstone, siltstone and shale of the Legendre Formation prograded northwestward over the Athol Formation (Figure 5). Although the Athol and Legendre formations attain a combined thickness of up to 5 km in the Lewis Trough of the Dampier Sub-basin (Miller and Smith, 2011 Release of Australian Offshore Petroleum Exploration Areas Release Areas W11-10 and W11-11,Beagle Sub-basin, Lambert Shelf and Dampier Sub-basin, northern Carnarvon Basin Western Australia Page 4 of 24 1996), they are thin or missing from much of Release Areas W11-10 and W11-11, except at Bugle 1 where they are over 400 m thick (Apache Energy Ltd, 1999b). From the end of the Bathonian to the Callovian, major syn-rift faulting occurred in the lead up to continental breakup and formation of the Argo Abyssal Plain. A marine transgression from the north and west (Stephenson et al, 1998) deposited shallow marine claystone and sandstone of the Calypso Formation over the Callovian (JC) unconformity (Figure 5) in the Dampier Sub-basin. The formation is largely absent from the Beagle Sub-basin, where transcurrent fault movements resulted in a major phase of structuring (Blevin et al, 1994). Continental breakup, marked by the basal Oxfordian (JO) unconformity (Figure 5), was followed by rapid thermal subsidence and the Oxfordian–Tithonian deposition of thick (up to 1–2 km), organic-rich, deep marine Dingo Claystone (Figure 5) in the major depocentres of the Dampier Sub-basin. Reservoir-quality turbidite, submarine fan, shoreline and fluvial sandstone of the Angel Formation (Figure 5) were deposited around the basin margins, fed by erosion of the structural highs (Hocking, 1990). In the Beagle Sub-basin and over the Lambert Shelf, the Upper Jurassic succession is thin or absent (Figure 4; Blevin et al, 1994). Renewed extension occurred during the Berriasian to early Valanginian in the lead up to the opening of the Cuvier and Gascoyne Abyssal Plains. Initial uplift and erosion (marked by the K unconformity; Figure 5) was followed by deposition of the marine Forestier Claystone (Figure 5), the prodelta equivalent of the Barrow Group sandstone in the Barrow and Exmouth subbasins. The claystone is generally thin (<100 m) but forms a regional seal across the deeper depocentres of the Dampier and Beagle sub-basins. In the inboard areas of the Beagle and Dampier sub-basins and over the Lambert Shelf, localised submarine fan and shelf sandstone deposition occurred (Figure 5). This Berriasian sandstone is an important reservoir in the Legendre oil field of the Dampier Basin (B.O.C. of Australia Ltd, 1969), immediately west of Release Area W11-10. Continental breakup during the Valanginian triggered widespread erosion in the Northern Carnarvon Basin (marked by the Valanginian KV unconformity; Figure 5), followed by a marine transgression that eventually submerged the Beagle and Dampier sub-basins and the Lambert Shelf. Localised deposition of the paralic to shallow marine Birdrong Sandstone and the glauconitic Mardie Greensand was followed by a basinwide deposition of the marine Muderong Shale during the Valanginian to Aptian (Figure 5). The Muderong Shale is a regional seal across much of the Northern Carnarvon Basin, but is generally less than 100 m thick within the Release Areas. The M. australis Sandstone, a well sorted, glauconitic sandstone with a typical thickness of 10–20 m, was deposited locally in submarine fan, shelf and paralic environments within this interval (Figure 5; Dyson, 1998; Crowley, 1999). This sandstone is a significant reservoir in a number of fields on the Enderby Terrace of the Dampier Sub-basin, e.g. Stag and Wandoo. 2011 Release of Australian Offshore Petroleum Exploration Areas Release Areas W11-10 and W11-11,Beagle Sub-basin, Lambert Shelf and Dampier Sub-basin, northern Carnarvon Basin Western Australia Page 5 of 24 A marine regression during the Aptian, marked by the KA unconformity (Figure 5), was followed by fine-grained shelf deposition as the Northern Carnarvon Basin became part of a subsiding passive continental margin. Initial deposition of the Aptian–Albian Windalia Radiolarite was followed by the widespread deposition of the Gearle Siltstone and its open-ocean equivalent, the Haycock Marl, during the Albian to Turonian (Figure 5). The Albian– Turonian succession is 100–200 m thick in parts of the Release Areas. A major transpressional event produced the regional KS/KC unconformity at the Santonian–Coniacian boundary (Figure 5), resulting in fault reactivation and inversion (Romine et al, 1997; Cathro and Karner, 2006). A basin-wide transition to carbonate-dominated deposition occurred during the Santonian (Hocking, 1990). The Toolonga Calcilutite was deposited during the Santonian to Campanian, followed by the calcareous claystones of the Withnell Formation and the Miria Marl during the Campanian to Maastrichtian (Figure 5). By the Paleocene, the northwest Australian margin had become a prograding carbonate shelf, punctuated by episodes of siliciclastic deposition during lowstands (Romine et al, 1997). These lowstand–transgressive cycles also formed backfilled incised-valley systems, which may potentially provide stratigraphic traps (Romine et al, 1997). The Cenozoic carbonate-dominated succession typically attains 100 m to 600 m thickness within the Release Areas. In the Miocene, a major compressional event associated with the collision of the Australia–India and Eurasia plates affected the entire northwestern Australian margin (Longley et al, 2002). This event caused tilting, inversion and renewed fault movement (Malcolm et al, 1991; Cathro and Karner, 2006). Episodic deformation appears to have continued to at least the Pliocene– Pleistocene (Cathro and Karner, 2006). 