A floating production system incorporating a single anchor leg system (SALS) has been installed in Castellon field in the Mediterranean offshore Spain and taken into production by Shell Espana in August 1977. This paper presents a description of the system, its design, construction and field installation. Operational experience during the first 5 months is also reviewed.


In September 1976, Shell Espana decided to develop a marginal field through one well. The field is located in the Mediterranean, 40 miles offshore Tarragona, Spain, in about 380 ft waterdepth. Various schemes were evaluated and the SALS was selected.

The SALS production system conceived by Single Bouy Moorings, Inc. and further developed with Shell Internationale Petroluem Mij. (Fig. 1) comprises a 60,000 DWT tanker (IldeFonso Fierro now baptized DELTA) permanently moored by a rigid buoyant yoke, connected to a tension riser. The single point mooring allows the tanker to weather vane seeking the position of least resistance to wind, waves and current.

The processing and well control equipment, including a workover rig for wireline well re-entry, is installed on deck of the tanker. A 4" ID Coflexip line connects the well with the riser, yoke and tanker. Separated gas is burned in incinerators and in the ship?s boilers. Produced oil is stored into the tanker holds. A shuttle tanker periodically lifts the oil for transport to customers.

The overall system, classified by Lloyds and Bureau Veritas, was designed, constructed and installed in 11 months and the first crude produced on 8 August 1977.

The floating production system includes several new features of significant importance for the development of marginal fields, such as: separator and gas disposal facilities on the tanker deck, facilities to burn associated gas under the ship?s boilers, final hook-up of the system without crane barge support, a combined tension/production riser and installation of the anchor point by semi-submersible which was also required to complete the single well.


The floating production system in Castellon field incorporates following major components :

  • Underwater completed well

  • SALS including flowline

  • Tanker connected to SALS with process and storage facilities

They are described in detail below. Particular attention has been given to provide an operationally safe production system, of which important features are also reviewed below. The parameters for the design of the system are presented in attachment 1.

Underwater completion, controls and workover facilities

The downhole completion comprises a single production packer and 5" production tubing with a surface installed near the top of the string.

The completion arrangement at seabed level, including the X-mas tree is shown in Fig. 3. It is a simple diver assisted completion, in which minor workovers are carried out by vertical re-entry with tools run on wireline. It is very similar to a number of underwater completions made by the Shell Group in the Persian Gulf and in the South China Sea, off North Borneo, between 1966 and 1972. These wells have a successful production history, without any major repairs being required.

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