The situation occurred at the Oselvar field, located 250 km southwest of Stavanger at water depths of 75 metres. Dong Energy, the Danish exploration and production company, is the operator of the field (55%). License partners are Bayerngas Produksjon Norge (30%) and Norwegian Energy Company (15%). Three production wells are currently being developed using the Maersk Giant rig.
After connecting the high pressure (HP) riser, there was a need to retrieve the subsea control module. However, investigations proved that a crash point made it impossible to get access to the control module without first removing the HP riser. The initial plan was to execute a comprehensive operation involving plugging the well and pulling out the HP riser system.
This would have been a costly and time-consuming operation with several possible HSE challenges, but given the information and time available, this was thought to be the only option.
A cost effective alternative
However, Dong Energy wanted to explore other ways of solving this problem and contacted Aker Solutions.
The visualisation experts at Aker Solutions had previously executed successful projects with Dong Energy, including delivering handbooks, posters and animations. As a result, a library with 3D models of all subsea installations from the Oselvar field already existed.
With 3D data available, personnel from Dong Energy and Aker Solutions could start working on the problem the following day. They used visualisation technology from Aker Solutions' integrated operations centre, the IPort, located at Forus just outside Stavanger, Norway.
A 3D simulation of the subsea tree, the crash point, the equipment and all its surroundings was made. The tool for replacing the subsea control module was customised in 3D. Critical measurements and pictures were sent to subsea personnel at Aker Solutions’ base in Ågotnes and the actual tool was customised.
They customised the actual tool, and returned pictures and critical measurements to the IPort for a final verification in 3D simulation. A 3D sequence was then recorded and sent to the rig. The rig used the pictures and measurements to cut the frame surrounding the HP riser at the seabed, and pictures of the underwater operation were sent to the IPort for verification.
The personnel located in the IPort, the subsea personnel testing the actual equipment at Ågotnes, and the personnel on the rig had an on-going dialogue to ensure that all modifications became successful. The IPort centre, having the facilities necessary to maintain mutual dialogue during operations, turned out to be very valuable. It promoted clear communication and common understanding between all parts involved.
"By using 3D interface checks in the IPort, Dong Energy has been able to replace a SCM on the first Oselvar well, where it was necessary to modify subsea equipment with ROV according to images from the IPort. We used 23 hours of rig time, instead of the alternative solution which required pulling out the HP riser system. Our estimated savings are minimum 14 days of rig time; about NOK 100 million," says Hasse Herland, completion engineer, Dong Energy.
This was all done with no downtime on the rig. The operation to remove the SCM was prepared in the IPort while the rig was doing other planned operations.
The operation was performed successfully on Thursday October 14.
"The Oselvar operation is yet another example of how our knowledge and technology offer safe and very cost-effective solutions to rig and oil field operators. By creating 1:1 visualisations we help the operators to improve performance and reduce cost," says Ole Paulsen, head of Aker Solutions’ CoE for Visualisation Technology.