2011 Release of Australian Offshore Petroleum Exploration Areas Release Areas W11-10 and W11-11,Beagle Sub-basin, Lambert Shelf and Dampier Sub-basin, northern Carnarvon Basin Western Australia Page 6 of 24 EXPLORATION HISTORY Since the Legendre 1 oil discovery in 1968, the Dampier Sub-basin has experienced intensive petroleum exploration activity. Over 55 field discoveries had been made by the early 2000s with an historical drilling success rate of over 40% (Longley et al, 2002). Exploration from the 1970s to the 2000s resulted in a string of oil and gas discoveries concentrated along the Legendre Trend (Figure 1 and Figure 3), e.g. Rosemary 1 (1973), Talisman 1 (1984), Saffron 1 (1994), Reindeer 1 (1997), Caribou 1 (1998), Sage 1 (1999) and Corvus 1 (2000), and along the Madeleine Trend, e.g. Angel 1A (1972), Lambert 1 (1974), Wanaea (1989) and Cossack (1990). Over the Enderby Terrace (Figure 1 and Figure 3), gas was initially discovered at Hampton 1 (1974), but discoveries since the 1990s have revealed the area’s potential for both oil and gas, e.g. Wandoo 1 (1991), Stag 1 (1993) and Antler 1 (1996). Recent discoveries in the northeastern Dampier Basin, such as Amulet 1 (2006; Tap Oil Ltd, 2006) have extended the known oil province along the Legendre Trend to the boundary with the Beagle Sub-basin (Figure 1 and Figure 3). The Beagle Sub-basin is a frontier area within the Northern Carnarvon Basin, where only 25 wells have been drilled. Initial exploration drilling during 1971– 1992 tested a variety of play types, but no hydrocarbon shows were recorded except at Bruce 1 (1979; minor oil and gas) on the boundary between the Beagle Sub-basin and the Lambert Shelf. In 1993, Nebo 1 encountered oil in the Callovian Calypso Formation, confirming the presence of an active petroleum system in the central Beagle Sub-basin (Osborne, 1994). However, other wells subsequently drilled in the same area were dry. From the late 1990s onward, the discovery of Mutineer, Pitcairn and Bounty oil fields in the far northern Dampier Sub-basin has stimulated new exploration in the boundary zone between the Beagle and Dampier sub-basins (Figure 1 and Figure 3). Oil has been discovered at Fletcher 1 (Tap Oil Ltd, 2008), located on a continuation of the highly prospective Madeleine Trend (Figure 3) in the Dampier Sub-basin. Release Areas W11-10 and W11-11 (Figure 1) overlap the former exploration permit WA-1-P in the southeastern Dampier Sub-basin and the Beagle Subbasin. The earliest oil and gas discoveries in the Dampier Sub-basin, including Legendre, Angel and Rosemary, were made within this permit. Exploration during the 1970s to 1990s by successive permit holders has resulted in the drilling of eight wells within the Release Areas. Release Area W11-10 overlaps the former permit WA-352-P surrendered by Drillsearch Energy Ltd in early 2010, and includes portions of Release Area W09-19 previously offered during 2009. Release Area W11-11 overlaps the former permit WA-291-P relinquished by Rialto Energy Ltd in 2010. 2011 Release of Australian Offshore Petroleum Exploration Areas Release Areas W11-10 and W11-11,Beagle Sub-basin, Lambert Shelf and Dampier Sub-basin, northern Carnarvon Basin Western Australia Page 7 of 24 Well Control There are six wells within the southwestern part of Release Area W11-10 and two wells within the western part of Release Area W11-11 (Figure 1). Release Area W11-10 adjoins the intensively explored Legendre Trend and outer Enderby Terrace of the Dampier Sub-basin (Figure 3) and over 40 wells have been drilled within 20 km of the western boundary of this Release Area (Figure 1). Eight additional wells occur within 40 km of the northwestern and northern limits of Release Areas W11-10 and W11-11 (Figure 1). There are no nearby wells to the east and south of the Release Areas, in the adjacent Roebuck Basin, or over the Lambert Shelf. De Grey 1 (1971) De Grey 1 was drilled by B.O.C. of Australia Ltd (1972) in the southern Beagle Sub-basin, near the boundary with the Dampier Sub-basin. It is located 1 km north of the Release Area W11-10 (Figure 1) in water 95 m deep. It was designed to test stacked Triassic stratigraphic pinch-outs over a deeper, rotated fault block on the De Grey Nose (Figure 3). The well reached a total depth of 2088 mRT in Triassic limestone underlying a thick sandstonedominated