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Petrel Sub-basin

Release Areas NT17-2, W17-1, W17-2, offshore Western Australia and Northern Territory

Highlights

Bids close on Thursday 22 March 2018

  • Proximal to the Blacktip gas field and the Marina gas accumulation
  • Ichthys pipeline transits NT17-2 & W17-1. Proximal to existing Bayu‑Undan and Blacktip pipelines
  • Shallow water depths of 65–130 m
  • Proven plays in anticlines, tilted fault blocks and structural/stratigraphic traps
  • Proven oil and gas petroleum systems
  • Release areas NT17-2 and W17-1 are considered to be lightly explored, refer to supporting information.
  • Further guidance available, refer to 2017 Special Notices.

Release Areas NT17-2 and W17-1 are in the northern Petrel Sub-basin of the Bonaparte Basin, to the north of the undeveloped Petrel gas accumulation and are within 200 km of Darwin. NT17-2 comprises 90 graticular blocks (7195 km2) with 70‑120 m water depths. To the west, W17-1 is 28 full and 12 part graticular blocks (2830 km2) that are in slightly deeper water (100‑130 m). Release Area W17-2 is located in the central Petrel Sub-basin, less than 300 km from Darwin in water depths of up to 70 m (Figure 1). This Release Area comprises 10 full and 2 part graticular blocks (900 km2) and is immediately north of the Blacktip gas field, and proximal to the Marina, Penguin and Polkadot gas accumulations. Gas production from the Blacktip field commenced in 2009 via the Blacktip pipeline (Figure 1).

The Petrel Sub-basin is an asymmetric, northwest-trending Paleozoic rift in the eastern Bonaparte Basin. The sub-basin contains a thick Paleozoic succession overlain by thinner Mesozoic and Cenozoic sediments (Figure 2 and Figure 3). Sedimentation in the sub-basin commenced in the Cambrian. A northwest-trending rift was initiated in the Late Devonian to Mississippian and was subsequently filled by a thick succession of marine to fluvio-deltaic sediments. Structurally, the Petrel Sub-basin comprises a broad northwest-trending syncline that plunges to the northwest, resulting in exposure of lower Paleozoic sediments in the southern onshore area (e.g. in Bonaparte 1 and Ningbing 1) and in the progressive sub-cropping of upper Paleozoic, Mesozoic and Cenozoic sediments offshore. Late Triassic compression produced uplift and erosion along the southern margin. The upper Paleozoic–Mesozoic succession exceeds 15 000 m in thickness in the central and northern parts of the Petrel Sub-basin.

The Petrel Sub-basin is a proven Paleozoic hydrocarbon province containing numerous gas accumulations, including the producing Blacktip, Petrel and Tern gas fields, as well as the Turtle oil and gas accumulation and the Barnett oil accumulation. Permian marginal marine, fluvial and glacial reservoirs within the Kulshill Group are proven hydrocarbon reservoirs in the Blacktip structure. Structural traps containing Devonian to Triassic reservoirs are sealed by Carboniferous to Jurassic shales and carbonates.

Oil and gas in Permo–Carboniferous reservoirs in the southern Petrel Sub-basin are sourced from a lower Carboniferous petroleum system as seen in the Turtle and Barnett accumulations (Figure 2 and Figure 3). This includes source rocks within the Bonaparte Formation (Langfield Group equivalent) and the Tanmurra Formation (Weaber Group). Sufficient deep drilling has not been undertaken in the western Petrel Sub-basin to fully evaluate the western extent of the petroleum system, although Marina 1 and Lesueur 1 both had gas and oil shows in the Carboniferous–lower Permian succession (Figure 2, Figure 3 and Figure 4b). The identification of the Beehive Prospect (Figure 4e) to the southeast of the Release Area in Carboniferous and Ordovician rocks, raises the possibility of unevaluated older plays. The Release Areas offer a range of play types including horst blocks and rotated fault blocks, as well as inversion-related anticlines, fault-dependent closures, fault rollover anticlines and stratigraphic traps (Figure 4a-e).

3D seismic coverage is minimal, with the Petrel 3D survey overlapping a small portion of Release Area W17-1 and the Blacktip 3D grid abutting Release Area W17-2. The 2D seismic data coverage is good across the Release Areas except in the southeast corner of NT17-2 (Figure 5).