Australian producer BHP Billiton has begun assessing how to repair its Neptune tension leg platform (TLP) in the deepwater Gulf of Mexico (GOM) after discovering “structural anomalies” last week.

BHP evacuated the platform’s personnel after irregularities in the hull were found during visual inspections. However, BHP since has determined that the crews may return to work on the platform, said spokeswoman Teresa Wong. The company has begun more inspections of the hull structure, and an assessment is under way to determine “the appropriate course of action” to mitigate the undisclosed problems. Pending an assessment, a revised start-up date will be issued.

The $1.1 billion Neptune TLP originally was scheduled to ramp up at the end of 2007. Once onstream, Neptune is expected to produce up to 50,000 b/d of oil and 50 MMcf/d of natural gas. Recoverable reserves at the Neptune field are estimated by BHP to range from 100 million boe to 150 million boe. Seven initial subsea wells are to be tied back to the TLP, with the oil and gas exported to shore via the existing Caesar and Cleopatra trunk lines. The Neptune field comprises Atwater Valley Blocks 573, 574, 575, 617 and 618, and water depths range from 4,200 feet to 6,500 feet.

The TLP is located about 120 miles off the Louisiana coast in Green Canyon Block 613 in about 4,230 feet of water. The 5,900-ton hull was completed by Signal International LLC in Port Arthur, TX, and is said to be the first of its kind for the fabrication yard. According to BHP, the TLP design is similar to the Chevron Corp./BHP Typhoon platform in Green Canyon Blocks 237 and 238.

BHP operates Neptune with a 35% working interest. Partners in the venture are Marathon Oil Corp. (30%), Woodside Petroleum Ltd. (20%) and Repsol YPF SA (15%). When BHP approved the project for development in June 2005, it estimated total costs at US$850 million.

Neptune was discovered in 1995 and was the first discovery in the Western Atwater Foldbelt. An initial appraisal well (Neptune-2) was drilled in 1997. BHP took over operatorship in 2002, subsequently drilling four appraisal wells, with two sidetracks, to delineate the field.

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