Lower–Middle Jurassic succession. The Triassic–Jurassic boundary could not be determined due to lost circulation. The limestone at total depth is likely to be the Cossigny Member of the Mungaroo Formation, given its revised age of Early–Middle Triassic (Ingram, 1990). No significant hydrocarbons were encountered in the well. However, very minor gas readings were registered in the Jurassic, Cretaceous and Cenozoic sections, where potential reservoir-quality sandstones were encountered. Subsequent remapping showed that there is no closure near the well (Blevin et al, 1993). Hauy 1 (1972) Hauy 1 was drilled by B.O.C. of Australia Ltd at the boundary between the Enderby Terrace of the Dampier Sub-basin and the Lambert Shelf. It is located within Release Area W11-10 (Figure 1) in 66 m of water.The well tested for potential hydrocarbons trapped in Lower Triassic to Albian sediments on the southwestern flank of the De Grey Nose (Figure 3). Cenozoic sediments were not conclusively identified at the well due to poor recovery and lack of fauna in sediments that were recovered. The Mesozoic succession consisted of Albian–Aptian claystone and siltstone and ?Hauterivian–Barremian sandstone, directly overlying a Middle Triassic claystone. A thin Lower Triassic sandstone separated the Middle Triassic section from the altered dolerite basement of indeterminate age. The well reached a TD of 825 mRT. No hydrocarbon shows were recorded in the well and wireline logs indicated that all porous sandstones were 100% water saturated. Picard 1 (1972) Picard 1 was drilled by B.O.C. of Australia Ltd in the Beagle Sub-basin, 13 km north of Release Area W11-10 (Figure 1) in water 141 m deep. It was designed to test the crest of a large, north-trending Jurassic horst, draped by 2011 Release of Australian Offshore Petroleum Exploration Areas Release Areas W11-10 and W11-11,Beagle Sub-basin, Lambert Shelf and Dampier Sub-basin, northern Carnarvon Basin Western Australia Page 8 of 24 a Lower Cretaceous seal (Figure 4). The well reached a total depth of 4216 mRT within a thick section of Lower Jurassic sandstone with interbedded claystone, siltstone and minor coal. No significant hydrocarbons were encountered. Only minor fluorescence and very minor gas readings were recorded in the Cretaceous–Jurassic section, with wireline logs indicating that the Jurassic section is water saturated. Reactivation of northtrending bounding faults during the Late Cretaceous to Paleogene may have breached the structure (Blevin et al, 1993) and, therefore, compromised trap integrity. Analysis by Surdam and Warme (1984) and Robertson Research (1986) concluded that the Lower–Middle Jurassic Athol and Legendre formation claystones have good to very good oil source potential. Cossigny 1 (1972) Cossigny 1 was drilled by B.O.C. of Australia Ltd (1973) to test the faulted north-eastern flank of the De Grey Nose (Figure 3) in the southern Beagle Sub-basin. It is located 16 km northwest of Release Area W11-10 (Figure 1) in water 113 m deep. It encountered Upper Cretaceous marl, claystone and calcilutite and Toarcian–Middle Jurassic siliciclastics, overlying a thick section of Middle to Upper Triassic Mungaroo Formation. The Mungaroo Formation consisted of sandstone with claystone, siltstone and minor coal, and included limestone and dolomite of the Cossigny Member. The well reached a total depth of 3203 mRT in the Middle Triassic Mungaroo Formation. No significant hydrocarbons were encountered. Very minor gas readings were recorded in the Triassic–Jurassic section. The well is considered to be a valid test of structure at the Upper Cretaceous and Cenozoic levels, but it is unclear whether closure was present at the Jurassic or Triassic levels (Battrick, 1987). The presence of a thick Lower Cretaceous sandstone unit, as opposed to the predicted sealing shale, suggests the absence of an adequate seal. Poissonnier 1 (1974) Poissonnier 1 was drilled by B.O.C. of Australia Ltd. within Release Area W11-11 (Figure 1) in 83 m of water. It was designed to test the Lower Triassic sandstone within a down-faulted compartment at the boundary between the Bruce Terrace of the Beagle Sub-basin and the Lambert Shelf (Figure 3). The well intersected comparatively thin Lower Cretaceous and Upper Jurassic successions dominated by glauconitic sandstone and claystone, and ?Toarcian and Triassic successions of interbedded sandstone, claystone and siltstone with minor coal. It reached a total depth of 1962 mRT in a basement of intermediate to basic igneous rock. No significant hydrocarbons were encountered. However, minor gas readings were recorded throughout the Lower Jurassic and Triassic section with various sidewall cores and Triassic sandstone ditch cuttings exhibiting minor fluorescence. A sandstone sidewall core at 1170 mRT had a brown stain associated with fluorescence. Subsequent remapping indicated that there is little closure at the Callovian and base-Cretaceous unconformity levels, and that the Triassic sandstone target was not intersected at the optimal crestal location (Battrick, 1987). 