Coordination is the key to successful well decommissioning project
No two subsea well decommissioning projects are exactly alike – each provides its own distinct set of challenges. Yet there is a common thread running through most of them, and that is the requirement for strong project management and coordination. Nexen Petroleum U.K. in Aberdeen, UK, was well aware of this when it approached Acteon company OIS, which has recently taken over from WellCut Decommissioning Services, to help with a survey and four-well abandonment programme in the North Sea Scott field. One of Nexen’s main concerns was to establish a skilled and focused group of service providers capable of working together as an effective team.
OIS has considerable experience of conducting decommissioning projects, from site assessment through to final reporting, and was tasked with, first, planning the programme, which was to be based on a previously undertaken well categorisation study, and, second, directing the work. This included assembling all the necessary players, defining their roles and responsibilities, and performing a thorough risk assessment of the entire operation.
Well survey
The project commenced with a 10-well survey using a DP2 vessel and a work-class remotely operated vehicle (ROV). At this point, the opportunity was taken to remove entangled fishing nets from the wells before the four-well abandonment phase of the offshore programme got under way.
For the well survey activities, OIS used sister Acteon companies Trident and UWG plus four other specialist contractors. Trident provided the survey equipment for the vessel and marine support services during the works and mobilisation phases. The survey activities were managed by OIS using the Island Offshore vessel the Island Vanguard and Oceaneering International ROVs. UWG took care of wellhead cap removal, drifting the wells and net clearance.
Decommissioning
The team of subcontractors assembled by OIS for the main decommissioning works included Acteon companies UWG, InterAct, Claxton and Trident. Norse Cutting & Abandonment (NCA) provided the abrasive cutting services; eight other companies were also involved. For the abandonment operation, OIS used a suspended well abandonment tool (SWAT®) supplied and refurbished by UWG, and abrasive cutting equipment from NCA to abandon four of the wells. Two of these were category 1; the others were 2.1 and 2.2.
Trident supplied the necessary survey equipment and marine support services, subcontracting the supply of transponders and subsea positioning equipment to Seatronics. UWG provided offshore operations personnel, and Claxton provided SWAT-tooling and offshore-operations personnel. InterAct delivered the well classification, the preliminary procedures and the health, safety and environment submittals.
It was the record of more than 130 successful suspended well abandonments by Acteon companies that convinced Nexen of the value of choosing OIS.
Once the project was under way, Nexen added to the work scope by asking for assistance in severing another well in the field, one that had been recently suspended using a semisubmersible after encountering equipment problems during the abandonment phase. After an engineering review, and with Nexen’s agreement, the rig was moved off location, and OIS’s chartered vessel was brought in to carry out the intervention and severance. The operation was completed, with considerable overall cost savings, within eight hours of the rig leaving the location.
When the wells had been cut, the wellheads were recovered to the back deck of the vessel ready for component recycling and environmentally friendly disposal, which fulfilled the agreement to return the seabed to its original condition.
Key challenges
The project presented several challenges. One of them was managing and optimising the performance of new abrasive severance technology. The NCA abrasive cutting system had to interface with equipment from other subcontractors and had not been used at the water depth in this case. OIS arranged a series of interface engineering meetings and managed them on behalf of Nexen. In addition, the vessel used at Scott field was new, so there was a shakedown period during which minor problems were addressed and overcome. Finally, and not least, the team of subcontractors that OIS selected were all based in different places, so effective communications were vital to optimise the overall performance.
The result, according to Nexen, was a smooth operational process in which all personnel and equipment reached the vessel in good time and worked together as planned.
Performance
Effective well decommissioning of this sort requires precise planning, careful project and contract management, and a positive working environment where the emphasis is on safety and teamwork. Interface engineering and project and operations management logic were vital to the smooth running of the operation. OIS handled specific key contracts, and provided risk management supervision to keep all parties working to the highest standards of offshore safety and to ensure that the quality of the work delivered was maintained throughout.
Over the course of the operation, an excellent working relationship developed between Nexen and OIS, one that is expected to progress and mature through an agreement for further work in 2009 and 2010. The success of the well-abandonment campaign at Scott field required skills and technology drawn from across the Acteon group of companies and beyond. Contributions from all the subcontractors were necessary for achieving Nexen’s aims, but underpinning the team’s success was effective project, contract and operations management.
SWAT’s the benefit?
A SWAT unit can be deployed from the back deck of a vessel or through a moon pool. After any fishing nets and debris have been cleared, the cap has been removed and the well has been drifted, the SWAT unit is landed on the wellhead where it is used to perforate the casing and place a cement plug in the well. Engineers can then sever the wellhead using an explosive charge or an abrasive severance method.
Using the SWAT system removes the need for expensive drilling rigs and diver intervention, and can save field operators up to £400,000 per day: savings that are made up of drill rig costs and the anchor-handling vessel charges incurred when moving a rig to a new location.