Angel in its firmament
  from: Offshore Engineer
  by: Darius Snieckus
  Friday, May 16, 2008

Clough Aker Joint Venture has laid claim to a new ‘world height record’ following successful installation of the topsides for the North West Shelf Venture’s Angel platform off Western Australia. Darius Snieckus reports.

The transport and floatover installation of the Woodside Energy-operated Angel gas platform’s 7500t topsides was completed by the Clough Aker JV, aided by Dockwise heavylift vessel Black Marlin, last month in the penultimate phase of a A$40 million EPCI contract signed in late-2005.

Following outfitting in Batam, Indonesia, Black Marlin arrived at the Pasir Gudang, Malaysia yard of fabricator Malaysian Marine & Heavy Engineering (MMHE) in February to collect the topsides.

By mid-March, the Dockwise vessel was ballasted down to loading draft and the link beams installed so that the wires for the four 27-strand jacks – with a pulling force of 2000t – could be pulled into the onboard anchors. It took 13 hours to skid the topsides on to Black Marlin.

The journey to location, in 80m of water some 50km east of Woodside’s two existing fixed platforms on the North West Shelf, North Rankin A and Goodwyn A, took six days.

April’s installation of the Angel topsides – in a floatover operation similar to that employed by the Clough Aker JV in 2003 for ConocoPhillips’ 11,500t Bayu-Undan CUQ deck in the Timor Sea, using Dockwise sister vessel Blue Marlin (OE August 2003) – also established a new industry benchmark for installed deck height, reports the JV’s topside installation project manager Thor Hevroy.

The topsides sit atop a 21m high deck support unit, weighing a further 850t. ‘Due to the extreme installed height with respect to sea level, this was a unique floatover challenge worldwide,’ says Hevroy.

Angel’s 7500t jacket had earlier been delivered on J Ray McDermott’s Intermac 650 launch barge and installed by the J Ray derrick barge DB30. The jacket is secured by eight drilled and grouted, piled foundations, each weighing more than 3000t.

As OE went to press, the Clough Aker JV had completed its hookup work, with all 15 risers installed and jacket-to-topside leg welds completed. Demobilisation of the scaffolding and jacket temporary platforms was under way and collection of the temporary mooring system for the floatover operation was imminent, prior to carrying out a final ROV survey.

Unusually for Woodside and a platform this size, the Angel gas platform is designed to operate in normally unmanned mode. It will have drying and dehydration facilities but power and control will come from the North Rankin A (NRA) platform, whose control room and control systems are also being upgraded under the A$1.6 billion Angel gas development.

CTC Marine was last month expected to begin installing the 51km power cable that will link NRA with Angel. Three umbilicals will also be installed to connect the Angel platform to adjacent FMC-supplied subsea trees. Angel's three subsea satellite wells will be tied back to NRA via a new 50km, 30in subsea pipeline - installed by J Ray McDermott - tied into the first North West Shelf trunkline and commingled with NRA production for onshore processing at the North West Shelf Venture's Karratha plant.

Angel has an estimated resource of 1.8tcf. Its anticipated production levels are up to 800mmscf/d of gas and up to 50,000b/d of condensate.

Meanwhile, the North West Shelf Venture partners last month sanctioned the A$5 billion North Rankin 2 development, designed to recover remaining low pressure gas from the North Rankin and Perseus gas fields via a new fixed platform (NRB) bridge-linked to NRA in 125m of water (OE July 2006).

Following completion of the North Rankin 2 project, which will also cover required tie-ins and refurbishment of NRA, both platforms will be operated as a single integrated facility. Start-up is expected in 2013. OE

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