2011 Release of Australian Offshore Petroleum Exploration Areas Release Areas W11-10 and W11-11,Beagle Sub-basin, Lambert Shelf and Dampier Sub-basin, northern Carnarvon Basin Western Australia Page 9 of 24 Jarman 1 (1978) Jarman 1 was drilled by Woodside Petroleum Development Pty Ltd to test a large northeast-trending, unfaulted anticline within the Cossigny Trough, to the north of the main depocentre of the Beagle Sub-basin (Figure 3). The well is located 7 km west of Release Area W11-10 (Figure 1) in 134 m of water. The encountered stratigraphy was dominated by Tithonian to Upper Cretaceous claystone and marl overlying Middle Jurassic to Kimmeridgian fluvio-deltaic to marine sandstone, siltstone and claystone. The well reached a total depth of 2906 mRT in Middle Jurassic sandstone and siltstone. No significant hydrocarbons were encountered. However, four sidewall cores within the Jurassic section exhibited weak to moderate fluorescence. Subsequent remapping indicates that the well was positioned off the crest of the anticline (Battrick, 1987). Furthermore, continued fault movement into the Cenozoic suggests that the structure would only be able to trap hydrocarbons migrating vertically since about the Middle Miocene. Bruce 1 (1979) Bruce 1 was drilled by Stirling Petroleum N.L. in the inboard part of the Bruce Terrace in the southern Beagle Sub-basin (Figure 3). It is located within Release Area W11-11 (Figure 1) in water 78 m deep. It was designed to test the sediments within a wrench-controlled anticline down-dip of a northeasttrending fault (Figure 4). The well reached a total depth of 2168 mKB within the Lower Triassic Locker Shale after intersecting a section of Mungaroo Formation claystone, siltstone and sandstone below the Cossigny Member. Strong, bright fluorescence was noted in sidewall cores and cuttings from the Middle Triassic sediments. A sidewall core at about 1700 mKB had visible brown oil staining, however, geochemical studies indicated the hydrocarbons to be immature. Subsequent remapping indicates that, although the well was drilled inside structural closure at the Middle Triassic level, it was outside closure at the level of the Lower Cretaceous seal (Blevin et al, 1993). Leakage via the basin-bounding fault immediately to the southeast is also probable (Battrick, 1987). In the adjacent Roebuck Basin, the Phoenix gas discovery is hosted at the same stratigraphic level as the hydrocarbon occurrences at Bruce 1. Lawley 1 (1981) Lawley 1 was drilled by Hudbay Oil (Australia) Ltd to test a horst block in an inboard area of the Enderby Terrace, near the flank of the Lambert Shelf (Figure 3). It is located in Release Area W11-10 (Figure 1) in 61 m of water. The encountered stratigraphy deviated significantly from that predicted, in the absence of Upper Cretaceous and Jurassic successions, replaced by thick Lower Cretaceous and Lower–Middle Triassic interbedded sandstone, claystone, siltstone and minor limestone. The well reached a TD of 1120 mRT in an altered granite gneiss basement, without encountering any significant hydrocarbon indications. Traces of patchy, dull yellow fluorescence were noted on some quartz grains below 690 mRT. Interpretation of wireline logs indicates that no free or residual hydrocarbons were present in the well. The well contains a large proportion of unconsolidated, porous sands that are water wet (Hudbay Oil (Australia) Ltd, 1982). 2011 Release of Australian Offshore Petroleum Exploration Areas Release Areas W11-10 and W11-11,Beagle Sub-basin, Lambert Shelf and Dampier Sub-basin, northern Carnarvon Basin Western Australia Page 10 of 24 Talisman 1 ST2 (1984) Talisman 1 ST2 was drilled by Marathon Petroleum Australia Ltd in the northeastern Dampier Sub-basin, approximately 6 km northwest of Release Area W11-10 (Figure 1). It was designed to test the hydrocarbon potential of the Upper Jurassic (Tithonian) sandstone draping over a fault block. Additional objectives were Kimmeridgian–Oxfordian and Middle–Lower Jurassic sandstones within the underlying fault block. The well, drilled in 78 m of water, reached a TD of 2925 mKB in Middle Jurassic sediments. The stratigraphy was essentially as predicted. Oil shows and relatively high gas readings were recorded from 1865 mKB, in the Lower Cretaceous, to TD. The gross interval 1917–1971 mKB (Lower Cretaceous to Tithonian) had significant hydrocarbon shows during drilling and wireline logs indicated that this interval has good oil potential. This interval was tested and oil was recovered in four RFTs; the maximum recovery was 9.5 L of 41.4º API oil at 1962 mKB. Drill Stem Testing of three zones in this interval flowed oil, with the maximum flow of 4778 bopd (759.7 m3/d) of 41.6º API oil recorded over the interval 1961–1968 mKB. Wireline log interpretation and evaluation indicates that all potential reservoir sections from 1971m KB to TD have very high water saturations and are considered to be non-productive. Talisman 1 ST2 was temporarily