For deepwater field developments, subsea production systems are frequently envisaged by operators. A basic architecture consists of a central manifold gathering the production of several wells (satellite and/or template wells) and exporting, it to a process facility This scheme allows a large flexibility for the field development Today, installed subsea manifolds are not vex-$ numerous However, their number is expected to increase in the next couple of years.
The need to have cost-effective systems led oil companies to revise their philosophy reliability, simplicity and maintainability are now the main objectives in addition to the reduction of investment and operation costs For that purpose, new concepts and new technology for subsea production equipment have to be proposed New ideas such as insert components, running tools or specialized ROVs, flowlme/umbi1ical pulling-in and connection systems, operating robots, and new control system technology has been investigated and are presented in this chapter.
Drilling is now performed in deeper and deeper water, and any hydrocarbon strike in great water depth leads operators and equipment suppliers to develop various systems or concepts to bring such fields on stream In particular, subsea production technology is more and more considered as a viable alternative when the water depth increases It can permit the replacement of huge fixed platforms by simpler equipment lying on the sea bed Moreover, subsea technology permits a better exploitation of shallow reservoirs satellite wells are drilled vertically into different parts of the reservoir, which could not be reached by deviated drillings from a single fixed platform
Such subsea wells have to be linked to a surface facility Two alternatives are possible either individual flowlines link each well independently to the surface, or production of several wells is brought to a central point where it is commingled in a common export line towards a surface facility.
Since it is normally required that it shall be possible to isolate each well from the others, the junction of the satellite well flowlines and the main export line will require valves The structure receiving the valves, the piping, the flowline connecting equipment etc is the manifold. It is often also a central point for other functions, such as TFL-servicing, dispatching of water injection or gas-lift lines to certain wells, and dispatching of remote control links to the wells The manifold structure may also include subsea template wells In all cases, manifolds aim at reducing the number of production and control lines, and limiting (or suppressing in some cases) the surface equipment
Subsea equipment needs maintenance As it is considered difficult or even impossible to repair seabed equipment, a modular arrangement is used allowing the retrieval of defective equipment which can be repaired or replaced on the surface That reduces the duration of sea operations and improves the ability to maintain equipment in good and safe conditions Another reason for interest in a modular arrangement is the flexibility given for a field development Additional producing wells or injection wells can be envisaged in a step-by-step development.