Wandoo Offshore Oil Platform
The Wandoo oilfield located 75 kilometres north-west of Dampier, WA, in the relatively shallow water depth of 55 metres. The construction of the Wandoo B Offshore Oil Platform involved five separate engineering elements to recover the oil from the Wandoo reservoir. The engineering solutions adopted to recover and process the oil had to be delivered within tight time and budget constraints. The total project budget for the Wandoo Development was A$480m and of this, $375m was committed to the design and construction of the facilities and infrastructure work.
The Wandoo Alliance delivered an operating offshore oil platform ahead of schedule and under budget despite a number of potentially crippling incidents on the way. These major achievements would not have been possible without the alliance and the engineers it brought together.
The key construction elements of the development were:
The casting basin at Bunbury, Western Australia
The geology of the area was complex which in turn created a complicated ground water regime. The casting basin was excavated to a depth of 15 metres, some 12 metres below the sea.
The concrete gravity substructure (CGS)
The CGS is an 81,000 tonne deadweight concrete structure which provides storage capacity for 400,000 barrels of crude oil. The CGS was constructed in the casting basin at Bunbury and, upon completion, was floated and towed 1,700 kilometres to the Wandoo oilfield. A total of 28,000 cubic metres of concrete was used in constructing the CGS as well as 8,500 tonnes of reinforcing steel and 550 tonnes of prestressing strand.
The 6,500 tonne processing topside
The 6,500 tonne topside facility for processing the oil and gas is supported by the four CGS legs. The topside structure is an integrated three level deck 70m by 40m by 18m total height. The topside was designed in Perth and fabricated in Singapore at the Keppel FELS ship yard. A significant proportion of the components were fabricated in Australia and shipped to Singapore.
Five flexible sub-sea pipelines linking the platform with Wandoo A and the export tanker loading buoy
Flexible pipelines, fabricated in Fremantle, were placed on the sea floor and then covered with protective rock armour. These pipelines, connecting Wandoo B with the Wandoo A monopod and the load-out facility, cover a length of over 9 kilometres.
Transporting, installing and hooking up the CGS and topside in the open sea
The complex process of transporting the CGS and the topside from their construction sites to the oilfield posed many risks and challenges. Avoiding serious weather patterns such as cyclones and storms and sticking to a tight time frame to ensure the two pieces arrived and could be installed and hooked up at the right time involved careful planning. Obstacles and disruptions along the way had to be managed efficiently and effectively to ensure the project stayed on track and on budget.
An Interim Alliance was formed in September 1994, leading to project sanction and the full alliance in December 1994. Construction commenced in February 1995 and was completed by March 1997. The Wandoo Alliance was headed up by Leighton Engineer Mr Jim Holt as the Project Director. The stakes were high and the risks extreme, as the weather alone could have literally devastated the project, but instead it was delivered in just 26.5 months from project sanction in 1995 to first oil production in March 1997, some nine months ahead of industry norms.