NASNet® Kings Quay
Subsea 7 selected the Imenco NASNet® Long Baseline (LBL) system to provide in-water positioning support for the installation activities at the Samurai, Khaleesi, and Mormont developments which all tie back to the King’s Quay semi-submersible in the Gulf of Mexico.
All subsea positioning operations, including cut to lengths were undertaken using NASNet® with final metrology calculations completed by an industry leading Lidar system.
Imenco supported the Subsea 7 Project team through a comprehensive planning phase. Taking account of the operational needs and seabed topography to establish the most efficient locations for the seabed network, a total of 17 NASNet® Stations were deployed covering an area of 93 km² in a water depth of approximately 1200mtrs. The planning ensures an adequate number of expected ranges along with line-of-position geometry throughout the network. Geometric Support (GSUP) analysis ensures all required locations are served by a balanced position solution with the NASNet® Stations in view.
The seabed network calibration was completed using an Autonomous Surface Vessel (ASV) with the entire installation and calibration of all 17 station’s and 3 seabed reference units completed within 48hrs.
When compared against 17 NASNet® Station solution with approximately 5 times the number of conventional transponders each set at (a generous elevation) of 3.5 meters, a very limited workable solution can be expected. This is largely due to seabed topography interference with the achievable ranges from near seabed locations.
17 Sleds
75 Conventional Stations
The project commenced in April 2021 with equipment preparation at our USA Lafayette facility, followed by an offshore project scope from August 2021 through to April 2022. Several vessels were utilized concurrently for the offshore works and the project was completed successfully ahead of schedule.
The NASNet® system was used to position all subsea assets, touchdown point monitoring (TDPM) of all pipelines with constant monitoring of each during the entire critical pipe lay operations. A significant advantage during long pipe-lay operations where pipe may be abandoned for several days during re-spooling operations, NASNet® broadcast LBL function allows any vessel/Rov within the field to monitor TDPM where pipe movements can be quickly identified, and the appropriate remedial actions undertaken.
Subsea 7 analyzed the NASNet® performance achieved on this project and established the positioning accuracies of the system compared to results obtained from the Lidar spool-piece metrologies. All comparisons exceeded customer expectations with results between 12 mm and 18cm reported across the entire 93 km² project area.
Imenco personnel were utilized to aid operations offshore on each vessel, however it was observed that the need for the Imenco personnel diminished as the survey crews became familiar and confident in the system with all operations ultimately undertaken by the customer’s own survey personnel.
The project realized significant cost savings by selecting NASNet® and having full field coverage allowing for unplanned project scope changes to be easily undertaken. Management of Change activities when encountered can require significant planning by the Project Team but with NASNet® full field coverage there is never any need to plan or suffer additional cost associated with subsea array re-deployments.
On this project NASNet® was complimented as being a key part in helping aid this project completion ahead of schedule as well as helping reduce costs.
