Hebron mega-project on track for first oil offshore Newfoundland in 2017
ST JOHN'S, Newfoundland and Labrador -- Exxon Mobil’s senior manager for the Hebron oil field development project, 217 mi southeast of St. John’s, said earlier this week that work remains on schedule, and he also outlined some of the design challenges that engineers have faced. Speaking to a luncheon crowd at the Arctic Technology Conference in St. John’s, Geoff Parker, Hebron senior project manager, said that “The conditions presented challenges that we factored into building the 230-m-high platform.”
As some background, Hebron was discovered in 1980, in 93 m of water, but FEED work did not begin until 2010. The field is believed to contain at least 700 MMbbl of recoverable oil. Construction began in earnest during 2012, after government officials approved the development application. Much of the work has been done at the Bull Arm fabrication site along the Newfoundland coastline, where the field’s stand-alone gravity base structure (GBS) has been built.
The GBS stands 120 m tall, measures 130 m across at the base, and the shaft diameter is 35 m. It will support 52 well slots, and oil storage, which will be offloaded to shuttle tankers, is 1.2 MMbbl. The GBS will support an integrated topsides deck, and its concrete volume is 132,000 m2, more concrete, noted Parker, “than the Empire State Building.”
Parker said that managers’ and engineers’ two most important design considerations have been ice and waves. “We face icebergs, high waves, and lots of fog. The integrity of the structure is paramount. It has to be towed out in difficult conditions. This is the region, after all, where the Titanic was hit by an iceberg. So, iceberg management is a routine activity here. But we still have to factor in the possibility of one hitting the structure.
“A non-linear, finite element analysis was used to redistribute forces and reduce peak moments in the ice wall of the GBS,” continued Parker. Wave loads were determined by using a combination of model tests. The shaft wall thickness is 1,600 mm (5.25 ft) in places.”
As alluded to earlier, the GBS was built at Bull Arm, which is also the site for construction of the topsides. It will be where all final assembly of the platform takes place. “During the fourth quarter of 2012 is when construction began in earnest,” said Parker. “In May 2013, we started pouring concrete. All the walls were built with a slip-forming technique. Construction of the GBS stayed in drydock until a height of 27 m was reached. We then towed it out into the nearby deepwater fjord in July 2014. In September of that year, the larger slip-form activity was undertaken, and the next major milestone was completion of the center circular shaft, to a height of 122 m.
“The GBS, as it stands now, is mechanically complete,” continued Parker. “It will undergo a submersion test, and then it will be mated with the topsides.” Speaking of the topsides, it is 158 m long, 70 m wide (excluding the helideck) 110 m high, and the weight is 65,000 tonnes. Crude oil production capacity will be 150,000 bpd, with water volume of 200,000 to 350,000 bpd. The water injection capability will be 270,000 to 470,000 bpd, with gas handling capacity of 215 MMcfd to 300 MMcfd. There will be accommodation for 220 workers.
“The threat of icebergs actually influenced the topsides design, in addition to the GBS,” said Parker. “We wanted to be sure to account for some of the larger icebergs, where their height is great enough, that they could interact with the topsides. We wanted to minimize that potential problem.”
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