The ability to maintain any subsea production system is the cornerstone to its success

Careful design of the system and its components may reduce the number of areas requiring maintenance, better component reliability may make maintenance less frequent, built-in redundancy may make it possible to postpone maintenance once a failure occurs and continue production, but at some stage during the life of a subsea production system, maintenance will be required Maintenance of equipment m shallow water is by now well established, it uses techniques and equipment in every-day use on land, with only minor modifications for subsea use Lifting and positioning of equipment by the use of cranes and winches, cleaning and inspection, cutting and welding, and the use of hand and hydraulic tools by divers are all routine and are carried out within environmental limits much as they would be on land Production equipment itself has not changed significantly from the surface equipment from which it was derived.

Even the introduction of Remotely Operated Vehicles (ROVs) has had a very limited effect on the design and maintenance philosophy of shallow-water production equipment, ROVs being used principally for observation and inspection, diver back-up and simple manipulative tasks

The advent of the need to conduct maintenance in deep water does, however, require a radical new approach land-based techniques and equipment cannot be adapted successfully for use beyond diver depths, so the new techniques must be remotely operated from the surface These new techniques will bring benefits to shallow-water production as they are potentially more cost-effective maintenance techniques than current diver intensive methods

It is important that sufficient time and attention be given to these new techniques at the early stages of any project as they have a major effect on production system layout, equipment design and operating philosophy. Better identification and planning for both routine and potential maintenance requirements is needed to compensate for the dexterity of divers and their ability to improvize Alternative means of carrying out specific tasks must be designed in, since modification to a production system installed in deep water will be difficult

Since these remotely operated intervention techniques are largely new, they must be thoroughly tried and tested, preferably early m the project, and certainly before installation Finally, the overall cost of maintenance and intervention must be considered, and the most cost-effective combination of capital, development and continuing expenditure planned for


It is becoming apparent that some common philosophies for the Maintenance/intervention of deepwater subsea production systems are being adopted throughout the industry

However, the technical solutions to these common problems that have been seen to date vary enormously in concept This is probably due to the fact that each development is unique in terms of production size (number of wells, satellite completions, water injection, etc), in location (water depth, proximity to existing developments and supply bases) and in environment (wind and wave spectra and current profiles) Furthermore, each operating company has preferred operating techniques and will develop along the lines of current in-house research and development programmes

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