Subsea

Subsea is fully submerged ocean equipment, operations or applications, especially when some distance offshore, in deep ocean waters, or on the seabed. The term is frequently used in connection with oceanography, marine or ocean engineering, ocean exploration, remotely operated vehicle (ROVs) autonomous underwater vehicles (AUVs), submarine communications or power cables, seafloor mineral mining, oil and gas, and offshore wind power. Subsea is fully submerged ocean equipment, operations or applications, especially when some distance offshore, in deep ocean waters, or on the seabed. The term is frequently used in connection with oceanography, marine or ocean engineering, ocean exploration, remotely operated vehicle (ROVs) autonomous underwater vehicles (AUVs), submarine communications or power cables, seafloor mineral mining, oil and gas, and offshore wind power. Oil and gas fields reside beneath many inland waters and offshore areas around the world, and in the oil and gas industry the term subsea relates to the exploration, drilling and development of oil and gas fields in these underwater locations. Under water oil fields and facilities are generically referred to using a subsea prefix, such as subsea well, subsea field, subsea project, and subsea developments. Subsea oil field developments are usually split into Shallow water and Deepwater categories to distinguish between the different facilities and approaches that are needed. The term shallow water or shelf is used for very shallow water depths where bottom-founded facilities like jackup drilling rigs and fixed offshore structures can be used, and where saturation diving is feasible. Deepwater is a term often used to refer to offshore projects located in water depths greater than around 600 feet (180 m), where floating drilling vessels and floating oil platforms are used, and remotely operated underwater vehicles are required as manned diving is not practical. Subsea completions can be traced back to 1943 with the Lake Erie completion at a 35 ft (11 m) water depth. The well had a land-type Christmas tree that required diver intervention for installation, maintenance, and flow line connections. Shell completed its first subsea well in the Gulf of Mexico in 1961 Subsea oil production systems can range in complexity from a single satellite well with a flowline linked to a fixed platform, FPSO or an onshore installation, to several wells on a template or clustered around a manifold, and transferring to a fixed or floating facility, or directly to an onshore installation. Subsea production systems can be used to develop reservoirs, or parts of reservoirs, which require drilling of the wells from more than one location. Deep water conditions, or even ultradeep water conditions, can also inherently dictate development of a field by means of a subsea production system, since traditional surface facilities such as on a steel-piled jacket, might be either technically unfeasible or uneconomical due to the water depth.