A concept study and Front End Engineering Design (FEED) project carried out by Xodus Group has determined that a North Sea operator will save up to £59 million by adopting a Not Normally Attended (NNA) status ahead of decommissioning the field.

The North Sea field recently completed well plugging & abandonment (P&A) programs for two platforms. A third platform is not due to commence for at least two years and although it operated as a manned facility, it ceased production several years ago.

The operator required support to convert the platform to a minimum facilities asset which would significantly reduce abandonment support costs over a six-year period until the final decommissioning program commences.

Following a competitive tender process, Xodus initiated a concept study in October 2017 which was closely followed by a FEED project in December 2017. The transition of the platform to NNA status has now been completed.

Babak Alnasser, Xodus’ Technical Safety & Risk Manager

Babak Alnasser, Xodus’ Technical Safety & Risk Manager and project manager for the work, said: “The objective of the project was to look at the technical and economic feasibility of taking the manned platform with all the associated maintenance, inspection, operation and cost that goes along with it, and move it to a minimum facilities asset.

“With it being the first asset in the operator’s portfolio that is transitioning to NNA mode, there was always going to be significant learning. However, the close collaborative working relationship between the companies and the coordination between our multi-discipline teams led to the successful delivery of the project.”

Further information:

• Primary means of access to the asset during the next few years would be via boat, facilitated by the installation of a boat landing access structure prior to the commencement of the NNA operating mode. Similarly, the topsides and export pipeline would be engineered down and cleaned (EDC) and air-gapped and full platform isolations would also be in place prior to NNA mode. A full operations and maintenance (O&M) philosophy was developed by Xodus during the FEED which was endorsed by the operator through consultation with key stakeholders.
• The existing maintenance routines for equipment on the asset were rationalised to the point where the minimum requirements to maintain the remaining facilities, which included existing and new equipment, were derived and a significantly reduced operational expenditure profile was presented. The key to the concept study was that the reduced OPEX profile was demonstrated with a keen eye on ensuring that the level of risk presented was as low as reasonably practicable, something which becomes amplified when assets are transitioned to a point where manning is only required on a campaign basis.
• The use of new technologies to support the platform operation in NNA mode was also explored by Xodus. The use of solar arrays to provide the power supply to critical equipment including remote well monitoring, navigational aids, and intruder monitoring was explored and specifications were developed over the course of the FEED phase. Communications between the platform packages and onshore monitoring systems were also specified during the project to enable an integrated digital dashboard to be developed to provide a snapshot of the status of the asset at any point in time.