Wet Tree Systems
For wet tree system, the subsea field layout usually comprises two types: subsea wells clusters and direct access wells. Direct access is only applied in marginal field development. All such developments are usually based on semi-submersible floating production and drilling units (FPDUs) with oil export either via pipeline or to a nearby floating storage and offloading (FSO) unit, providing direct and cost-effective access from the surface to the wells to allow for workover or drilling activities directly from the production support, especially for deepwater interventions. A subsea cluster of wells gathers the production in the most efficient and cost-effective way from nearby subsea wells, or (when possible) from a remote /distant subsea tie-back to an already existing infrastructure based on either a floating production, storage and offloading (FPSO) or a floating production unit (FPU), depending on the region considered. The subsea tie-back system normally can be regarded as a supplement for subsea cluster well developments. The FPUhas variousways to export the oil or gas. Typically a barge, semi-submersible, or even a mini-TLP type vessel is used. The FPSO usually utilizes a ship-shaped or barge-type vessel as the host structure that is moored either via a turret and weathervaning system to allow for tandem offloading or spread moored with offloading via a distant buoy or still in tandem mode. For both subsea well clusters or subsea direct-access wells, the three main riser options would be vertical top tensioned risers, steel catenary risers, and flexible risers. Pending use of the above field architectures and risers in conjunction with particular flow assurance design criteria, these wet tree system would be the most effective.
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