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Calder Graben

Release Area NT17-1, offshore Northern Territory

Highlights

Bids close on Thursday 19 October 2017

  • Adjacent to Barossa, Caldita, Evans Shoal and Evans Shoal South gas accumulations
  • Shallow to moderate water depths, 80–370 m
  • Plays include rollover anticlines, horst structures, drape and unconformity traps
  • Multiple potential oil- and gas-prone source rocks in the adjacent depocentre
  • This release area is considered to be lightly explored, refer to supporting information
  • Further guidance available, refer to 2017 Special Notices

Release Area NT17-1 straddles the Calder Graben, Malita Graben and Darwin Shelf of the northern Bonaparte Basin, and the westernmost Money Shoal Basin (Figure 1). Recent drilling in the area include the Barossa Field appraisal wells (2014-15), Blackwood 2 (2013), Evans Shoal North 1 (2013) and Heron South 1 (2012). The Release Area lies approximately 250 km offshore from Darwin.

The Malita Graben and Calder Graben form a major northeast-trending rift system that lies between the Petrel Sub-basin, the Darwin Shelf and Money Shoal Basin to the south, and the Sahul Platform to the north (Figure 1). The graben were initiated by Early Jurassic rifting associated with the break-up of Gondwana and contain a thick (up to 10 000 m) succession of late Paleozoic to Mesozoic sedimentary rocks (Figure 2) overlain by Cenozoic sedimentary rocks. The Darwin shelf and Money Shoal Basin, to the south and east respectively, have relatively shallow basement with a thin Jurassic succession overlain by thicker Cretaceous and younger sediments. The succession accumulated mostly due to passive subsidence. Late Cretaceous to recent faulting in the Release Area was formed by compressional reactivation relating to the convergence between the Australia-India plate and Southeast Asian microplates to the north.

The fluvio-deltaic Jurassic Plover Formation is the primary source and reservoir for the Sahul Platform, Troubadour Terrace, Malita Graben and Calder Graben gas accumulations. Gas shows have also been found in fractured carbonates of the Lower Cretaceous Darwin Formation, and sandstones of the Upper Jurassic Elang Formation and Upper Jurassic–Lower Cretaceous Frigate Shale. Condensate sourced from the Cretaceous Echuca Shoals Formation (e.g. Blackwood 1ST1) indicates there could also be an underexplored liquids play in the region.

Potential play types including inversion anticlines and submarine fans are depicted in Figure 3.