TWO new records have been set in north-west European waters in recent weeks, one by StatoilHydro with a live pipeline hot tap, while an alliance comprising Island Offshore, FMC Technologies and Aker Well Service has set a new water-depth world record for subsea riserless wireline intervention from a ship.
The world’s deepest hot-tap operation on a pressurised pipeline was carried out in the Ormen Lange field in the Norwegian Sea during early-August.
The objective of the task was to connect a spur pipe template to a producing pipeline, and it was designed to save on more costly alternatives, according to Bjorn Kare Viken, VP marine technology and operations at StatoilHydro.
Two hot taps were conducted at a water depth of 860m (2,821ft) to tie in the template to the southern part of the Ormen Lange field’s export infrastructure.
StatoilHydro says the two hot taps were monitored and controlled from the surface, assisted by 100 sensors, 23 cameras and 18 subsea computers deployed on the seabed to transmit data via heavy-duty cables.
“We’re a world leader in this technology, which will also be important for future projects,” said Viken.
“Substantial cost savings can be achieved when developing mature areas.
“That’s because the method allows existing pipelines to be used, so marginal fields can be tied back to older infrastructure with good capacity.
“Using remotely-operated hot-tapping makes it possible to pursue operations in deep waters where divers can’t be used.”
Energy has reported on hot taps before, and one of the keys to success is thorough preparation, especially attention to risk analysis and understanding.
The technology also has to be carefully tested by putting it through one or more dry runs.
In essence, hot-tapping operations involve carrying out repairs, replacements or tie-ins on pipelines that remain pressurised throughout such operations.
That makes it possible to avoid expensive shutdowns and simplifies the tie-in of new pipeline systems to existing infrastructure.
Ormen Lange ranks as one of the biggest and most demanding gas-field developments ever attempted in European waters, which means that shutdowns must be kept to the absolute minimum. Switching to West of Shetland, the Island Offshore, FMC Technologies and Aker Well Service alliance has been carrying out intervention work on BP’s Schiehallion field at a water depth of 401m (1,316ft) and in the face of challenging sea currents that run at up to 2.5 knots (nearly 3mph).
The vessel used for this operation was the Island Constructor, a sophisticated purpose-designed and built intervention unit that is capable of operating in water depths to 600m (1,968ft).
The North Sea Alliance was formed in 2004 to provide integrated wireline services to the growing subsea intervention market.
Presently, the alliance operates a trio of monohull vessels specifically designed for intervention tasks.
According to Island, since 2005, interventions have been performed on about 50 wells, providing services such as scale milling, gauging and logging operations, plug setting and re-perforating requirements.
There is a huge global market now growing for deepwater subsea intervention and it is likely that records will tumble over the next few years as this sub-sector gains momentum.