2018 Release Areas

Acreage Release 2018: Northern Carnarvon Basin

The Northern Carnarvon Basin is located on Australia’s northwest margin and covers an area of approximately 535 000 km2, predominantly offshore, in water depths of up to 4500 m (Figure 1). It contains a Paleozoic, Mesozoic and Cenozoic sedimentary succession up to 15 000 m thick, which is dominated by deltaic to marine siliciclastics and shelfal carbonates of Mesozoic to Cenozoic age (Figure 2). Two Mesozoic petroleum supersystems (Westralian 1 and Westralian 2) have been identified and numerous commercial oil and gas discoveries have been made within the basin. The basin is Australia’s premier hydrocarbon producing province and contains an established network of oil, condensate and gas production infrastructure (Figure 3). As of February 2018, the total oil and natural gas liquids and natural gas and ethane reserves (proved and probable) for the Carnarvon Basin are 820 MMbbls (142.61 GL) and 53 369 PJ, respectively (EnergyQuest, 2018).

The 2018 Acreage Release offers a variety of Release Areas across the Northern Carnarvon Basin (Figure 1), presenting opportunities ranging from large areas in underexplored regions, to single blocks for cash bidding in mature exploration areas with known accumulations.

Release Areas W18-4 and W18-5, Beagle Sub-basin, offshore Western Australia

Highlights

Round two bids close 21 March 2019

  • Underexplored area with active petroleum system confirmed by Nebo 1 oil discovery.

  • Immediately northeast of producing oil and gas fields within one of Australia’s premier offshore petroleum basins.

  • Recent major discoveries in nearby Roebuck Basin at Phoenix South 1, Phoenix South 2, Roc 1 and Roc 2.

  • Proximal to established offshore and onshore production infrastructure and major new development projects.

  • A range of possible structural and stratigraphic plays.

  • Shallow to deep water, 70–450 m

Release Areas W18-4 and W18-5 lie 120–170 km north-northeast of Dampier, Western Australia, in the Beagle Sub-basin of the Northern Carnarvon Basin (Figure 4). Both are large areas covering much of the central and southern regions of the Beagle Sub-basin, with the southeastern corner of Release Area W18-4 also straddling the edge of the Lambert Shelf and the Bedout Sub-basin of the Roebuck Basin (Figure 4). Water depth across the areas deepens gradually from the southeast to the northwest over a range of 70–450 m.

The Beagle Sub-basin is a complexly structured depocentre dominated by a series of north-trending Triassic–Jurassic horsts/graben extending northwards of a northeast-trending depocentre. These graben contain over 10 km of sediment and, along with the horsts, have developed as a result of wrench movements within a pre-existing rift fabric. The sediments are upper Paleozoic to Lower Cretaceous pre- and syn-rift siliciclastics overlain by an Upper Cretaceous to Holocene post-rift carbonate succession.

The discovery of a small oil accumulation at Nebo 1 (Osborne, 1994) and production from Fletcher/Finucane (Santos, 2015b) proves the presence of active petroleum systems within the Beagle Sub-basin. Release Area W18-5 is also located close to numerous hydrocarbon accumulations within the Dampier Sub-basin to the southwest, of which the oils at Exeter/Mutineer (Santos, 2015a) display some geochemical similarities to that from Nebo 1 (Preston and Edwards, 2014).There is also renewed interest in the region following the recent successes at Roc and Phoenix South along trend to the northeast in the neighbouring Roebuck Basin. These discoveries have highlighted the potential for gas and liquids generation from the Triassic and Lower Jurassic succession that is well developed across the Beagle Sub-basin and Roebuck Basin, and contains numerous potential source rock units.

Although well coverage is not dense within the Beagle Sub-basin, 9 exploration wells (drilled between 1971 and 2007) are located within in each Release Area (Table 1). These wells provide useful stratigraphic information and have confirmed the presence of effective reservoir, seal, and source units (Figure 5). Many of the wells drilled in the 1970s that were unsuccessful were based on seismic data of variable quality and are now identified as being off structure (Table 1). The Release Areas now have improved seismic data coverage, with several 3D seismic surveys, including Polly 3D (Figure 6), and more are planned for imminent acquisition, including the Polarcus Capreolus Phase II MC3D which will cover much of these Release Areas.

Although the Release Areas are in an underexplored part of the Northern Carnarvon Basin, they are located close to established petroleum production infrastructure that could facilitate the development of commercial discoveries, as well as commercial centres and transport networks along the Western Australian coast (Figure 3 and Figure 4).

