The potential need to produce hydrocarbons from deepwater offshore fields, has created a fundamental requirement to develop highly subsea equipment which can be simply and effectively maintained without the aid of divers

Many approaches to diverless maintenance of subsea production facilities have been considered in recent years Those addressed in the paper range from one atmosphere systems to state-of-the-art deepwater systems currently under development for potential application in the hostile waters of the Northern North Sea, West of Shetlands and elsewhere By overviewing the evolution of subsea production systems it is intended to provide a context into which some of the more highly focused technical papers presented at this session may be placed

The paper is presented in four major sections The first is a history of the evolution of subsea production systems up to the first major milestones in dry one atmosphere systems (Garoupa Field development) and in wet hyperbaric systems (Central Cormorant UMC) The second section catalogues the large number of current projects and outlines principal features and common objectives The third and fourth sections concentrate on subsea manifolds/templates which form the hub of most proposed deepwater developments

A methodology is proposed by which they may be designed in a logical way and the three key stages of the process are explored These are the development of a basis of design, the selection of the maintenance intervention systems and the analysis of reliability and production availability Representative subsea manifolds/templates are compared in the fourth section to illustrate the effects of the decisions taken during design on the template layout and methods of operation and maintenance


Early History

The first underwater completion, using a land type Christmas tree, was made in the shallow waters of Lake Erie, Canada, in 1947 Drilling in coastal and lake(Fig. 1 is available in full paper) waters was commonplace by this time, having started at the Summerland Beach, California, as early as 1887 However the placement of the Christmas tree on the lake bed rather than on the drilling platform was a significant advance

In the 1950s major breakthroughs were made in deepwater drilling technology, although the impact of these on oil and gas production was not felt until the early 1960s Development programmes by Shell Oil Company and others resulted in the first semi-submersible drilling rig, dynamic positioning, heave compensation, underwater BOPS, and positioning systems for re-entry These laidthe foundations for the deepwater production technology in use today

Offshore drilling and production continued throughout the decade, but primarily in shallow water from small platforms using land-based technology In 1956 Shell once more pointed in the direction of things to come by building a prototype one-atmosphere chamber to house wellhead equipment on the sea floor for test purposes.

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