BHP Billiton (35%) approved spending about US$300m on the development, and Woodside Energy (USA), a wholly owned subsidiary of Woodside Petroleum (20%), also gave the financial go ahead to spend $170m.
The other partners, Marathon Oil Corp (30%) and Repsol subsidiary, Maxus (US) Exploration (15%) have also approved their expenditure.
It is estimated the field contains from 100 to 150 million barrels of oil equivalent. The project is due to come online in late 2007.
Neptune will have a design capacity to produce up to 50,000 barrels of oil and 50 million cubic feet of gas per day.
The development is a major step forward for both Australian partners.
Neptune will expand BHP Billiton's producing assets in the gulf, the group's president of energy, Philip Aiken said.
“Neptune will be our first operated, deepwater standalone facility in the gulf and represents a significant milestone towards building a core business in that region,” he said.
”With [the] Mad Dog [field], which came onstream this year, Atlantis, which will start up in 2006, and now Neptune, BHP Billiton’s net production from the gulf will exceed 100,000 barrels of oil equivalent per day by the end of 2007,” Aiken said.
Neptune will also provide Woodside’s first deepwater Gulf of Mexico oil production.
The field is about 120 miles from the Louisiana coast. It comprises Atwater blocks 573, 574, 575, 617, and 618, in water depths ranging from 4,200 feet to 6,500ft. The production facility will be located in about 4,250ft of water.
A standalone, tension leg platform has been selected, part of proposed facilities, wells, and completions that are proven designs successfully used in the deepwater part of the gulf, BHP Billiton said.
The first oil is expected by the end of 2007 with seven initial subsea wells connected to the platform.
The wells, subsea systems, flowlines, floating systems, topsides and risers will be designed, procured, fabricated and operated by BHP Billiton on behalf of the Neptune joint venture partners.
The oil and gas will be exported to shore via the existing Caesar and Cleopatra trunk lines.