Release Area W18-6, Dampier Sub-basin, offshore Western Australia

Highlights

Prequalification for W18-10 closes on 4 October 2018, with the cash bidding auction to be held on 7 February 2019

  • Within one of Australia’s premier offshore producing basins

  • Release Area includes the Sage oil accumulation

  • Shallow water depths, 60–70 m

  • Within one of Australia’s premier offshore producing basins

  • Close to numerous oil and gas accumulations including Saffron, Reindeer, Gungurru and Wandoo

  • Oil-prone Upper Jurassic and gas-prone Triassic to Middle Jurassic source rocks

  • Stacked structural and stratigraphic targets at Triassic, Jurassic and Lower Cretaceous levels

Release Area W18-6 comprises two graticular blocks in the central Dampier Sub-basin, 85 km northwest of Dampier and 120 km northeast of Barrow Island (Figure 7). The Release Area contains the Sage oil accumulation, and is in the vicinity of numerous other oil and gas accumulations including Saffron, Reindeer, Wandoo and Gungurru. This Release Area is considered mature in exploration status and is available for cash bidding.

The Dampier Sub-basin is one of a series of large rift depocentres of the Northern Carnarvon Basin, and contains a Paleozoic to Cenozoic sedimentary succession 10–20 km thick (Figure 8). The Dampier Sub-basin hosts proven petroleum systems, with Upper Triassic, Lower–Middle and Upper Jurassic source rocks that have expelled hydrocarbons which are now reservoired in both structural and stratigraphic traps. Gas is predominantly sourced from Triassic to Middle Jurassic fluvial-deltaic sediments of the Mungaroo and Brigadier formations, the Murat Siltstone, and the Athol and Legendre formations. Oil is predominantly sourced from the Upper Jurassic Dingo Claystone. Structural trap styles in the sub-basin include tilted fault blocks, fault dependent rollovers, anticlines, drape features and horsts.

The existing data coverage for the Dampier Sub-basin is shown in Figure 9. Two exploration wells are located within the Release Area, the oil discovery Sage 1 (1999), and the dry well Rosemary North 1 (1982) (Table 2). The Release Area is also entirely covered by 3D seismic data, including the Panaeus MC3D and Rosemary 3D seismic surveys. The Release Area is close to established infrastructure that could facilitate the development of discoveries (Figure 3 and Figure 7).

Release Area W18-7, Rankin Platform, offshore Western Australia

Highlights

 Prequalification for W18-10 closes on 4 October 2018, with the cash bidding auction to be held on 7 February 2019

  • Within one of Australia’s premier offshore producing provinces

  • Gas province with numerous multi-Tcf accumulations, including the Wheatstone, Pluto, Iago, Brunello and Julimar gas fields

  • Proven Triassic horst plays and Cretaceous structural and stratigraphic plays

  • Regional and intraformational claystone seals

  • Proximal to infrastructure including the Pluto LNG Export Pipeline to the Karratha gas plant, and the Wheatstone Pipeline to Onslow

  • Shallow water depths, 60–130 m

Release Area W18-7 comprises a single graticular block in the vicinity of the Iago, Wheatstone, Pluto and Brunello/Brokenwood/Brulimar gas accumulations, 160 km northwest of Dampier and 65 km north of Barrow Island (Figure 10). This Release Area is considered mature in exploration status and is available for cash bidding.

The Rankin Platform is a northeast-trending structural high forming the eastern flank of the Exmouth Plateau, which consists of a series of tilted fault blocks, formed in response to the final stages of the break-up of eastern Gondwana (Vincent and Tilbury, 1988). It separates the plateau from the Dampier and Barrow sub-basins to the east, and is characterised by major extensional fault systems. The Rankin Trend has been intensively explored and includes the Gorgon, Julimar–Brunello, Iago, Goodwyn, Perseus and North Rankin gas fields (Figure 10). All of these accumulations have been sourced from fluvial-deltaic sediments within the Triassic Mungaroo Formation and mostly marine sediments of Lower–Middle Jurassic formations within the adjacent Barrow and Dampier sub-basins. The Lower Cretaceous Muderong Shale provides a regional top seal. Intraformational claystones within the Berriasian–Valanginian Barrow Group, Forestier Claystone and equivalents, the Toarcian–Callovian Athol and Legendre formations, and the Triassic Mungaroo Formation (Figure 11) have the potential to provide the seals for stacked hydrocarbon-bearing reservoirs.

The Release Area contains two exploration wells that were drilled in the 2000s, Carey 1 (2006) and Emersons 1 (2011). Neither well was a discovery (Table 3) but both provide useful stratigraphic information. The Release Area is entirely covered by 3D seismic data, including the Davros MC3D and Joy 3D surveys (Figure 12).

The Release Area is in the immediate vicinity of petroleum production infrastructure, including two gas pipelines connecting the Rankin Platform gas fields with the Karratha Gas Plant, as well as the Wheatstone Pipeline to Onslow (Figure 3 and Figure 10).