suspended as an oil discovery. The Talisman oilfield was subsequently in production from 1989 to 1992 and represented the first oil production in the Dampier Sub-basin. Cygnus 1 (1989) Cygnus 1 was drilled by Arco Australia Limited on the Enderby Terrace in the northeasetrn Dampier Sub-basin (Figure 3). It is located within Release Area W11-10 (Figure 1), 3 km south-southeast of Bugle 1, 13 km west-northwest of Buck 1, in 73 m of water. It was designed as a test of the Lower Jurassic North Rankin and the Upper Triassic Mungaroo formations on a northeasttrending faulted anticline. The well encountered thick interbedded shale, sandstone and siltstone of the Middle Jurassic Legendre Formation and the Lower Jurassic Athol Formation (referred to as the ‘Lower Dingo Claystone’ by Arco Australia Ltd, 1989) overlying the North Rankin and Brigadier formations. The underlying Mungaroo Formation consisted of an Upper Triassic sand-dominated braided stream succession, and a Middle Triassic shaly fluvio-deltaic succession. The well reached a total depth of 2470 mDF within Middle Triassic Mungaroo Formation without encountering any significant hydrocarbons. The lack of hydrocarbons may be due to: the sandy nature of the Athol Formation providing ineffective seal to the North Rankin Formation; immature and low-quality source rocks, or lack of a viable migration pathway from deep kitchen areas to the north (Arco Australia Ltd, 1989). Kanji 1 (1994) Kanji 1 was drilled by Ampolex Ltd on the Enderby Terrace in the Dampier Sub-basin (Figure 3). It is located within Release Area W11-10 (Figure 1) in 57 m of water. The well was drilled to appraise the hydrocarbon potential of an interpreted four-way dip closure of Lower Cretaceous sediments unconformably draped over a Triassic tilted fault block. The primary objective 2011 Release of Australian Offshore Petroleum Exploration Areas Release Areas W11-10 and W11-11,Beagle Sub-basin, Lambert Shelf and Dampier Sub-basin, northern Carnarvon Basin Western Australia Page 11 of 24 of the well was the M. australis Sandstone. Triassic Mungaroo Formation sandstone within an underlying horst block constituted a secondary objective. The well reached a TD of 1288 mRT in Middle Triassic sediments. All unit tops, except the main unconformity, were shallow to prognosis. The Lower Cretaceous section was sandier than predicted and the Locker Shale was homogeneous rather than intercalated as predicted. Sandstones within the Lower Cretaceous section are of excellent reservoir quality and have a logderived average porosity of 25%. The Triassic section also displays excellent reservoir qualities. No hydrocarbon shows were encountered during drilling. The absence of hydrocarbons is attributed to an invalid structure and seal at the M. australis Sandstone level or a lack of effective migration pathways (Ampolex Ltd, 1995). Buck 1 (1997) Buck 1 was drilled by Apache Northwest Pty Ltd on the Enderby Terrace in the eastern Dampier Sub-basin (Figure 3). It is located within Release Area W11-10 (Figure 1) in 71 m of water. It tested an interpreted faulted three-way anticline in Lower Cretaceous (Berriasian) sandstones, overlying a deepseated Permian to Lower Jurassic tilted fault block. Although the encountered stratigraphy was close to prediction, the reservoir-quality Berriasian sandstone in the well was thin. Further reservoir-quality, water-wet sandstones were encountered within the Middle Jurassic Legendre, Lower Jurassic North Rankin, and the Triassic Mungaroo formations. The well reached a TD of 1050 mRT in limestone and siltstone of the Cossigny Member within the Mungaroo Formation. No hydrocarbon shows were recorded and the well was plugged and abandoned as a dry well. Reinterpreted mapping places the Buck 1 well location on the edge of the mapped structure and it may be outside closure due to lateral velocity variations (Apache Energy Ltd, 1999a). Bugle 1 (1997) Bugle 1 was drilled by Apache Northwest Pty Ltd to test the hydrocarbon potential of the North Rankin Formation on a northeast-trending, tilted fault block on the Enderby Terrace in the northeastern Dampier Sub-basin (Figure 3). Secondary targets were sandstones in the Middle Jurassic Legendre Formation and Lower Cretaceous sandstones. The well is located within Release Area W11-10 (Figure 1), 3 km north-northwest of Buck 1, in 79 m of water. It reached a TD of 1833 mRT within the Triassic Mungaroo Formation. The section penetrated was essentially as predicted, although Lower Jurassic to Triassic formation tops came in slightly high. Potential reservoir quality sandstones were encountered at all three objective levels but no hydrocarbon shows were recorded. The lack of hydrocarbons is interpreted to be due to a lack of cross-fault seal at the North Rankin Formation and base Cretaceous levels, and the possible lack of structure at the top Lower Cretaceous (Apache Energy Ltd, 1999b). There is also the possibility that hydrocarbons failed to migrate into the structure. 