Eastern Exmouth Plateau

Release Area W17-7, offshore Western Australia

Highlights

Bids close on Thursday 22 March 2018

  • Lies within Australia’s premier offshore petroleum basin
  • Proximal to Perseus, Goodwyn and North Rankin multi-Tcf gas accumulations
  • Shallow to moderate water depths, 100–500 m
  • Triassic fault blocks, stacked reservoirs, variety of structural/stratigraphic trap styles
  • Large undrilled areas with potential for discovery of new plays
  • Proximal to producing platforms and gas pipelines
  • Further guidance available, refer to 2017 Special Notices

One Release Area is offered on the eastern Exmouth Plateau, and is centred approximately 170 km north of Dampier (Figure 1). Release Area W17-7 (20 graticular blocks) extends over the Victoria Syncline from the northern Rankin Platform. It lies wholly within 50 km north and northwest of the Perseus, North Rankin and Goodwyn gas accumulations, in moderately deep water (100–500 m).

The extensive 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 long-lived periods of extension prior to continental breakup in the Middle Jurassic and Early Cretaceous for the northern and combined western and southern margins, respectively. The Triassic fluvio-deltaic Mungaroo Formation has been the primary exploration target for many explorers on the plateau and acts as both source and reservoir. Other reservoirs include the Upper Triassic Brigadier Formation, the Upper Jurassic Jansz Sandstone and sandstone units within the Lower Cretaceous Barrow Group. The Lower Cretaceous Muderong Shale forms an uppermost regional seal. Trap styles present on the Exmouth Plateau include fault dependent closures and drapes associated with Triassic fault blocks, and stratigraphic traps of Upper Jurassic (mostly Oxfordian) and Lower Cretaceous sediments (Figure 3).

The Rankin Platform is a northeast-trending structural high forming the eastern flank of the Exmouth Plateau. It separates the plateau from the Dampier and Barrow sub-basins to its 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 1). All of these accumulations have been sourced from fluvio-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 2) have the potential to provide the seals for stacked hydrocarbon-bearing reservoirs. Two gas pipelines connect the Rankin Platform gas fields with the Karratha Gas Plant (North West Shelf Gas, 2016).

Immediately to the northeast of the Release Area, Cue Energy Resources plans to drill its large ‘Ironbark’ prospect (Cue Energy, 2016), which comprises Mungaroo Formation sands straddling permits WA-409-P and WA-359-P, and lies just over 50 km from the North Rankin Complex. BP has recently farmed into permit WA-409-P with an option to enter WA-359-P for 2017 (Offshore Energy Today, 2016).

Figure 4 shows the data coverage on the eastern Exmouth Plateau, in the vicinity of the Release Area. The well Eastbrook 1 provides the only gas show within the Area, while Zeus 1, Gandara 1 and La Rocca 1 provide additional stratigraphic information to the north. In addition, further outboard wells such as Artemis 1, Banambu 1 and Banambu Deep 1 may provide further valuable information on the stratigraphic and structural setting of the northern flank of the Victoria Syncline. The Area has good 2D seismic coverage, with an average line spacing of less than 5 km. The Area is also covered by large sections of 3D seismic surveys Banambu 3D MSS, Meo NWS 3D MSS, Rosie 3D MSS, Zeus 3D MSS and Rose 3D MSS. Oilex Limited has used the last of these to define several leads (Oilex Ltd, 2010). Multiclient surveys Zeus 3D MSS and Zeebries 3D MSS, acquired by Fugro/CGG (Grahame and Silva-Gonzalez, 2013), will form part of a major reprocessing project (‘Olympus Project’) by Spectrum for a suite of 3D surveys covering the eastern Exmouth Plateau and adjoining Rankin Platform (Spectrum, 2016).