Terra Nova switching valves

Moira Baird
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Saturation divers installing new equipment on Grand Banks seabed

Midway through a four-week maintenance shutdown at the Terra Nova oilfield, operator Suncor Energy is using a dozen saturation divers on the sea floor to replace valves at six wells.

Terra Nova FPSO, a massive floating production, storage and offloading vessel used in the oil and gas industry, heads along the Newfoundland Coast near St. John's in this file photo.

Their job is to remove six annular choke valves and install new ones in water depths of 105 metres.

It’s the first time this kind of diving installation has been done on the Grand Banks seabed, and it’s part of a scheduled round of repairs and inspections for the Terra Nova floating production, storage and offloading (FPSO) vessel. Suncor started the shutdown July 12.

“The turnaround itself is progressing consistently with our plan,” said John Downton, spokesman for Suncor.

“We’re roughly half-way through the work scope.”

The Acergy Discovery, a subsea construction vessel, and its team of saturation divers arrived at the oilfield last Saturday morning. The diving work is scheduled to take 10 days to complete.

The valves are part of well equipment known as Christmas trees — steel-framed boxes that also house pipes and pressure gauges to control the flow of oil from a well. When that equipment was installed on the seabed earlier this decade, Downton said no divers were used for the job.

“Those valves were built into the Christmas tree assembly so it was a complete unit that was installed,” Downton said.

“Now what we have to do is dismantle the unit and replace the valves.”

Six valves will be replaced on six gas-injection wells. Those valves control the amount of gas that is injected into the reservoir to help oil flow to the FPSO.

“What we’re doing now is replacing them to improve their overall performance and to help us improve the overall performance of the reservoir as well,” John Downton, Suncor spokesman

“What we’re doing now is replacing them to improve their overall performance and to help us improve the overall performance of the reservoir as well,” Downton said.

Gary Vokey, Suncor’s Terra Nova asset manager, described plans to replace the valves in a speech at the NOIA conference held in June.

“The replacement of the valves is not related to safety or environmental considerations, but rather to allow to better us to direct gas and water for sub-surface pressure maintenance.”

He also said it’s a first in the waters off Newfoundland, but not for the “experienced team of divers” doing the job.

“It is the first time a project like this has been done in our operating area. Project engineers and diving personnel have rehearsed the procedures on shore by mocking up the subsea hardware and validating the various steps to ensure it can be carried out safely and efficiently.

“It is an innovative project and it speaks to the abilities of our local suppliers.”



Geographic location: Terra Nova, Newfoundland

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