2011 Release of Australian Offshore Petroleum Exploration Areas Release Areas W11-10 and W11-11,Beagle Sub-basin, Lambert Shelf and Dampier Sub-basin, northern Carnarvon Basin Western Australia Page 12 of 24 Bloodwood 1 (2002) Bloodwood 1 was drilled by Mobil (Legendre) Pty Ltd on the Enderby Terrace in the Dampier Sub-basin (Figure 3). It is located 16 km west of Release Area W11-10 (Figure 1) in 62 m of water. It tested the Barremian M. australis Sandstone within the crest of a northeast-trending, tilted fault block. Cretaceous formation tops were considerably deeper than predicted and the M. australis Sandstone attained a thickness of 144.7 m. Minor oil shows were recorded in the upper 20 m of the M. australis Sandstone, with a sidewall core at 581 mRT recording yellow fluorescence, a slow to moderate milky white streaming cut and thin film residue. Although gas readings for the upper M. australis Sandstone are unavailable, two minor gas peaks were recorded in the lower M. australis Sandstone and the Muderong Shale. The lack of significant hydrocarbon accumulation is probably due to leakage across the bounding fault (Apache Northwest Pty Ltd, 2003), but the shows suggest that Bloodwood 1 lies on a migration pathway. The well terminated in the Middle Jurassic Athol Formation at a TD of 834 mRT. 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_BeaglesbLambertslfDampiersb_AR11.xls 2011 Release of Australian Offshore Petroleum Exploration Areas Release Areas W11-10 and W11-11,Beagle Sub-basin, Lambert Shelf and Dampier Sub-basin, northern Carnarvon Basin Western Australia Page 13 of 24 Data Coverage The southwestern part of Release Area W11-10 lies at the edge of dense 2D and 3D seismic data coverage over the Dampier Sub-basin. Seismic data are generally of good quality, especially for the more recent surveys. Advances in 3D seismic data acquisition and processing technologies since the 1990s have significantly improved exploration success in the region (Longley et al, 2002). Some of the more significant data sets include the SPA East Dampier 9SL/92-3 (S92DDS) survey (1992) by Australian Seismic Brokers, Vermeer A92V survey (1992) by Ampol Exploration Ltd, SPA 2SL/94-95 (GPDB95) Dampier Well Tie survey (1994) by GECO-Prakla, Halina (1995) and Maria (1996) surveys by Minora Resources, and the Panaeus 99C 3D survey (1999) and Panaeus East 3D survey (2001) by PGS Exploration Pty Ltd. Seismic data coverage is less dense in the eastern part of Release Area W11-10 and the northern part of W11-11 located within the Beagle Sub-basin. Some of the more significant datasets include the B86A survey (1986) by BHP Petroleum Ltd, H93B survey (1993) by Hadson Energy Ltd, and Mavis survey (2000) by Magellan Petroleum Australia Ltd. The southeastern part of Release Area W11-10 and the southern half of Release Area W11-11 over the Lambert Shelf have a very sparse coverage of 2D seismic data, including the De Grey Nose survey (1973) by B.O.C. of Australia Ltd, Lambert Shelf HL80 (1980) and HL81 (1981) surveys by Hudbay Oil Ltd, Cossigny D95 survey (1995) by Discovery, a tie line for the Leveque Shelf LS93 survey (1998) by GHD-Gardline Surveys JV, and the Mavis survey (2000) by Magellan Petroleum Australia Ltd. Large areas of sparse or no data occur within the southeastern part of Release Area W11-11. Regional 2D seismic data acquired by Geoscience Australia include the Barrow/Dampier survey 110 (1990), deep seismic survey 101 (1991–1992) and high-resolution survey 136 (1994). Several lines from these surveys traverse the Release Areas, including the data-poor southern parts of both areas. In 2007, the long-offset New Dawn 2D multi-client seismic survey was completed over the Northwest Shelf together with the acquisition of gravity and magnetic data (Petroleum Geo-Services ASA, 2010). Several of the survey lines traverse the Release Areas. Satellite-based synthetic aperture radar (SAR) and airborne laser fluorosensor (ALF) data are also available within, and in the vicinity of, the Release Areas. O’Brien et al (2003) present a summary and an assessment of these data sets. Open-file seismic data, as well as seismic interpretation, well and destructive analysis reports, are available from Geoscience Australia. 2011 Release of Australian Offshore Petroleum Exploration Areas Release Areas W11-10 and W11-11,Beagle Sub-basin, Lambert Shelf and Dampier Sub-basin, northern Carnarvon Basin Western Australia Page 14 of 24 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 W11-10 and W11-11,Beagle Sub-basin, Lambert Shelf and Dampier Sub-basin, northern Carnarvon Basin Western Australia Page 15 of 24 PETROLEUM SYSTEMS AND HYDROCARBON POTENTIAL Table 1: Petroleum Systems Elements Summary Sources Reservoirs Dingo Claystone (Upper Jurassic, marine, oil prone); Legendre Formation (Lower–Middle Jurassic, fluviodeltaic to marginal marine, gas and oil prone); Athol Formation (Lower–Middle Jurassic, marine to marginal marine, gas and oil prone); Murat Siltstone (Lower Jurassic, marine, gas and oil prone); Brigadier Formation (Upper