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Vulcan Sub-basin

Release Areas AC17-2, AC17-3 and AC17-4, Territory of Ashmore and Cartier Islands


AC17-2 and AC17-3 bids close 19 October 2017

AC17-4 bids close 22 March 2018

  • Proven oil and gas producing province; adjacent to Swan and Cash Maple gas fields and the Montara oil accumulation.
  • Shallow water depths of 100-240 m
  • Potential for structural and stratigraphic Triassic–Jurassic, Cretaceous and Paleogene plays
  • Further guidance available, refer to 2017 Special Notices.

Release Area AC17-4 is located in the Vulcan Sub-basin, western Bonaparte Basin in the Timor Sea (Figure 1), approximately 250 km offshore and 700 km from Darwin. The Release Areas cover two (165 km2), seven (~585 km2) and six (~500 km2) whole graticular blocks, respectively, in water depths of up to 240 m. Release Areas AC17-2  is situated in the Swan graben adjacent to the Ashmore. AC17-3 is located on the Montara Terrace and AC17-4 overlies the Montara Terrace and Heywood Graben and extends partly into the Caswell Sub-basin.

The Vulcan Sub-basin is a northeast-oriented Late Jurassic extensional depocentre that contains Permian–Holocene sediments (Figure 2). The sub-basin comprises a complex series of horsts, graben and marginal terraces. It is a proven hydrocarbon province which includes several producing oil fields of the Montara Project (Skua, Swift‑Swallow, Montara), as well as several other oil fields (Jabiru, Challis‑Cassini, Puffin) and sub-economic accumulations (Figure 1). The Release Areas are adjacent to the Cash‑Maple, Swan and Crux gas fields, the greater Montara oil fields and a number of discoveries including the Maret 1, Eclipse 2 and Vesta 1 oil and gas accumulations, Bilyara 1 and Tahbilk 1 gas accumulations and Talbot oil accumulation. Development options for the Cash‑Maple gas and oil accumulation are currently being considered. Examples of play types identified in the vicinity of the Release Areas is shown in Figure 3.

The Swan and Paqualin graben form the major source kitchens in the Vulcan Sub-basin, containing mature oil- and gas-prone source rocks in the Jurassic lower Vulcan, Montara and Plover formations. Hydrocarbons at Cash‑Maple gas field are reservoired in the Montara, Plover and Challis formations while the Swan gas field is in the Puffin Formation. The Jabiru oil field lies within the Montara Formation. In addition, numerous wells in the immediate vicinity of the Release Areas have oil and gas shows in the Plover (Audacious 1, Augustus 1, East Swan 1, Swallow 1), lower Vulcan (Elm 1, Vulcan 1B), upper Vulcan (Paqualin 1, Swan 1, Octavius 1, Keeling 1) and Johnson (Snowmass 1, Puffin 2) formations (Figure 1). The temporal and spatial distribution of effective source rocks, their expulsion history and migration pathways in the Vulcan Sub-basin are given in Figure 4. Structural traps containing Triassic to Jurassic sandstone reservoirs are sealed by Lower Cretaceous claystones of the Echuca Shoals Formation (Figure 3). These traps are commonly either horsts (some complexly faulted), or tilted fault blocks. Upper Jurassic and Upper Cretaceous submarine fan sandstones are proven exploration targets within the sub-basin. A well-to-well correlation across the Vulcan Sub-basin from Anson 1 on the Londonderry High to Rainbow 1 on the Ashmore Platform identifying sand and mud-prone intervals is shown in Figure 5.

Data coverage for the Vulcan Sub-basin is extensive (Figure 6), with 2D and 3D seismic data available and numerous wells drilled. Release Area AC17-4 is penetrated by Maret 1 and Circinus 1 ST1.