Subsea manifolds

Subsea facilities are easily decommissioned as they are relatively small and easy to lift. However, subsea manifolds and templates can weigh in excess of 1,000 tons and will require heavy lift barges for removal. 

As the first well is being drilled the template is connected to the host facility with flowlines, umbilicals and risers. A Chemical Injection Umbilical will also typically be laid to the template or subsea facility and connected to a distribution manifold. 

If one or more clusters of single wells are required then an Underwater Manifold System can be deployed and used as a subsea focal point to connect each well. The subsea trees sit on the seabed around the main manifold (compared to the template). 

The manifold is typically a tubular steel structure (similar to a template) which is host to a series of remotely operated valves and chokes. It is common for subsea tree control systems to be mounted on the manifold and not on the individual trees. A complex manifold will generally have its own set of dedicated subsea control modules (for controlling manifold valves and monitoring flowline sensors). 

Modern subsea trees, manifolds, (EH), etc., are commonly controlled via a complex Electro-Hydraulic System. Electricity is used to power the control system and to allow for communication or command signalling between surface and subsea. Signals sent back to surface will include, for example, subsea valve status and pressure/ temperature sensor outputs. Hydraulics are used to operate valves on the subsea facilities (e.g. subsea tree and manifold valves). The majority of the subsea valves are operated by hydraulically powered actuator units mounted on the valve bodies. 

At present, the well fluids from the four installed subsea wells flow through 4 in. 10-cm Coflexip seabed lines to the SALS mam told, then through a six-bore product swivel, and finally, through the mooring yoke to the receiving manifold on the FPSU. Well subsurface safely valves and wing valves are controlled hydraulically from a control panel on the FPSU deck by control lines routed through a 20-borc swivel on the SALS. 

Offshore deep-water oil and gas fields are increasingly developed with subsea production systems. By subsea production systems, we understand production (X-mas) trees, templates, manifolds, pumps, separators, and associated equipment that are placed on the seabed. 

---