Triassic, fluvio-deltaic to marine, gas prone); Mungaroo Formation (Middle–Upper Triassic, fluvial to marginal marine, gas prone). M. australis Sand and other sandstone intervals within Muderong Shale (Lower Cretaceous, marine to marginal marine); Berriasian sandstones within Forestier Claystone (Lower Cretaceous Barrow Group equivalents, marine to fluvio-deltaic); Angel Formation (Upper Jurassic, marine to fluvial); Calypso Formation (Middle–Upper Jurassic, marine to marginal marine); Legendre Formation (Lower–Middle Jurassic, fluviodeltaic to marginal marine); Athol Formation (Lower–Middle Jurassic, marine to marginal marine); North Rankin Formation (Lower Jurassic, fluvio-deltaic to marine); Brigadier Formation (Upper Triassic, fluvio-deltaic to marine); Mungaroo Formation (Middle–Upper Triassic, fluvial to 2011 Release of Australian Offshore Petroleum Exploration Areas Release Areas W11-10 and W11-11,Beagle Sub-basin, Lambert Shelf and Dampier Sub-basin, northern Carnarvon Basin Western Australia Page 16 of 24 marginal marine); Seals Basal transgressive sand underlying Locker Shale (Lower Triassic, marginal marine). Gearle Siltstone (Lower Cretaceous, marine); Muderong Shale (Lower Cretaceous, marine to marginal marine, regional seal); Forestier Claystone (Lower Cretaceous, marine to fluvio-deltaic); Dingo Claystone (Upper Jurassic, marine); Calypso Formation (Middle–Upper Jurassic, marine to marginal marine); Athol Formation (Lower–Middle Jurassic, marine to marginal marine); Murat Siltstone (Lower Jurassic, marine); Cossigny Member, Mungaroo Formation (Middle Triassic, marine, regional seal) Locker Shale (Lower Triassic, marine). Cenozoic incised valley and channel stratigraphic traps; Lower Cretaceous unconformity and basement onlap stratigraphic traps; Upper Jurassic–Lower Cretaceous submarine fan, shoreline and estuarine sandstone stratigraphic traps; Middle Jurassic to Lower Cretaceous horst, tilted fault block and low-side rollover traps; Triassic to Lower Cretaceous anticlines and faulted anticline traps; Middle Jurassic to Lower Cretaceous drape and anticline traps over Triassic to Jurassic fault blocks; Middle–Upper Triassic Mungaroo Formation pinchout traps; Triassic transgressive sandstone stratigraphic traps at Play Types 2011 Release of Australian Offshore Petroleum Exploration Areas Release Areas W11-10 and W11-11,Beagle Sub-basin, Lambert Shelf and Dampier Sub-basin, northern Carnarvon Basin Western Australia Page 17 of 24 the base of the Locker Shale. Petroleum Systems In the Dampier Sub-basin, two proven petroleum systems are recognised. A gas-prone system is sourced from Triassic to Middle Jurassic fluvio-deltaic sediments of the Mungaroo and Brigadier formations, Murat Siltstone, Athol and Legendre formations (Figure 5 and Figure 6). An oil-prone system, responsible for the accumulations along the Legendre and Madeleine trends and the Enderby Terrace (Figure 3), is primarily sourced from the Upper Jurassic Dingo Claystone (Figure 5 and Figure 6; Boreham et al, 2001; Edwards and Zumberge, 2005; Edwards et al, 2007). The Oxfordian (W. spectabilis biozone) interval of the claystone in the eastern Dampier Subbasin (Thomas et al, 2004), deposited during a maximum flooding stage in a restricted marine embayment, is particularly organic-rich (van Aarssen et al, 1996; Norvick, 2002). Mixed sourcing is apparent in some accumulations, e.g. the Middle and Upper Jurassic sources for the Angel gas field (Longley et al, 2002; Thomas et al, 2004). The oil discovery at Nebo 1 (1993) demonstrated the presence of an active petroleum system within the Beagle Sub-basin. Potential source rock intervals are expected at similar stratigraphic intervals to the Dampier Sub-basin, but well data indicate that the Dingo Claystone is often thin or absent, and source quality of the Mungaroo Formation and the underlying Locker Shale (Figure 5) is poor (Surdam and Warme, 1984). Moreover, the oil at Nebo 1 was derived from a probable Lower–Middle Jurassic lacustrine source (Stephenson et al.,1998) and is distinct from oils in the Dampier Sub-basin and other basins of the North West Shelf (Edwards and Zumberge, 2005). Potential reservoirs over the Legendre Trend and the Enderby Terrace of the Dampier Sub-basin include Upper Triassic to Middle Jurassic fluvial to shallow marine sandstones, Upper Jurassic marine to fluvio-deltaic sandstones, and Lower Cretaceous marine sandstones, including the Berriasian Sandstone within the Forestier Claystone and the Barremian M. australis Sandstone (Figure 5 and Figure 6). The M. australis Sandstone is particularly significant as a reservoir over the Enderby Terrace, where it is often glauconitic. In the Beagle Sub-basin, the Mungaroo and Legendre formations (Figure 5) are known to host reservoir-quality sandstones. The Upper Jurassic succession is commonly missing in the Beagle Sub-basin, but the Callovian Calypso Formation (Figure 5) is a significant potential reservoir in places. The Triassic transgressive sandstone at the base of the Locker Shale (Figure 