eSubsea provide structural analysis and design of subsea protection structures (SPS). The SPS for the subsea production system will be analysed for the lifting load case and in-place loads such as dropped objects and fishing gear interaction according to NORSOK U-001.
Subsea template structures and manifolds are foundations for well heads x-mas trees, manifold structures, control systems, etc. If there is fishing activities in the area there is most often a requirement that all equipment are protected with their own SPS including panels (often in GRP) to avoid hooking up with fishing gear and at the same time provide dropped object protection. This means that template and manifolds structures will be heavier and an alternative is to design and install a separate manifold protection structure which cover the subsea production system equipment.
Dropped Object and Protection against Fishing Gear
The purpose of the subsea protection structure is to protect the subsea modules from damage due to impacts either from dropped objects or fishing activities. The integrated protection structures also use the protective structural framework as bearing members for lifting the subsea module.
The complexity of the structure is based on the local requirements for fishing protection and the Field Operators preferences. The most stringent fishing protection requirements (Norway North Sea) require full over-trawlable structures whilst others accept that fishing gear may impact the structure without damage to the subsea module internals, this is called “fishing-friendly” and is accepted in most parts of the world.
For deep water developments, or were fishing is not applicable (areas where there is no fishing or in fishing exclusion zones near the production facility), only dropped objects will be a requirement. Some fields have fishing exclusion zones in a 500 m radius from the structures and ensure these are known and clearly marked on fishing maps.
The SPS will need to with stand the horizontal loads from the trawling/fishing equipment which is typically 20 to 30 Tonn from trawl board impact or the trawl itself being dragged over the structure. The design of the SPS needs to be snag free and the corner protectors need to penetrate sufficiently into the seabed in order for the trawl ground not to snag.
If the protection structure is separate from the subsea structure, it will need to be fixed to the seabed using suction anchor, piles or ballast weights.