ABERDEEN, UK – Atkins has completed a project supporting BP on a well rejuvenation exercise in the southern North Sea.
To sustain gas production from the Ravenspurn North ST-3 platform, BP has been stimulating the 14 wells using concentric coiled tubing to suck out any obstructions and debris, and improving the well completion design with high integrity liners.
However, the operation demanded over 5 km (3.1 mi) of concentric coiled tubing for each well. This, and the support materials, could have imposed a severe strain on the normally unmanned wellhead platform. The coiled tubing equipment alone weighed 210 metric tons (231 tons), but the platform’s crane can only lift a maximum of 12 metric tons (13.2 tons).
Atkins collaborated with BP and BJ Services to adapt an existing technique to spool coiled tubing from a supply vessel onto a fixed platform without the need for heavy lifts.
This method had been used previously by BJ for conventional coiled tubing, but this was to be the first instance of a concentric coiled tubing deployment from a vessel on to a fixed platform. However, Atkins’ review and checks of the jacket structure capacity confirmed that all proposed scenarios could be accommodated.
As an example, at one location where the design wave height is 18.5 m (60.6 ft), waves more than 10 m (33 ft) high are commonplace, and tidal currents are more than 1m/s, the well equipment was designed to have weak points to lessen the risk of the supply vessel damaging the platform through loss of control.
Using a detailed computer model of the platform, the team determined that all safety checks were completed efficiently.
Ann Davies, well intervention engineer at BP, said: “This project is extremely important to the future of the Ravenspurn field in the Southern North Sea, and performing heavy duty work on a small unmanned installation comes with many challenges. Getting the concentric coiled tubing and associated equipment safely onboard is vital in gaining access to these wells.”
Vivian Zhao, Atkins project manager, said: “We have looked after BP’s 25 southern gas assets for the last 10 years and because we maintain the platforms’ analysis models as part of our integrity management role, we were able to carry out meticulous safety checks at all points of this challenging process…
“The project effectively boat spooled more than 17,000 ft [5,181 m] of concentric coiled tubing and has been hailed the world’s first of its kind.”
ONLINE SPECIAL: BP deploys novel intervention on Ravenspurn North
Atkins has completed a project supporting BP on a well rejuvenation exercise in the southern North Sea.