5 and Figure 6) may provide a potential reservoir in the inboard parts of the Beagle Sub-basin, Enderby Terrace and the Lambert Shelf. The Lower Cretaceous Muderong Shale (Figure 5 and Figure 6) is an effective regional seal across the Dampier Sub-basin. It has encouraged lateral drainage of hydrocarbons from the deeper parts of the sub-basin into 2011 Release of Australian Offshore Petroleum Exploration Areas Release Areas W11-10 and W11-11,Beagle Sub-basin, Lambert Shelf and Dampier Sub-basin, northern Carnarvon Basin Western Australia Page 18 of 24 accumulations in basin margin areas, such as the Enderby Terrace. Finegrained facies within the Jurassic to Lower Cretaceous successions are significant additional seals in the deeper parts of the sub-basin. The Middle Triassic Cossigny Member of the Mungaroo Formation (Figure 5 and Figure 6) is a regional seal in the Beagle Sub-basin and the adjoining Bedout Sub-basin (Roebuck Basin). In the inboard areas of the Beagle Sub-basin, Enderby Terrace and Lambert Shelf, the Jurassic to Lower Cretaceous formations are often sandy or absent due to erosion and the Lower–Upper Cretaceous formations may provide local seals (Figure 6). The Lower–Middle Triassic Locker Shale may also act as a seal to the basal Triassic sandstone (Figure 5 and Figure 6) and older reservoir targets in the inboard areas. Play Types The main structural play types in the southeastern Dampier Sub-basin, southern Beagle Sub-basin and Lambert Shelf are Middle Jurassic to Lower Cretaceous horsts, tilted fault blocks and low-side rollovers, Triassic to Lower Cretaceous anticlines and faulted anticlines, and drapes and anticlines over Triassic to Jurassic fault blocks (Figure 6). Potential stratigraphic plays are found in Upper Jurassic to Lower Cretaceous submarine fan, shoreline and estuarine sandstones, pinchouts within the Triassic Mungaroo Formation, Lower–Middle Triassic transgressive sandstone at the base of Locker Shale, and unconformity traps (below the Lower Cretaceous) as well as basement onlaps found generally in the inboard areas (Figure 5 and Figure 6). Stratigraphic plays are particularly significant in inboard areas such as the Lambert Shelf where structuring has been comparatively weak. Critical Risks The marginal location of Release Areas W11-10 and W11-11 relative to the main basin depocentres imply that the source rocks may be thin, immature and/or of low quality, and some of the areas may be outside the range of lateral hydrocarbon migration from the main source kitchens. Poor seal development due to erosion or high sand content, leakage via basin-bounding faults, lack of closure, and biodegradation pose further potential risks to hydrocarbon accumulation in the area. Late-stage fault reactivation may have resulted in seal breaching and delayed charge from vertical migration. The dominance of lateral fault motion within the Beagle Sub-basin has resulted in a history of trap development, charge and preservation considerably more complex than that in a typical extension-dominated rift system (Blevin et al, 1994). 2011 Release of Australian Offshore Petroleum Exploration Areas Release Areas W11-10 and W11-11,Beagle Sub-basin, Lambert Shelf and Dampier Sub-basin, northern Carnarvon Basin Western Australia Page 19 of 24 FIGURES Figure 1: Location map of Release Areas W11-10 and W11-11 in the Beagle and Dampier sub-basins and the Lambert Shelf, Northern Carnarvon Basin. Figure 2: Graticular block map and graticular block listings for Release Areas W11-10 and W11-11 in the Beagle and Dampier subbasins and the Lambert Shelf, Northern Carnarvon Basin. Figure 3: Structural elements of the southern Beagle and Dampier subbasins and the Lambert Shelf, Northern Carnarvon Basin. Figure 4: Cross-section across the Beagle Sub-basin to the northern Lambert Shelf based on AGSO seismic line 110/02. See Figure 3 for location of cross-section. Figure 5: Generalised stratigraphy of the Dampier and Beagle subbasins, tied to the geological timescale after Gradstein et al (2004) and Ogg et al (2008). Note that the Phoenix 1 gas discovery is located in the adjacent Bedout Sub-basin, Roebuck Basin. Figure 6: Possible play types in Release Areas W11-10 and W11-11, based on AGSO seismic line 110/02. 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THOMAS, G.P., LENNANE, M.R., GLASS, F., WALKER, T., PARTINGTON, M., LEISCHNER, K.R. AND DAVIS, R.C., 2004—Breathing new life into the eastern Dampier Sub-basin: an integrated review based on geophysical, stratigraphic and basin modelling evaluation. The APPEA Journal, 34 (1), 123-147. VAN AARSSEN, R., ALEXANDER, R. AND KAGI, R.I., 1996—The origin of Barrow Sub-basin crude oils: a geochemical correlation using land-plant biomarkers. The APPEA Journal, 36 (1), 131–144. Front page image courtesy of Petroleum Geo-Services. 2011 Release of Australian Offshore Petroleum Exploration Areas Release Areas W11-10 and W11-11,Beagle Sub-basin, Lambert Shelf and Dampier Sub-basin, northern Carnarvon Basin Western Australia Page 24 of 24