The $1.6 billion Angel Gas Project involved a number of firsts for the North West Shelf Venture (NWSV), including becoming the first NWS large-scale gas production facility to become operational in 13 years. Construction was completed on 28 June 2008 when the last of the subsea tie-in spools was installed and first gas was produced from the project to supply the burgeoning energy requirements of the Asia Pacific region.
Unique design and transport
Situated approximately 120 kilometres northwest of Karratha and 49 km east of the North Rankin A platform, Angel’s steel-leg platform stands in about 80 metres of water and is supplied by three subsea production wells, enabling a production capacity of 800 million cubic feet per day (MMcf/d) of raw gas and up to 50,000 barrels per day (bbl/d) of condensate. Associated infrastructure includes the new 49 km, 30 inch diameter subsea pipeline that is tied back to North Rankin A, the first destination for gas produced from the Angel field.
The Angel platform’s design also means that it can be safely and securely powered and remotely controlled from North Rankin A via a subsea power cable.
From North Rankin A, the gas is then transported via the main Rankin trunkline to the LNG facility on the Burrup Peninsula, northwest of Karratha, building on and strengthening supply to the plant’s existing five LNG trains. At the plant, Angel’s gas is converted into LNG and then delivered to customers.
The three subsea wells are individually connected back to the Angel platform by dedicated steel flowlines and electro-hydraulic control umbilicals. The subsea trees are made up of a large-bore 7 inch conventional tree design, with an 18 inch interface to both the workover riser system and wellhead.
During construction, 4,500 tonnes of steel piles were drilled and grouted into the seabed to secure the 8,000 tonne jacket, which was fabricated in China. The 7,500 tonne topsides facilities deck was completely constructed at the fabrication yard in Malaysia and installed in one piece at the site, using a process known as “˜floatover installation’. Using this method to install the topsides was one of many firsts for Woodside during the project.
Innovation and industriousness
Angel’s main offshore construction phase began on 28 October 2007 with the installation of the jacket and piles, which took 40 days. The laying of the flowlines began in December 2007 and was completed within just 34 days, despite the work crew having lost twelve days to Tropical Cyclone Melanie, which hit with severe winds of up to 125 km/hour and threatened to develop into a category three cyclone.
Work on laying the 20 inch diameter export pipeline, which began in February 2008, was repeatedly disrupted by cyclones Nicholas, Ophelia and Pancho. Cyclone Pancho was the strongest storm of Australia’s 2007-08 regional cyclone season, reaching category four status and winds of up to 165 km/h.2 Despite losing 38 days due to these setbacks, the work crew succeeded in completing the job within 75 days.
Installation of the subsea tie-in spools began in March and was uninterrupted, taking just 64 days to complete. Angel installation team leader Jim Forsyth said that competent preparation, effective communications and good management on the worksite were all successfully combined to meet the challenges posed, including the achievement of remote power.
The process of remotely powering the new offshore Angel platform from the existing North Rankin A – widely acknowledged as the hub of NWSV’s gas and condensate production – began with one of the project’s most demanding and intricate operations. North Rankin A’s main switchboard had to be modified to include a 6.6 kilovolt (kV) feeder panel, and this had to be done while the platform continued operating.
Eric Resch, Angel’s lead project engineer for the North Rankin A brownfield work, said that the success of the procedure was due to timing. “The work was done by shutting down half of the switchboard while North Rankin A operated off the other half. This was achievable if you timed the work for periods of reduced production rates,”? Mr Resch said.
The work team at North Rankin A also installed a 22 kV switchboard and transformer. North Rankin A was connected to Angel by a 50 km piece of subsea power and fibre optic cable, which transmits power at 22 kV, approximately 100 times higher than a standard household.
Contracts
In February 2005, NWSV operator Woodside Energy awarded the project’s first contract, a front-end engineering and design (FEED) contract for development of the Angel Gas Field to Eos – a joint venture between WorleyParsons and KBR.
At the time, Woodside said that the Angel project represented “another major step in development of the NWS”? and would significantly boost offshore production capabilities.
The same month also saw Woodside award a $45 million contract to a Clough/Aker Kvaerner joint venture for all installation, engineering and construction activities relating to the installation of Angel’s platform topsides.
The NWSV participants officially sanctioned the project and reached a final investment decision of $1.6 billion in mid-December 2005. A few days later, the Eos joint venture – after having recently completed the project FEED – was awarded the Engineering, Procurement and Construction Management for Angel.
In July 2006, a $200 million contract for substructure and pipelay installation for the platform development was awarded to J. Ray McDermott. The contract involved transportation of the jacket and piles from a fabrication yard in China to the offshore installation site, as well as the launch, upend and set down of the jacket.
Angel’s working team
The office workforce for the Angel development peaked at 320 people, with several hundred more involved in the fabrication yards and offshore installation works. The final offshore commissioning was carried out by a small crew of
64 people.
In commendation of Angel’s workforce, Woodside’s Executive Vice President of the NWS Eve Howell said “The safe completion of the Angel Platform, on time and under budget, is a credit to the project teams involved in successfully delivering this major development.”?
Facing the future
Though the work team acknowledges the collaborative accomplishment that has been reached, there are still a few more achievements they are aiming for.
Angel Project Manager Ian Widdicombe said “Commencing production on schedule is important but we still have some work to do.
“We want to clean up the wells, achieve a fully remote operation, ensure we have ongoing reliable production and, finally, have an unmanned platform.”?
The realisation of plans to make Angel the NWSV’s first unmanned platform, controlled from North Rankin A, is the next big step forward for the already successful development.