Woodside in Londonderry move

WOODSIDE Petroleum has staked a claim over an area of the Londonderry High and Petrel Sub-basin with the award of a new permit off the Western Australian coastline, which is ideally located to send gas east to Darwin or to further support its WA LNG interests.
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Haydn Black

Reporter

The new block, WA-522-P, sits between undeveloped Tern, Petrel, Frigate and Blacktip fields to the east and the Prometheus/Rubicon fields are right on its western edge.

Woodside secured the block after successfully bidding in the 2014 acreage offer for WA14-1.

The Londonderry High is an offshore, Permo-Triassic horst and graben complex that forms the inboard, southwestern part of the Bonaparte Basin on Australia's northwest continental shelf.

The Petrel Sub-basin is rich with oil and gas targets, however most discoveries have so far been non-commercial.

Eni successfully started the Blacktip field in Northern Territory waters in 2009, but more recent attempts by Santos, GDF Suez (now Engie) and SK Energy to develop floating LNG business in the area failed despite the presence of some 2-3 trillion cubic feet of gas.

The 7806sq.km block is less than 20km offshore at its closest point to shore, and is just 400km from Darwin.

WA-522-P has just one well penetration, Kufpec's 1993 well Torrens-1, located about 90km from the coast.

The well returned both oil and gas shows.

While the top of the Hyland Bay Formation were significantly low to prognosis, due to an inappropriate velocity used in time-depth conversion, oil shows were seen in the Fossil Head Formation below 1517m and there were possible minor moveable oil and gas at low saturations in the overlying Tern Member.

It is now believed that the failure of the Permian-aged Hyland Bay Formation to contain oil was due to the lack of significant structural closure.

A similar explanation may account for the lack of shows in the main objective, the Keyling Formation.

The Treachery Shale was well developed and provided a potential seal to the underlying Kuriyippi Formation.

No significant shows were recorded and porosities were low, averaging 9%.

The well reached total depth at 2497m, just 70m above magnetic basement of probable Proterozoic age.

The proven Permian petroleum systems in the region have charged numerous gas accumulations.

There is also a known oil and gas prone lower Carboniferous petroleum system in the southern Petrel Sub-basin within the Bonaparte Formation as proven by the onshore Vienta, Waggon Creek and Weaber fields that sit in the onshore part of WA, south of Kalumburu, and the Tanmurra Formation that hosts the Turtle-Barnett oil discoveries to the south-east.

Sufficient deep drilling has not been undertaken in the western Petrel Sub-basin to fully evaluate the western extent of the older petroleum system, although Marina-1 and Lesueur-1 both had gas and oil shows in the Carboniferous-lower Permian succession close to the block, and MEO Australia has defined a large 708 billion cubic feet of gas and 22MMbbl target at the Breakwater prospect that it hopes to drill with Origin Energy (50%) in 2017, which could upgrade the area with success.

Marina-1, the last discovery in the area, was drilled at a non-crestal location, meaning there could be a significant attic accumulation updip that remains to be tested.

Woodside's entry to the area comes as infrastructure is expanding, and the proposed Northern Gas Pipeline could change the dynamics for gas exploration in the offshore areas, giving explorers fresh impetus to assess gas targets.

Any gas discovered could be sent east to backfill one of the two Darwin LNG plants as the Ichthys pipeline is immediately north of the new block. From Darwin the NGP offers access to the entire East Coast gas market.

There were over 30 wells drilled into the Londenderry High in 2003 alone, resulting in numerous oil shows, strong gas shows and several sub-commercial gas discoveries at Promethius-1 and Rubicon-1, however, there are no commercial discoveries to date.

Eni operates WA-34-R, and it is understood that Tap Oil is looking to sell its 12% interest as it seeks to divest itself of its Australian holdings.

The Londonderry High takes in the eastern part of Woodside's block, with the Petrel Sub-basin prominent in the east.

The wider Bonaparte Basin one of the nation's most prolific offshore hydrocarbon- producing basins.

All through the basin there are marginal undeveloped fields and shows that hint at unrealised potential.

The United States Geological Survey's mean estimate for undiscovered hydrocarbons in the wider offshore Bonaparte Basin is for 930 million barrels, 3Bbbl of natural gas liquids and 54 trillion cubic feet.

With several trillion cubic feet of undeveloped fields in the vicinity and untested potential, a pipeline to Darwin and two LNG trains with room for expansion, it is possible that Woodside sees some sort of long-term aggregation strategy built around its new block.

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