Release Area W18-8, Barrow Sub-basin, offshore Western Australia

Highlights

Prequalification for W18-10 closes on 4 October 2018, with the cash bidding auction to be held on 7 February 2019

  • Within one of Australia’s premier offshore producing basins

  • Gas province with numerous multi-Tcf accumulations, including the Gorgon, John Brookes, Spar, Rosella and Maitland gas fields

  • Proximal to Barrow Island facilities

  • Shallow water depths, 70–90 m

  • Oil-prone Upper Jurassic and gas-prone Triassic to Middle Jurassic source rocks

  • Proven multi-level structural and stratigraphic plays in Triassic, Jurassic and Lower Cretaceous strata

Release Area W18-8 comprises a single graticular block in the vicinity of the East Spar, Rosella, Maitland, John Brookes and Gorgon gas accumulations, 114 km north of Onslow and 30 km northwest of Barrow Island (Figure 13). This Release Area is considered mature in exploration status and is available for cash bidding.

The Barrow Sub-basin contains a Mesozoic to Cenozoic sedimentary succession, with maximum thicknesses of 10–20 km. The region offers proven petroleum systems of Late Triassic and Jurassic age. Both oil and gas accumulations exist within this sub-basin, offering a range of play types to be targeted. Gas is assumed to be sourced from Triassic to Middle Jurassic fluvial-deltaic rocks of the Mungaroo and Brigadier formations, Murat Siltstone, and Athol and Legendre formations (Brikké, 1982; Cook et al, 1985; AGSO and Geotechnical Services, 2000; Longley et al, 2002; Figure 14). Oil is sourced mainly from the Upper Jurassic Dingo Claystone with additional contributions from the Lower Jurassic section (van Aarssen et al 1994, 1996, 1997, 1998; Longley et al, 2002; Edwards and Zumberge, 2005). Structural plays include tilted fault blocks and rollovers, anticlines and drapes, and horsts. Stratigraphic plays include pinch-outs, unconformity traps and transgressive sandstone packages at the base of the Locker Shale.

Although the Release Area contains no wells, East Spar 2 (1993), which encountered gas, is proximal to its western border. The Release Area also has complete 3D seismic data coverage provided by several surveys including the Greater West Anchor 3D MSS and West Barrow Multi-Client 3D MSS (Figure 15).

The Release Area is close to existing infrastructure that will facilitate further development, including the Barrow Island facilities, and active gas pipelines to both Barrow and Varanus islands (Figure 3 and Figure 13).

Release Areas W18-9, W18-10, W18-11 and W18-12, Exmouth Plateau, offshore Western Australia

Highlights

Round one bids close 18 October 2018 for W18-9, W18-11, and W18-12

Prequalification for W18-10 closes on 4 October 2018, with the cash bidding auction to be held on 7 February 2019

  • Within one of Australia’s premier offshore producing provinces

  • Deepwater gas province with multi-Tcf gas accumulations

  • Proximal to Io-Jansz, Scarborough, Pinhoe and Satyr gas accumulations

  • Deep water depths, >950 m

  • Triassic fault blocks, stacked reservoirs, variety of structural/stratigraphic trap styles

  • Large undrilled areas with potential for discovery of new plays

Release Areas W18-9, W18-10, W18-11, and W18-12 are located on the Exmouth Plateau, ~150–200 km northwest of Onslow, Western Australia (Figure 16). All areas are in deep water (>950 m) and lie close to multiple large gas accumulations, including the Io-Janz, Scarborough, Pinhoe and Satyr gas fields. Release Area W18-10 is considered mature in exploration status and is available for cash bidding.

The Exmouth Plateau is a deep-water marginal plateau and is the most westerly of the structural elements that constitute the Northern Carnarvon Basin. The plateau is underlain by 10–15 km of flat-lying and tilted, block-faulted Paleozoic to Mesozoic sedimentary rocks, deposited during periods of extension prior to continental breakup in the Middle Jurassic and Early Cretaceous. The Triassic fluvial-deltaic Mungaroo Formation (Figure 17) has been the primary exploration target for many explorers and acts as both source and reservoir, while Upper Triassic carbonate platforms also have reservoir potential. Other reservoirs include the Jansz Sandstone and sandstone units within the Barrow Group and Brigadier Formation (Figure 17). The Lower Cretaceous Muderong Shale forms a regional seal. Trap styles present on the Exmouth Plateau include fault-dependent closures and drapes associated with Triassic fault blocks, Upper Triassic pinnacle reefs, and stratigraphic traps of Late Jurassic (Oxfordian) and Early Cretaceous age.

Figure 18 shows the data coverage on the Exmouth Plateau in the vicinity of the Release Areas. Release Area W18-12 has scattered well coverage, with four exploration wells drilled between 1979 and 2013 (Table 4), including a single gas discovery at Zeewulf 1. A single dry well, Jacala 1, is located in Release Area W18-11 (Table 4). Although Release Areas W18-10 and W18-9 contain no wells, their immediate proximity to existing gas fields and access to good quality seismic provides geological context. All Release Areas have good coverage with both 2D and 3D seismic data, notably the Eendracht 3D, Aragon MC3D, Willem/Pluto North 3D and Foxhound MC3D surveys (Figure 18).

Release Area W18-9 is close to existing infrastructure that could facilitate the development of discoveries, including an active gas pipeline to Barrow Island (Figure 3 and Figure 16).